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5
Parasitic Losses of Energy
INTRODUCTION
The role of parasitic losses of energy has been important throughout the history of the 21st Century Truck Partnership (21CTP). The latest statement of overall goals for reduction of parasitic energy loss is in the Partnership’s updated roadmap (DOE, 2006a). The goals in this area have been refined substantially since the version of the year 2000 (DOE, 2000).
The energy audit data for the parasitic loss elements for the baseline and the target goals is given in Table 5-1, listed by goal.
GOALS AND OBJECTIVES
The technical goals and milestones for parasitic losses given in the latest versions of the 21CTP Roadmap (DOE, 2006a):
Goal 1:
Develop and demonstrate advanced technology concepts that reduce the aerodynamic drag of a class 8 highway tractor-trailer combination by 20 percent (from a current average drag coefficient of 0.625 to 0.500).
Goal 2:
Develop and demonstrate technologies that reduce essential auxiliary loads by 50 percent (from current 20 hp to 10 hp) for class 8 tractor-trailers.
Goal 3:
(21CTP-003)—Develop and demonstrate light-weight material and manufacturing processes that lead to a 15 to 20 percent reduction in tare weight (for example, a 5,000-lb weight reduction for class 8 tractor-trailer combinations).
Goal 4:
A. Increase heat-load rejected by thermal management systems by 20 percent without increasing radiator size to accommodate future increased engine power requirements or allow reduced radiator and cooling system size at constant power.
B. Develop and demonstrate technologies that reduce powertrain and driveline losses by 50 percent, thereby improving class 8 fuel efficiencies by 6 to 8 percent.
Goal 5:
Reduce tire rolling resistance values relative to existing best-in-class standards by 10 percent without compromising cost or performance. (This has not been an active area of research.)
The five goals are discussed in the text that follows.
GOAL 1:
DEVELOP AND DEMONSTRATE ADVANCED TECHNOLOGY CONCEPTS THAT REDUCE THE AERODYNAMIC DRAG OF A CLASS 8 TRACTOR-TRAILER COMBINATION BY 20 PERCENT (FROM A CURRENT AVERAGE DRAG COEFFICIENT OF 0.625 TO 0.5)
Background
The 21CTP’s efforts in the area of aerodynamic drag reduction followed directly from activities undertaken under the DOE Heavy Vehicle Aerodynamics Multiyear Program Plan (MYPP) (DOE, FCVT, 2006a), which had its beginning at the First DOE Workshop on Heavy Vehicle Aero dynamic Drag, held in Phoenix, Ariz., on January 30-31, 1997 (McCallen et al., 1998). The goal of the group as stated in the MYPP was as follows (DOE, 2006b):
The goal of the proposed activities is to develop and demonstrate the ability to simulate and analyze aerodynamic flow
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TABLE 5-1 Energy Audit—Baselines and Targets (80,000-lb Gross, 65-mph Level Road)
Goal/Technical Area
Baseline
Target
Delta
Improvement (percent)
Primary Technology Goals
Goal 1: Aerodynamic losses
85 kW/114 hp
68 kW/91 hp
17 kW/23 hp
20
Goal 2: Auxiliary loads
15 kW/20 hp
7.5 kW/10 hp
7.5 kW/10 hp
50
Goal 3: Reduce tare weight
12,245 kg/27,000 lb
9,795 to 10,410 kg/21,600 to 22,950 lb
1,837 to 2,450 kg/4,050 to 5,400 lb
15 to 20
Other Technology Goals
Goal 4: Thermal management and friction and wear
Goal 4a: Waste heat rejection
Increase in cooling heat rejection by 20 percent without increasing radiator size.
Goal 4b: Powertrain losses
9 kW/12 hp
4.5 kW/6 hp
4.5 kW/6 hp
50
Goal 5: Rolling resistance
10 percent reduction relative to existing best in class
SOURCES: DOE, 2000; DOE, FCVT, 2006.
around heavy truck vehicles using existing and advanced computational fluid dynamics (CFD) tools. The final products are validated CFD tools that can be used to reduce aerodynamic drag of heavy truck vehicles and thus improve their fuel efficiency.
The team included participants from DOE national laboratories, universities, and the National Aeronautics and Space Administration (NASA). Visits were made to truck and trailer manufacturers to get their views on the issues to overcome in order that lower drag heavy vehicles would be commercially viable. Workshops were held and reports on the work of the various participants were issued on a regular basis through 2005. These reports are available at the DOE Scientific and Technical Information web site.1 In each working group report the project goals were reaffirmed in the following form through 2003 (with some variation in the items listed in parentheses in the last line):
Perform heavy vehicle computations to provide guidance to industry
Using experimental data, validate computations
Provide industry with design guidance and insight into flow phenomena from experiments and computations
Investigate aero devices (e.g., boattail plates, side extenders, …)
In the report of the July 2004 meeting of the working group (the last line was changed as follows including the bold type for the last part of the statement).
Investigate aero devices with emphasis on collaborative efforts with fleet owners and operators.
The reports for 2005 reaffirm this statement of goals. Reports on the work on aerodynamic drag from 2006 appear in a different form as parts of the annual progress report of the Heavy Vehicle Systems Optimization Program (DOE, FCVT, 2005a) and the 2000 Heavy Vehicle System Review (NRC, 2000a).
The work began, as the goal statement reflects, with a primary focus on computational tools and with experiments expected to serve the purpose of supporting the computational tool developed, as opposed to the experimental program being a parallel path for development of drag reducing design features. The computational tools on which the majority of resources were expended were codes that had their origins at the national laboratories. By 2001 a number of truck manufacturers were invited to the working group meetings and made presentations on their approaches to aerodynamic development. The principal manufacturers all had small in-house teams who had a history of doing experimental development in wind tunnels and who had recently begun evaluating and using commercial computational fluid dynamic (CFD) codes. Although the truck manufacturers were somewhat interested in the claims of the team about the potential power of their CFD codes, their opinion was that the only way the features would become feasible for industry use would be if the features were incorporated into commercial codes that would be accessible to all and maintained for customers over time.
The DOE heavy vehicles team organized a conference on the aerodynamics of heavy vehicles (DOE, 2004). Kevin Cooper of the National Research Council, Canada, gave the keynote paper, “Commercial Vehicle Aerodynamic Drag Reduction: Historical Perspective as a Guide” (Cooper, 2004). Cooper gave a concise history of prior work on truck aerodynamics and demonstrated that data were already available to allow assessment of the potential of a number of drag reducing devices including tractor-trailer gap closure, trailer skirting, and boat-tailing, and had been available for several
1
Available at http://www.osti.gov/.
