Heavy-duty truck engines are central to all aspects of the 21st Century Truck Partnership (21CTP) vision: improved thermal efficiency, reduced oil dependency, low-exhaust emissions, low cost, and improved safety are aspects of that vision. Although diesel engines used in most trucks are the most efficient on-road transportation power plants available today, with diesel engines only approximately 42 percent of the fuel energy is converted to mechanical work, resulting in a loss of the energy input by means of the fuel of approximately 58 percent (DOE, 2010a). Additional improvements in the thermal efficiency of diesel and gasoline engines are still possible. However, there are thermodynamic limitations, which means that only a modest portion of the 58 percent of energy that is lost today can ever be recovered. In addition to petroleum-based fuels, these engines can be powered by nonpetroleum fuels from a number of feedstocks. The engine, together with the fuel characteristics and exhaust emission control devices, governs the level of exhaust emissions so critical for compliance with regulations, environmental impact, and public perception. The engine is critical to the safety of the heavy vehicle because it provides braking power, as well as adequate power for the vehicle to blend with traffic. This chapter covers engine programs, fuel programs, aftertreatment systems, high-temperature materials, and health concerns related to emissions from diesel engines.
Several members of the 21CTP are global companies, and they bring to the Partnership the perspective of technologies used in markets around the world. The committee also was given a presentation on a joint Department of Energy (DOE)/Swedish Ministry of Energy research project that combined U.S. and European technology.
Diesel engines derive their efficiency from high-efficiency thermodynamic processes, fuel with a high heating value, and minimal mechanical losses. These engines achieve their efficiency by means of a high compression (expansion) ratio, high rates of combustion under overall lean fuel conditions, and the use of air-to-fuel ratio (instead of throttling) for managing load control, thus avoiding part-load pumping losses. Turbocharging increases engine power density and recovers some of the exhaust energy. Diesel engines operate at relatively low speeds, which reduce mechanical friction losses, and high power density is achieved primarily through high brake mean effective pressure (BMEP).1
Owing to its low fuel consumption, reliability, and low life-cycle cost, the diesel engine has continued to be the preferred power source for commercial vehicles, urban buses, and military vehicles worldwide. The cost of complying with emissions regulations for traditional diesel combustion has given rise to reconsideration of alternative power plants such as heavy-duty spark-ignition engines, and gasoline engines have even regained market share in Class 6 trucks (DOE, 2011a; NRC, 2010). High worldwide demand for diesel fuels has driven their price above gasoline in the United States, furthering this trend. In addition, U.S. national average diesel fuel taxes were 5 cents per gallon higher than for gasoline in January 2011, as reported by the American Petroleum Institute.
Modern highway truck diesel engine brake thermal efficiency (BTE) peaks at about 42 percent, compared to 33 percent for commercial gasoline, spark-ignition engines. This 42 percent peak efficiency represents significant improvement since the 1970s when highway diesel BTE peaked around 35 percent. Key elements for achieving a BTE of 50 percent have already been demonstrated in test laboratories, and demonstration is expected within the next few years in research vehicles meeting emissions standards.
1 The brake mean effective pressure is the ratio of the shaft work leaving the engine to the displacement of the engine. This ratio is expressed in units of pressure, hence the name. BMEP is a useful metric in that it assesses the work output per unit of engine displacement, so it can be used to compare the performance of engines of different displacements.
Most advances in thermal efficiency will be achieved through continued improvements in combustion, air handling, fuel injection equipment, and other subsystems. In addition, an effective exhaust heat recovery system may be necessary for achieving 50 percent BTE. However, the design of a waste heat recovery (WHR) system must take into account the temperature requirements of exhaust emission control devices as well as considerations such as weight, space, cost, reliability, and durability. In order to be commercially viable, the WHR system needs to last for the life of the engine, which carries an emissions warranty of 435,000 miles, but typically has a design life of 600,000 to 1 million miles. The 55 percent BTE stretch goal will require the research and development (R&D) of technologies discussed below in this chapter and should include comparable BTE improvements over the entire engine operating map, especially for those conditions used in a duty-cycle-weighted BTE.
Exhaust emissions of diesel engines have been regulated since 1973 by the California Air Resources Board (CARB) and since 1974 by the U.S. Environmental Protection Agency (EPA). After 1974, diesel engine manufacturers achieved remarkable reductions in oxides of nitrogen (NOx) (~99 percent) and particulate matter (PM) (99 percent) emissions by modifying their engines and adding aftertreatment devices. Through 2006 heavy-duty diesel engines were certified at 2.5 g/bhp-h of NOx + HC and 0.10 g/bhp-h PM (<0.05 g/bhp-h for transit buses). In 2007 the regulations allowed a phase-in of sales-averaged NOx at approximately 1.2 g/bhp-h2 and PM at 0.01 g/bhp-h (DOE, 2006).
Compliance with the 2007-2010 federal emissions standards is perhaps the strongest example of progress by diesel engine manufacturers since the National Research Council (NRC) Phase 1 review of the 21CTP in 2007 (NRC, 2008). Until 2007, exhaust aftertreatment had not been required or utilized to meet emissions standards for heavy-duty diesels (except for limited use of oxidation catalysts on buses and medium-sized trucks). The 2007-2010 regulations were intended by the EPA to be “aftertreatment-forcing.” Aftertreatment technologies for PM were necessary in 2007, and all new truck heavy-duty diesel engines were equipped with diesel particulate filters (DPFs). Catalyst-based DPFs used with ultra-low-sulfur diesel fuel (<15 parts per million [ppm]) achieve PM reductions in excess of 90 percent from 2006 levels. In October 2006, ultra-low sulfur diesel fuel became the mandatory on-highway fuel, thus enabling the use of DPFs and other types of exhaust aftertreatment (NRC, 2008).
For 2010, NOx emissions standards were lowered another 83 percent to 0.20 g/bhp-h NOx + HC, along with 0.01 g/bhp-h PM. These standards have been met by most engine original equipment manufacturers (OEMs) by a combination of cooled exhaust gas recirculation (EGR) and selective catalytic reduction (SCR) for NOx control and an actively regenerated DPF for particulate control. Meeting the requirements of 2010 exhaust emissions regulations required significant in-cylinder control, high-performing aftertreatment for NOx and PM systems, and engine thermal management that includes a degree of control over exhaust mass flow rate, exhaust temperature, and exhaust oxygen. Thermal management, an essential element in the integration of engine and aftertreatment, allows both the DPF and the SCR to operate at peak efficiency over a wide range of duty cycles. In contrast to most manufacturers, which use SCR for NOx control, Navistar is planning to achieve the NOx standard with an EGR-only system and the PM standard with a DPF (Navistar, 2010).
Substantial effort across the industry went into the design of systems for storing and metering urea on the vehicle; these systems are required to support SCR systems. Considerations of freeze protection, contamination, labeling, and stability had to be accounted for. In addition, the infrastructure for distributing and dispensing urea at refueling outlets had to be developed. The industry adopted the name of Diesel Exhaust Fluid (DEF) for the aqueous urea solution. It was found that there is an optimum balance between in-cylinder control of NOx and PM and aftertreatment control of NOx and PM. The primary parameter determining this optimum balance is the operating cost, driven by both fuel consumption and DEF consumption. Fuel consumption has been affected by some of these emission control strategies, such as fuel used to regenerate particulate filters and DEF usage for the SCR system.
Another key enabling system technology is high-pressure common rail fuel systems with high-pressure capabilities exceeding 2,400 bar and allowing multiple injections per cycle. In addition, advancements in turbomachinery have resulted in variable-geometry turbochargers, the use of multiple turbochargers (in series and parallel) with aftercooling and intercooling, and turbocompounding. The turbomachinery serves several purposes in engine performance and emissions control, including airflow for high BMEP and transient response, EGR delivery and control, enhanced engine braking, and exhaust thermal management. EGR systems were introduced in 2002 and have mainly been high-pressure loop with cooling by means of the engine coolant. Some low-pressure loop EGR systems have also been introduced to the market. The first stage of implementation of on-board diagnostics (OBD) was completed on heavy-duty 2010 engines with a second stage in 2013.
As discussed in DOE (2006), engine controls deserve mention here, because historically, controls requirements for diesel engines have lagged those for gasoline engines in passenger cars. For the truck diesel engine, controls were primarily limited to one or two degrees of freedom (i.e.,
2 The NOx and nonmethane hydrocarbon (NMHC) standards were phased in for diesel engines between 2007 and 2010. The phase-in was on a percent-of-sales basis: 50 percent from 2007 to 2009 and 100 percent in 2010. In 2007, most manufacturers opted to meet a Family Emission Limit (FEL) around 1.2 to 1.5 g/bhp-hr NOx for most of their engines (average of 0.2 g/bhp-h NOx standard for 2010 and about 2.2 g/bhp-h NOx portion of the 2.5 g/bhp-h NMHC + NOx standard for 2006).
fuel injection delivery and timing). The future controls requirements in the heavy-duty diesel engine environment was realized with the introduction of EGR and the ongoing implementation of more sophisticated multipulse fuel injection systems and strategies. With the introduction of single- and multistage exhaust aftertreatment systems in 2007 and 2010 and the continuing progress of multimode combustion toward production feasibility, coupled with legislated or customer-demanded expansion of onboard sensing and diagnostic features, the minimum required capability of heavy-duty control systems hardware and software has increased as much as several orders of magnitude.
At present there is no expectation that new regulations will be promulgated to further reduce criteria emissions from new engines. Regulation for PM on a particle number basis has been introduced for vehicles and engines in Europe, and California has studies under way on this subject. The EPA and the Department of Transportation/National Highway Traffic Safety Administration (DOT/NHTSA) announced proposed standards for fuel consumption and greenhouse gas (GHG) emissions for medium- and heavy-duty vehicles and engines on October 25, 2010 (EPA/NHTSA, 2010) and issued final standards on September 15, 2011 (EPA/NHTSA, 2011).
• Advanced Combustion Engine
—Combustion and Emission Control (shared between light- and heavy-truck engines
—Heavy Truck Advanced Combustion Engine
—Waste Heat Recovery/Solid-State Energy Conversion
• Fuels Technology
—Advanced Petroleum-Based Fuels-Heavy Trucks
—Non-Petroleum-Based Fuels and Lubes-Heavy Trucks
• Materials Technologies
—Propulsion Materials Technology-Heavy Trucks
—High Temperature Materials Laboratory Progress in these areas since 2007 is discussed below in this chapter.
Brake Thermal Efficiency Improvements
The DOE’s targets for the improvement of engine brake thermal efficiency have evolved over the years, sometimes in ways that can be confusing, because different statements of a given goal can lead to varying interpretations. At the time of the NRC Phase 1 report published in 2008, the goals were set at 50 percent BTE in 2010 and 55 percent in 2013. These goals were in terms of the peak efficiency demonstrated by an engine in a test cell, where “peak efficiency” means the efficiency achieved by the engine at its best operating point. In general, peak efficiency occurs at relatively low speed and high load. As shown later in this section, the goal of a 50 percent peak BTE demonstration by 2010 was not met, but the technologies required to achieve this goal have been demonstrated successfully.
The DOE has now revised the goal to require 50 percent BTE at a load representative of over-the-road vehicle cruise conditions by 2015. This change was recommended in the NRC Phase 1 report (NRC, 2008). The actual speed and load point are not defined by the DOE in its goal statements, but in the SuperTruck projects (see Chapter 8 in this report), 65 miles per hour (mph) level road cruise is established as the operating point for 50 percent BTE. The committee believes that this is a reasonable operating point to target for high BTE, but it should be understood that this is a more difficult target than the old peak point target. At cruise, the engine must run at a load that is likely to be lower than the peak efficiency operating load, and the engine speed may also be higher than the peak efficiency speed. The goal of 55 percent peak BTE has now been delayed from 2013 to 2018.3 This stretch thermal efficiency goal of 55 percent in prototype engine systems would lead to a corresponding 10 percent gain in over-the-road fuel economy relative to the earlier 50 percent BTE goal at a corresponding condition representing 65 mph level road load cruise. The committee believes that this will be a very difficult goal to achieve.
Research and Development Programs
The DOE and the heavy-duty engine industry have been working in public-private partnerships to develop and demonstrate advanced diesel engine technologies and concepts that improve engine thermal efficiency while meeting the EPA’s 2010 emissions standards. The two technology goals established by the 21CTP for improving brake thermal efficiency of heavy-duty engines are discussed in this section (DOE, 2011a).
Programs and Projects Directed Toward Achieving 21CTP Goal 1
21CTP Goal 1: Develop and demonstrate an emission compliant engine for Class 7-8 highway trucks that achieves 50% brake thermal efficiency in an over-the-road cruise condition, improving the engine fuel efficiency by about 20% (from approximately 42% thermal efficiency today) by 2015 (DOE, 2011a).
The goal for 50 percent BTE discussed in the NRC Phase 1 report (NRC, 2008) was for the peak efficiency condition.
3 As noted in this chapter in the discussion on the 21CTP Goal 2, the 55 percent BTE goal in the 21CTP updated white paper, “Engines” (DOE, 2011a) is for a prototype engine system in the laboratory by 2015. In the DOE Multi-Year Program Plan, the goal is for 2018 in a prototype engine (DOE, 2010d).
|Start: August 2005
Finish: July 2010
|4% BSFCa improvement below 750 kPa BMEP|
|Start: October 2005
Finish: March 2010
|15 L engine: 10.2% improvement in brake thermal efficiency (2010 in-cylinder NOx control)
15 L engine: 16.4% improvement in brake thermal efficiency (2010 emissions with SCR NOx technology)
6.7 L engine: 14% improvement in fuel economy (Tier 2 Bin 8 emissions met without NOx aftertreatment)
NOTE: Acronyms are defined in Appendix I.
a Brake specific fuel consumption (BSFC) is a common and convenient measure of the thermal efficiency of an engine. It is the ratio of the mass of fuel consumed to the work produced by the engine; lower BSFC means higher thermal efficiency. It is different from efficiency in that it measures fuel consumption, whereas the efficiency is a dimensionless ratio that measures the portion of the fuel energy input that gets converted into work output. The two are related to one another through the energy content of the fuel.
SOURCE: DOE (2010b) Annual Merit Review.
However, as noted above, the DOE revised the goal for 50 percent BTE so that it is now for an over-the-road cruise condition. Programs and projects directed toward the development of technology required to achieve Goal 1 include High Efficiency Clean Combustion (HECC), Waste Heat Recovery (WHR), the “NZ50” project at Detroit Diesel Corporation (DDC), and others (DOE, 2011a). These programs and projects are reviewed in this section. Cost-effectiveness was not part of these R&D projects, but cost-effectiveness evaluations will be a required outcome of the SuperTruck projects, as discussed in Chapter 8.
High Efficiency Clean Combustion
A key objective of the HECC program has been to design and develop advanced engine architectures that improved BTE by 10 percent compared to the 2006 product, according to the presentation to the committee.4 The essence of the work was the development of clean combustion in the form of low-temperature, highly premixed combustion combined with lifted flame diffusion controlled combustion. Using these technologies, 10 percent engine BTE improvement targets have been achieved using no NOx aftertreatment. When integrating HECC-developed technologies with SCR NOx aftertreatment system, further engine efficiency enhancements were demonstrated. The results from the HECC projects are listed in Table 3-1 and shown in Figure 3-1.
