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4 Powertrain Technologies
Pages 64-124

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From page 64...
... Examples would include new materials and manufacturing methods, and new chemistries or catalysts for aftertreatment systems. Changes in emissions regulations and fuels could also cause a shift in greenhouse gas (GHG)
From page 65...
... External combustion engines, such as Stirling, Rankine, and Brayton closed-cycle heat engine cycles, are presently not used in road vehicles as prime movers, but find application as waste-heat recovery systems. 4.2 MARKET TRENDS IN ENGINE USE Diesel engines continue to be dominant in Class 8 trucks and recently gained market share in Class 6.
From page 66...
... are well suited for SI engines.1 • The cost of fuels for SI engines is expected to remain below that for CI fuels (diesel) for considerable time due to large world demand for diesel fuel.
From page 67...
... . FIGURE 4-4 Technology allowed increased compression ratio (black)
From page 68...
... system. In a recent simulation study comparing SI and diesel engines for medium- and heavy-duty vehicles, Southwest Research Institute (SwRI)
From page 69...
... Interestingly for the Phase II rule, NHTSA and EPA selected a 6.8-L Ford V-10 engine to build a fuel map for use in the Greenhouse Gas Emissions Model for vocational vehicle simulation. This engine fuel map emulated a 627 g/bhp-h CO2 performance.
From page 70...
... Recommendation 4-1: As SI engines continue to be improved, NHTSA and EPA should reassess the future balance in MHDVs between SI and CI, and the reductions in GHG and fuel consumption that might be achieved with a more challenging efficiency requirement for SI engines, including an optimized low-carbon or renewable fuel. An assessment on the extent that high-efficiency technologies emerging in light-duty SI engines can be adapted to MHDVs should be carried out and could be part of an "interim evaluation" for MHDVs.
From page 71...
... collaboratives. These efforts support diesel engines' continuing ability to meet requirements for criteria emissions as well as fuel efficiency and GHG emissions.
From page 72...
... The introduction of SCR allowed higher engine-out emissions of NOx, and an associated 5 percent reduction in fuel consumption of the 2010 engines compared with the 2007 engines. However, a trade-off required an addition of about 2 percent (per unit diesel fuel uses)
From page 73...
... Anthony Greszler10 effectively summarized the NOx-fuel consumption trade-off as follows: • Trade-off between NOx and engine efficiency has been long established: o In-cylinder NOx reduction is highly detrimental to diesel cycle combustion efficiency. o Improvements in aftertreatment can lower NOx (at potentially high cost)
From page 74...
... • Focusing GHG regulation on vehicle rather than engine can help to lower NOx emissions at any regulated NOx standard. A key conclusion is that vehicle-level GHG improvements reduce the power demand, reduce fuel consumption, and thus reduce NOx (in g/ton-mile, for example)
From page 75...
... . For reaching a cycle standard of 0.02 g/hp-h NOx, what is needed, per MECA, is FIGURE 4-9 CO2 and NOx emissions from certification data over 14 years reveal progress and advantages of engine/ aftertreatment development and integration.
From page 76...
... Finding: Diesel engines using the well-known diffusion-dominated compression-ignition combustion are presently the most efficient engines for MHDVs, with progress evident for further reductions in CO2 and fuel consumption, and NOx emissions. Supported by the U.S.
From page 77...
... Equally significant, there are features of LTC that also can enhance engine efficiency and reduce GHGs. The fundamental technical issue or barrier to LTC combustion in diesel (and SI)
From page 78...
... and direct injection for the high-reactivity fuel (often diesel fuel)
From page 79...
... Research activity includes investigating the optimization of fuel composition for such approaches to obtain combustion at appropriate compression ratios and engine operating temperatures. Volatility of the fuel also plays a role in FIGURE 4-12 Drive-cycle fuel economy comparison of low-temperature combustion schemes: port fuel injection (PFI)
From page 80...
