ACEEE recommends steps for enhanced data gathering and analysis essential to developing next phase of heavy-duty vehicle fuel efficiency and GHG regs
27 September 2013
A newly released working paper from the American Council for an Energy-Efficient Economy (ACEEE) outlines the organization’s recommendations to policymakers for developing the next phase of fuel efficiency and greenhouse gas (GHG) emissions standards for heavy-duty vehicles in the United States expected in 2015.
The focus of the paper is less on the range of technologies that might be applied to deliver the requisite reductions (ACEEE also published a short fact sheet briefly touching on technology approaches) and more on enhanced and improved data gathering, analysis and dissemination that will be required to inform the development of the next phase of the standards.
The first standards for fuel efficiency and greenhouse gas (GHG) emissions of heavy-duty vehicles in the United States were adopted in 2011 by the National Highway Traffic Safety Administration and the U.S. Environmental Protection Agency. The standards mark a major step toward greater fuel efficiency for trucks and buses. In the next phase of the standards, expected in 2015, the agencies have an opportunity to capture additional savings by pulling a wider array of efficiency technologies into the market and by tailoring the standards more closely to the wide array of covered vehicles and their duty cycles.
Detailed knowledge of the characteristics and usage of US heavy-duty vehicles is essential to designing a sound regulatory program. Moreover, the second phase of the program should be informed by manufacturers’ response to the first phase: what vehicle improvements they are making to meet the fuel efficiency targets; how their choices of efficiency technologies relate to vehicle application and duty cycle; and how they are using the flexibility provisions of the program. Finally, it will be necessary to evaluate vehicles’ on-road performance, since that will be the real measure of the program’s success.
Hence extensive data collection, dissemination, and analysis is essential to further work on the program. More generally, this information is also needed to understand the fuel usage and emissions characteristics of heavy-duty vehicles so that effective mitigation measures can be developed.—Langer (2013)
Under the current heavy-duty rule, manufacturers group engines and vehicles into families of similar products and test or simulate the performance of representatives of each family. Data to be submitted are the same for the GHG and fuel efficiency rules. Manufacturers must obtain a certificate of conformity for each family of engines or vehicles to be sold. The application for the certificate of conformity requires information on engine or vehicle specifications, as well as on emissions and fuel consumption.
In general, suggests Therese Langer, the author of the working paper, the data collected by the agencies under the first phase of the rule is the minimum required to demonstrate compliance. As a result, she notes, certain information that is central to fuel efficiency is not collected.
In particular, the rule requires that a vehicle’s emissions be certified based not on its actual engine and transmission, but on a standard engine and transmission. Consequently, in certifying a vehicle, manufacturers are not required to identify the engine and transmission sold with the vehicle. This is a hindrance to understanding the vehicle market, to determining actual fuel efficiency, and to moving toward a program based on full-vehicle performance.—Langer (2013)
Another fundamental issue, she notes, is the extent of public access to vehicle data. The US Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration (NHTSA), the two agencies responsible for the heavy-duty standards (as well as light-duty standards) suggested that they will try to publish a trends report analogous to the current light-duty vehicle trends report (earlier post) on a frequent basis.
Plans for the content and format of this report have not been announced, Langer observed.
Extensive data collection is now underway, and more will be done as implementation of the heavy- duty fuel efficiency and greenhouse gas rule progresses. Major gaps remain, however, including data on the powertrains of new vehicles, fuel efficiency performance of actual vehicle configurations sold, and comprehensive survey data on the US. vehicle stock. In addition, there is considerable uncertainty regarding the form and extent of data dissemination to the public.—Langer (2013)
The working paper makes 7 recommendations, divided into three groups, to address the situation. The groups are 1) during implementation of the first heavy-duty standards, and prior to promulgation of the second phase of the program; 2) in the development of the rule for the second phase of the program; and 3) in the FY 2015 federal budget process. Recommendations in the first two groups are directed to EPA and NHTSA. The recommendations in the third group are directed to DOE, EPA, and NHTSA.
Group 1: Implementation of the heavy-duty fuel efficiency and greenhouse gas rules in 2013–2014. EPA and NHTSA should:
Post all data collected in rule implementation that is not Confidential Business Information (CBI) on the web in a timely fashion and in a form conducive to analysis.
In annual compliance reports for the heavy-duty rule, report on each manufacturer’s use of special provisions (e.g., early credits, alternative engine certification, advanced and innovative technology credits), application of credit carry-forward/carry-back, and credit balance.
Produce an annual report on trends in heavy-duty vehicle technology, carbon dioxide emissions, and fuel economy.
Consolidate analysis and reporting of data on heavy-duty pickups and vans with light-duty reporting. These vehicles should be included in the agencies’ light-duty databases and in EPA’s annual Light- Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends report.