4 Donald Stanton, Cummins, Inc., “Cummins-Peterbilt Super Truck Program,” presentation to the 21CTP committee, September 9, 2010, Washington, D.C.
Richard W. Kruiswyk,
|Start: October 2005
Finish: June 2010
|10% improvement in BTE was not achieved.
9% improvement target: 7 percent “virtual” demonstration.
Demonstrated turbocompounding vs. Brayton cycle for bottoming.
Demonstrated improvements in turbocharger compressor and turbine efficiencies.
|Start: June 2005
Finish: March 2010
|10% improvement in BTE (8% from WHR).
(Generation 1, No NOx AT, electric accessories)
10% improvement in BTE (6% from WHR).
(Generation 2, SCR NOx AT, no electric accessories)
Both generations included Organic Rankine Cycle.
NOTE: Acronyms are defined in Appendix I.
SOURCE: DOE (2010b).
The historical thermal efficiency data shown in Figure 3-1 indicate a drop in 2002, with only minor improvements until 2010. This drop was caused by measures applied by engine manufacturers to meet requirements for lower NOx emissions (NRC, 2010, Figure 4-2). With NOx requirements now stabilized, engine manufacturers will be able to refocus efforts on thermal efficiency improvements.
Waste Heat Recovery
The objective of the WHR program is to improve engine BTE by 10 percent (i.e., from 42 percent to 46 percent BTE) by capturing and converting wasted heat energy to useful work. A bottoming cycle or turbocompounding captures heat from engine exhaust gas recirculation, charge air, and exhaust streams. WHR systems were designed and developed so that a bottoming device could be coupled to the engine either mechanically or electrically through a high-speed generator. The results from these projects are listed in Table 3-2. The Cummins WHR system is shown in Figure 3-2 (Nelson, 2010).
The highest-quality source of heat for WHR comes from the EGR stream, as illustrated in Figure 3-2. As the effectiveness of SCR is further improved, the use of EGR is likely to
Kevin Sisken and
|Start: February 2007
|Goal: 10% improvement in BTE.
Results: Combustion, 4% (2% more expected); controls, 3%; turbocharger, 1%.
Demonstration for High
William de Ojeda,
|Start: October 2005
Finish: May 2010
|Goal: 5% BSFC at 2010 emissions, no AT
Fuel economy improved 4% to 5.5% (with PCCI, VVA, and combustion feedback).
Load range for LTC extended to 16.5 bar BMEP
Finish: 3rd Quarter, 2009
|Achieved 5% to 8% lower BSFC with internal EGR and VVA.|
|Ford Motor Company,
|Start: October 2007
Finish: June 2010
|Goal: Demonstrate a turbocharger with 3% to 5% fuel economy improvement at Tier II Bin 5 emissions.
2010 DEER presentation (Sun et al., 2010): Not obvious if the goals were met.
NOTE: Acronyms are defined in Appendix I.
SOURCE: DOE (2010b).
decline, which would reduce the potential benefit of WHR. If only the lower-quality heat sources (post-aftertreatment exhaust gas, charge air, and coolant) were available to be captured, the efficiency of the WHR system would be expected to decrease. Therefore, the trade-off between the use of higher-efficiency SCR systems with the decrease in effectiveness of the WHR system will need to be balanced.
Detroit Diesel/Daimler, Navistar, General Motors, and Ford Motor Company also had projects summarized in Table 3-3.
Volvo had a project that started in October 2007 and finished in September 2009. It was funded at $9 million, with the DOE contributing $3 million and Volvo $6 million (subtopic 6B of DOE-FOA-00002395). The results showing lower brake specific fuel consumption (BSFC) by 3 percent were presented at the DOE 2009 Merit Review. It appears that this project is also reported as the Bilateral Program being conducted by Volvo Powertrain North America and Volvo AB of Sweden.6 It is jointly funded by the DOE and the Swedish Energy Agency. The objectives are to reduce CO2 by 10 percent while meeting 2010 EPA criteria emissions, develop an engine platform capable of biodiesel fuel, and develop multifuel vehicles and drivelines. The FY 2010 accomplishments were as follows (DOE, 2009):
• A turbocompound engine showed 5 percent lower fuel consumption. Computational fluid dynamics (CFD) modeling shows that a high-performance piston can improve BTE by 1 percent.
• Analysis of mechanical, electrical, and electromechanical transmission alternatives to connect the turbocompound power turbine to the crankshaft showed the mechanical transmission best for fuel consumption.
• Hybridization simulation showed 2 percent to 8 percent fuel consumption reduction in European applications and zero percent to 2.2 percent in typical U.S. applications.
• A biofuel B209 endurance truck test was initiated (DOE, 2009).
The nine diesel engine programs and projects reviewed above are examples of DOE public-private partnerships. As indicated previously, several programs exceeded their goals of 5 percent or 10 percent improvement in BTE. Not all programs met their goals, but some programs sorted out technologies and identified them for further development.
5 Funding Opportunity Announcement (DOE, 2010b) available at http://www1.eere.energy.gov/vehiclesandfuels/pdfs/de-foa-0000239.pdf.
6 E-mail, Rich Bechtold to committee member, David Merrion, November 18, 2010, report II.A.20 “Very High Fuel Economy, Heavy-Duty, Narrow-Speed Truck Engine utilizing Biofuels and Hybrid Vehicle Technologies.”
7 B50, a point on the EPA supplemental engine test (SET), 50 percent load, mid-speed.
8 C100, a point on the EPA SET, 100 percent load, high speed.
9 B20, 20 percent biofuel mixed with diesel fuel.
The demonstrations of BTE improvements were accomplished mainly at peak BTE operating conditions, with 42 percent as the baseline. As discussed in the NRC Phase 1 report (NRC, 2008), the BTE goal should be demonstrated at a more representative road load cruise condition, which is now incorporated in 21CTP Goal 1. The Cummins demonstrations, such as those shown in Figure 3-1, were at a highway cruise condition.
The current SuperTruck projects call for the contractors to demonstrate the 50 percent BTE target at cruise load on engines installed in vehicles by the end of 2014. If the contractors are able to meet the target, this would enable the 21CTP Goal 1 to be met by 2015. It should be noted that the SuperTruck projects include efforts to reduce the load that the vehicle places on the engine as well as to improve the efficiency of the engine. By lowering the load on the engine, the SuperTruck projects will actually make reaching the 50 percent efficiency goal at cruise conditions more difficult (see Chapter 8 for more detail). There is some risk that the engine thermal efficiency goal will not be met, or that meeting the goal will require complex and expensive technology that would be difficult to implement in production and which may not be cost-effective.
Finding 3-1. The committee reviewed nine diesel engine programs that were funded at a total of more than $100 million by the DOE and industry and that included the HECC program, the WHR program, and others. Some programs met or exceeded their goals, for example achieving a 10.2 percent improvement in BTE versus a 10 percent goal, whereas others did not quite meet the goals of 5 percent or 10 percent improvement in BTE. By combining HECC and WHR, each demonstrating greater than 10 percent improvement in BTE, together with other technologies, it should be possible to improve BTE by 20 percent to achieve the original DOE target of 50 percent peak BTE. However, the DOE target of 50 percent peak BTE was not met by the original goal of 2010.
FIGURE 3-3 Schematic representation of the evolution of combustion processes to be used at different engine loads and speeds. Acronyms are defined in Appendix I. SOURCE: Gurpreet Singh, DOE, “Overview of the DOE Advanced Combustion Engine R&D Subprogram,” presentation to the committee, November 15, 2010, Washington, D.C.
Finding 3-1a. The DOE has shifted the original target of 50 percent peak BTE by 2010 to a new target of 50 percent BTE at an operating point representative of vehicle load during highway cruise operation. This makes the efficiency target more difficult to meet and may require complex and expensive technology that extends beyond the technologies demonstrated on engines to date. These technologies will not necessarily be production-feasible or cost-effective.
Programs and Projects Directed Toward Achieving 21CTP Goal 2
21CTP Goal 2: Research and develop technologies which achieve a stretch thermal efficiency goal of 55% in prototype engine systems in the laboratory by 2015 (DOE, 2011a).
In the public-private DOE partnerships discussed, industry participants have provided technology roadmaps of their strategies for achieving brake thermal efficiencies of 50 and ultimately 55 percent. Improving the efficiency of the in-cylinder conversion of fuel energy into shaft work is an important component of each participant’s roadmap. To do this, all of the participants project incorporating new modes of combustion into their engine operation. Figure 3-3 is an example of the integration of new combustion technologies, like HECC and low-temperature combustion (LTC), that will be needed to achieve the efficiency targets of the program (NRC, 2008).
Gaining the requisite fundamental understanding of the phenomena governing advanced combustion modes, such as those shown in Figure 3-3 (early pre-mixed charge compression ignition [PCCI, LTC] and lifted flame diffusion
controlled combustion), is the focus of the DOE combustion activities within the national laboratories, industry, and academia. These advanced modes of combustion are achieved through synergistic interactions between the auto-ignition and reaction kinetics of the fuel, the thermodynamic states within the cylinder—the pressure, and distributions of temperature, fuel, oxygen, nitrogen, and the recirculated exhaust gases—and the rate of the mixing within the cylinder. The mixing processes are manipulated through fuel injection characteristics and in-cylinder fluid mechanics, which in turn are influenced by the shape of the combustion chamber and subject to manipulation through the intake and exhaust processes, which can be controlled by engine valve actuation. To maintain robust combustion throughout the engine operating range with multimode combustion requires the dynamic manipulation of a wide range of engine control variables. The goals of the DOE laboratory and university research programs are to develop the fundamental understanding and tools necessary to facilitate such a high level of engine combustion control.
This fundamental research is conducted under the Advanced Engine Combustion Memorandum of Understanding (AEC MOU) between industry and national laboratories that was initiated in 2003. The partners involved in the AEC MOU include 10 engine producers (Caterpillar, Cummins, Detroit Diesel, Navistar/International, John Deere, Mack/Volvo, General Electric, General Motors, Ford, and Chrysler), 5 energy companies (Chevron, ConocoPhillips, Shell, ExxonMobil, and BP), and 6 national laboratories (Argonne National Laboratory [ANL], Lawrence Livermore National Laboratory [LLNL], Los Alamos National Laboratory [LANL], Oak Ridge National Laboratory [ORNL], Sandia National Laboratory [SNL], and the National Renewable Energy Laboratory [NREL]). The energy companies joined the AEC MOU in late 2006 and brought a research focus involving fuel effects on advanced combustion strategies. The MOU was recently unanimously renewed by the partners through 2013.
|Title||Organization||DOE Funding: FY 2009 Budget||DOE Funding: FY 2010 Budget|
|KIVA 4 Development (advanced computer program)||LANL||$290,000||$290,000|
|Computationally Efficient Modeling of High-Efficiency Clean Combustion||LLNL||$1.0 million||$1.0 million|
|Chemical Kinetic Research on HCCI and Diesel Fuels||LLNL||$400,000||$400,000|
|Stretch Efficiency for Combustion Engines: Exploiting New Combustion Regimes||ORNL||$250,000||$250,000|
|HCCI and Stratified-Charge Compression Ignition Engine Combustion Research||SNL||$750,000||$750,000|
|Heavy-Duty Low-Temperature and Diesel Combustion Modeling||SNL||$580,000 with $115,000 subcontract to UW-Madison||$660,000 with $115,000 subcontract to UW-Madison|
|Combustion Modeling Large Eddy Simulation Applied to LTC/Diesel/ Hydrogen Engine Combustion Research||SNL||$450,000||$450,000|
|Low-Temperature Diesel Combustion Cross-Cut Research||SNL||$570,000||$660,000|
|Optimization of Advanced Diesel Engine Combustion Strategies||University of Wisconsin–Madison||$360,000||$1.2 million|
NOTE: Acronyms are defined in Appendix I.
SOURCE: DOE (2010b). Available at http://www1.eere.energy.gov/vehiclesandfuels/resources/proceedings/2010_merit_review.html.
As part of the 21 CTP Phase 2 review process, a list of nine DOE-funded projects focused on advanced combustion that were directly attributed to the 21CTP was supplied by the DOE to the committee. These projects are listed in Table 3-4 and were budgeted in FY 2010 for $5.66 million.
There is interaction and leverage between these projects and other DOE-supported combustion projects, but these projects were specifically designated by the DOE as being under the 21CTP umbrella, so the discussion below is limited to these projects.
Researchers participating within each of the nine projects have developed collaborative teams consisting of industry and academic partners. Academic participants are required to establish a 20 percent cost share. Everyone participates in two group research meetings per year and in an annual merit review as part of the DOE’s Energy Efficiency and Renewable Energy (EERE) program. Project directions and continuation are based on the scores received in the merit review. The presentations given at the merit review are available to the public (DOE, 2010b).
The focus of the research projects listed in Table 3-4 is the development of a greater fundamental understanding of the processes that need to be sensed, and controlled, for the integration of advanced, high-efficiency clean combustion processes, into the engine operating map. The work includes the continued development of the advanced computer program KIVA, which is the framework that researchers use for model development, and the development of higher-resolution turbulence models for better spray and fluid-mixing simulation. Comprehensive kinetic routines for diesel-like, gasoline-like, and representative biofuels are an important aspect of the research. These routines identify the critical chemical kinetic pathways that must be included in the simulation for accurate results, which in turn allows for the development of reduced kinetic schemes that are critical for computational efficiency. Reduced kinetic schemes are only one aspect of developing computationally efficient simulations. Research is being supported that addresses computationally efficient methods of solving thermodynamic, fluid mechanic, and chemical kinetic coupled systems.
An integral part of this fundamental research consists of the detailed experimental measurements that identify the important phenomena occurring within the reacting systems, which aids in the model development and serves as a basis for the comparison of model predictions. Spatially and temporally resolved data are being obtained with advanced optical diagnostics techniques. Such measurements have elucidated the effects of in-cylinder temperature and mixture stratification on LTC processes, differences in particulate formation processes for varying combustion regimes, and details of the fuel distribution and wall interactions associated with pulsed injection, an important component of controlling LTC processes. Finally, work is being supported that endeavors to combine all of the advanced understanding and perform optimization studies and to push the efficiency boundaries by pursuing advanced combustion concepts to reach the stretch efficiency goals.
The fundamental combustion and emissions research to date under the AEC MOU has led to significant advances in the understanding of various strategies for achieving LTC. Critical aspects of how HCCI and diesel LTC progress, how their heat release rate and combustion phasing can be controlled, the sources of hydrocarbon (HC) and carbon monoxide (CO) emissions when the LTC approaches are pushed to limits of operation, and fuel effects on LTC are being unraveled.