... in a modified DD15 engine with natural gas and diesel fuel as the two RCCI fuels. Brake thermal efficiency was improved 3.8 to 5.7 percent over the diesel baseline, peaking at about 46 percent, with 74 to 86 percent replacement of diesel fuel on an energy basis (Singh, 2015)
From page 81...
... Vehicle simulations with experimental LTC engine maps, as well as full light-duty (LD) vehicle tests have shown moderate potential fuel consumption benefits if practical emissions and operational challenges are overcome.
From page 82...
... The government-industry R&D portfolio should include determination of overall GHG reduction via LTC in comparison to advanced conventional combustion engines, including the applicability of WHR to both engine systems. The market uptake of LTC should be tracked and reported.
From page 83...
... The small (3 percent) quantitative separation between the two CO2 base cases implies that the combined effects of the NG engine efficiency gap13 and the methane tailpipe leakage basically eliminate the low-carbon advantage of natural gas.
From page 84...
... market as of January 2018.15 Finding: The thermal efficiency of the Westport HPDI natural gas engine appears comparable to current compression-ignition diesel engines, thus potentially providing a strong net CO2 reduction in heavy-duty engines, in contrast to SI natural gas engines with their efficiency impediment compared to diesels. Finding: Natural gas as a replacement fuel for diesel can contribute to reduced GHG emissions with the magnitude depending on the efficiencies of the engines and impact of NG leakage.
From page 85...
... . Two-stroke spark-ignition and diesel engines have been used in a number of on-highway vehicles and remain popular in handheld equipment and applications where power/weight and simplicity are imperative.
From page 86...
... . Simulated vehicle fuel consumption is described in Chapter 6.
From page 87...
... In November 2016, Wrightspeed and the Ratto Group introduced a refuse hauler powered by a gas turbine generator range extender hybrid, reported to achieve 70 percent reduction in fuel use in the refuse hauler operation compared to a conventional powertrain.17 In this special application, diesel engines are not able to meet emission standards and thus the alternative engine in the hybrid is SI. The single-shaft turbine generator is 80 kW but with the batteries and electric motors the max power is closer to 300 kW.
From page 88...
... In the example of Figure 4-17 engine heat rejection accounts for 24 percent of the fuel consumed, and exhaust sensible heat accounts for another 26 percent. Technologies and techniques exist or are under development that can recapture a portion of this rejected heat and help reduce vehicle emissions as well as reduce fuel consumption.
From page 89...
... Overall, WHR increased the system efficiency (i.e., decreased the fuel consumption) by about 6 to 7 percent.
From page 90...
... NHTSA and EPA's RIA noted a potential 25 percent penetration in some Class 8 segments by the end of the Phase II rule period. Recommendation 4-6: Industry and government should continue to research, develop, and apply WHR systems where technical and economic considerations are reasonable to capture this opportunity to reduce fuel consumption.
From page 91...
... . FIGURE 4-19 Organic Rankine cycle waste heat recovery system.
From page 92...
... energy production, together with improvements in vehicle fuel consumption, has improved the U.S. energy security position with regard to dependence on imports of petroleum.
From page 93...
... CARB studies show that renewable diesel can reach up to 70 percent greenhouse gas reduction compared to petroleum diesel, depending on feedstock and processing methods (Propel Fuels, 2015)
From page 94...
... Biodiesel reduces greenhouse gas emissions by 20 percent to about 80 percent (depending on fuel source and analysis) (EPA, 2009; Pradhan et al., 2012)
From page 95...
... Hence, unlike diesel fuel, there appear to be GHG benefits in SI engine fuels by future improvements in performance properties such as octane number. Tier 3 rules for criteria emissions include a further reduction in gasoline fuel sulfur level to 10 ppm starting in 2017.
From page 96...
... (ACT, 2015) , effectively resulting in an unacceptable payback period, since NG fuel consumption is exacerbated by its poorer engine efficiency.
From page 97...