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decades. He cited a number of important sources that do not appear in any references in the reports on the DOE HV program. Cooper challenged the following claims, which appeared in the then-current version of the MYPP (McCallen et al., 1998).
At present the aerodynamic design of heavy trucks is based largely upon wind tunnel estimation of forces and moments, and upon qualitative streamline visualization of flow fields. No better methods have been available traditionally, and the designer/aerodynamicists are to be commended for achieving significant design improvements over the past several decades on the basis of limited quantitative information.
The trucking industry has not yet tapped into advanced design approaches using state-of-the-art computational simulations to predict optimum aerodynamic vehicles. Computational analysis tools can reduce the number of prototype tests, cut manufacturing costs, and reduce overall time to market.
Cooper went on to report on a case study undertaken over a three-week period (which again validated the size and plausibility of the existing program goals) leading up to his presentation in which the Canadian National Research Council took an existing truck model, fabricated tractor and front trailer skirts, fabricated beveled base panels to emulate a simple boat tail, fabricated skirts for the area behind the trailer wheels, fabricated a gap seal between tractor and trailer, and fabricated a filler block to completely close and fill the gap. Design had to be done before the fabrication. In one 8-hour shift of wind tunnel time the effect of these parts singly and in selected combinations on drag was measured over yaw angles from −20 to +20 degrees. The results get close to the Technology Roadmap target of a drag coefficient of 0.5, even though the tractor itself is not as streamlined as a number of currently available tractors.
Another project carried out under the Heavy Vehicle Aerodynamic Drag Program is quite distinct and has been an active project for almost the entire period from the initial MYPP. The project explored the potential for pneumatic devices to actively control flow separation in critical regions to reduce drag. This project has provided some substantial drag reductions. However, the methodology remains questionable for practical use because of the complexity of the active devices. The project team from the Georgia Tech Research Institute continues to develop the systems.
As mentioned earlier, input from truck manufacturers beginning about 2001 indicated that commercial CFD codes were more likely to become useful tools for industry than the codes developed in the national laboratories due to ease of use issues and code maintenance. A project was added to the program led by Argonne National Laboratory to evaluate commercial codes by applying selected ones to the same geometries that were the subject of simulation in the ongoing projects using national laboratory codes.
Around 2004, a project was initiated under a contract with the Truck Manufacturers Association, with the title “Test, Evaluation, and Demonstration of Practical Devices/Systems to Reduce Aerodynamic Drag of Tractor/Semi-trailer Combination Unit Trucks.” The participants were Freightliner LLC, International Truck and Engine Corp., Mack Trucks, Inc., and Volvo Trucks NA. Reports on this project appear in the 2005 and 2006 annual progress reports on the Heavy Vehicle Systems Optimization Program (DOE, FCVT, 2005a, 2006). Each of the companies focused on a different aspect of the tractor-trailer aerodynamics. The combined results in 2006 indicate a potential for meeting the 20 percent reduction in drag that has been the target since the first technology roadmap.
Goals, Targets, and Timetables
The goal for aerodynamic drag reduction has been a 20 percent reduction of drag coefficient from 0.625 to 0.5 since the first technology roadmap (DOE, 2000). Although mention has been made from time to time of achieving the target by a particular date, the working documents have not included timetables as part of the primary goals and objectives.
In fact, the frequently restated goals of the program appearing in every report of a workshop meeting as quoted in the background section do not mention the technology roadmap goal for drag coefficient or a timeline, but instead are stated in terms of process. DOE should make sure that truck manufacturers have commercial CFD codes that are usable for making aerodynamic drag calculations.
Progress Toward Objectives
As reported by McCallen, devices have been identified that will reduce drag to the target levels.2 A reading of the reports and related information as cited in the background section indicates that methods and devices capable of achieving the target levels were already available as the MYPP was being put together. Practical problems of implementation were and remain major barriers to application of known techniques. Since the barriers to implementing modified aerodynamic designs are potentially different for each fleet owner or operator, CFD design tools may prove to be helpful to truck and trailer manufacturers in exploring the multitude of design changes to address the needs of individual fleet owners. It appears that these CFD programs have been developed to handle aerodynamic design issues, because they are currently used by race car builders.
2
Rose McCallen et al., “DOE’s Effort to Reduce Truck Aerodynamic Drag through Joint Experiments and Computations.” Presentation on work performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract W-7405-ENG-48. April, 2006. Available at http://www1.eere.energy.gov/vehiclesandfuels/pdfs/hvso_2006/02_mccallen.pdf. Accessed June 2, 2008.
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GOAL 2.
DEVELOP AND DEMONSTRATE TECHNOLOGIES THAT REDUCE ESSENTIAL AUXILIARY LOADS BY 50 PERCENT (FROM CURRENT 20 HP TO 10 HP) FOR CLASS 8 TRACTOR-TRAILERS
Background
In all modern vehicles powered by internal combustion engines, there are auxiliary components and subsystems that are necessary to operate the vehicle. Examples of these auxiliaries are the alternator, power steering pump, air conditioning compressor, and pneumatic air compressor. Additional power requirements which consume energy that otherwise would propel the vehicle and are closely associated with the powertrain but nonetheless reduce the overall efficiency of the vehicle include the oil pump, coolant pump, fuel injection pump, fuel supply pump, transmission, and differential gear sets. This group of components and subsystems are addressed in the chapter under Goal 4: Thermal Management and Friction and Wear.
Engine Accessories
The parasitic losses associated with auxiliary loads are approximately 20 hp for a typical heavy-duty vehicle (DOE, FCVT, 2006). To minimize additional power transfer losses, these components are normally directly driven by the engine crankshaft or camshaft through a series of the serpentine belts, chains or gear sets. The decision to drive these auxiliaries off the crankshaft or camshaft is influenced by in-vehicle packaging constraints, rotational speed ranges of the individual components and other system dynamic factors such as torsional excitation, system natural frequencies, and under-hood heat sources.
Besides the actual design and internal mechanical losses of the auxiliaries themselves, a condition that directly impacts their efficiency of operation is their direct connection to the engine. This results in many non-optional compromises that reduce operational efficiency over the engine and vehicle duty cycle. One example of this compromise is the power steering pump; where sufficient pressure to navigate the vehicle under low speed conditions results in excess pressure at high vehicle speeds, where limited power steering assistance is needed.
