Reducing Fuel Consumption and Greenhouse Gas Emissions of Medium- and Heavy-Duty Vehicles, Phase Two Final Report (2020) / Chapter Skim
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5 Technologies for Reducing the Power Demand of MHDVs
5 Technologies for Reducing the Power Demand of MHDVs
Pages 125-172
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From page 125... ...
, to describe the three vehicle power demand (VPD) energy consumers: aerodynamic drag, rolling resistance, and inertia/braking loss.
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Technology Goal 2: Develop and demonstrate low-rolling-resistance tires that can reduce vehicle rolling resistance and wheel weight for a Class 8 tractor-trailer. Demonstrate 35 percent reduction in rolling resistance
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The status of the research, development, and deployment achieved for each of the six vehicle power demand fuel consumption domains is found in the following sections. 1 Sharpe,B., ICCT.
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, and the trucking industry to develop an inclusive new baseline for vehicle power demands as described in the above finding, for a circa 2025 vehicle that includes an extended period of operation. 5.2 AERODYNAMIC DRAG REDUCTION This section addresses aerodynamic development only for Class 8b combination tractor-van trailers.
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From page 129... ...
The fuel gallons/1,000 freight-ton-miles metric is also referred to as "freight efficiency." Certification was achieved via exercise of the EPA's Greenhouse Gas Emissions Model (GEM) simulation utilizing supplier data for the incumbent combination vehicle.
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. TABLE 5-4 GEM Inputs for the Baseline Class 7 and 8 Tractor Class 7 Class 8 Day Cab Day Cab Sleeper Cab Low Roof Mid Roof High Roof Low Roof Mid Roof High Roof Low Roof Mid Roof High Roof Engine 2017 MY 2017 MY 11L 2017 MY 2017 MY 2017 MY 2017 MY 2017 MY 15L 2017 MY 2017 MY 11L Engine Engine 350 11L Engine 15L Engine 15L Engine 15L Engine Engine 455 15L Engine 15L Engine 350 HP HP 350 HP 455 HP 455 HP 455 HP HP 455 HP 455 HP Aerodynamics (CdA in m2)
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Some of those valuable estimates can be found in the 21st Century Truck Partnership activities and the SuperTruck projects. Also the examples in SmartWay give insights on the drag reduction of particular devices.
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Recommendation 5-2: The magnitude of the ambient turbulence intensity and close-proximity vehicle passing turbulence scenario should be evaluated by EPA and NHTSA to quantify its significance. 4 Therolling resistance coefficient (kg force per metric ton)
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. In addition, some expected results are discussed from yet-to-be-completed projects.6 Four project teams variously identifying similar aerodynamic component modifications, which are described in detail in the Annex to this chapter entitled "Summary of SuperTruck Projects." In most cases, the ST project work will first seek optimum performance of potential aerodynamic features.
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134 REDUCING FUEL CONSUMPTION AND GREENHOUSE GAS EMISSIONS OF MEDIUM- AND HEAVY-DUTY VEHICLES FIGURE 5-2 Features identified to reduce aerodynamic drag of Cummins-Peterbilt SuperTruck. SOURCE: Peterbilt Motors Co.
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. 5.2.4 Expect Continuing Advancements in Aerodynamics and Computational Fluid Dynamics Methods Discovery of new approaches to reducing aerodynamic drag continues as well as the development of more powerful CFD tools for analysis.
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136 FIGURE 5-5 Scale-model demonstration of sail effect, as well as the physical forces involved. SOURCE: Salari (2016)
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Recommendation 5-3: Given the incentive for aerodynamic drag reduction, the rapid progress in CFD, and emerging innovations, the post-2027 potential for reducing Cd should be reevaluated in an interim review.
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This section will highlight several areas of concern and areas for potential development of tires and other methods for reducing the rolling resistance of commercial vehicles today and into the future. Box 5-1 lists a number of parameters that must be considered in the design of a tire.