Higher efficiencies in heavy-duty truck engines have also been shown in the laboratory. Implementation of diesel LTC approaches has begun in heavy-duty diesels for a portion of the fuel burned during moderate- to light-load parts of the engine operating range, providing significant engine-out emissions reduction. In general, higher injection pressure, multipulse injection, and EGR use have allowed a greater fraction of the reactive mixtures during diesel combustion to be pushed toward LTC conditions, contributing to the lower engine-out emissions that have been achieved. Highlights of two of these research projects are summarized here.
• Gasoline HCCI: HCCI—or, more generally speaking, low-temperature combustion strategies—applied in the laboratory environment, using conventional gasoline, have achieved light-load operation down to engine idle conditions and loads as high as 16 bar brake mean effective pressure (limited by the laboratory engine head design) offering the possibility of an engine operating with LTC over a large portion of the engine map. Peak indicated efficiencies in a light-truck-size engine of 48 percent were achieved with NOx levels less than the 2010 standard, near-zero soot levels, and controlled heat release to provide low noise and preclude engine knock (Ra et al., 2010).
• Dual-Fuel LTC: Recent research in heavy-duty engines with dual-fueled (gasoline- and diesel-fueled) HCCI/LTC approaches are indicating potential for 50+ percent brake thermal efficiencies, controlled heat release rates, and 2010 emissions levels. Dual-fuel operation has been achieved from 4 to 17 bar BMEP in a heavy-duty laboratory engine, while achieving NOx levels below the 2010 standard and near-zero soot levels. The start of combustion timing is controlled by the diesel fuel injection, and the heat release rate is controlled by the gasoline fraction.10,11 This work has recently been extended, with encouraging results to bio-based fuels and single fuels with the addition of a cetane improver (Splitter et al., 2010).
The improved fundamental understanding has also advanced computational tools for engine design. Most engine designers are increasingly and aggressively using computational tools developed through support by DOE’s Vehicle Technologies Program for experimental research and engine CFD development efforts. The growing use of computational tools for engine design is exemplified by Cummins introduction of the ISB 6.7-liter (L) light-truck (Class 2b) diesel in 2007. This diesel engine was computationally designed with much reduced testing to confirm performance. The design process led to reduced design time and a more robust design with reduced fuel consumption while meeting 2010 emissions standards (for trucks over 8,500 lb using chassis dynamometer certification). The future introduction of more robust computational design tools able to simulate the full range of engine combustion approaches (conventional mixing-controlled diesel combustion premixed and stratified flame propagation, the LTC bulk ignition and combustion
10 Gurpreet Singh, DOE, “Overview of the DOE Advanced Combustion Engine R&D Subprogram,” presentation to the committee, November 15, 2010, Washington, D.C.
11 Kevin Stork, DOE, “DOE Fuel and Lubricant Technologies R&D,” presentation to the committee, November 15, 2010, Washington, D.C.
processes) has very strong potential to lead to even faster evolution and improvement of cost-effective engines.
Finding 3-2. The DOE-funded research in advanced engine combustion at the national laboratories, in industry, and at universities is well managed and addresses important aspects for achieving an integration of advanced combustion processes that should be important enablers for achieving the 55 percent BTE goal as well as providing ongoing improvements. There also appears to be good interaction between the researchers performing the work and the industry stakeholders. Efforts to achieve 55 percent BTE are going to require complex and expensive technologies. It will be some time before it becomes clear whether there is a production-feasible and cost-effective way to achieve the 55 percent BTE target. The committee believes that this target carries considerable risk, even at the test cell demonstration stage.
Recommendation 3-1. The 21CTP fundamental research program should continue to provide important enablers for the 55 percent BTE goal, and the DOE should continue to look for leverage opportunities with other government- and industry-funded projects.
Future Engine R&D in the SuperTruck Program
The DOE, in 2010, announced three SuperTruck project awards to demonstrate engine and truck efficiency enhancements for Class 8 vehicles in real-world conditions (see Chapter 8). The aim of these developments is to foster quicker introduction of new technologies into the marketplace, thereby achieving energy savings later in this decade. The DOE made the decision to carry out future engine R&D under the SuperTruck program, but it retained Goals 1 and 2 discussed above. Key engine technology demonstrations under the 5-year SuperTruck program include the following:
• Engine Goal 1: Develop and demonstrate a 2010 emissions compliant engine system for Class 8 trucks that achieves 50 percent BTE at an over-the-road cruise condition by improving engine efficiency 20 percent from 42 percent BTE today, by 2015 (DOE, 2011a). This improvement in engine BTE will provide at least 20 percentage points of the 50 percent improvement in vehicle freight efficiency (ton-miles per gallon) (equivalent to 33 percent improvement in fuel consumption [gallons per 1,000-ton-miles]), which is the overall goal of the SuperTruck program.
• Engine Goal 2: Research and develop technology pathways using modeling and analysis to achieve a stretch goal of 55 percent BTE in a 2010 emissions compliant engine system in the laboratory, by 2015 (DOE, 2011a).12 This efficiency gain would be equivalent to an additional 10 percent gain in over-the-road fuel economy when prototype concepts are fully developed for the market.
• Daimler Trucks/Detroit Diesel: Technologies listed in the September 9, 2010, presentation to the committee are as follows
—Advanced fuel injection,
—More efficient operating point,
—Waste heat recovery,
—Next generation controller,
—Higher engine out NOx,
• Cummins: Technologies listed in Cummins’s September 9, 2010, presentation to the committee, the Cummins’s presentation to the DOE DEER Conference September 29, 2010, and the company’s presentation during the committee’s site visit to the Cummins on November 8, 2010 (see Appendix B) are as follows:
—Electrically driven components,
—Waste heat recovery: EGR, charge air, exhaust heat, mechanical coupling,
—Variable valve actuation (VVA),
—Base engine: peak cylinder pressure, friction, parasitic.
• Navistar: Technologies listed in Navistar’s September 9, 2010, presentation to the committee and its presentation during the committee’s site visit to the Navistar,
12 The DOE uses the term “stretch” for goals that cannot be achieved by incremental or small improvements and are thus very difficult to achieve, which seems appropriate for federal programs. The committee supports the use of this terminology because this thermal efficiency goal will be difficult to achieve.
13 Derek Rotz, Daimler, “Daimler’s SuperTruck Program,” presentation to the committee, September 9, 2010, Washington, D.C.
14 Donald Stanton, Cummins, “Cummins-Peterbilt SuperTruck Program,” presentation to the committee, September 9, 2010, Washington, D.C.
15 Anthony Cook, Navistar, “Navistar’s Super Truck Program,” presentation to the committee, September 9, 2010, Washington, D.C.
Inc., Truck Development and Technology Center on January 13, 2011, are as follows:
— Combustion efficiency improvement:
Injection pressure, nozzle, bowl optimization, combustion feedback control, cylinder head and port;
— Air system enhancements:
Turbocharger efficiency, hybrid EGR system;
— WHR (turbocompounding and Rankine):
Rankine cycle—Common cycle used to generate electricity, fluid development for typical truck engine heat range;
Turbocompounding—Dual turbines, visco-mechanical drive to the crankshaft, microturbine;
Minimize regeneration, opportunistic regeneration, PM-NOx balance;
— Friction reduction/insulation: Low friction, weight reduction, electrification of engine accessories, drive mechanism improvements, heat rejection reduction, insulated exhaust ports and manifolds;
Effective compression ratio control, cylinder deactivation;
— Dual fuel (gasoline and diesel).
The SuperTruck engine programs are a continuation of the previously discussed DOE diesel engine programs and have the same goals as those previously discussed. It is unlikely that other heavy-duty diesel engine programs will be funded by the DOE. (Also see the Findings and Recommendations in Chapter 8 regarding the SuperTruck projects.)
In the 21CTP projects to date, as described earlier in this chapter, 50 percent BTE has not been demonstrated in an engine in a vehicle. Significant advancements have been made for individual technologies, which, if combined in an engine, are expected to provide the key elements required to improve BTE by 20 percent to achieve the 50 percent BTE goal. The requirement to demonstrate 50 percent BTE at an over-the-road cruise condition poses an additional task, because the best point for BTE is typically at a higher load. Adding to this task will be the significantly reduced power demand at the over-the-road cruise condition resulting from the SuperTruck vehicle improvements.
The SuperTruck project teams revealed few, if any, plans concerning the research and development of technology pathways to achieve a stretch goal of 55 percent BTE. Moving toward this goal is expected to build on the future achievement of the 50 percent BTE goal and to rely heavily on the DOE-funded research programs in advanced engine combustion discussed in the previous section. Without having specific plans to review for this goal, the committee considers the 55 percent BTE very high risk, although it might be achievable.
Finding 3-3. Future engine R&D for Goal 1, develop and demonstrate 50 percent BTE at over-the-road cruise conditions by 2015, and for Goal 2, research and develop technology pathways to achieve a stretch goal of 55 percent BTE in a 2010 emissions-compliant engine system in the laboratory by 2015, will be carried out under the SuperTruck program. The engine programs outlined by the three SuperTruck project teams appear to be comprehensive and are expected to achieve the 50 percent BTE goal, although there is risk in being able to achieve the goal at a cruise condition with the significantly reduced power demand level of the SuperTruck. Developing engine technology pathways to achieve the stretch goal of 55 percent BTE in an engine in a laboratory by 2015 is considered very high risk, but might be achievable.
Recommendation 3-2. The DOE should ensure that the engine R&D for the goal of 50 percent BTE at over-the-road cruise conditions and the stretch goal of 55 percent BTE in an engine in a laboratory that will now be carried out under the SuperTruck program receive the appropriate share of the SuperTruck funding and benefit extensively from the DOE-funded research programs in advanced engine combustion.
The EPA is developing several candidate types of engines specifically for application to its series hydraulic hybrid truck programs.16 Although the DOE is not funding the EPA, the EPA’s work fits under the 21CTP. The engines that are under development by the EPA are (1) optimized alcohol engines and (2) homogeneous-charge compression ignition engines. The BTE values of these engines are approaching the 42 percent BTE of current diesel engines, as shown in Table 3-5.
High-Efficiency Alcohol-Fuel Engines
The EPA has been developing optimized alcohol-fueled engines for the high-octane E85 fuels that can potentially provide a cost-effective engine technology suitable for both conventional and hybrid vehicles for the medium-duty fleet truck market. The high-octane number of alcohol, together with its latent heat of vaporization, enable the use of high compression ratios and boosted applications. Alcohol’s high laminar flame speed relative to gasoline permits greater charge dilution with EGR, reducing the need for throttling at light to moderate loads while still allowing stoichiometric operation that facilitates the use of a three-way catalyst (Brusstar and Gray, 2007). The EPA has achieved current diesel levels of BTE with E85 fuel using conventional three-way catalysts to meet the 2010 emissions standards.
16 John Kargul, EPA, “Clean Automotive Technology, Cost Effective Solutions for a Petroleum and Carbon Constrained World,” presentation to committee subgroup, October 26, 2010, Ann Arbor, Michigan.
|Engine Type||Exhaust Gas Recirculation Rate (%)||Brake Thermal Efficiency (%)|
|Alcohol fueled engine: E85||20||41|
|Homgenous-charge compression ignition engine:|
|Gasoline port injection||50-60||39|
SOURCE: John Kargul, EPA, “Clean Automotive Technology, Cost Effective Solutions for a Petroleum and Carbon Constrained World,” presentation to the committee subgroup, October 26, 2010, Ann Arbor, Michigan.
Finding 3-4. The EPA has demonstrated that optimized E85 alcohol-fueled engines using conventional three-way catalysts for meeting 2010 emissions standards can achieve current diesel levels of BTE that can potentially provide engine technology suitable for both conventional and hybrid vehicles for the medium-duty fleet truck market.
Homogenous-Charge Compression Ignition Gasoline Fuel Engine
The EPA’s early development of an HCCI engine was focused on potential applications in a series hydraulic hybrid vehicle (Sun et al., 2004). This HCCI engine operated on commercial 87 octane gasoline. In 2008, the California South Coast Air Quality Management District, CARB, and IC Bus (a Navistar company) became interested in demonstrating gasoline HCCI engine technology in a shuttle bus application. A Cooperative Research and Development Agreement (CRADA) project was formed, and the EPA applied its gasoline HCCI technology to a Navistar 6.4 L diesel engine (provided by Navistar) for use with the series hydraulic hybrid technology in a shuttle bus (provided by Navistar). Features of this engine are shown in Table 3-6. The engine was mapped to meet the following control strategy targets: best efficiency, stable operation with the coefficient of variation of indicated mean effective pressure (IMEP) less than 3 percent, maximum rate of pressure rise approximately equal to 6 bar/deg, and NOx emissions less than 0.2 g/kW-h on the unique test cycle (discussed later in this section).
The EPA emphasized that the HCCI engine can operate successfully because the series hydraulic hybrid engine operates over a narrow operating region of the engine map and has only slow transients. The engine is controlled to operate through a narrow region that encompasses the best BTE at each engine speed encountered. The response time for a transient ramp-up of power (from idle to a demanded power level) was controlled to 3 seconds to maintain stable combustion, whereas a typical response time for an engine directly driving the wheels is in the 50 to 100 millisecond (msec) range. Likewise, the response time for a down-power command was controlled to 1 second. The series hydraulic hybrid application reduces the need for rapid transients. However, the EPA is continuing its research to maintain stable combustion through the entire engine operating range to broaden the potential applicability of the HCCI engine concept beyond the series hydraulic hybrid application. EPA tests on the HCCI engine, using a unique test cycle that reproduces the engine operating conditions for the series hydraulic hybrid heavy-duty vehicle, have shown that NOx and PM emissions are below the levels required by the 2010 emissions standards without aftertreatment.17 HC and CO emissions are controlled with oxidation catalysts.
|Base engine||6.4 L base engine (base was a diesel engine)|
|Compression Ratio||16.5:1 CR|
|Turbocharger||Variable geometry turbocharger with intercooler|
|Cooling||Coolant and air-cooled EGR|
|Fuel Injection||Port fuel injection|
|Throttle||Unthrottled except for starting|
|Ignition||Spark Plugs in place of diesel fuel injectors (used for 10-20 seconds during starting)|
|Sensors||Combination combustion pressure sensors and glow plugs (in place of glow plugs)|
|Four knock sensors (each sensor serves a pair of adjacent cylinders)|
|Aftertreatment||No SCR or DPF|
120 kW versus 130 kW for base diesel engine
|Fuel||Can operate on gasoline, diesel, M25, and M50|
SOURCE: John Kargul, EPA, “Clean Automotive Technology, Cost Effective Solutions for a Petroleum and Carbon Constrained World,” presentation to the committee subgroup, October 26, 2010, Ann Arbor, Michigan.
The EPA is continuing to address the following challenges for the HCCI combustion concept: controlling ignition and
17 Personal communication from John Kargul, EPA, to the committee, February 1, 2011.
combustion, expanding the useful operating range to lower BMEP levels and idle, operating without pressure transducers, managing transient operation, and reducing HC and CO emissions.
Finding 3-5. The EPA has developed an HCCI engine that operates in the HCCI mode at all times using low-pressure, port fuel injectors suited to the unique operating conditions of a series hydraulic hybrid vehicle. The unique operating conditions include a narrow range of operation at the best BTE condition for each engine speed, with only slow transient response times for changes in power demands. At these unique operating conditions, NOx and PM are below the levels required by the 2010 emissions standards without aftertreatment; HC and CO emissions are controlled with oxidation catalysts.