Group 2: Formulating the second heavy-duty fuel efficiency and GHG rule.
Expand data collection in the second phase of the program. Regardless of the structure of the second phase of the program, collect and report actual powertrain specifications of each vehicle. Collect all inputs required for simulation of vehicle fuel efficiency. Require manufacturers to report sufficient fuel efficiency performance data to permit buyers to assess fuel consumption over customized duty cycles. In particular, provide fuel efficiency results over each discrete test cycle.
Group 3: FY 2015 federal budget process.
The agencies should prioritize reinstating the VIUS or developing a new census for vehicles in the 2015 budget. At the same time, they should pursue options to include the survey within existing appropriations by distributing the cost across agencies and programs.
Ensure adequate support for voluntary programs that yield data on heavy-duty vehicle operation.
Funding for the working paper was provided by the Energy Foundation and the International Council on Clean Transportation.
Therese Langer (2013) Heavy-Duty Vehicle Fuel Efficiency Data in the United States
The first law of thermodynamics can be applied to design high performance reciprocating internal combustion engine (RICE). A RICE has four strokes. The first stroke transfers one pound of ambient air into the cylinder with V1 = 15.6 ft3 and E1 = cvT1 = 95.73 Btu. The second stroke is a thermodynamic compression process transforming piston work done W into working fluid internal energy E. The conservation of energy law (pV = mRT) assures that as state (1) changed to state (2) the products of p1/p2, V1/V2, and T2/T1 remain unchanged even cylinder gas has no time to reach equilibrium. Since p2/p1 = (V1/V2)k and cvT2/cvT1 is equal to E2/E1:
E2/E1 = (V1/V2)k-1 (1)
V2/V1 = (E1/E2)1/(k-1) (2)
where “E” is the sum of total internal energy distribution within the total cylinder volume “V”. Both E and V are state variables and k is not change in each thermodynamic process. Equation (1) is used to compute the internal energy increase from E1 to E2 as the moving piston compresses the cylinder volume from V1 to V2 without heat energy Q transfer. Equation (2) is used to compute the cylinder volume expansion from V2 to V1 as the internal energy decreases from E2 to E1. At the beginning of the third stroke, a combustion process 2-3 takes place. Heat energy Q converted from fuel chemical energy increases E2 to E3 with E3 = E2 + Q and simultaneously increases V2 to V3 with V3 = V2(E3/E2)1/(k-1) according to Equation (2). An expansion process 3-4 reduces E3 to E4 with E4 = E3(V3/V4)k-1. The fourth stroke transfers total mass of cylinder and E4 out off the cylinder. Based on internal energy E balance, input is E2 + Q and E4 is not transformed into work done. Therefore IFCE = (E2 + Q - E4)/(E2 + Q) = 1 – E4/(E2 + Q).
Equations (1) and (2) are the only equations required for designing high performance reciprocating internal combustion engines. Equation (1) satisfies the conservation of energy law for the thermodynamic process where only work transfer taking place. Equation (2) satisfies the conservation of energy law for the thermodynamic process where both heat and work transfer taking place.
Roadmap for a RICE to Achieve the Highest Possible Fuel Efficiency with Minimum Engine Out Emissions
The IFCE of 1 – E4/(E2 + Q) is a short clear roadmap for a RICE to achieve the highest possible fuel efficiency with minimum engine out emissions. It is clear that E2 can be increased by selecting a high compression ratio which also provides a high compression temperature to burn out whatever combustible substances in the cylinder. By having a constant-V combustion process, E4 can be reduced. However, constant-V combustion process leads to high combustion temperature T3(E3/cv) at which NOx forms. For this reason, a two-stage combustion process is created to prevent NOx formation. A two-stage adiabatic combustion process begins at state (1) of a compression process 1-2, followed by a constant-volume combustion process 2-3a. The heat addition during the constant-volume combustion process 2-3a is limited to ensure that the combustion temperature at the end of this process is below the temperature at which NOx forms. To meet higher loading and torque requirements, the constant-volume combustion process 2-3a is followed by a constant-internal energy combustion process 3a-3b. During the constant-internal energy combustion process, Q is determined by required torque/power with E3b = E3a + Q and V3b must equal to V3a(E3b/E3a)1/(k-1 in order to satisfy the law of conservation of energy. An expansion process 3b-4 completes the thermodynamic processes of a RICE. Without this roadmap, ACEEE recommended steps for enhanced data gathering and analysis essential to develop next phase of heavy-duty vehicle fuel efficiency and GHG reduction can not achieve the intended goals.
Posted by: Pao Chi Pien | 28 September 2013 at 03:14 PM