Under the 21CTP program, several projects directed toward the optimization of operational parameters for auxiliaries have been conducted. The most noteworthy of these has been the More Electric Truck (MET) program conducted by Caterpillar.
The MET program focused on the design, development, and demonstration testing of electrically powered auxiliary components and systems that would allow anti-idling operation (main engine shut-off, yet offering auxiliary power for accessories and/or cabin heating/cooling). The subsystems included:
Modular HVAC Unit
Shore Power Electrical Converter
Integrated Starter-Generator
Electric Oil Pump
Electric Compressed Air Module
Electric Water Pump
In addition, the necessary power distribution architecture was developed, integrated and tested, as were the supervisory control algorithms. The removal of these auxiliaries from the engine system loads also reduces the radiator heat loading, since less fuel is consumed by the main engine for the same propulsion energy.
Caterpillar reported a demonstrated fuel economy improvement of 1 to 2 percent in over-the-road operation. Assuming an average operational power of 250 hp, this represents a reduction in auxiliary loading of about 2.5 to 5 hp.
The anti-idling of the main engine was offset by the use of a small diesel powered auxiliary power unit (APU) and a shore-power converter for use in an electricity-enabled overnight parking center. This strategy demonstrated the potential to provide an additional 5 to 7 percent yearly fuel savings. A more detailed discussion concerning idle-reduction technologies and programs conducted under the 21CTP program are included in Chapter 6 of this report.
Other Parasitic Loss Reduction Program
During the period FY 2005-FY 2007, many other programs were classified under the general heading of “Reducing Essential Power Loads by 50 Percent.” Although some of these may tend to cross over into other technical areas of focus, such as secondary energy recovery through turbo-compounding, they all are associated with increasing the percentage of fuel energy that is used to propel the vehicle. A partial list of these programs includes:
Advanced Brake Systems for Improved Undercarriage Aerodynamic Flow
Evaluated impact of new brake materials and designs on undercarriage aerodynamic flow
Assessed effect of design and material improvements on necessary brake cooling, under-hood temperature and overall vehicle thermal management
Evaluate Autothermal Diesel Reformer
Assessed fuel injection technology that could allow autothermal diesel reformation that would produce hydrogen to be used by on-board fuel cell APU
Optimize Boundary Layer Lubrication Mechanisms for improved friction characteristics and component life
Developed a model for scuffing mechanism based upon adiabatic shear instability
Established and validated performance and failure prediction methodologies for lubrication systems
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Applied X-ray-based techniques to characterize tribofilms
Eaton Corporation demonstrated methods to improve drivetrain efficiency achieving a 2.5 percent improvement in vehicle fuel efficiency
Reduce Engine Friction by Advanced Tribological Concepts
Evaluated potential friction reduction through the use of advanced lubricants, additives, and low-friction engineered surfaces
Developed engine/vehicle models to predict fuel economy savings
Predicted fuel economy improvement of 0.5–1.4 percent with low friction surfaces
Improved Cooling Fan and System Performance and Efficiency
Designed and demonstrated 5 percent flow and 10 percent efficiency improvement of large axial fan
Demonstrated improvements of aerodynamic fan shroud
Demonstrated high pressure air fine debris filtration for high performance radiators
Determine Feasibility of Nanofluid Application in Heavy Vehicle Engine Cooling for Improved Efficiency
Designed, fabricated and tested experimental test facility
Quantified experimental test section heat losses
Evaluate boiling critical heat fluxes and pressure drops of nanofluids Efficient Cooling in Engines with Nucleate Boiling
Reduced cooling system size by development of more efficient heat transfer method
Developed two-phase flow engine cooling heat transfer rates and pressure drops
Determined practical limits of engine coolant boiling
Develop Nanofluids with Ultra-high Thermal Conductivity
Developed gold-based nanoparticle-water suspension that increased thermal conductivity by 10 percent over water
Conducted laminar flow experiments and developed analytical model for effective viscosity of nanofluids
Determine Erosive Effects of Nanofluids for High Efficiency Radiator Systems
Analyzed and developed predictive models for erosion of radiator systems caused by the use of nanofluids
Measured baseline data on erosion of aluminum radiator systems due to use of Cu-based nanofluid
Evaluated tribological effects of nanofluids
Develop Integrated Under-hood Thermal Analysis for Cooling System Optimization and Radiator Size Reduction
Developed predictive capability in cooperation with Cummins to identify hot-spots inside divided engine compartments of off-road machine
Prototypical test rig constructed at Caterpillar and experiments conducted to validate 1D and 3D simulation methods
Validated integrated system analysis methodology for effects of ventilation on heat rejection and component temperatures
Powertrain System Efficiency Improvement through Reduction of Friction and Wear
Cooperative program conducted with Eaton Corporation to reduce friction and parasitic energy losses in truck transmissions and axles
Conducted friction predictions utilizing a range of surface characteristics, lubricants and surface topographies of gears
Demonstrated significant potential for parasitic energy loss reduction
Calibrated rough surface contact model using test data
Developed and calibrated in-situ boundary film analysis capability
Finding 5-1. The More Electric Truck program demonstrated an integrated system to reduce idling emissions and fuel consumption. The test program showed significant progress toward achieving the objectives of Goal 2 in Chapter 5 (“Develop and demonstrate technologies that reduce essential auxiliary loads by 50 percent, from the current 20 hp to 10 hp, for Class 8 tractor-trailers”) and Goal 6 in Chapter 6 (“Produce by 2012 a truck with a fully integrated idling-reduction system to reduce component duplication, weight, and cost”). It did so by demonstrating 1 to 2 percent estimated reduction in fuel use including significant truck idling reductions. According to DOE, this translates into an overall annual fuel savings for the U.S. fleet of 710 million to 824 million gallons of diesel fuel (about $2 billion per year at $2.75 per gallon).
Recommendation 5-1. Given the potential of this program to save fuel, the committee recommends that the 21CTP continue the R&D of the identified system components that will provide additional improvements in idle reduction and parasitic losses related to engine components that are more efficient and provide better control of energy use. The program should focus also on the cost-effectiveness of the technologies.3
3
Finding and Recommendation 5-1 are identical to Finding and Recommendation 6-7 (in Chapter 6, “Engine Idle Reduction”).