The U.S. Army Research, Development and Engineering Command’s Tank-Automotive Research, Development and Engineering Center (TARDEC) provided input on engines, fuels, and hybrid vehicles.18,19 The presentation on U.S. Army engine programs, at the November 15, 2010, committee meeting, prepared by Paul Skalny, mainly covered vehicle programs under the National Automotive Center (NAC). The NAC serves as the Army focal point for the development of dual-use automotive technologies and their application to military ground vehicles. The engine program presented was part of a program on the M1114 High Mobility Multipurpose Wheeled Vehicle (HMMWV), with a goal of 70 percent fuel economy improvement over a blended cycle, and included a “high efficiency engine.” Other vehicle improvements contributing to this goal included an integrated starter/generator (ISG) with new technology batteries and a solar panel, reduced rolling resistance, electrification of accessories, driveline improvements including a 6-speed high-efficiency automatic transmission, and weight reductions through use of lightweight materials (aluminum, titanium, and carbon-fiber composites) coupled with component design modifications.
The meeting at TARDEC of a committee subgroup on January 10, 2011 (see Appendix B), included discussions of engine programs for both combat and tactical vehicles. The Army has National Security Exemptions from the EPA for the following: (1) JP-8 fuel exclusion from on-road 2006 and off-road 2007 diesel fuel regulations, (2) 2007+ heavy-duty on-road emissions standards, (3) 2004 and later EPA on-road emissions standards, and (4) Tier IV EPA nonroad emission standards. Thus, in the near term the Army buys older-emissions standard engines that meet Tier II or Tier III emissions standards, export engines, and in some cases older, remanufactured engines. In the midterm, in addition to the foregoing, the Army plans to buy modified on-road commercial off-the-shelf (COTS) and Tier IV engines minus cooled EGR and exhaust aftertreatment. The Army’s primary bulk fuel is JP-8; diesel is used for specialized engines and aviation gasoline is used in light aircraft. JP-8 requires the addition of an oil lubricant for some fuel systems, including common rail fuel systems. Long-term plans are under development.
TARDEC conducts tests of high power density propulsion systems in which additional requirements of operating at high ambient temperatures (125°F) and low heat rejection are required. The Army defines power density as follows:
Power density = sprocket wheel power/total propulsion system volume.
The Army’s goals for power density are as follows:
• Bradley Vehicle (baseline): Power density = 3 bhp/ft3
• Future Combat Systems: Power density = 4.6 (goal = 6) bhp/ft3
• Research Target: Power density = 8 to 10 bhp/ft3
Low heat rejection helps to improve power density by reducing excess fan power. Cooling, fuel effects, and air filtration are continuing challenges for the Army’s ground vehicle propulsion systems. Examples of some of these high power density programs are listed in Table 3-7.
|Engine||Specific Power||Output||Revolutions per Minute BSHRa||Power Density|
|I-4||125 bhp/L||440 kW (590 bhp)||4,250 0.6 kW/kW||NA|
|V-6||125 bhp/L||750 bhp||4,250 0.6 kW/kW||NA|
|OPOCb||Greater than 125 bhp/L||220 kW (295 bhp)||3,800 0.45 kW/kW||8 bhp/ft3|
|4.7 L I-6||200 bhp/L||940 bhp||5,400 0.6 kW/kW||8 bhp/ft3|
NOTE: NA, not available.
a Brake specific heat rejection.
b Opposed piston opposed cylinder.
18 Bill Harris, U.S. Army, “Review of the TARDEC Programs,” presentation to the committee, November 15, 2010, Washington, D.C.
19 Peter Schihl and John Rzepecki, “TARDEC Programs,” presentation to a committee subgroup, January 10, 2011, Detroit, Michigan.
Auxiliary Power Unit for M1 Main Battle Tank
At tactical idle, the Ml Main Battle Tank uses 17 gal/h of fuel. A renewed investigation of auxiliary power units (APUs) that can be packaged in the available 8 ft3 is under way, with the goal of significant reductions in tactical idle fuel consumption. The following two candidates are being investigated: Patrick Power Rotary Diesel 1.5 gal/h at 9 kW power output; the next-generation target power output is 17 kW; and Altec Tech. Corp. Fuel Cell (1.1 gal/h at 10 kW power output).
Adaptation of Commercial Engines for Military Use
The purpose of the programs on the adaptation of commercial engines for military use is to assess the minimum modifications necessary to adapt 2007- or 2010-compliant engines for use in Army ground vehicles. Targets for these programs are as follows: 48 percent BTE, brake specific heat rejection (BSHR) = 0.6 kW/kW, removal of both EGR and diesel particulate filter, and meeting of 1998 EPA heavy-duty emissions standards (for unarmored wheeled vehicles). Meeting the targets for these programs will require the peak BTE to be improved by approximately 20 percent and the heat rejection to be reduced by approximately 20 percent in order to reduce cooling fan parasitic losses. These programs, together with results to date, are listed in Table 3-8. As shown in the table, none of the engines tested to date has met the aggressive BTE goal of 48 percent, although all of them reached the heat rejection target of 20 percent reduction.
The Automotive Research Center (ARC) is a university-based U.S. Army Center for Excellence for advancing the technology of high-fidelity simulation of military and civilian ground vehicles. The ARC was established at the University of Michigan in 1994 and now includes Wayne State University, Oakland University, the University of Iowa, Clemson University, Virginia Polytechnic Institute and State University, and the University of Alaska, Fairbanks. The center has increased emphasis on energy-efficient propulsion systems for ground vehicles (Genzale et al., 2010). The research topics of the ARC are directly relevant to the military—for example, lightweight blast-resistant materials and issues of track vehicle dynamics. However, there is overlap in the areas of propulsion. The military is actively researching the potential of hybrid powertrains, both hydraulic and electric. There is active research on the fundamentals of batteries and battery performance in hybrid vehicles, and there is work in understanding engine operation with fuels other than diesel, mainly JP-8.
|Awards||Contractor and Engine||Brake Thermal Efficiency Achievement and Baseline||Amount of Contract|
|FY 2009||Cummins: 2007 ISL 8.9 L I-6||43.5 to 45.2% (Baseline: ~42%)||$2.5 million to $3.0 million|
|Mack: Euro IV MP8 13.1 L I-6||~44% (Baseline: ~39%)||$1.0 million|
|FY 2010||AVL: 2010 Ford 6.7 L V-8||43 to 43.5% (Baseline: ~40%)||$1.0 million|
|AVL: Euro Ford Euro V Lyon 4.4 L V-8||NA||NA|
|Ricardo: 2007 Navistar 6.4 L V-8||NA||$2.5 million|
NOTE: NA, not available.
Three Broad Agency Announcements (2010-2013)
The U.S. Army is launching a 4-year program to advance the state of the art by developing new powertrain technologies that will improve overall efficiency by reducing fuel consumption, providing exportable electrical power, reducing noise, and developing powertrains that consume a wide range of fuels. The three programs are summarized in Table 3-9.
The DOD engine programs have completely different objectives from those of the DOE and EPA programs. Those of the DOD programs include, for example, high power density, low heat rejection, 1998 emissions requirements (except 20- to 40-ton vehicles), and primarily JP-8 fuel. The DOD fuel programs are discussed later in this chapter, and the hybrid programs are addressed in Chapter 4.
Finding 3-6. The DOD has engine programs that are cooperative between industry and universities and have goals of improved BTE and other goals more specific to the Army.
Recommendation 3-3. The DOD and the DOE should increase their awareness of one another’s programs and look for opportunities to share technologies on areas of joint interest, such as thermal efficiency. One way to encourage interaction is for the DOE to invite DOD program participants to
|Vehicle||Contractor||Engine/Transmission||Horsepower||Amount of Contract|
|7- to 9-ton light vehicle||Cummins||Cummins 6.7 L ISB Eaton Ultra-Shift||150 to 300||$7.0 million|
|15- to 19-ton medium vehicle||Sapa Group.||DDC 15 L Binary Logic Longitudinal||350 to 500||$7.8 million|
|20- to 40-ton heavy vehicle||SWRI||Up-Powered Cummins 15 L ISX Kertrain 32-speed cross drive||750 to 1,000||$9.67 million|
NOTE: All with 44 percent BTE or greater and 0.6 kW/kW BSHR or less. Acronyms are defined in Appendix I.
present their findings at the DEER (Diesel Engine-Efficiency and Emissions Research) Conference.20
The NRC (2008) Phase 1 includes 12 findings and 12 recommendations regarding engines (Findings 3-1 through 3-12 and Recommendations 3-1 to 3-12). The 21CTP concurred with many of the recommendations and incorporated several of them in the SuperTruck contracts (see Appendix C). The 21CTP responses to Findings 3-1 and 3-8 and Recommendations 3-1 and 3-8 did not concur with the NRC (2008) comments about the 50 percent BTE goal for 2010 and the 55 percent BTE goal for 2013. However, the committee observes that the 21CTP has now changed the year for meeting the 50 percent BTE goal to 2015 and that the 55 percent BTE is now a stretch goal for a prototype engine system in the laboratory for 2015.
Fuels are important in attaining the vision of the 21CTP in three ways:
1. Fuel formulation impacts the conditions that must be established within the cylinder to achieve advanced combustion regimes;
2. Nonpetroleum fuels are a direct route to displacing petroleum-based liquid energy carriers, with biofuels offering the potential for reducing CO2; and
3. Improved properties of petroleum-based fuels can improve engine operation and reduce emissions.
In December 2000, regulations were finalized that required, by 2006, much lower sulfur content in diesel fuel (a maximum of 15 ppm). Ultra-low sulfur diesel (ULSD) fuel was deemed necessary to enable catalyzed diesel particulate filters, including the use of a broader range of catalytic NOx aftertreatment devices, and mitigate engine damage from potential sulfuric acid formation in recirculated exhaust gases. Other fuel properties have been shown to impact engine-out emissions (DOE, 2006). For example, oxygen-containing fuels and additives have been found to reduce PM emissions. However, the understanding of the effects of fuel properties on emissions is still highly empirical. Similarly, the relation between fuel properties and low-temperature combustion modes is far from well understood, although considerable progress has been made in the past few years. Modified fuel specifications and new fuel formulations may facilitate expanding the operating range of new combustion regimes like homogeneous- charge compression ignition as well as improving the operation of conventional diesel engines. The changing of fuel specifications to achieve specific goals needs to be balanced with the cost to refineries for making the needed changes. It is unlikely that changes in diesel fuel properties will occur without EPA regulations to require them, and this can only occur if the changes facilitate reduced emissions.
Nonpetroleum diesel fuels can be produced from renewable resources such as seed oils and animal fat, as well as synthesized from natural gas, oil sands, coal, biomass, and other resources. Processes for the production of diesel fuel from these sources continue to be explored, but commercial production has been limited. The production of biodiesel is growing slowly in the United States. The use of syncrudes from oil sands in Canada has grown considerably. Fischer-Tropsch (F-T) diesel fuels, synthesized from natural gas, have been studied in numerous engine tests to determine
20 Subsequent to the committee’s review of 21CTP programs, the DOE and the DOD entered into the Advanced Vehicle Power Technology Alliance (AVPTA) partnership on July 18, 2011. See, for example, “DOE, Army Alliance Underlines Achieving Energy Security” by Chris Williams, available at http://www.army.mil/article/62727/. Accessed October 18, 2011.
|Project Title||Organization||FY 2009 Budget||FY 2010 Budget|
|Advanced Petroleum Based Fuel Effects on Combustion||ORNL||$750,000||$950,000|
|Fuels for Advanced Combustion Engines||NREL||$550,000||$550,000|
|Advanced Petroleum Based Fuels||NREL||$1.8 million||$1.5 million|
|Quality, Performance and Emission Impacts of Biofuels and Biofuel Blends||NREL||$3.2 million||$1.8 million|
|Kinetic Modeling of Fuels||LLNL||$325,000||$500,000|
|Non Petroleum-Based Fuels: Effects on Emission Control Technologies||ORNL||$845,000||$1.1 million|
|Non Petroleum-Based Fuels: Effects on Advanced Combustion||ORNL||$895,000||$1.47 million|
|Fuel Effects on Advanced Combustion: Optical Heavy-Duty Engine Research||SNL||$600,000||$730,000|
|Advanced Lean Burn Direct Injection Spark Ignition Fuel Research||SNL||$600,000||$630,000|
NOTE: Acronyms are defined in Appendix I. Some of the projects included in Table 1-2 for the fuels budget are applicable to both light- and heavy-duty vehicles so that the total of $12.244 million is not the same as noted in this table, Table 3-10.
SOURCE: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. Available at http://www1.eere.energy.gov/vehiclesandfuels/resources/proceedings/2010_merit_review.html.
their impact on emissions, because higher cetane number21and reduced PM are the primary benefits. Imported F-T liquids have been used as blending material in California diesel fuels since 1993. F-T diesel and biodiesel have a lower energy density than that of conventional diesel fuel, so the uniformity and quality of these new fuels need to be defined and improved to allow for the engine and emission control system to take advantage of them. Furthermore, if alternative fuels are to be used interchangeably with conventional diesel, it may become necessary to recognize the fuel and to compensate within the engine in order to achieve optimal efficiency and to maintain emissions control. Sensors (real or virtual) may be needed to accomplish this, along with control hardware and software.
Lubricant properties can also have a profound effect on emissions, by impacting the durability of exhaust aftertreatment devices. The sulfur and “ash” content of lubricants need to be minimized to prevent degradation of NOx adsorber catalyst performance and to optimize cleaning intervals and regeneration phenomena in DPFs. Research continues on the fuel-savings potential of low-friction and low-viscosity lubricants while maintaining engine and transmission durability and reliability.
The remainder of this section addresses DOE fuels programs, DOD fuels programs, advanced petroleum fuels, biofuels, alternative fuels, and lubricants.
DOE Fuel Programs
To address the challenges described above, the 21CTP has maintained a portfolio of research programs investigating advanced petroleum-based fuels (budget for this was eliminated for 2011, which is discussed later in this section) and non-petroleum-based fuels. The DOE supplied to the committee a list of nine DOE-funded projects focused on advanced petroleum based fuels (APBF) and non-petroleum-based fuels (NPBF) that were directly attributed to the 21CTP. These projects are listed in Table 3-10; the total budget for FY 2010 is $9.23 million.
