National Research Council Review Calls for Continuation of 21st Century Truck Partnership But With Major Revamping
A recently-published review of the 21st Century Truck Partnership (21CTP)—a federal effort to reduce fuel usage and emissions while increasing safety in heavy-duty vehicles—by the National Research Council found that many of the key 21CTP program goals have not been met because some of the goals were not plausible, from either an engineering or funding perspective. Other goals were not met because some of the technologies proposed for meeting the goals were not applied, according to the report.
However, the 21CTP has also has had a number of successful programs since its beginnings in 2000, and the review committee recommended continuation of the program, but with it revised and better balanced to match current funding and technology levels.
The amount of fuel consumed annually by heavy-duty trucks and buses in the US has more than doubled over the past 35 years and now accounts for 21% of the total surface transportation fuel used in the United States.
The key benefit of the 21CTP is the coordination of research programs directed toward the goal of reducing fuel usage and emissions while increasing heavy vehicle safety. Federal involvement is bringing stakeholders to the table and accelerating the pace of development. Very few US manufacturers of trucks and buses or heavy-duty vehicle components have the R&D resources to develop new technologies individually. Thus, the 21CTP is giving some of those companies access to extraordinary expertise and equipment in federal laboratories, in addition to seed funding that draws financial commitment from the companies to push forward in new technology areas.
The National Research Council (part of the US National Academy of Sciences) formed the Committee to Review the 21st Century Truck Partnership in response to a request from the director of the DOE’s Office of FreedomCAR and Vehicle Technologies.
In addition to making recommendations on management of the program, priority-setting and funding, the review committee made specific findings and recommendations in the areas of engine systems and fuels; heavy-duty hybrid vehicles; parasitic losses; engine idle reduction; and safety.
Engine systems and fuels. DOE had set three primary goals for engine systems and fuels:
Achieving 50% thermal efficiency while meeting 2010 emission standards by 2010;
Research and develop technologies to achieve 55% thermal efficiency by 2013; and
Identify and validate fuel formulations making possible 5% replacement of petroleum fuels by 2010.
The review committee found that although DOE had concluded that the 50% thermal efficiency goal has been achieved, the experimental test results showed that none of the industry partners achieved the goal of 50% thermal efficiency at 2010 emissions standards with a complete engine system.
Each partner either failed to test a complete engine system on an engine dynamometer and used analysis to project results or failed to achieve 50 percent thermal efficiency at 2010 emissions standards with a complete system...Moreover, the work that was accomplished was at the intrinsically more efficient peak torque condition rather than at an engine speed and load representative of 65 mile per hour (mph) road load.
The DOE failed to clearly specify the goal, the committee found, and each of the three industry partners (Caterpillar, Cummins and Detroit Diesel) used different test procedures for measuring thermal efficiency; did not use required EPA test procedures with aged engine and aftertreatment systems to demonstrate 2010 emissions compliance; and used different technical approaches to achieve the 50% goal, with no explanation or technical analysis was provided to justify the different approaches.
A validated system model should have been used to compare test data with analytical projections to determine if each feature was performing as expected.
Among other recommendations in this area, the committee suggested that objective and consistent criteria should be used to assess the success or failure of achieving such a key goal of the 21CTP as the attainment of 50% thermal efficiency. The committee also suggested that achieving compliance with 2010 emissions with a “one-off” prototype engine designed to demonstrate 50 percent thermal efficiency may be too stringent a goal.
The emission objective levels should be revised to be the demonstration of emissions at a single point, where the emission level selected to be demonstrated should have the potential for meeting the 2010 emissions as specified by EPA test procedures.
The committee also concluded that achieving the 21CTP’s goal of 50% peak thermal efficiency would not result in actual 50% thermal efficiency for a typical Class 8 tractor-trailer combination on a level road at a constant speed of 65 mph and a GVW of 80,000 lb.
Even if 50-percent thermal efficiency were to be achieved at, or near, the peak torque condition, up to a 7 percent improvement (3.4 percentage point improvement) task would still remain to achieve 50 percent thermal efficiency at the 65 mph road-load condition.
As a result, the committee recommended that the 21CTP clearly define, in addition to the peak thermal efficiency condition, the specific 65-mph road-load condition for demonstrating 50% thermal efficiency.
With all of that as a consideration, the committee found that the DOE is shifting prematurely to component research to support the 2013 stretch goal of 55% thermal efficiency before completely demonstrating the earlier 2010 goal of 50%.
Importantly, after analyzing the results of the lengthy and extensive efforts carried out in the area of Low Temperature Combustion (LTC), it is considered unlikely that this technology will be a successful enabler of the 55 percent stretch goal at any time in the near term, as it cannot be adequately controlled over the full range of operating conditions of heavy-duty engines and has not demonstrated inherent fuel-consumption advantages. Based on the open literature, the chances for success of LTC as a practical technology appear limited.
The committee suggests that DOE should complete the demonstration of the 50% thermal efficiency goal before embarking on the 55% goal. The committee also suggested limiting the number of participants in the coming phases.
DOE had included an investigation into thermoelectric energy conversion systems as part of the drive for 55% efficiency. The committee found that the work is still at too basic a stage of development to be included in an applied program such as the 21CTP at this time.
Further, it is hard to envision that a thermoelectric device could absorb a significant amount of exhaust energy without imposing an undue backpressure on the engine system. The thermoelectric conversion systems are at a very basic stage and seem to have been “lumped” into the 21CTP as a matter of budgetary convenience for more basic work going on primarily at the National Laboratories. The thermoelectric conversion research should be removed from the 21CTP program until a more advanced level of technical maturity is attained.