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GOAL 3:
DEVELOP AND DEMONSTRATE LIGHTWEIGHT MATERIAL AND MANUFACTURING PROCESSES THAT LEAD TO A 15 PERCENT TO 20 PERCENT REDUCTION IN TARE WEIGHT (FOR EXAMPLE, A 5,000-LB WEIGHT REDUCTION FOR CLASS 8 TRACTOR-TRAILER COMBINATIONS)
Background
An important objective of the program was to explore vehicle weight reduction opportunities through the applications of lightweight materials, including high strength steels, aluminum, and advanced composites. Previous demonstration programs have shown the potential to reduce the weight of light vehicles by over 20 percent using high strength steels, and by as much as 50 percent using carbon reinforced composites (NRC, 2000b), and similar opportunities were cited for application to U. S. Army trucks (NRC, 2003). The primary barriers to weight reduction in vehicles are the costs not only of the raw material but also of the manufacturing technology required for production. Most vehicles today, including heavy trucks, utilize mild steel for body applications—the fabrication, assembly, and joining technologies for mild steel are well developed and optimized for low cost. Nevertheless, the transition to high strength steels from mild steel is relatively straightforward and has been progressing well in the automobile industry because, while there is a modest premium for the higher-strength steels, existing fabrication and body assembly processes need little modification. Aluminum presents more of a challenge because of its inherently higher raw material cost, and also because of differences (from steel) in fabrication and joining. Carbon reinforced composites, while offering the greatest weight reduction potential, require special methods for fabrication and assembly, and are only now being used by a commercial aircraft manufacturer for extensive application in the fuselage and wing structures.4 In addition, carbon fiber costs are very high (several dollars per pound compared with mild steel at well under a dollar a pound), and carbon fiber costs may remain high as demand grows in the aircraft industry.
Goals, Targets, and Timetables
The overall goal for the program was to develop and demonstrate, by 2012, lightweight material and manufacturing processes that would enable a reduction in vehicle weight of from 10 percent to 33 percent depending on vehicle type (DOE, 2006a). For Class 8 trucks, the goal was a weight reduction of from 15 percent to 20 percent in tare weight, which is equivalent to a 5,000 lb weight reduction for a Class 8 tractor-trailer combination. Cost targets associated with the weight reduction targets were not cited in DOE (2006a). The approach included the application of lightweight materials to specific vehicle components and systems, resulting in hardware demonstration projects. Materials under consideration included aluminum, high strength and stainless steels, and composite materials including carbon reinforced composites. The total lightweight materials budget averaged from $8 million to $9 million from 2000 through 2005, and was reduced to $2.7 million in 2006. As a result of the reduction of the total 21CTP budget in FY 2007, the lightweight materials program was discontinued. Nevertheless the committee has reviewed the program to date.
Progress Toward Objectives
Numerous separate projects were initiated to support the program, spanning the application of steel, aluminum, titanium, magnesium, and glass and carbon reinforced composites. A number of different partners from industry, notably involving major truck manufacturers, participated in the program. Several of the projects (taken from 21CTP Project Quad Sheets (DOE, 2007) and the 2005 merit review (DOE, FCVT, 2005b) are listed below:
Carbon fiber composite hoods and fairings for class 8 trucks
Ultralight (stainless steel) transit bus
SPF (super plastic forming) aluminum vehicle body panels
Cast magnesium metal matrix composites for components (e.g. transmission case)
Friction stir joining (FSJ) in application to using tailor welded blanks for aluminum panels
Titanium processing development for application to truck leaf springs
Investigation of non-homogeneous microstructures due to heat treatment of steel
Equal channel angle extrusion processes development for aluminum alloy metal matrix composites
Lightweight diesel engine components (cylinder and liner)
Development of graphite foams for lightweight heat exchangers
Advanced materials for friction brakes
Lightweight trailer project
Basic studies of ultrasonic welding
While this is not the complete list of lightweight projects, it serves the committee’s purpose of discussing the strategy employed in the lightweight materials program. Evaluating a number of different materials is a good approach to use early in this type of program, as it enables identification of “best applications,” in order to “down-select” the best material for a specific application. And indeed, certain materials are likely to be the most promising for specific components and subsystems. In addition it is important to fund supporting projects such as joining and materials processing for
4
See www.boeing.com/commercial/787family/background.html.
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advanced materials. On the other hand, funding so many disparate projects seriously constrains the budget allotted to each individual project, and therefore the progress of the weight reduction program.
Nevertheless, good progress was made on the individual projects, and in many cases the results demonstrated the potential for achieving significant weight reduction in various components and subsystems. However, it was not possible to determine whether or not the program would likely meet the objective of 15 percent to 20 percent weight savings because a full system analysis of a truck incorporating the various lightweight components was not presented. In addition, the issues of material costs and costs of developing new fabrication, joining, and assembly systems for production remain to be resolved. Of course, it is appropriate that the truck manufacturers, rather than the federal government, be responsible for both full system integration and production implementation; nevertheless it would have been instructive to have had a preliminary analysis of the net weight reduction of a heavy truck due to the integrated application of the individual component projects (as was attempted for the steel bus project).
Due to the aforementioned reduction in the 21CTP budget, the lightweight materials program has been terminated. Yet it might be instructive to consider logical next steps. Prior to production, an original equipment manufacturer (OEM) would develop prototype vehicles with the new materials technology fully integrated into the vehicle. The prototype vehicles would undergo stringent validation schedules to ensure durability, corrosion resistance, resistance to ultraviolet exposure for painted surfaces, reliability, and maintainability. At the same time, the OEM would begin a cost analysis to predict the finished cost of a production vehicle. The cost analysis would include the investment required to establish, if necessary, a new body shop (where the body panels are fabricated and joined), a new paint shop (new painting process for lightweight materials), and a new assembly line. Production technologies and systems are considered to be important competitive assets, and therefore manufacturing technologies are sometimes treated as company confidential. For this reason, it would be expected that the truck manufacturers would pursue scale up and production individually.
In summary, the initial strategy and goals of the lightweight program were sound. Many of the individual projects made good technical progress resulting in a number of options for truck manufacturers to consider for further development and deployment. Indeed, a few projects were carried to production (e.g., composite truck bed for pickups). Clearly as these technologies mature and as they move into production, the responsibility should shift from the 21CTP to the individual original equipment manufacturers.