As with the advanced combustion research programs, researchers participating within each project on APBF and NPBF have developed collaborative teams consisting of industry and academic partners. Participants are involved with group research meetings and an annual merit review as part of the EERE program. Project directions and continuation are based on the scores received in the merit review. The presentations given at the merit review are available to the public.22
The research programs include powertrain-system-level and fundamental investigations. Projects range from evaluating the effects of differences in fuel composition on achieving advanced combustion strategies and their impact on proposed aftertreatment systems, to developing comprehensive chemical kinetic mechanisms for non-petroleum-based fuels, primarily bio-derived fuels. In addition, fundamental experiments are being done using advanced optical diagnostics to evaluate the impact of nonpetroleum fuels on the combustion subprocesses known to be important with petroleum fuels, such as fuel spray development, vaporization, and in-cylinder mixing. Differences have been observed and correlated with characteristics of the fuels (Genzale et al., 2010; Kook and Pickett, 2009; Mueller et al., 2009). Also, some of the activities within the 21CTP seem to focus on light-duty gasoline-
21 The cetane number is a measure of the ignition quality of diesel fuel.
22 See http://www1.eere.energy.gov/vehiclesandfuels/resources/proceedings/2010_merit_review.html. Accessed on May 18, 2011.
like fuels. To logically include these as part of the 21CTP, one would expect to see projects aimed at investigating gasoline-like fuels for heavy-duty applications. This could be very timely and strategic with the expected excess supply of gasoline in the next 30 years (discussed below). A small part of one research project is investigating dual-fuel use, but this project appears to be in a light-duty engine and states as one of its motivations the increased use of ethanol to help meet the requirements of the Energy Independence and Security Act (EISA) of 2007 (Public Law No. 110-140).
DOD Fuels Program
The military fuels program has an objective of minimizing the amount of fuel used through engine and vehicle efficiency improvements and increasing the amount of nonpetroleum fuels used. The military would prefer to use the same fuel in all of its vehicles, and JP-8 is the desired single fuel. The Army, through TARDEC, has the unique role of qualifying alternative jet fuels for use in tactical/combat vehicles having diesel engines. TARDEC is concerned over fuel lubricity and the wide variations that the Army sees in its worldwide fuel surveys of JP-8, its primary fuel. For example, cetane index varies from 33 to 50, density by about 6 percent, and volumetric energy density by about 5 percent. These variations affect engine operation and vehicle range. Fuel-quality sensors are needed to minimize these adverse effects. For ground vehicle use, the Army would like the cetane number of JP-8 to be at least 50.
Although the Army would like to use less petroleum-derived fuels, it realizes that it will be difficult to do so. It is exploring biodiesel fuels; however, the lower energy density of these fuels is a negative. The military has a very rigorous procedure for qualifying alternative fuels, which by itself could prevent any from qualifying. A recent report from the RAND Corporation stated that the U.S. military would derive no meaningful benefit from increased use of alternative fuels, because the technologies needed were unproven, too expensive, and too far from commercial scale to have any impact in the next decade (Bartis and von Bibber, 2011).
The Army keeps many of its engines for 40 to 50 years, and so there is concern about the compatibility of newer fuels and lubricants in these engines. For example, diesel engine fuel pump life can be an issue with low-lubricity fuels. Also, the newer low-sulfur, phosphorus and ash lubricants will not be compatible with these engines.
Advanced Petroleum Fuels
For many years to come, trucks will be powered by diesel engines, and the fuel for these engines will be diesel-like fuel. This fuel will continue to be made mainly from petroleum, in spite of considerable efforts to develop processes for making biodiesel fuel and to use alternative fuels. For the United States in 2008, 95 percent of transportation fuel was from petroleum, 3 percent was biofuels (essentially all ethanol that is not usable in diesel engines), and 2 percent was natural gas.23 This distribution will change with time, with the biofuels portion increasing slowly, but petroleum will be the dominant source for many years. For example, in BP Energy Outlook 2030, BP predicts that biofuels will supply 3 to 4 percent of world transportation energy by 2030, whereas oil will supply almost 90 percent (BP, 2011).
Thus, it is surprising and disappointing that the DOE efforts on petroleum-based fuels have been eliminated from the FY 2011 budget. For FY 2011, the DOE Fuels Technology Budget request was $11 million, down from the $24 million appropriation for FY 2010, with none of it for petroleum fuels.24 However, the DOE has remained active in programs that address diesel fuel properties, whether they are petroleum-derived or not. Programs such as Fuels for Advanced Combustion Engines (FACE), which provides a fuels matrix considering variations in cetane number, aromatics content, and T90, are worthwhile and should be continued. Also, the involvement on fuels with the U.S. Coordinating Research Council (CRC) and the American Society for Testing and Materials (ASTM) should be continued.
Diesel fuel properties vary considerably, both for petroleum-derived fuels and for those containing biomass-derived-components. As engines continue to be fine-tuned for improved fuel consumption and reduced emissions, variations in fuel properties, such as cetane number, aromatics and sulfur concentration, and T90, become more important. For example, the Alliance of Automobile Manufacturers’ annual diesel fuel-quality survey for 2005 reported that cetane quality varied from under 42 to over 50, with 80 percent of the samples under 46 cetane number and 20 percent over 46.
Truck engine manufacturers, through the Worldwide Fuel Charter, have expressed a desire for a minimum diesel fuel cetane number of 55 for markets with the highest degree of emission control, such as the United States. This cetane number is considerably higher than the current United States average in the mid-40s, and it is typical of cetane quality in European diesel fuel. A higher cetane number would improve engine thermal efficiency and cold starting, reduce engine noise, white smoke, and odor emissions (ACEA, 2006). It would improve the ability of diesel-hybrid trucks to restart in stop and go operations, especially at low temperatures. The 2006 version of the Worldwide Fuel Charter (WFC, 2006) provides sufficient evidence to conclude that there is a very large, still unexploited potential for improvements in road fuels, which will provide major reductions in pollutant emissions both in vehicles already on the road as well as in future dedicated vehicles. However, the committee is not aware of conclusive test results showing the effects of cetane number on the engine thermal efficiency and exhaust emis-
23 Patrick Davis, DOE, “NAS Review of 21CTP—Phase 2,” presentation to the committee, September 8, 2010, Washington, D.C.
sions of modern U.S. heavy-duty diesel engines or engines with advanced-concept combustion systems.
A series of trends needs to be explored in order to make proper decisions on future diesel fuels, whether they are petroleum- or biomass-derived:
1. In the United States and worldwide, future demand for diesel fuel is expected to continue to increase in spite of the forthcoming truck-fuel-consumption standards in the United States and elsewhere (EIA, 2011a).
2. In the United States, demand for gasoline is expected to decline as a result of more stringent fuel economy standards, greater use of ethanol, and the increased use of battery-driven light-duty vehicles. Worldwide, even with higher fuel economy standards, the demand for gasoline may increase because of the growth of vehicle sales in Asia (EIA, 2011b).
A presentation to the committee showed that even with improvements in vehicle fuel consumption, total truck petroleum consumption would continue to increase through 2035, dominated by the increase for heavy-duty trucks.25 This will have major implications for refineries in the United States, which will see the ratio of gasoline to diesel fuel production change from highly gasoline-biased to highly distillate-fuel-biased, and will necessitate changes in refinery configuration and operation.
The United States for many years has been a large importer of petroleum, mainly to meet the needs of transportation. If demand for diesel fuel continues to increase, reducing gasoline demand might not have the desired favorable impact on petroleum imports because diesel fuel production will become the controlling factor. Continuing to add ethanol to gasoline for use in light-duty vehicles, be it from corn or cellulosic materials as prescribed by the Renewable Fuels Standards (RFS) in the Energy Policy Act of 2005 (Public Law 109-58), might not contribute to reducing petroleum imports, if increasing diesel fuel demand must be met. The major efforts in the United States to develop and commercialize cellulosic ethanol, many supported by the DOE, may be counterproductive. It may be wise to redirect the DOE biofuels programs to the development of hydrocarbons for use in distillate fuels (diesel fuel and jet fuel) and away from oxygenated fuels for use in gasoline. Also, the DOE will also need to consider efforts toward combustion system development, which uses gasoline-like fuels in high-efficiency, heavy-duty engines.
In looking ahead, the government, in cooperation with industry, could look at maximizing the miles driven per barrel of petroleum used. Studies of this type were done more than 40 years ago, but there have been none of note recently. Because one of this nation’s major goals is to reduce petroleum imports, the DOE could also explore how the nation might use petroleum in the most efficient manner. Such a study would include the following factors:
1. What is the optimum distribution (gasoline/distillate/other) of the barrel to maximize miles or work done per barrel of petroleum processed?
2. What are the optimum ignition characteristics, cetane quality of diesel fuel and octane quality of gasoline?
3. How many grades of each fuel, at what specific octane and cetane qualities, would be optimum?
Such a study would look at the impacts of the continued use of ethanol in gasoline. It could show the potential for reducing petroleum demand and providing fuels tailored for future optimized internal combustion engines. A cost-benefit analysis should be included to compare the costs of the required refinery modifications, with the savings in reduced automotive fuel use. Transition to such an optimal fuel and engine combination would have to be facilitated through the development of engines that are capable of adjusting to the fuel characteristics.
For many years, biofuels have been held out as the “holy grail” that could reduce petroleum imports and greenhouse gas emissions and provide domestic jobs. The DOE has been heavily involved with developing technology and processes for cellulosic ethanol and biodiesel fuels, with the ultimate goal of commercialization. Biodiesel fuels were envisioned as ideal supplements or replacements for petroleum-derived diesel fuel. Congress established the Renewable Fuels Standards in 2005, which set a goal of 36 billion gallons of biofuels by 2022. Congress has provided tax credits and incentives for biofuels production, including that of ester-based and renewable diesel fuels, and they were recently extended. A recent study conducted by Sandia National Laboratories and General Motors concluded that there are no theoretical barriers to achieving the stated goal of producing 90 billion gallons of ethanol per year by 2030.26 A number of practical obstacles were identified however. In particular, investment in cellulosic ethanol production needs long-term protection against oil and feedstock price volatility. Capital costs are significant, and investment risk needs to be managed. Technology improvements, particularly in cellulosic conversion yields, are critical and must be sustained over a number of years. Finally, large-scale development of energy crops is necessary. An NAS-NAE-NRC (2009) report concluded that the resources for biomass were available in the United States and that significant biofuels could be produced by 2020. However, the applicabil-
25 Kevin Stork, DOE, “DOE Fuel and Lubricant Technologies R&D,” presentation to the committee, November 15, 2010, Washington, D.C.
26 Available at http://www.sandia.gov/news/publications/white-papers/90-Billion-Gallon-BiofuelSAND2009-3076J.pdf. Accessed May 18, 2011.
ity of the forecasts in the NAS-NAE-NRC (2009) report for fuels used in heavy-duty diesel engines remains an open issue.
With all of the above, what success has occurred, and what is the outlook for biofuels, especially for biodiesel fuels that could be used in truck diesel engines? To date, the only success has been with corn-based ethanol, which is added to gasoline across the United States for use in gasoline engines. This policy has been clouded with controversy over “food for fuel,” tax credits, and the reduction of greenhouse gas emissions. To date, the commercial production of cellulosic-derived ethanol, envisioned in the RFS, has not occurred, and the production of biodiesel (essentially fatty acid methyl ester [FAME] and other esters) and renewable diesel (a biomass-derived feedstock used in refineries for diesel fuel production) has been minimal. For 2011, the RFS targets for all biofuels are these: biomass-derived diesel, 0.8 billion gallons; advanced biofuels, 1.35 billion gallons; cellulosic biofuels, 5 to 17.1 million gallons; total renewable fuels (almost all corn-derived ethanol), 13.95 billion gallons. Compared with Energy Information Agency (EIA) values for annual gasoline consumption in the United States in 2009 of 138 billion gallons, and diesel fuel consumption in 2008 of 42 billion gallons, these amounts are very small (EIA, 2011a,b). By 2022, the RFS requirement is 4 billion gallons of advanced biofuels, which can be just about any renewable fuel except corn-based ethanol. Even if all of this was biodiesel fuel, it still would meet only about 10 percent of diesel fuel demand.
To meet future RFS requirements, significant advancements in technology and reductions in cost are needed for biofuels. Many years are expected to be required to explore the different approaches to producing biofuel, which are currently at the fundamental laboratory research stage, and to transition promising technologies from the laboratory to large-scale production. The DOE has been actively involved in process development, in monitoring the quality of the biofuels produced, and in understanding their use in engines and vehicles. A significant portion of the DOE effort at the National Renewable Energy Laboratory has been in the generation of cellulose-derived fuels, primarily ethanol. Insufficient work is being done in the generation of hydrocarbon fuels, which are better suited for diesel engines.
In looking toward bio-derived hydrocarbons for diesel fuel, there are two options:
1. Generate a biodiesel fuel, such as FAME or other esters, from a specific feedstock, such as soybeans, and blend that into existing diesel fuel.
2. Generate a bio-crude oil (renewable diesel fuel) that can be used at the refinery in the production of diesel fuel.
Much of the effort to develop diesel biofuels has been directed toward the development of ester-based fuels such as FAME. These fuels are now blended, to a limited extent in the United States, commercially in diesel fuel, and to a greater extent in Europe. But, they are not without problems relating to low-temperature operability and deposits.
Bio-mass derived dimethyl ether (DME) has received attention, especially in Europe, as a sulfur-free diesel fuel substitute because of its high cetane number (55) and very low emissions of PM, NOx, and CO. It would require minor engine modifications, and would need a special system for distribution and storage, which could be a major stumbling block.27
Others are working on renewable diesel fuels, which essentially use biomass feedstocks to generate a hydrocarbon blend that is processed at a refinery during the production of diesel fuel. It results in a finished diesel fuel that is essentially the same as a completely petroleum-derived fuel, with very similar properties.
The California Environmental Protection Agency has recently compared FAME with renewable diesel fuel and concluded that renewable diesel fuel is a better option for the following reasons: it is all hydrocarbon and is chemically more like diesel fuel; it is compatible with current diesel fuel infrastructure and engines; and it avoids unwanted effects associated with ester-based biodiesel fuels (FAME), such as lower volumetric energy content, instability, hygroscopicity, injector fouling, and low-temperature operability, among other factors. The U.S. EPA recently approved a prototype renewable diesel fuel as an “advanced biofuel.”28
The DOE has encouraged production of renewable diesel fuel. On January 20, 2011, DOE Secretary Steven Chu announced29 a loan guarantee of $241 million to support the construction of a 137 million gallon per year renewable diesel facility that will use animal fats, used cooking oil, and other waste grease as feedstock. Many more of these plants will be needed to make a significant dent in biodiesel fuel supply.
The use of other sources for biodiesel fuel production has not yet been successful. For example, a recent United Nations Food and Agricultural Organization report stated that biodiesel from the Jatropha plant that grows in arid climates could not make a significant contribution toward reducing oil dependence (UNFAO, 2010).
Algae have been receiving much attention as a potential source of biofuels. In the United States, major energy companies such as ExxonMobil and Chevron have invested hundreds of millions of dollars, the DOE’s National Renewable Energy Laboratory has an extensive R&D program, and the DOE has invested $24 million in three programs to tackle key hurdles in the commercialization of algae-based
27 A study of DME as an alternative fuel for diesel engine applications (TP 13788E) is available at http://www.tc.gc.ca/eng/innovation/tdc-summary-13700-13788e-718.htm (accessed July 5, 2011).