The review committee also concluded that it is unlikely that the goal of identifying and validating nonpetroleum fuel formulations, optimized for use in advanced combustion engines, will be achieved by 2010. The committee recommended that DOE continue to work with biodiesel developers and users to assure compatibility when biodiesel is blended with conventional diesel fuel and problem-free use of biodiesel fuels in diesel engines. Development of refining technology to make acceptable diesel from shale oil or tar sands is not high-risk research suitable for federal funding, the committee found, and should be left to the private sector. The committee called for DOE to develop specific plans, including key actions and timetables, for 5% replacement of petroleum fuels.
Heavy-duty hybrid vehicles. Specific 2012 goals for heavy-duty hybrid vehicles in the 21CTP program are:
Develop a new generation of drive unit systems that have higher specific power, lower cost and durability matching the service life of the vehicle. Develop a drive unit that has 15 years of design life and costs no more than $50/kW by 2012.
Develop an energy storage system with 15 years of design life that prioritizes high power rather than high energy, and costs no more than $25/kW peak electric power rating by 2012.
Develop and demonstrate a heavy hybrid propulsion technology that achieves a 60% improvement in fuel economy, on a representative urban driving cycle, while meeting regulated emissions levels for 2007 and thereafter.
The committee found that R&D on heavy-duty hybrid trucks and buses has shown significant progress, achieving 35-47% fuel economy improvements in hybrid-electric delivery vans and urban buses, with specialized applications and the hydraulic hybrid delivery van in the 50-70% range. Hurdles still remain to achieving the fuel economy improvement targets for a broader range of heavy-duty hybrid vehicle (HHV) applications, reducing the cost, and improving HHV reliability sufficiently to achieve broader commercial success. In addition, the committee concluded, there are opportunities for significant system-level improvements that would make HHVs more attractive to original equipment manufacturers (OEMs) and users, such as the merging of hybrid propulsion and idle reduction features, including start-stop operation and creeping under all-electric power.
The committee recommended that development and demonstration of heavy-duty hybrid truck technology should be continued as part of the 21CTP program in order to reduce barriers to commercialization.
Noting that progress has been hindered by the decision to focus on component-level technology rather than on systems, the committee suggested coordination of all 21CTP heavy-duty hybrid truck development and demonstration activities to maximize the system benefits of this technology and to accelerate its successful deployment in commercial trucks and buses.
On the energy-storage side, the committee concluded that challenges with lithium-ion anode/cathode materials and chemical stability under high power conditions will likely preclude achieving the 15-year durability targets by 2012.
The committee also noted that the metrics used for comparing battery technologies differ from manufacturer-to-manufacturer, agency-to-agency, and even for different evaluations within a given agency. Metrics should be standardized or modified to enable more accurate comparisons across different battery technologies for transportation use, it recommended, with universal terminologies defined, published, and recommended for adoption by the various battery manufacturers.
The committee also called for an expanded research effort and associated funding focus on ultracapacitors or supercapacitors as “hybrid” storage systems, in combination with batteries.
Parasitic losses. DOE goals for the 21CTP in the area of parasitic losses are:
Develop and demonstrate advanced technology concepts that reduce the aerodynamic drag of a class 8 highway tractor-trailer combination by 20% from a current average drag coefficient of 0.625 to 0.500.
Develop and demonstrate technologies that reduce essential auxiliary loads by 50% from current 20 hp to 10 hp for Class 8 tractor trailers.
Develop and demonstrate lightweight material and manufacturing processes that lead to a 15-20% reduction in tare weight (for example a 5,000-lb weight reduction for Class 8 tractor-trailer combinations).
Increase heat-load rejected by thermal management systems by 20% without increasing radiator size to accommodate future increased engine power requirements or allow reduced radiator and cooling system size at constant power.
Develop and demonstrate technologies that reduce powertrain and driveline losses by 50% thereby improving Class 8 fuel efficiencies by 6-8%.
Reduce tire rolling resistance values relative to existing best-in-class standards by 10% without compromising cost or performance.
The committee founds that the More Electric Truck program demonstrated an integrated system to reduce idling emissions and fuel consumption with significant progress toward achieving some of the objectives in this area. The committee recommended 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.
The committee also recommended trimming a number of the technology initiatives in this area that appear technically unfeasible or are in conflict with other initiatives in other areas.
Engine idle reduction. DOE’s goal for the engine idle reduction activity is to promote the research, development, and deployment of technologies that substantially reduce energy consumption and exhaust emissions due to idling. Specific targets include:
Develop and demonstrate add-on idling-reduction equipment that meets driver cab comfort needs, has a payback time of 2 years or less, and produces fewer emissions of NOx and PM than a truck meeting 2010 emission standards, by 2009.
Develop a truck with a fully integrated idling-reduction system to reduce component duplication, weight and cost, by 2012.
Develop and demonstrate a viable fuel cell Auxiliary Power Unit (APU) system for on-road and off-road transportation applications in the 5-30- kilowatt (kW) range, capable of operating on hydrogen directly, or using a carbon-based fuel with a reformer.
Noting that idle reduction is one of the most effective ways to reduce pollutant emissions (especially locally) and improve fuel consumption, the committee found that several important lines of research are carried on in the 21CTP. The committee recommended that he 21CTP should continue to support R&D for the technologies that reduce idle time and address the remaining technical challenges (including California emission requirements, completely integrated APU/HVAC (auxiliary power unit/heating, ventilation, and air-conditioning) systems, and creep devices).
Review of the 21st Century Truck Partnership (Committee to Review to 21st Century Truck Partnership, National Research Council, June 2008)