Due to the 2007 budget reduction, DOE management elected to terminate the lightweight materials project in order to maintain as much resource as possible focused on engine and emissions technology. The committee agrees with that decision for several reasons. First of all, improvements to the engine have greater potential for reducing fuel consumption than do technologies associated with vehicle weight reduction.5 In addition, many of the materials under consideration have been used in commercial automotive application; therefore, the opportunity for new discovery through research seems less likely than is the case for engine and emissions technology. Finally, as previously mentioned, further development and production implementation of the vehicle materials technology should be the responsibility of the manufacturers rather than that of the federal government.
Finding 5-2. The 21CTP lightweight materials research was terminated as a result of the 2007 budget reduction.
Recommendation 5-2. The committee agrees with the decision to terminate lightweight materials research in order to provide as much budget resource as possible to continue research in engine efficiency and emissions reduction technologies, as improvements in engine efficiency offer greater potential for overall gains in vehicle fuel efficiency.
Finding 5-3. Prior to termination of the lightweight materials program, several lightweight material projects demonstrated weight reduction potential for truck components. However, the program did not achieve the longer term objective (planned for 2012) of demonstrating a 5,000-pound weight reduction for a complete class 8 tractor trailer combination.
Recommendation 5-3. Due to the termination of the project in 2007, it will be the responsibility of truck manufacturers to take the next steps of system integration, product validation, and ultimately production of a lightweight truck. Although an interim step of system integration at the pre-production stage would have been useful, it is not inappropriate that the OEMs now assume responsibility for continuation of the work, as the next steps will require development of a business case which comprehends material costs and the costs of modifying existing manufacturing systems to accommodate the introduction of advanced materials.
GOAL 4A:
THERMAL MANAGEMENT AND FRICTION AND WEAR—INCREASE HEAT-LOAD REJECTED BY THERMAL MANAGEMENT SYSTEMS BY 20 PERCENT WITHOUT INCREASING RADIATOR SIZE
The background and approach for Goal 4A are described in the 21st CTP Roadmap and Technical White Papers (DOE, 2006a) and are discussed and summarized below.
The focus of this goal is to reduce truck radiator size through efficient cooling systems, advanced nanofluid cool-
5
Ken Howden, DOE, FCVT, “Partnership History, Vision, Mission, and Organization,” Presentation to the committee, Washington, D.C., February 8, 2007, Slide 21.
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ants and improved under-hood design through the use of advanced modeling techniques. Exhaust gas recirculation (EGR) is the most common near-term strategy for reducing NOx emissions, but is expected to add 20 to 50 percent to the coolant heat-rejection requirements. Thus, there is a need to package more cooling capability into a smaller package space without increasing cost. Benefits in fuel efficiency are projected to be achieved through the development of high-performance heat exchangers and cooling media (fluids) which will reduce the need for high-output engine water pumps.
Longer term, the trend toward hybrid vehicles is expected to further increase the demand on coolant heat rejection systems. In diesel hybrid vehicles, there are up to five separate cooling systems (for the engine, batteries, motors, electronics, and charge air).
These demands for improved thermal management systems have created a need for new and innovative thermal management technologies that will require long-term R&D. Several research areas were identified by DOE and industry that could provide both near-term and long-term solutions to these thermal management challenges. The research areas identified were as follows:
Intelligent thermal management systems
Use of higher electrical bus voltage to enable the use of variable speed electric pumps and fans
Variable shrouding
Integration of thermal management components into the vehicle structure
Advanced heat exchangers and heat-transfer fluids
Innovative, enhanced airside heat-rejection concepts
New materials, such as carbon foams, for cooling system components
Nanofluids for improving heat transfer properties of coolants and engine oils
Mitigation of heat exchanger fouling
Advanced thermal management concept development
Heat pipes
Cooling by nucleate-boiling
Waste-heat recovery (e.g., thermoelectric generators)
Simulation code development
CFD for airflow and temperatures of the powertrain, under-hood aerodynamics and airflow, lubricant cooling, vehicle-load predictions, cooling systems, and control systems
Experimental database
Thermal signature management (the committee assumed that this area was focused on military applications)
Masking technologies to mask overall signature
Masking technologies to mask specific cargoes
Finding 5-4. The committee noted that the above list of research areas was extensive and comprehensive. However, the list appeared to be significantly more ambitious than the budget for the 21st CTP could fund. The committee assumed that this was the case since no projects or results from any of the above research areas were provided.
Recommendation 5-4. In addition to identifying a list of research areas that could provide solutions to thermal management challenges, DOE should develop, fund, and implement plans for pursuing the key areas that will lead to the successful accomplishment of the specific 21CTP Goal 4A. DOE’s first step should be to assess the candidate technology or technologies that have the highest potential for meeting the requirements of Goal 4A.
This goal and its status were briefly discussed with the committee and the following information was provided: “Track and laboratory tests met or exceeded goals, validation test is underway.”6 Unfortunately, a description of the track and laboratory tests that had been performed, the engineering details and the results from these tests, or a description and timetable for the validation test reported to be under way were not described for the committee.
Finding 5-5. Based on the above observations, the committee was not able to accurately assess the progress on this goal or the expectation of whether this goal can be successfully achieved.
Recommendation 5-5. DOE should provide periodic status reports on the 21CTP goals that include the technical status vs. the program plan, funding vs. budget, and the expected future accomplishments vs. the program plan.
System changes for heavy duty trucks are always complicated by the fact that truck manufacturers are assemblers of components specified by the truck buyer. As such, cooperative engineering design and development relationships may not exist between the suppliers of the many different components assembled into the thermal management system. The engine supplier may specify the thermal loading requirement for radiators, after coolers, oil coolers, and the controls to manage their interactions.
Since the combinations of component characteristics and controls required to optimize such systems may span the capabilities of many supply companies, it may be necessary for DOE to sponsor new sets of relationships to attack these problems. Many of the suppliers required for such a cooperative effort are not presently participants in the 21CTP.
On the other hand, several elements in the thermal management systems, such as water and oil pumps, are key items in meeting engine life and reliability goals for the engine manufacturers. These components are matched to the engine to meet torque, speed, cylinder pressure and thermal
6
Rogelio Sullivan, DOE, “Parasitic Energy Loss Reduction,” Presentation to the committee, Washington, D.C., February 8, 2007, Slide 5.