28 See http://www.epa.gov/otaq/fuels/renewablefuels/compliancehelp/triton-determination.pdf. Accessed May 22, 2011.
biofuels.30 In spite of all of this effort, algae-based biofuels are not on the horizon. A study presented to the National Petroleum Refiners Association (NPRA) meeting in March 2010 (NPRA, 2010) concluded: “significant production seems a minimum of five years off and likely 10 years.” The same study said: “even the current algae-oil technology leaders have big cost hurdles facing them, with algae-derived crude liquids likely to cost between $6 and $20 per gallon” (NPRA, 2010). A study from Wageningen University in the Netherlands concluded that the cost of producing biodiesel from algae is 3.5 times more than the cost of producing biodiesel from crude oil, and twice as much as producing it from rapeseed. The study also stated that it would be 10 to 15 years before commercial production would be feasible, and the cost would have to go down by a factor of 10 (Wijffels and Barbosa, 2010). Even the DOE’s National Algae Biofuels Technology Roadmap concluded that the technology is at an early stage and will require years of development to reach commercialization (Wijffels and Barbosa, 2010). As stated above, the development time for new biofuels will be long, measured in decades.
The International Energy Agency’s report Status of 2nd Generation Biofuels Demonstration Facilities in June 2010 concluded: “A high number of projects are being pursued, but only few facilities in the demonstration phase are actually operating” (Bacorsky et al., 2010). An Australian program has reduced the cost of algae-derived biodiesel fuel by a factor of four to $11 per gallon and admits that further reduction is not a simple process (Wards, 2011). A Japanese report concluded that Japan’s biofuel industry would have a hard time surviving without government subsidies (Ethanol and Biofuels News, 2010). The situation is similar throughout the world.
Finding 3-7. In spite of efforts to reduce the fuel consumption of light-duty and heavy-duty vehicles and to develop biomass-derived fuels (an effort which, except for corn-based ethanol, has not progressed as much as had been expected), petroleum will remain the primary source of light-duty and heavy-duty vehicle fuel for many years to come. Whereas future U.S. gasoline demand is expected to be flat for the next 20 years, diesel fuel demand is expected to grow, necessitating changes in refinery operations.
Recommendation 3-4. The DOE should reinstate its program for advanced petroleum-derived fuels (they will be transportation’s primary fuels for many years to come) with the objective of maximizing the efficiency of their use.
One of the DOE’s original 21CTP goals was to replace 5 percent of petroleum fuels with fuels from nonpetroleum sources by 2010. In the NRC Phase 1 report (NRC, 2008), it was stated that this was unlikely to happen, especially for fuels for heavy-duty diesel engines, and this has been the case. Other than ethanol from corn for use in gasoline-fueled engines and the use of natural gas in fleet vehicles, success with alternative fuels has been limited. About 110,000 natural gas vehicles are on U.S. roads today, with about 66 percent of those being transit buses. In 2009, 26 percent of all new transit bus orders were for natural-gas-fueled buses.31
Interest remains in utilizing natural gas, either directly or as a feedstock, for the production of diesel fuel. The natural gas resources of the United States can be greatly expanded through the fracturing of shale deposits, providing a greater opportunity for the use of natural gas resources in producing transportation fuels. However, there is concern about the adverse effects of methane emissions in the fracturing process and about the impacts of those emissions on global warming.
There is also interest in coal, oil shale, and tar sands. However, high costs, environmental issues, and greenhouse gas emissions have stymied most of these efforts. Commercial success for coal and shale oil is unlikely in the next 10 to 20 years, especially if the price of petroleum remains relatively low. The production of transportation fuels from Canadian tar sands has been a commercial success, but not without environmental controversy.
Gasoline fuel for heavy-duty applications is currently receiving attention in several areas. First, evidence is emerging that some gasoline engines are replacing some diesel engines in pickup, delivery, and other smaller trucks as a lower-cost alternative to the 2010 emissions-standards-compliant diesel engines. Second, R&D work is under way on gasoline-fueled heavy-duty HCCI engines. Work on this type of engine at the EPA was previously described in this chapter. Other research work on similar gasoline-fueled HCCI engine concepts is also under way.
There are no simple and inexpensive substitutes for petroleum-based liquid energy carriers. However, the global demand and diminishing growth in petroleum reserves mandate that alternatives be pursued. Because of the tremendous utility, high energy density, and specific energy of liquid hydrocarbon fuels, the DOE should continue to follow progress in utilizing alternative resources to generate transportation fuels, especially hydrocarbon fuels for heavy-duty diesel engines. The DOE should focus on processes likely to be commercially successful in the next 10 to 20 years.
Lubricants for truck engines will have to provide reduced fuel consumption, powertrain durability, and emissions-control-system compatibility. The DOE recognizes this.
Regarding emissions, the DOE has been active in the Collaborative Lubricating Oil Study on Emissions (CLOSE) project. Of particular concern is the effect of sulfur from the fuel and the engine oil and of phosphorus from the engine oil on emission-control-system performance, especially regarding PM and NOx.
It is well known that reducing powertrain friction, through design changes and the use of more efficient engine oils and transmission fluids, can reduce fuel consumption. Significant reductions in powertrain friction, and improvements in lubricants, especially for light-duty vehicles, have occurred in the past 20 years. The DOE recognizes that not as much progress has been made with heavy-duty vehicles, especially with their lubricants. For instance, the use of 5W engine oils is recommended for most light-duty engines, and 0W engine oils are now recommended for some, whereas 15W engine oils are recommended for most heavy-duty engines, primarily to provide the necessary bearing oil-film thickness, because heavy-duty diesel engines have significantly higher bearing unit loads than do typical light-duty engines.
The DOE has an objective of reducing “parasitic losses in system efficiency by developing improved engine and transmission lubricants.”32 The target benefits are as follows: for 2016, 10 percent engine/15 percent drivetrain friction reduction, leading to approximately 1.5 percent fuel economy benefit; for 2030, 25 percent engine/35 percent drivetrain friction reduction leading to approximately 3 to 4 percent fuel economy benefit. Considering what has already been done to reduce powertrain friction, these are very ambitious targets. To help achieve these goals, the DOE is supporting research to develop and improve the understanding of microfluidic transport, ionic liquids, and lubricant film formation.33
The DOE includes the retrofit of improved engine and transmission fluids in its plans and projected fuel economy improvements. This is a problematic strategy for several reasons:
• Before lower-viscosity engine oils are recommended, either for factory fill or in-use lubricants, manufacturers and truck owners will have to be assured that engine durability is not compromised.
• Transmissions are very sensitive to the quality of the transmission fluids. Fluids are not changed frequently, and manufacturers and operators will need great assurance before risking the use of a retrofit transmission fluid.
A critical development goal is for backward-compatible products, which would minimize the complications of supplying multiple products in the industry. A program that relies on retrofit of lubricants absolutely needs to be conducted in conjunction with the engine and transmission suppliers and users, and with the engine oil and transmission fluid developers and suppliers. Without their involvement, it has zero chance of success.
The process for periodic enhancements of heavy-duty diesel truck engine lubricating oil has been initiated, beginning nearly a year ago as the EPA and DOT/NHSTA GHG emissions and fuel efficiency rule was anticipated (EPA/NHTSA, 2010). This primary objective is an improved fuel efficiency contribution through the implementation of a high temperature high shear (HTHS) viscosity property. Early industry testing with HTHS controlled oils has shown promise for fuel consumption reduction while other parameters continue to protect traditional performance. HTHS can be managed relatively independently from traditional viscosity designations (e.g., 10W30 and 15W40 are frequently used diesel oil viscosity specifications). Fuel consumption results are shown to be duty-cycle-specific. The results characterizing over-the-road cycles may experience up to a 1 percent reduction, whereas an urban/suburban pickup and delivery cycle may achieve up to 1.5 percent reduction or more.34
Bio-derived lubricants are not receiving much attention. However, the DOT has provided $370,000 to the National Ag-based Lubricant Center at the University of Northern Iowa to study the feasibility of using readily biodegradable soy-based lubricants in railroad engines (Ethanol and Biofuels News, 2010). Because diesel engines are involved, the DOE should maintain cognizance of this study.
Finding 3-8. The DOE recognizes the importance of reducing truck powertrain friction and the need for improved lubricants that reduce fuel consumption.
Recommendation 3-5. The DOE must work closely with industry in exploring improved lubricants that reduce fuel consumption, especially with regard to using such lubricants in existing truck engines and transmissions.
Three Different Sets of 21CTP Goals for Fuels and Lubricants
To determine the current goals for the 21CTP fuels program, the committee addressed the following comments to the Partnership:
The 21CTP fuels and lubricants goals stated in the NRC (2008) Phase 1 report were:
• By 2010, identify and validate fuel formulations optimized for use in advanced combustion engines exhibiting high efficiency and very low emissions, and
32 Kevin Stork, DOE, “DOE Fuel and Lubricant Technologies R&D,” presentation to the committee, November 15, 2010, Washington, D.C.
33 Kevin Stork, DOE, “DOE Fuel and Lubricant Technologies R&D,” presentation to the committee, November 15, 2010, Washington, D.C.
34 Private communication between Gregory Shank, Volvo Powertrain, and the committee, September 8, 2010.
facilitating at least 5 percent replacement of petroleum fuels.
• By 2010, identify and exploit fuel properties that could increase efficiency and reduce overall tailpipe emissions through (1) lower engine-out emissions, including new low-temperature combustion regimes, and (2) enhancement of aftertreatment performance for 2010 emissions regulations.
• By 2013, identify non-petroleum fuel formulations (i.e., renewables, synthetics, hydrogen-carriers) for advanced engines and new combustion regimes for the post-2010 time frame that enable further fuel economy benefits and petroleum displacements while lowering emissions levels to near zero, thus adding incentives for using non-petroleum fuels.
A draft white paper presented to the committee on November 15-16, 2010, provided the following new list of 21CTP fuels and lubricants goals (DOE, 2010a). The new Goal 3 repeats the earlier Goal 1, and the new Goal 4 repeats the earlier Goal 3. The status of each goal is provided in the comments following each goal. Little or no progress has been made on these goals because DOE funding reductions in fuels and lubricants technologies have resulted in no funding for heavy-duty fuels and lubricants R&D.
• New 21CTP fuels and lubricants Goal 1: “Establish the influence of fuel and lubricant sulfur on emission-control technologies.”
Status: The 21CTP engine white paper dated August 30, 2010, states: “The sulfur and ash content of lubricants are sufficiently high to be factors in degradation of performance of NOx adsorber catalysts and to influence the cleaning intervals and regeneration phenomena in DFPs, for example.” No progress was reported to the committee for this goal.
• New 21CTP fuels and lubricants Goal 2: “Identify and exploit fuel properties that reduce overall tailpipe emissions through lower engine-out emissions, including new low-temperature combustion regimes and enhancement of aftertreatment performance.”
Status: The 21CTP engine white paper dated August 30, 2010, states: “The understanding of fuel property effects on emissions is highly empirical. Similarly, understanding the relation between fuel properties and low-temperature combustion modes is far from well-understood.” The DOE reported that high-volatility diesel (HVD) fuel increased efficiency and lowered emissions for PCCI operation according to optical engine studies, which showed that liquid fuel films on the piston are avoided.
• New 21CTP fuels and lubricants Goal 3: “By 2010, identify and validate fuel formulations optimized for use in advanced combustion engines exhibiting high efficiency and very low emissions, and facilitating at least 5 percent replacement of petroleum fuels.”
Status: This DOE goal was discussed in detail in the NRC Phase 1 report (NRC, 2008). For this present review, the DOE reported that it contributed to an improved biodiesel ASTM specification, resolving shortcomings of the ASTM D6751 specification issued in 2002. The DOE also reported on studies under way to determine the factors (including radiative heat transfer, reaction rates, and combustion temperatures) that result in increased NOx emissions when fueling with biodiesel. A set of common research fuels were developed, analyzed, and distributed for understanding low-temperature combustion (the FACE project), although a low-temperature combustion engine for testing these fuels had not been identified. The NRC Phase 1 report did not contain plans for achieving the goal of replacing 5 percent of petroleum fuel with nonpetroleum fuels by 2010. The DOE subsequently reported that zero percent reduction in petroleum consumption for the total heavy-duty truck fleet was achieved in 2010, but forecasted a 5 percent reduction in 2015.35
• New 21CTP fuels and lubricants Goal 4: “By 2013, identify non-petroleum fuel formulations (e.g., renewables, synthetics, hydrogen-carriers) for advanced engines and new combustion regimes for the post-2010 time frame that enable further fuel economy benefits and petroleum displacements while lowering emissions levels to near-zero, thus adding incentive for using non-petroleum fuels.”
Status: The NRC Phase 1 report (2008) stated that this goal “was intended to emphasize the development of non-petroleum fuel formulations beyond biodiesel,” previously addressed by Goal 1. Similar to Finding 3-15 in the NRC Phase 1 report, the DOE provided little insight into the scope and magnitude of the effort to address this goal. The Phase 1 report stated, “It appears unlikely that the fundamental mechanisms that control the formation of HC, NOx, and particulate emissions in a diesel engine can be dramatically altered with a change in fuel formulation to the extent that the emissions could approach zero.”
Another draft 21CTP engine white paper dated February 25, 2011 (DOE, 2011a) states the goal for fuels as follows:
• “Through experiments and models with FACE fuels and other projects, determine the most essential fuel properties, including renewables, needed to achieve 55 percent engine brake efficiency, by 2014.”
35 Kevin Stork, DOE, “Fuel & Lubricant Technologies R&D Overview for NAS Review of 21CTP,” presentation to the committee, November 15, 2010, Washington, D.C.
Status: Plans for achieving this goal were not reviewed with the committee. As noted in an earlier section, significant progress in low-temperature combustion has been realized through the use of gasoline or dual gasoline and diesel fuels. The DOE should recognize this progress in defining this goal and developing specific plans for achieving the goal.
Finding 3-9. The DOE established three different sets of goals for the fuels program from 2008 to 2011, which made an assessment of progress against the goals difficult. In total, little progress has been made toward the achievement of these DOE goals, which were not specified goals of the 21CTP.
Recommendation 3-6. The DOE fuel goals should be re-evaluated in line with the FY 2012 budget and the recommendations of this report. Specific plans for achieving these goals should be established.
Considerable effort and research funding have been focused on improving aftertreatment systems as part of the 21CTP. This effort is complementary to the development of combustion processes that would minimize or preclude the in-cylinder formation of criteria pollutants. It is most appropriate to think of the combustion processes within the cylinder and the aftertreatment devices within the exhaust as an interconnected system. Minimal emissions leaving the combustion chamber result in reduced demands on the aftertreatment system, allowing for simpler, less expensive aftertreatment systems. Also, highly effective aftertreatment systems can facilitate different engine calibrations for better efficiency, which would otherwise have been precluded because of emission constraints. Aftertreatment research and development must be done with an eye toward the likely progress in combustion system development.
In addition, aftertreatment systems are the subject of extensive research within the technical community. Consequently it is critical for the 21CTP be aware of the broad scope of activities taking place outside of its program and to make sure that the research activities within its purview address fundamental concerns and are not already being done as part of the research and development efforts of the other agencies or industry.