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ran a small test to determine the correlation between the coefficient of rolling resistance and the stopping distance of a combination vehicle. The conclusion from that report is quoted in the RIA: "The results of this research suggest that tire rolling resistance is not a reliable indicator of Class 8 tractor-trailer stopping distance" (EPA and NHTSA, 2016a, p.
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FIGURE 5-8 Tire rolling resistance progress estimated from 1995 to 2013, and projected to 2022, showing dual tires (blue) and wide-base singles (red)
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Recommendation 5-5: Prior to the promulgation of the next phase of regulations, additional work should be done by NHTSA with current commercial vehicle tires and loadings to determine the balance needed among tread wear, rolling resistance, and traction. Vehicles should be outfitted with all required safety systems, such as stability control.
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NOTE: Appears with permission of Daimler Trucks North America's Product Compliance and Regulatory Affairs Department. SOURCE: Kayes (2015)
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. FIGURE 5-13 Wet traction peak and slide numbers vs ISO 28580 rolling resistance for asphalt and concrete.
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European regulations require this information be made available to the public. Recommendation 5-6: NHTSA should work with manufacturers to implement a method of making information on tire rolling resistance available to users.
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. FIGURE 5-16 EU tire labeling for wet grip, showing parameters by vehicle class.
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. Other reports have discussed the importance of tire pressure to optimize tire rolling resistance and traction.
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Transmission controls also have methods of controlling the vehicle to encourage driver intervention. Such techniques could be used to ensure action is taken to properly inflate tires when using a tire pressure monitoring system.
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5.3.5 Alternative Methods to Reduce Rolling Resistance Tire Configuration. Rolling resistance can be reduced by minimizing the amount of rubber on the road other than by using next-generation wide-based single tires.
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Additional Axles to Allow More Weight per Vehicle Adds to Rolling Resistance. Other sections of this report discuss how different tire and axle configurations can improve the productivity of commercial vehicles.
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. 5.3.7 Future Developments A limited number of items are known to the committee to be in development related to both tires and alternative methods for reducing the rolling resistance of commercial vehicles.
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The press release mentions evaluations suggesting it has better fuel efficiency. More research is needed to establish developments that will lead to tires with reduced rolling resistance or better construction to prevent losses from flexure, either in the sidewalls or in the treads.25 Retreading of Next-Generation Wide-Based Singles.
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primarily through tire rolling resistance and unrecovered energy used when accelerating or grade climbing. The energy needed to overcome these resistances is essentially linearly dependent on truck weight.
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In cases where the vehicle is weight limited (meaning at its maximum allowable weight) , the mass reduction can be translated to additional payload for higher freight efficiency (fewer gallons per ton-mile)
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. Weight reduction technologies are also needed to maintain current freight efficiency levels because of legal requirements, notably the selective catalytic reduction (SCR)
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FIGURE 5-24 Sensitivity of fuel consumption to vehicle weight of Class 8 vehicle simulated on 5 test cycles. Further details about the SwRI vehicle modeling are provided in Chapter 6.
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Examples of recent lightweighting studies and demonstrations are shown in Table 5-7. All four of the SuperTruck teams included weight reduction in their strategies for achieving the program goal of 50 percent increase in freight efficiency, ranging from two to five percentage points, or 4 to 10 percent improvement over the baseline.
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. Walmart report on Freightliner Total weight reduction 2010 (125BBC)
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Studies of cost effectiveness of weight reduction have often found lightweighting to be one of the less attractive options, perhaps because the materials substitution options are the most considered. Meszler and colleagues; 2015 review of technology cost effectiveness reviewed the prior studies and produced a range of costs for lightweighting shown in Figure 5-25.
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. Finding: The cost of weight reduction is highly variable and dependent on the technical approach, and can range from a negative cost to over $10 per pound.