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load requirements. As such, the capacity and power use of the systems, which are usually direct drive from the engine, probably exceed the real requirements at speeds and loads away from the torque peak maximum load condition. This fact means that potential for system efficiency improvements may exist over a good portion of the engine operating map. Currently the engine builders use very reliable belt and gear drives for oil and water pumps to meet engine life and reliability goals. If newly developed systems such as variable speed drives with flexible controls are to be engineered in the truck systems, the long-term durability and reliability of the systems will have to be demonstrated to engine builders and truck buyers. These development demonstrations will be costly and take many years to complete. The Caterpillar “More Electric Truck” project and presentations by Cummins indicated that the engine manufacturers have begun to think along such lines but the present state of progress was difficult for the committee to assess.7
Finding 5-6. The achievement of present program targets would require the involvement of a wide range of new program participants and the sharing of responsibilities among new program partners, inherently incorporating higher technical and durability risks than the present approaches. Truck manufacturers are assemblers of components specified by the truck buyer, and cooperative design and development relationships may not exist between suppliers.
Recommendation 5-6. DOE should determine if the above approach for achieving Goal 4A is feasible within the scope of the 21CTP and containable within the available budget. DOE should take a strong leadership role with appropriate funds to bring manufacturers and suppliers together for systems research and development for Goal 4A and Goal 3.
GOAL 4B:
THERMAL MANAGEMENT AND FRICTION AND WEAR—DEVELOP AND DEMONSTRATE TECHNOLOGIES THAT REDUCE POWERTRAIN AND DRIVELINE LOSSES BY 50 PERCENT, THEREBY IMPROVING CLASS 8 FUEL EFFICIENCIES BY 6 TO 8 PERCENT
The background and approach for Goal 4B were also described in the 21CTP Roadmap and Technical White Papers (DOE, 2006a) as discussed and summarized below. Friction, wear and lubrication are important considerations in many approaches for reducing energy consumption. Consequently, DOE identified the following opportunities for improvements:
Engine efficiency. Improved friction and piston/ring lubrication can improve engine efficiency.
Driveline components (transmission, axles, etc.). Advances in lubrication and friction can reduce the losses in driveline components.
Engine emissions and aftertreatment systems. Lubricant formulations and coatings can impact exhaust particulate matter as well as exhaust sulfur and phosphorous content, which can affect exhaust after-treatment systems.
The 21CTP roadmap (DOE, 2006a, p. 1) states that the long-term objective of this goal is the development of tools and technology to reduce parasitic friction losses in the engine, driveline and auxiliary components. The following barriers and challenges in friction and wear reduction were identified:
Although reducing the viscosity of drivetrain fluids will reduce viscous and windage losses, current designs, materials, and lubricant additives are inadequate to maintain component durability and reliability when used with low-viscosity fluids.
The current levels of phosphorous-based additives (ZDDPs) used in engine lubricants will rapidly degrade the performance of emission-control devices. However, reducing the level of phosphorous and other metal-containing additives will accelerate the wear of critical engine components and degrade engine durability and reliability. Thus, a delicate balance must be maintained.
Cost-effective technologies for high-volume manufacturing of low-friction, wear-resistant materials, surface treatments, and additives are lacking.
Integration of component designs with advanced materials, engineered surfaces, and lubricants into complete systems is poor.
The following major topics addressing both short-term and long-term friction, wear, and lubrication technologies were identified by DOE and industry for improving fuel economy, while maintaining system durability and reliability:
Integration of mechanistic friction and wear models into codes to predict and mitigate parasitic energy losses
Advanced materials and coating technologies that lower friction, reduce wear and improve reliability
Engineering surfaces to improve friction and lubrication properties
Lubricant additives
Boundary layer lubrication studies to control friction, durability and reliability
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Vinod K. Duggal, Cummins Engine Company, Inc., “Diesel Engine R&D and Integration,” Presentation to the committee, Washington, D.C., February 9, 2007, Slide 8.
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Finding 5-7. The committee noted that the DOE list of research topics in friction, wear and lubrication was extensive and comprehensive. However, the list appeared to be significantly more ambitious than the budget for the 21CTP could fund. The committee assumes that this was the case since no projects or results from any of the above research areas were provided.
Recommendation 5-7. In addition to identifying a list of topics addressing friction, wear, and lubrication technologies, DOE should develop, fund and implement plans for pursuing key areas that will lead to the successful accomplishment of the specific 21CTP Goal 4B. DOE’s first step should be to conduct detailed friction testing of a range of heavy-duty diesel engines, transmissions, and final drives to determine those with best-in-class friction. With respect to engines, previous industry light- and heavy-duty engine friction reduction investigations that included lightweight-low friction piston and piston ring designs, low friction coatings and surface finishes, reduced engine bearing sizes and other design modifications should be reviewed to determine opportunities for reducing engine friction below best-in-class levels. From this assessment, other candidate technologies with the highest potential for meeting the requirements of the engine portion of Goal 4B should be identified. Likewise, the efficiencies of transmissions and final drives on heavy-duty trucks should be measured and compared with the efficiencies of best-in-class light-duty vehicles, normalized for load differences, thereby providing insight for friction reductions in heavy-duty truck transmissions and final drives. From this assessment, other candidate technologies with the highest potential for meeting the requirements of the driveline portion of Goal 4B should be identified.
The committee was not provided with the detailed approach and plans to achieve a 50 percent reduction in parasitic losses in the powertrain and driveline, which would yield a 6 to 8 percent improvement in fuel efficiency. However, some insights into this goal were provided by reviewing the following information, which was available to the committee:
Driveline losses. DOE has a target for reducing drive-train losses from 9 kW (Table 5-1) by 50 percent to 4.5 kW. Reducing the fuel energy used by 4.5 kW (from a total fuel energy used of 380 kW as shown in Figure 3-1) would reduce fuel consumption by 1.2 percent.
Powertrain losses. Baseline engine losses are shown to be 220 kW in the energy audit of a typical Class 8 tractor-trailer combination at 65 mph road load (Figure 3-1). A further breakdown of these losses into coolant loss, exhaust heat loss and friction loss was not provided to the committee. However, by using a typical FMEP value for a direct injected diesel engine (Heywood, 1988, p. 724), the friction losses were estimated by the committee to be approximately 30 kW. The goal of a 50 percent reduction in engine friction would reduce the total fuel energy used by 15 kW (from a total fuel energy used of 380 kW), which would reduce fuel consumption by 3.7 percent.
The above insights indicate that, even if DOE can achieve a 50 percent reduction in powertrain and drivetrain losses, a reduction in fuel consumption of only 5 percent (sum of 1.2 percent for drivetrain and 3.7 percent for powertrain) could be achieved. This is a shortfall relative to the goal of 6-8 percent.