To this end, the research structure of the 21CTP aftertreatment program is well organized. The research programs are built around teams with participation from national laboratories, universities, and relevant stakeholder industries. This is directly stated in the goals of their aftertreatment program. The research focuses on developing new technologies and on gaining an enhanced fundamental understanding of catalysis and governing phenomena limiting the effectiveness of current approaches. Success in these programs could lead to combining multiple aftertreatment approaches into a single unit, developing catalysts with higher resistance to poisoning, and implementation of retrofit systems.
The 21CTP aftertreatment research has already helped manufacturers meet the EPA 2007 and 2010 new-engine emissions standards. The system architecture generally being applied to meet U.S. EPA 2010 emissions is shown in Figure 3-4. The attainment of these emission standards is providing substantial health and environmental benefits by reducing ground-level ozone and fine particulates (mass as well as number), in addition to regional haze. Thus, con-
FIGURE 3-4 Emission control system architecture generally being applied to meet 2010 new engine emissions standards of the Environmental Protection Agency. Acronyms are defined in Appendix I. SOURCE: DOE (2011a).
tinued research into improved aftertreatment is extremely important.
Diesel particulate filters have reduced diesel particulate matter by approximately 90 percent. Particulate matter emitted from modern diesel engines is typically in the size range of 10 to 250 nanometers (μm). There are concerns that current regulatory limits for particulate matter from engines, which are in terms of emitted mass, are not a proper measure of the health hazard. One particle of 10 micrometers (μm) diameter has approximately the same mass as 1 million particles of 100 nm diameter. There is evidence that particles smaller than 100 nm can pass through cell membranes and migrate into other organs. Research into the potential health impacts of very small particles is currently being sponsored by the Health Effects Institute (HEI). Proposals for new regulations exist in some countries, with suggestions to limit the particle surface area or the particle number. Although particulate number regulations are not in effect in the United States, they are being considered. Vehicles equipped with particulate filters should have no difficulty meeting newly proposed particle number regulations. However, as new combustion technologies, such as LTC and high injection pressure, lifted flame, mixing controlled combustion, are integrating into the engine map, it may be possible to meet the particulate mass regulation without a filter. Under such situations it will be important to understand the characteristics of the particulate number being emitted from these future combustion systems. Technologies to address this issue will be needed in the future.
Response to Recommendations from NRC Phase 1 Review
Prior to 2007, the aftertreatment goals of the 21CTP were focused on (1) meeting the 2007 heavy-duty engine emission standards and (2) eliminating the need for aftertreatment. In its Phase 1 review of the 21CTP (NRC, 2008), the committee found that no specific goals had been outlined for 21CTP diesel engine aftertreatment systems, but some goals had been set for eliminating aftertreatment. The committee found that the goal of eliminating aftertreatment did not appear to be achievable in the foreseeable future. The committee also found that the Crosscut Lean Exhaust Emissions Reduction Simulations (CLEERS), Diesel Crosscut Team (DCT), and CRADAs had contributed to many successful projects and programs. The NRC Phase 1 review recommended that specific goals should be set for aftertreatment systems (improved efficiency, lower fuel consumption, lower cost of substrates, lower-cost catalyst, etc.) and that the 21CTP should continue with the CLEERS, DCT, and CRADA activities for aftertreatment systems. The 21CTP accepted the recommendations of the NRC (2008) review and has adjusted its aftertreatment program to address them.
The 21CTP responded to the recommendations of the NRC Phase 1 review with a critical evaluation of the role of aftertreatment in meeting its overall program goals and has written a white paper specifying the role of aftertreatment within its program (DOE, 2011a). Formally the 21CTP has identified six goals specifically related to aftertreatment technologies. These goals are as follows with comments from the committee on the work supporting these goals.
• 21CTP Goal 1 related to aftertreatment technologies: “Improve performance and durability of NOx control technology through improved combustion and aftertreatment processes, sulfur management, reductant strategies, and improved materials.”36
Comment: This goal would appear to be met by further reduction of sulfur in the diesel fuel, and developments of SCR catalysts, lean NOx traps, DEF reductants, low temperature combustion, and iron and copper zeolite materials.
• 21CTP Goal 2 related to aftertreatment technologies: “Develop and apply advanced fuel injection, engine control strategies, new combustion regimes, air-handling, and aftertreatment for emissions reduction, with modeling, simulation and controls integrated in the approach.”
Comment: This goal would appear to be met through the various CRADAs and research projects discussed in this chapter.
• 21CTP Goal 3 related to aftertreatment technologies: “Develop and implement cost effective retrofit emission control technologies.”
Comment: OEM systems for PM control and NOx control have been supported, and these have made their way into retrofit (aftermarket) systems, but no direct support of retrofit systems or programs are evident.
• 21CTP Goal 4 related to aftertreatment technologies: “Determine the best configuration and controls for NOx and particulate matter (PM) reduction through engine/aftertreatment integration.”
36 Fundamental work is being done to improve the reduction efficiency (performance) of NOx aftertreament systems, with particular emphasis on high mileage (durability) where compliance with applicable standards is required. The higher the efficiency of the aftertreatment system the larger the cylinder-out NOx can be. The efficiency of the NOx aftertreatment system ends up constraining the allowable NOx leaving the cylinder. Constraining the cylinder-out NOx constrains what one can do to improve the efficiency of the engine—especially at high load. If the NOx reduction efficiency were 100 percent, the engine engineers would have great leeway in improving the engine efficiency—which they currently do not have. The closer one can get to this ideal the better. The objective of the research work in the 21CTP is to continually improve the NOx aftertreatment reduction efficiency at the least possible cost; thus the statement to improve performance and durability of the NOx control technology.
|Project Title||Organization||FY 2009 DOE Funding||FY 2010 DOE Funding||Link to Most Recent EERE Merit Review|
|CLEERS Coordination and Joint Development of Kinetics for LNT and SCR||ORNL||$200,000 $450,000||$200,000 $500,000||http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2010/emissions_control/ace022_daw_2010_o.pdf|
|Development of Advanced Diesel Particulate Filtration (DPF) Systems||ANL||$500,000||$500,000||http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2010/emissions_control/ace024_lee_2010_o.pdf|
|CLEERS: Aftertreatment Modeling and Analysis||PNNL||$750,000||$750,000||http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2010/emissions_control/ace023_lee_2010_o.pdf|
|Experimental Studies for DPF and SCR Model, Control System, and OBD Development for Engines Using Diesel and Biodiesel Fuels||Michigan Technological University||NA||$583,000||http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2010/emissions_control/ace028_johnson_2010_o.pdf|
|Combination and Integration of DPF-SCR Aftertreatment Technologies||PNNL||$200,000||$400,000||http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2010/emissions_control/ace025_rappe_2010_o.pdf|
|Development of Optimal Catalyst Designs and Operating Strategies for Lean NOx Reduction in Coupled LNT-SCR Systems||University of Houston||NA||$637,000||http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2010/emissions_control/ace029_harold_2010_o.pdf|
NOTE: Acronyms are defined in Appendix I. NA, not available.
Comment: This goal is being met through the support of many programs discussed in this Chapter. The “best” configurations are the systems developed by the OEMs.
• 21CTP Goal 5 related to aftertreatment technologies: “Achieve production-feasible, life-cycle effective, emission control system(s) that will meet NOx and PM regulations phasing in starting 2007, also with reductions of unregulated “toxic” emissions.” Comment: This goal was achieved, as discussed in the Health Effects section of this chapter.
• 21CTP Goal 6 related to aftertreatment technologies: “Research pathways to post 2010 regulations for emissions, such as toxics and carbon dioxide.” Comment: The regulation for carbon dioxide emissions from heavy-duty trucks will entail research into pathways for meeting this regulation. For a potential future regulation for particulate number, research will need to be carried out to develop an understanding of the characteristics of the particulate number being emitted from future diesel combustion systems.
Aftertreatment research in the 21CTP is overseen by the DOE, EPA, and 21CTP industry partners. Approximately $37 million has been spent for heavy-duty-truck aftertreatment research for the past 7 years and $3.6 million was the funding for FY 2010.
The development of effective exhaust gas aftertreatment systems and the optimal integration of these technologies as part of the engine-powertrain system are a critical aspect of meeting the goals of the 21CTP. Of specific interest to the 21CTP is the reduction of NOx within a lean exhaust environment and effective capture and regeneration of particulate matter from the exhaust stream. This happens to be the focus of the combustion research and development community at large, so the 21CTP not only contributes to, but also benefits from, the research activities of a much larger technical community.
As part of the Phase 2 review, the DOE supplied to the committee a list of research programs that should be considered as part of the 21CTP. The names of these projects, the lead agency performing the work, their DOE funding level, and a link to the most recent EERE merit review presentation are presented in Table 3-11.
The aftertreatment research projects currently supported by the 21CTP, listed in Table 3-11, cover a wide range of technologies. Included in the funding is support for the organizational structure called Crosscut Lean Exhaust Emission Reduction Simulations. CLEERS, which is managed through the Oak Ridge National Laboratory, acts as a coordinating body and a disseminator of the newest kinetic schemes and models for aftertreatment system simulation. This is done through its website.37
More specifically, CLEERS is a collaborative effort among the national laboratories ORNL, ANL, and the Pacific Northwest National Laboratory (PNNL), and industry and academia; CLEERS works to identify, prioritize, and coordinate R&D needs within industry to expedite the development of detailed technical data necessary to simulate lean NOx trap (LNT) and SCR. Through their efforts, LNT and SCR kinetics have been published, the toluene poisoning mechanism for SCR has been identified using surface spectroscopy, and new catalyst formulations for LNTs that are more sulfur-resistant have been developed. Most of the major catalyst suppliers and engine and vehicle manufacturers participate with national laboratories and academia in these activities.
Within the aftertreatment program, efforts are under way at the ANL to develop advanced diesel particulate filters. This effort involves collaboration with Corning, Caterpillar, the University of Illinois-Chicago, and the University of Wisconsin-Madison; it is focused on studying the oxidation processes to enable better control systems and optimization of regeneration strategies.
The PNNL is leading an effort on aftertreatment modeling and analysis. This work is being done through a new CRADA involving DOW, PACCAR, Ford, GM, and Cummins. The participants are working together to enhance the scientific understanding of DPF, SCR, and LNT technologies. Recent accomplishments include the identification of which hydrocarbons have detrimental effects to NOx reduction, why water can be an inhibitor to HC storage, and the role of the BaO/alumina interface in LNT performance with ceria as a supplement. These results feed into models that are important in aftertreatment design and control strategy optimization.
Under 21CTP funding, Michigan Technological University is leading an activity with Cummins, Navistar, John Deere, Johnson Matthey, Watlow, ORNL, and PNNL to perform an experimental assessment of DPF and SCR models. This effort is being done with diesel and biodiesel fuels. The importance of particulate maldistribution within the DPF, NH3 loading in the SCR system, and the ability of different sensors in conjunction with state estimation models to monitor the state of the aftertreatment system effectively are being evaluated.
Funding for a research program being led by the University of Houston is exploring optimal catalyst design and operating strategies for lean NOx reduction in a coupled LNT/SCR system. Participants in this program include the University of Kentucky’s Center for Applied Energy, Ford, BASF Catalysts, and ORNL. The mechanisms of NOx reduction in LNT/SCR coupled systems are not understood. The program participants are also exploring catalyst synthesis with better desulfation and durability. Recently it has been determined the non-NH3 mechanisms may be important in SCR kinetics for Fe-zeolite systems.
Finally, a research program is being led by the PNNL with PACCAR and DAF Trucks looking at an advanced aftertreatment system consisting of an integrated DPF and SCR for simultaneous particulate and NOx control from the same device. The current focus of this work is to determine the optimal SCR catalyst loading that will maximize NOx reduction while minimizing the pressure drop across the DPF.
These projects have several global aims: to evaluate and address emission control technology barriers; address deficiencies in modeling capabilities and basic understanding; develop the understanding of degradation from sulfur in fuels; address the high platinum metal content and high cost; work to expand the effectiveness of catalytic systems to a broader temperature range; eliminate the inefficient use of fuel for regeneration of diesel particulate filters and desulfurization of NOx reduction systems, as well as poor reductant utilization (lean NOx catalyst, LNC); improve inadequate sensors for processing control diagnostics; and address cost and packaging constraints.
Finding 3-10. The research agenda of the 21CTP is focused on improving the NOx reduction performance of SCR and LNT systems, improving the efficiency of and reducing the fuel consumption associated with PM filter regeneration, and improving the ability to model aftertreatment systems. The DOE CLEERS program does a good job of coordinating the aftertreatment research programs within the 21CTP and disseminating the results to the technical community at large.
Finding 3-11. The demands on the aftertreatment system and its performance are intimately linked to the combustion process taking place within the cylinder. Consequently, the aftertreatment system must be developed and its performance evaluated in conjunction with the combustion system. The 21CTP realizes this, and its new goals for the aftertreatment program specifically state this.
Recommendation 3-7. The aftertreatment program within the 21CTP should be continued, and the DOE should continue to support the activities of CLEERS that interface with the activities of the aftertreatment technical community at large.
Finding 3-12. Particulate size distribution is not a problem with current diesel-type combustion using DPFs. However, as new combustion processes, possibly using different fuels ranging from petroleum-derived fuels to biofuels and synthetics, are integrated into future engine operating maps, it is important to assess particulate size distribution characteristics if particulate filter designs are changed or if DPFs are not used.
Recommendation 3-8. In light of the progress being made with new combustion technologies, which show potential for very low cylinder-out NOx and particulate emissions, the 21CTP should incorporate studies of particulate number emissions into their research portfolio.
|Title||Organization||FY 2009 DOE Funding||FY 2010 DOE Funding||Link to Reference|
|Advanced Collaborative Emission Study (ACES)||HEI, Lovelace Respiratory Research. Institute, CRC||$600,000||$600,000||http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2010/health_impacts/ace044_greenbaum_2010_o.pdf|
|Measurement and Characterization of Unregulated Emissions from Advanced Technologies||ORNL||$475,000||$450,000||http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2010/health_impacts/ace045_storey_2010_o.pdf|
|Collaborative Lubricating Oil Study on Emissions (CLOSE Project)||NREL||FY 2006-FY 2010 $892,000||(DOE)||http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2010/health_impacts/ace046_lawson_2010_o.pdf|
NOTE: Funding levels represent DOE funds only.
SOURCE: Information based on DOE Vehicle Technologies Program Merit Review (DOE, 2010b).
The health effects research within the 21CTP is coordinated through the Health Effects Institute. The HEI is a nonprofit corporation chartered in 1980 as an independent research organization to provide high-quality, impartial, and relevant science on the health effects of air pollution. Typically the HEI receives half of its core funds from the U.S. Environmental Protection Agency and half from the worldwide motor vehicle industry. The 21CTP’s support to the HEI represents a strong collaboration between the HEI, DOE, EPA, California Air Resources Board, Coordinating Research Council, Engine Manufacturers Association (EMA), American Petroleum Institute (API), engine and aftertreatment manufacturers, and lubricant suppliers. The objective of the research is to provide a sound scientific basis underlying any potential health hazards associated with the use of new powertrain technologies, fuels, and lubricants in transportation vehicles. Furthermore, the program endeavors to ensure that vehicle technologies being developed by the DOE Vehicle Technologies Program for commercialization by industry will not have adverse impacts on human health through exposure to toxic particles, gases, emanation of electromagnetic fields,38 and other effects generated by these new technologies. This is being done by characterizing the emissions from vehicles using advanced technologies and also screening these emissions for toxicity. In selected cases if necessary and where possible, the team will work to identify the components responsible for toxicity and engineer solutions to reduce the toxic components.