... differential. 4.9.5.1 Impacts of Natural Gas Leakage on Overall GHG Benefits of Natural Gas–Fueled MHDVs Recent studies on natural gas supply chain leakage have estimated that relatively low levels of methane emissions could detract from the GHG reduction benefit that might otherwise accrue from the use of this fuel relative to diesel.
From page 98...
... , with the majority occurring in production and with decreasing amounts in processing, transmission, and distribution. Another 6 grams CO2-equivalent per MJ is attributed to flaring and fuel consumption (Venkatesh et al., 2012)
From page 99...
... Reference R Reference (Phase II) 1% 1.1% 28 10% 144.9 1 High MS, no leak, 100 y 20% 0.0% 28 10% 151.7 5% 2 Mid MS, no leak, 100 y 10% 0.0% 28 10% 147.1 2% 3 High MS, mid leak, 100 y 20% 2.2% 28 10% 143.1 -1% 4 Mid MS, mid leak, 100 y 10% 2.2% 28 10% 142.7 -2% 5 Mid MS, high leak, 100 y 10% 4.6% 28 10% 137.9 -5% 6 High MS, high leak, 100 y 20% 4.6% 28 10% 133.6 8% 7 Mid MS, mid leak, 20 y 10% 2.2% 84 10% 130.5 -10% 8 High MS, mid leak, 20 y 20% 2.2% 84 10% 119.3 -18% 9 Mid MS, high leak, 20 y 10% 4.6% 84 10% 115.1 -21% 10 High MS, high leak, 20 y 20% 4.6% 84 10% 89.1 -39% NOTE: CO2e, carbon dioxide equivalent; GHG, greenhouse gas; GWP, global warming potential; MS, market share; NGV, natural gas vehicle; WTW, well to wheels.
From page 100...
... NG engines designed for direct injection of the fuel are found to have much reduced methane tailpipe and methane crankcase leakages, based on their fuel delivery and lean combustion characteristics. Recommendation 4-9: Given the significance of WTW methane leakages and losses on GHG reduction, NHTSA and EPA should monitor progress on all of those errant upstream methane emissions and use a regulatory approach that accounts for them along with the tailpipe GHG emissions.
From page 101...
... . To account for a potential bias in methane leakage rate estimates, and also to account for choices of GWPs with different integration periods,25 four scenarios were considered: (1)
From page 102...
... NOTE: CNG, compressed natural gas; LNG, liquefied natural gas; SI-ICEV, spark-ignition internal combustion engine vehicle; CI-ICEV, compression-ignition internal combustion engine vehicle; HEV, hybrid electric vehicle; BEV, battery electric vehicle; H2-FCEV, hydrogen fuel cell electric vehicle; mpg, miles per gallon. aThe baseline petroleum fuel pathway is marked.
From page 103...
... The methane leakage rate is defined as the volumetric percentage of natural gas produced that is lost through venting or fugitive leaks. It includes fugitive methane emissions from the natural gas system, boil-off leaks from production and storage of LNG, and crankcase and tailpipe methane leaks from FIGURE 4-22  Life-cycle GHG emissions of Class 2b pickup truck for different fuels, including electricity, diesel, gasoline, propane, natural gas, Fischer-Tropsch fuels with a variety of different assumptions on fuel source and end use.
From page 104...
... The break-even life-cycle methane leakage rate identifies the methane leakage rate at which the natural gas fuel pathway and vehicle would have the same life-cycle greenhouse gas emissions as diesel. The figure can be interpreted as follows: If the vehicle fuel efficiency of the natural gas vehicle is the same as that of the diesel vehicle (i.e., it has a value of 0 percent)
From page 105...
... that enables a NG vehicle to be lower emitting than a comparable diesel vehicle, as a function of relative fuel economy of natural gas vehicles (the percentage difference between the fuel efficiency of a natural gas–fueled vehicle and that of a diesel vehicle)
From page 106...