Furthermore, the engineering details of achieving 50 percent reduction in driveline and engine losses were not provided to the committee. However, past experience has indicated that major reductions in powertrain and drivetrain losses have not been achievable while retaining adequate durability and reliability. The committee concluded that due to the lack of an in-depth technical rationale and a plan to approach the goal, it is very unlikely that this goal can be achieved. The issues with the basis for calculating the percentage improvement must be resolved so that a realistic reduction in powertrain losses can be determined.
Having noted the above issues with this goal, the committee was concerned that “Track and laboratory tests met or exceeded goals, validation test is underway.”8 A description of the track and laboratory tests that had been performed, the engineering details and the results from these tests, or a description and timetable for the validation test which was reported to be under way were not described for the committee.
While the problems dealing with friction and wear inside the engine can be addressed by engine manufacturers associated with the 21CTP, the issues associated with the other driveline devices must be handled by other suppliers that are not currently participants in the 21CTP. Here again, the makeup of the truck building industry makes the required cooperative efforts difficult. The fact that the truck builders use components specified by the truck end-users means that the driveline efficiency responsibility may be shared by several manufacturers. A review of specifications on drive-line components indicated that, although torque and speed specifications were readily available, specifications regarding power losses were not easily obtained. Thus, buyers presently make such decisions absent of efficiency information. Since lubricant viscosity and additives will have an impact on both the efficiency and life of the driveline components, decisions will have to be made carefully so as not to reduce driveline component life as efficiency is improved. Changes to driveline systems will have to demonstrate life characteristics similar to those that exist today, thus the introduction
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Rogelio Sullivan, DOE, “Parasitic Energy Loss Reduction,” Presentation to the committee, Washington, D.C., February 8, 2007, Slide 5.
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of such systems will be costly and require several years of life validation demonstration.
The improvement of driveline efficiencies presents a significant problem for DOE. The required involvement of new suppliers and the costly requirement to demonstrate long-lived components may be beyond DOE’s budget limits.9
Finding 5-8. In contrast to the report by DOE to the committee, the analysis of the basis of this goal by the committee indicates that it is very unlikely that this goal can be achieved within the scope of the 21CTP. The achievement of the goal’s projected fuel savings appears to be very unlikely with accompanying high risks relative to component life.
Recommendation 5-8. DOE should reassess the basis of this goal and determine if 50 percent reductions in powertrain and drivetrain losses are technically feasible. Based on this assessment of technical feasibility, DOE should determine if this goal should be pursued based on its potential fuel savings vs. other competing programs within the 21CTP. If DOE determines that this goal should be pursued, they should then develop specific program plans, timing and funding.
GOAL 5:
ROLLING RESISTANCE TECHNOLOGY GOAL—10 PERCENT REDUCTION IN TIRE-ROLLING RESISTANCE VALUES RELATIVE TO EXISTING BEST-IN-CLASS STANDARDS WITHOUT COMPROMISING COST OR PERFORMANCE
Background
Rolling resistance of tires is one of the parasitic losses acting on trucks that increase fuel consumption. Although rolling resistance is generally considered a tire property, it is also recognized to be dependent on the texture and rigidity of the road surface. The 21CTP initially considered rolling resistance to be one of the areas warranting investigation inasmuch as it is estimated to consume about 51 kW of power during highway travel of a fully loaded Class 8 truck (DOE, 2006a, Table 3.1). The Partnership set a goal for 10 percent reduction relative to existing best-in-class standards (DOE, 2006a, Section 3.2). However, it failed to become an active area of investigation with the result that there has been little attention or discussion within the program.
Significance of Rolling Resistance
The 21CTP estimate of 51 kW of power to overcome rolling resistance of an 80,000 lb Class 8 truck operating at 65 mph on a level road corresponds to a rolling resistance force that is 0.6 percent of the vehicle weight. Of the total energy consumed (400 kW per hour) 12.75 percent is due to rolling resistance. However, of the mechanical energy needed to maintain the truck at speed arising from auxiliary loads, drivetrain losses, aerodynamic losses, and rolling resistance, rolling resistance constitutes 32 percent of the total. Thus, at stake is a loss equivalent to about one-third of the power needed to propel the truck. Consequently, the initial goal for a 10 percent reduction in rolling resistance at the outset of the Partnership would be expected to achieve a reduction in fuel consumption of about 3 percent. In terms of fuel savings at the national level, this 3 percent can be translated into gallons of fuel if it is assumed that the engine losses decrease in proportion to the reduction in power required. Using the Federal Highway estimate (DOE, 2006a, p. 5) that tractor-trailers consume 26.8 billion gallons of fuel annually, the savings would be about 800 million gallons per year just for tractor-trailers. For smaller trucks used in other vocational applications the savings are not well known, but are likely to be on the same order of magnitude. At the passenger car level it has been estimated (NRC, 2006, p. 4) that a 10 percent reduction in rolling resistance would translate into a fuel savings of 1 to 2 percent. Assuming a nominally conservative value of 2 percent savings from a 10 percent reduction in rolling resistance, U.S. petroleum consumption from trucks of class 3 through 8 trucks could be reduced by approximately 20 million barrels per year. (Note: This quantity was calculated based on the 2.6-million-barrel-per-day estimate for the year 2005 shown in the current 21CTP roadmap [DOE, 2006a, Figure 1-2].)
Suggestions for Government Initiatives
In the highly competitive tire market, the technology by which tires are designed to have specific attributes is proprietary to the manufacturers. Thus the opportunity for government agencies to develop partnerships and participate in developing improved tires is limited. Thus, it is not surprising that no tire manufacturers participated as partners in the 21CTP.
Designing tires for low rolling resistance is often in conflict with other performance objectives and hence falls under the purview of tire manufacturers. For example, using low-hysteresis materials in the tread to reduce rolling resistance directly conflicts with the need for tread hysteresis in order to maintain good wet traction. Similarly, reducing tread depth also reduces rolling resistance but at the cost of decreased tire life. Numerous other conflicts exist.
Recognizing that there is little opportunity for government agencies to participate in developing tire technologies, the question arises as to whether there is any mechanism for encouraging development and adoption of performance standards for rolling resistance. The industry itself supports standardization of tire and wheel related components through the Tire and Rim Association, Inc. In existence since 1903, the Association holds primary responsibility for establishing standards for dimensions, load ratings and inflation pressures
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Rogelio Sullivan, DOE, “Parasitic Energy Loss Reduction,” Presentation to the committee, Washington, D.C., February 8, 2007, Slide 5.