Three main efforts are under way as part of 21CTP and the Vehicle Technologies Program to evaluate potential health concerns related to heavy-duty diesel vehicles. These efforts aim to undertake high-risk mid- to long-term research; utilize unique national laboratory expertise and facilities; help create a national consensus; and work cooperatively with industry and other agencies. The three efforts are presented in Table 3-12.
Advanced Collaborative Emissions Study
The combination of advanced-technology, compression-ignition engines, aftertreatment systems, reformulated fuels, and oils developed to meet the 2007 and 2010 emissions standards are demonstrating reduced emissions. Substantial public health benefits are expected from these reductions. However, with any new technology it is prudent to conduct research to confirm benefits and to ensure that there are no adverse impacts on public health and welfare. This is the overall objective of the Advanced Collaborative Emissions Study (ACES) (DOE, 2010b; Greenbaum et al., 2010).
There are three phases to ACES:
1. In phase 1 (completed), the Southwest Research Institute (SwRI) characterized emissions from four 2007 engines. A final report was issued in June 2009.39
2. In phase 2, emissions from 2010 model year engines are being characterized.
3. In phase 3, health effects testing is being conducted by the Lovelace Respiratory Research Institute. In this phase, short-term biological screening and long-term
38 The World Health Organization website includes the statement: “To date no adverse health effects from low level, long-term exposure to radio frequency or power frequency fields have been confirmed but scientists are actively continuing to research this area.” Available at http://sho.int/peh-emf/about/what is EMF/en.index1.htm.
health effects tests are being conducted on the emissions from 2007 model year engines.
The ACES project funding totals $15.5 million, with the DOE contribution in FY 2009 and FY 2010 being $600,000 each year. The project will continue until mid-2013.
To date, the reported results from the 2007 engines include the demonstration of emission reductions below the 2007 standards as follows: PM, 89 percent below the 0.01 g/hp-h limit; CO, 98 percent below the 15.5 g/hp-h limit; NMHC, 95 percent below the 0.14 g/hp-h limit; and NOx, 10 percent below the 1.2 g/hp-h average limit. Unregulated emissions are 90 percent below those of a 2004 technology engine. NO2 emissions increased over those from the 2004 engines but are expected to go down in 2010; no results have been published yet. Short-term animal studies are complete, and a report is being prepared for review in 2011. The long-term exposure study is under way, with results expected in 2013.
Measurement and Characterization of Unregulated Emissions from Advanced Technologies
The project on the Measurement and Characterization of Unregulated Emissions from Advanced Technologies is largely focused on light-duty vehicles. However, some analysis of SCR systems is being done for the ACES project. Results reported to date have included detailed particulate characterization from direct-injection spark-ignition engines with gasoline and ethanol blends. In addition, the HEI is undertaking a review of the literature on ultra-fine particulates (UFPs). The review will encompass information on the contribution of mobile sources to atmospheric UFPs, health effects of UFPs, and the potential for environmental exposure leading to potential health effects in humans. Animal studies are being considered.
The presentation by the DOE’s James Eberhardt to the committee titled “Overview of DOE Health Impacts Research” provided the following observations that may indicate the need for further study:40
• “NO2 emissions have increased significantly at two sampling locations in the South Coast Air Basin since the introduction of 2007 MY trucks. (Starting in 2007, CARB introduced regulations to limit the increase in NO2 emissions from DPF equipped diesel engines.)
• Certain liquefied natural gas (LNG)-powered trucks are emitting large amounts of ammonia.”
Collaborative Lubricating Oil Study on Emissions (CLOSE) Project
The objective of the CLOSE project is to quantify the relative contributions of fuel and engine lubricating oil to motor vehicle particulate matter and semi-volatile organic compound emissions through the extensive chemical and physical characterization of emissions under a variety of engine operating conditions (Eberhardt and Louison, 2010). At the time of this review, testing from the HD compressed natural gas and diesel buses has been completed, and detailed analyses and source apportionment of exhaust from all vehicle samples are now under way.
Response to Recommendations from NRC Phase 1 Review
Recommendation 3-19 in the NRC (2008) Phase 1 report stated that the committee endorses the DOE multiparty effort to characterize the emissions and assess the safety and potential health effects of new, advanced engine systems, aftertreatment, fuels and lubricants (ACES), and recommends that this continue for the remainder of the study until results become available in the 2012-2013 time period. The DOE response to this recommendation was that it appreciates the endorsement of the ACES program and agrees with the NRC committee on its value.
Finding and Recommendation
Finding 3-13. The Advanced Collaborative Emissions Study, the Collaborative Lubricating and Oil Study on Emissions, and the project on Measurement and Characterization of Emissions from Advanced Technologies are comprehensive and cooperative projects that are investigating important issues related to heavy-duty diesel engine health effects. Based on the activities reported, the committee finds a high degree of collaboration among government agencies, national laboratories, and industry stakeholders.
Recommendation 3-9. The DOE should continue funding the Advanced Collaborative Emissions Study, the Collaborative Lubricating Oil Study on Emissions, and the project on Measurement and Characterization of Unregulated Emissions from Advanced Technologies until results are finalized and reported for all three studies.
Current heavy-duty diesel engines are extremely durable, in most cases performing reliably for more than 1 million miles in Class 8 truck applications. However, modern diesel engines have pushed the performance of materials to the limit. As the 21CTP develops the next generation of
40 James Eberhardt, DOE, “Overview of DOE Health Impacts Research,” presentation to the committee, November 15, 2010, Washington, D.C. See http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2010/health_impacts/ace00d_eberhardt_2010_o.pdf.
clean and efficient engines, new, higher-performance, lightweight, and cost-effective materials will be needed, as well as manufacturing and inspection methods and appropriate standards. An example of this need for materials is that the thermal efficiency of the diesel engine is enhanced with the ability to run the engine at higher peak cylinder pressures. Higher cylinder pressures and temperatures will challenge the current mechanical property limitations of many engine components, so new materials will be needed to achieve the engines’ efficiency potential. A second example is in the potential to reduce fuel consumption through the use of fuel injection systems with higher injection pressure, finer spray control, and multiple injection events. To realize these new fuel injection systems, new materials with higher strength, dimensional stability, and erosion resistance are needed. Lowering the rotation mass in valve trains and air-handling systems has the potential to improve engine response and thermal efficiency and to lower emissions. To capitalize on these potential performance improvements, cost-effective, lightweight material with superior mechanical properties is needed for valve train and air-handling components. Aftertreatment limitations include an incomplete understanding and optimization of catalysts, inadequate test methods for rapid age testing of catalysts, and inadequate sensors for process control or diagnostics. Other barriers to improved fuel efficiency are tribological limits of current lubricants.
The DOE’s Heavy Vehicle Propulsion Materials Team has been helpful in identifying commercial materials solutions introduced in 2007 engines. A number of these materials have been identified as enablers of higher-efficiency engines that are being developed for future engine technology. The Heavy Vehicle Propulsion Materials program has been instrumental in developing materials technologies for future engine technologies.
In general, advanced material needs include the following:
• Major engine components: cost-effective materials with higher strength and fatigue resistance (cylinder blocks, cylinder heads, pistons, cylinder liners, camshafts, crankshafts, bearings);
• Fuel injection systems: materials with higher strength, better dimensional stability, and erosion resistance;
• Valve train: cost-effective materials with lower reciprocating mass and greater wear resistance;
• Air-handling: corrosion-resistant materials for EGR systems; higher-strength and creep-resistant materials for turbocharger components;
• Exhaust systems: materials with higher strength and better creep resistance (DOE, 2011a).
As an example of advanced materials needs, cast components such as cylinder heads and engine blocks are limited at peak temperature and pressure by material tensile strength. Current engines with a peak cylinder pressure of 190 bar are approaching the design limit for traditional cast iron, with a tensile strength of 44,000 pounds per square inch. As cylinder pressures increase to 260 bar for engines with higher efficiency, midterm goals for tensile strength will be approaching 75,000 pounds per square inch, which exceeds the 65,000 pounds per square inch tensile strength for compacted graphite cast iron. Longer-term goals for tensile strength may approach 90,000 pounds per square inch as cylinder pressures approach 300 bar.41
Propulsion Materials Programs
There are a number of individual research programs in the area of propulsion materials for both light- and heavy-duty engines.42 This work is being conducted at the ORNL, ANL, PNNL, and LLNL. The majority of these programs are at the ORNL. Most are in cooperation with industrial partners of which many of the programs are CRADAs. The overall 21CTP budget for heavy vehicle propulsion materials had averaged about $5 million for the past decade. It was $4.86 million in FY 2009 and is $5.66 million in FY 2010. For FY 2011, the total budget for materials for internal combustion engines is expected to be $8.71 million, with an industry cost share of $5.15 million. Research areas include the following:43
• Internal engine components,
• Friction reduction,
• Fuel injection,
• Alternative fuel compatibility,
• Exhaust aftertreatment,
It is beyond the scope of this report to review each program individually, but a few are highlighted and listed in Appendix D. A complete list of 21CTP projects in the area of high temperature materials, conducted prior to 2007, can be found in project quad sheets for February 2007 (ORNL, 2007).
The DOE’s Heavy Vehicle Propulsion Materials Team also has been helpful in identifying commercial materials solutions that were introduced in 2007 engines. CF8C-Plus stainless steel was developed in an ORNL/Caterpillar CRADA. CF8C-Plus steel received a U.S. patent, and Caterpillar has filed foreign patent applications to facilitate commercial licensing. CF8C-Plus steel also received an
41 Response by 21CTP to committee question 52, Advanced Materials, received March 1, 2011.
42 Answers submitted by the 21CTP to committee questions.
43 Jerry Gibbs, DOE, “Materials Support for the 21st Century Truck: Lightweighting and Propulsion Materials,” presentation to the committee, November 15, 2010, Washington, D.C.
ASTM new-alloy designation. Caterpillar commercialized CF8C-Plus as the burner housing for the Caterpillar Regeneration System (CRS) on all CAT on-highway truck engines in January 2007. Deployed in the fall of 2006, more than 500 tons of CF8C-Plus steel have been cast to produce more than 35,000 CRS units.
The project continues in 2011 to explore thin-sections for turbocharger and manifold applications (Maziasz and Pollard, 2007).
Additional examples of successful projects that led to commercialization were presented on February 17, 2011, to committee members John Johnson and David Merrion.44Examples include the following:
• Development of high-performance inconel, titanium, and silicon nitride engine valves;
• Development of a piezoelectric control valve actuator for fuel injectors; and
• Exhaust aftertreatment research leading to improved catalyst durability, improved diesel particulate filter durability, and improved EGR cooler performance.
Finding 3-14. The propulsion materials program is addressing a broad range of materials issues associated with heavy-truck propulsion systems. Many of the initiatives are funded as CRADAs with significant industry cost sharing, showing strong support by industry for this area of work.
Recommendation 3-10. The DOE should fund programs in the areas outlined in its “21CTP White Paper on Engines and Fuels” (February 25, 2011) in the section “Approach to Reaching Goals” covering materials R&D for valve trains, major engine components, air-handling systems (turbochargers and EGR systems), and exhaust manifold sealing materials.
High Temperature Materials Laboratory
The High Temperature Materials Laboratory was established more than 20 years ago as a National User Facility to provide specialized, and, in some cases, one-of-a-kind instruments for materials research and characterization. The laboratory is located at the Oak Ridge National Laboratory housing six centers:
• Materials Analysis;
• Mechanical Characterization and Analysis;
• Residual Stress;
• Thermography and Thermophysical Properties;
• Friction, Wear, and Tribology;
Additional information on the HTML can be found in the NRC (2008) Phase 1 report, Chapter 3.
Capabilities of HTML that are of current value to the 21CTP through the Vehicle Technologies Program’s HTML User Program include the following (DOE, 2010d):45
• The Spallation Neutron Source (SNS)—a particle accelerator that provides neutron streams in short bursts, enabling the study of materials that are not in equilibrium and are changing dynamically;
• VULCAN—a diffractometer, which enables the investigation of stress formation in a material as it solidifies from the molten state as an alloy component (e.g., brake disk rotor, engine block);
• VENUS—which makes measurements of the absorption of neutrons by the various nuclei in the material. By doping some 6Li in with the predominant 7Li isotope, VENUS can create an image illustrating the flow of Li ions in a working Li-ion battery. Other applications of VENUS include viewing the lubricant flow in a working engine.
During FY 2009, HTML had 11 industry participants, 14 university participants, and 3 national laboratory participants. Projects focused on such topics as the following:
• Determine the effect of machining parameters on residual stress in ceramic diesel engine exhaust valves,
• Study the residual stresses resulting from piercing truck frame rails,
• Characterize the atomic structure of thermoelectric materials,
• Examine the plastic behavior of wrought magnesium alloys, and
• Determine the mechanical and thermal properties of fibrous diesel particulate filter materials.
These and other projects were described in detail in a presentation to committee members John Johnson and David Merrion on February 17, 2011.46
Perhaps just as important as the direct support of the 21CTP is the extensive benefit to the broader research and development community that comes from the research conducted at HTML. This research covers a wide range of challenging problems, for which solutions require the unique instrumentation at HTML as well as the expertise of the knowledgeable DOE researchers who oversee and operate the facility. The fact that many academic researchers, as well as industry research specialists, seek collaboration with
44 Ron Graves, ORNL, “Material Technology for the 21st CTP Program,” presentation to a subgroup of the committee, February 17, 2011, Oak Ridge, Tenn.
45 See 21CTP response to committee questions, submitted to the committee on November 12, 2010.
46 Edgar Lara-Curzio, ORNL, “Materials Characterization Capabilities at the High Temperature Materials Laboratory and HTML User Program Success Stories,” presentation to John Johnson and David Merrion, February 17, 2011, Oak Ridge, Tenn.
HTML speaks to the value of the facility to the advancement of knowledge on many fronts.
Finding 3-15. The High Temperature Materials Laboratory continues to be a valuable resource for materials research for the 21CTP, providing specialized and in many cases unique instrumentation and professional expertise. The expertise of those who oversee the laboratory, and therefore the value of HTML to all users, is enhanced by the participation of the HTML staff in the research.
Recommendation 3-11. The DOE should continue to provide 21CTP researchers and other potential users access to HTML, and it should make every effort to maintain support for HTML and to maintain the cutting-edge capability of the facility. Moreover, the DOE should provide sufficient funding for HTML, and for the research specialists who oversee and operate the facility, to enable continued research collaboration with the academic community, other government laboratories, and industry. In particular, HTML support should not be reduced to a level that allows only maintenance of the equipment for paying users.
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