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Vehicle OEMs routinely install the engine at a slight angle in order to minimize the losses in the universal joints of the driveline that take up the difference in angle from the engine flywheel to the input to the drive axle. 5.6 AUXILIARY LOADS Both auxiliary and accessory loads are consumers of fuel energy delivered by engine power, and through various paths. We consider here only diesel engines, the favored selection for Class 6 through 8 trucks.
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The alternator, as auxiliary, provides the vehicle electricity for lighting, heating/ventilating, powertrain electronics, battery charge, and myriad other functions. Auxiliaries satisfy vehicle functions, so are included as "vehicle power demands." They regularly evolve, often to satisfy occupant comfort-hotel loads (heating, ventilation, and air conditioning [HVAC]
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The auxiliaries converted to electrical power on the research demonstration vehicle were the HVAC, brake air compressor, and accessories: oil and water pumps. This system was prototyped and demonstrated on a Class 8 truck.
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Yet it is valuable to the intended project objectives to have had close engineering scrutiny of these components. Finding: There has been a modicum of agency funding to improving the vehicle power demand of auxiliaries.
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5.8.1 Cummins-Peterbilt Project The baseline tractor-trailer at the target 65,000 pounds GVW, performed in freight efficiency terms at 101 ton-miles per gallon, corresponding with the more useful LSFC of 9.9 gallons per 1,000 ton-miles, and the more familiar fuel economy figure of 6.45 mpg, over the long-haul duty cycle. This project has reported final performance results of a 76 percent increase in freight efficiency (50 percent goal)
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. FIGURE 5-27 Cummins-Peterbilt final SuperTruck in show paint.
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. These figures plus the corresponding remarkable fuel economy was 12.2 mpg, all tested at 65,000 pounds GVW in their Texas long-haul cycle.31 Daimler included a number of aerodynamic features in their final SuperTruck tractor's cab such as widening it to match the sleeper width, and raking back both the grill and windshield (see Figure 5-28)
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. 5.8.3 Volvo Group Project Volvo Trucks North America's SuperTruck project successfully demonstrated fuel efficiency of greater than 12 miles per gallon, 88 percent greater freight efficiency, and 70 percent better fuel efficiency than the baseline 2009 Volvo model VNL 670.32 Lightweighting was a key approach for Volvo.
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From page 168... ...
According to Navistar,33 the key features of their CataLIST truck are • Advanced integration of the Navistar® N13 Engine utilizing proprietary intelligent controls and high efficiency combustion; • Reduction in aerodynamic drag through replacement of cab- and hood-mounted mirrors with a series of cameras and interior-mounted monitors, which also yield equal or better indirect vision for the driver; • A new light-emitting diode (LED) headlamp system that reduces lamp size for a more aerodynamic shape and cuts electrical power requirements by greater than 80 percent, while improving luminous output and light color for improved night-time direct driver vision and reduced driver fatigue; • An all-new shape with a sloped windshield and wedged cab for improved aerodynamics, and innovative use of lighter-weight carbon-fiber panels in the upper body, roof headers, back panel, and dash panel; • A hybrid front suspension and lightwei.ght rear suspension that leverages lightweight alloys with composite materials, reducing weight and enabling an electronic ride height management system, which provides dynamic ride height and pitch control for improved aerodynamics; • An electronic ride height management system, which provides dynamic ride height and pitch control for improved aerodynamics; and • Aerodynamic improvements that reduce the trailer's drag coefficient by more than 30 percent.
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2013. 21st Century Truck Partnership, Roadmap and Technical White Papers.
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2015. The Place of Low Rolling Resistance Tires in EPA's Greenhouse Gas Reduction Strategy.
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2009. NHTSA Tire Fuel Efficiency Consumer Information Program Development: Phase 2 -- Effects of Tire Rolling Resistance Levels on Traction, Treadwear, and Vehicle Fuel Economy.
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2016. Prediction of Rolling Resistance and Tread Wear of Tires in Realistic Commercial Vehicle Application Scenarios.
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