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for tires in the United States, in addition to standards for rim dimensions, tubes, valves and other components.
Two standard tests for measuring rolling resistance exist as SAE recommended practices—SAE J1269, “Rolling Resistance Measurement Procedure for Passenger Car, Light Truck, and Highway Truck and Bus Tires” (SAE, 2006) and SAE J2463, “Stepwise Coastdown Methodology for Measuring Tire Rolling Resistance” (SAE, 1999). Both tests are conducted in a laboratory with the tire loaded against a 1.7-meter-diameter drum. While these test procedures are not identical to each other or to on-road operating conditions, they can be expected to provide good relative measures of rolling resistance.
Since precedent and test procedures exist, the government could add grading requirements for rolling resistance to the UTQGS (Uniform Tire Quality Grading System) if there is promise of its effectiveness. At least two barriers exist:
Consumer acceptance—Although the UTQGS was designed to assist consumers in making informed choices when buying passenger car tires, it is not universally effective. The effectiveness was evaluated in a 1992 telephone survey of individuals who buy tires for their own vehicles and individuals who buy tires for fleets of vehicles (Weiss, 1992). Approximately 80 percent of potential customers considered UTQGS information important to a purchase decision, although only about 30 percent of recent customers considered it in their last purchase. More than 50 percent of fleet buyers considered UTQGS information important in buying decisions.
Retread tires—More than 50 percent of the tires on long-haul trucks are retreads. A retread is simply new tread molded on to an existing, pre-used tire carcass. Rolling resistance depends both on the design and materials of the tread stock as well as the underlying structure. Thus, each retread will have a different rolling resistance value. Therefore, it is less practical to expect rolling resistance values to be measured for retread tires than for those produced by OEM tire manufacturers.
Finding 5-9. There is a precedent for government to establish performance measures for tires as illustrated by the Uniform Tire Quality Grading System (UTQGS) adopted by NHTSA in 1980 [Part 575.104 of the Consumer Information Regulations]. The UTGS applies to passenger car tires and requires manufacturers to grade new tires for tread wear, wet traction and temperature resistance. Tread wear is graded on a numerical scale, while traction and temperature resistance are graded on an alphabetic scale. There is no current requirement for grading rolling resistance, or for grading truck tires.
Recommendation 5-9. DOE, EPA, and DOT should arrange to gather and report information on the influence of individual truck tires on vehicle fuel consumption; to convey such tire information to both buyers and sellers; and to periodically reassess the effectiveness of this consumer information and the methods used for communicating it.
REFERENCES
Cooper, Kevin. 2004. Commercial Vehicle Aerodynamic Drag Reduction: Historical Perspective as a Guide. In Proceedings of a Conference on the Aerodynamics of Heavy Vehicles: Trucks, Buses, and Trains, December 2-6, 2002. Washington, D.C.: DOE.
DOE (U.S. Department of Energy). 2000. Technology Roadmap for the 21st Century Truck Partnership. Document No. 21CTP-001. Washington, D.C.: DOE, December.
DOE. 2004. Proceedings of a Conference on the Aerodynamics of Heavy Vehicles: Trucks, Buses, and Trains, December 2-6, 2002. Washington D.C.: DOE.
DOE. 2006a. 21st Century Truck Partnership Roadmap and Technical White Papers Doc. No. 21CTP-003. Washington D.C. December.
DOE. 2006b. FreedomCAR and Vehicle Technologies Program Multi-Year Program Plan, 2006–2011. Washington D.C.: DOE, EERE. October.
DOE. 2007. 21st Century Truck Partnership, Project Quad Sheets. Doc. No. 21CTP-004. Washington, D.C.: DOE, January.
DOE, FCVT. 2005a. Heavy Vehicle Systems Optimization Program, Annual Progress Report. Washington D.C.: DOE. Available at http://www1.eere.energy.gov/vehiclesandfuels/resources/fcvt_mypp.html. Accessed May 14, 2008.
DOE, FCVT. 2005b. Heavy Vehicle Systems Optimization Merit Review and Peer Evaluation, Annual Progress Report. Washington D.C.: DOE. Available at http://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/2006_hvso_merit_review.pdf; http://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/2005_hvsop_report.pdf Accessed May 14, 2008.
DOE, FCVT. 2006. FY 2006 Annual Progress Report for Heavy Vehicle Systems Optimization Program, Section I. Aerodynamic Drag Reduction. Washington D.C.: DOE.
Heywood, J. B. 1988. Internal Combustion Engine Fundamentals. McGraw-HiII Series in Mechanical Engineering. McGraw-Hill.
McCallen, R., D. McBride, W. Rutledge, F. Browand, A. Leonard, and J. Ross. 1998. A Multi-Year Program Plan for the Aerodynamic Design of Heavy Vehicles. UCRL-PROP 127753 Dr. Rev 1, February 1998. Available at http://www.osti.gov/bridge/servlets/purl/771203-eeW6Mf/native/771203.pdf. Accessed May 14, 2008.
NRC (National Research Council). 2000a. Review of the U.S. Department of Energy’s Heavy Vehicle Technology Program. Washington, D.C. National Academy Press.
NRC. 2000b. Review of the Research Program of the Partnership for a New Generation of Vehicles. Sixth Report. Washington, D.C.: National Academy Press.
NRC. 2003. Use of Lightweight Materials in 21st Century Army Trucks. Washington, D.C.: The National Academies Press.
NRC. 2006. Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance. TRB special report 286. Washington, D.C.: The National Academies Press.
SAE (Society of Automotive Engineers International).1999. Recommended Practice, “Stepwise Coastdown Methodology for Measuring Tire Rolling Resistance,” Doc. No. J2452, June. Available at http://www.sae.org/technical/standards/J2452_199906. Accessed June 2, 2008.
SAE. 2006. Recommended Practice, “Rolling Resistance Measurement Procedure for Passenger Car, Light Truck, and Highway Truck and Bus Tires,” Doc. No. J1269, September. Available at http://www.sae.org/technical/standards/J1269_200609. Accessed June 3, 2008.
Weiss, Sandra. 1992. “An Evaluation of the Uniform Tire Quality Grading Standards and Other Tire Labeling Requirements.” NHTSA Report Number DOT HS 807 805. Washington, D.C.: U.S. Department of Transportation, January.
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