... On the other hand, if the SI natural gas engine had a 25 percent efficiency disadvantage, a leakage rate of zero would be needed for natural gas to have any GHG advantage. Finding: With the present understanding of methane leakage levels and the efficiency of diesel versus natural gas engines, natural gas provides little or no GHG benefit over diesel-fueled vehicles.
From page 107...
... . FIGURE 4-27 Well-to-wheels analysis of GHG emissions of CNG vehicles and diesel-fueled vehicles.
From page 108...
... BOX 4-1 1. The bag-weighted fuel economy, in miles per gasoline gallon equivalent, varied in direct proportion to the Wobbe Index for all vehicles in the study.
From page 109...
... The better the lubricating oil is dispersed, the more efficient. Compared to the opportunity for fuel savings through the engine, with its 42 to 48 percent efficiency today, the transmission would appear to TABLE 4-8  Typical Transmission Types by Vehicle Weight Class Vehicle Weight Class Transmission Types 2b 4, 5 3 4 4 4 5 1, 2, 3, 4, 6 6 1, 2, 3, 4, 6 7 1, 2, 3, 4 8 1, 2, 3, 4 NOTE: 1, mechanical transmissions; 2, automated mechanical transmissions with dry or wet clutches; 3, automated mechanical transmissions with torque converters; 4, automatic transmissions; 5, continuously variable transmissions; 6, dual clutch transmissions; 7, hybrid transmissions, electric and hydraulic.
From page 110...
... Lubrication improvements come from changes in the lubricant and changes in the internal transmission design to better ensure fluid is moved to the gear interfaces effectively. Gearing changes are regularly improved to adapt to the preferred engine speeds for fuel consumption and the axle ratios available.
From page 111...
... POWERTRAIN TECHNOLOGIES 111   FIGURE 4-28 Power use inventory for Class 8 heavy truck: base (upper) , and with 21st Century Truck Partnership goals (lower)
From page 112...
... For passenger cars and light trucks, the trend is to increase the number of gears substantially. For heavy diesel engines, the trend is to flatten out the brake specific fuel consumption curves at the best fuel consumption points.
From page 113...
... POWERTRAIN TECHNOLOGIES 113 FIGURE 4-29 Transmission production share in passenger cars and light trucks.
From page 114...
... . FIGURE 4-31 Allison transmission share by vehicle weight class and vehicle type.
From page 115...
... It provides a reasonable example of the added cost of technology. Increased Shifting Density: As engine, transmission, and vehicle OEMs work to improve fuel consumption and reduce greenhouse gas emissions, engine speeds are decreasing.
From page 116...
... 116 REDUCING FUEL CONSUMPTION AND GREENHOUSE GAS EMISSIONS OF MEDIUM- AND HEAVY-DUTY VEHICLES   FIGURE 4-33 Automated mechanical transmissions payback calculator.
From page 117...
... As mentioned elsewhere, NHTSA should immediately be collecting information on the details of vehicle production. 4.11 AXLES AND DRIVELINES For fuel consumption purposes, axle developments related to gearing, lubrication, weight, and axle ratio are the most important.
From page 118...
... These developments appear to still be in the early concept and research phases. Such developments will provide small improvements in overall vehicle fuel consumption.
From page 119...
... 2012. Enabling High Efficiency Direct Injection Engine with Naphtha Fuel through Partially Premixed Charge Compression Ignition Combustion.
From page 120...
... 2015a. Proposed Rulemaking for Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles–Phase 2 Draft Regulatory Impact Analysis.
From page 121...
... 2009. Life-cycle assessment of energy use and greenhouse gas emissions of soybean-derived biodiesel and renewable fuels.
From page 122...
... 2014. Reducing the Fuel Consumption and Greenhouse Gas Emissions of Medium- and Heavy-Duty Vehicles, Phase Two: First Report.
From page 123...
... 2012. Reassessment of life cycle greenhouse gas emissions for soybean biodiesel.
From page 124...
... 2012. Uncertainty in life cycle greenhouse gas emissions from United States natural gas end-uses and its effects on policy.


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