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Technical Paper

Trends in Technical Efficiency Trade-Offs for the U.S. Light Vehicle Fleet

2007-04-16
2007-01-1325
Technology change can yield some combination of changes in fuel economy, performance, size, or other characteristics that influence the fleetwide fuel consumption. Thus, engineering progress can be manifest in multiple ways, reflected in the view that technical efficiency may improve even when fuel economy does not. This analysis quantifies underlying technical efficiency gains that reflect trade-offs between fuel economy and other attributes of light vehicles. Prior analyses yielded estimates of technical efficiency trends ranging from 1% per year to nearly 4% per year. Few analyses revealed consistent trends; most identify periods when progress was made at different rates. Using fleetwide (aggregate) data for U.S. light vehicles, exploratory data analysis and correlation techniques were applied to examine trends in energy-related variables. Individual trends for all variables are uneven over time.
Technical Paper

Mass Impacts on Fuel Economies of Conventional vs. Hybrid Electric Vehicles

2004-03-08
2004-01-0572
The strong correlation between vehicle weight and fuel economy for conventional vehicles (CVs) is considered common knowledge, and the relationship of mass reduction to fuel consumption reduction for conventional vehicles (CVs) is often cited without separating effects of powertrain vs. vehicle body (glider), nor on the ground of equivalent vehicle performance level. This paper challenges the assumption that this relationship is easily summarized. Further, for hybrid electric vehicles (HEVs) the relationship between mass, performance and fuel consumption is not the same as for CVs, and vary with hybrid types. For fully functioning (all wheel regeneration) hybrid vehicles, where battery pack and motor(s) have enough power and energy storage, a very large fraction of kinetic energy is recovered and engine idling is effectively eliminated.
Technical Paper

A Model of Fuel Economy and Driving Patterns

1993-03-01
930328
A simple analytic relationship between fuel economy, vehicle parameters and driving cycle characteristics is established. Using publically available information on vehicle characteristics, the model can be used to predict fuel economy with an accuracy of about 5% (standard deviation). The model is based on two approximations: 1) an engine map approximation, and 2) an approximation for tractive energy. This paper emphasizes the second approximation, especially the energy consumed by the brakes. The model reveals the structure of fuel use in a way difficult to achieve with case-by-case numerical results and it enables study of fuel use in modified driving cycles.
Technical Paper

Assessing and Modeling Direct Hydrogen and Gasoline Reforming Fuel Cell Vehicles and Their Cold-Start Performance

2003-06-23
2003-01-2252
This paper analyzes fuel economy benefits of direct hydrogen and gasoline reformer fuel cell vehicles, with special focus on cold-start impacts on these fuel cell based vehicles. Comparing several existing influential studies reveals that the most probable estimates from these studies differ greatly on the implied benefits of both types of fuel cell vehicles at the tank-to-wheel level (vehicle-powertrain efficiency and/or specific power), leading to great uncertainties in estimating well-to-wheel fuel energy and/or greenhouse gas (GHG) emission reduction potentials. This paper first addresses methodological issues to influence the outcome of these analyses. With one exception, we find that these studies consistently ignore cold-start and warm-up issues, which play important roles in determining both energy penalties and start-up time of fuel cell vehicles. To better understand cold-start and warm-up behavior, this paper examines approaches and results based on two available U.S.
Technical Paper

Assessing the Fuel Economy Potential of Light-Duty Vehicles

2001-08-20
2001-01-2482
This paper assesses the potential for car and light truck fuel economy improvements by 2010-15. We examine a range of refinements to body systems and powertrain, reflecting current best practice as well as emerging technologies such as advanced engine and transmission, lightweight materials, integrated starter-generators, and hybrid drive. Engine options are restricted to those already known to meet upcoming California emissions standards. Our approach is to apply a state-of-art vehicle system simulation model to assess vehicle fuel economy gains and performance levels. We select a set of baseline vehicles representing five major classes - Small and Standard Cars, Pickup Trucks, SUVs and Minivans - and analyze design changes likely to be commercially viable within the coming decade. Results vary by vehicle type.
Technical Paper

Total Fuel Cycle Impacts of Advanced Vehicles

1999-03-01
1999-01-0322
Recent advances in fuel-cell technology and low-emission, direct-injection spark-ignition and diesel engines for vehicles could significantly change the transportation vehicle power plant landscape in the next decade or so. This paper is a scoping study that compares total fuel cycle options for providing power to personal transport vehicles. The key question asked is, “How much of the energy from the fuel feedstock is available for motive power?” Emissions of selected criteria pollutants and greenhouse gases are qualitatively discussed. This analysis illustrates the differences among options; it is not intended to be exhaustive. Cases considered are hydrogen fuel from methane and from iso-octane in generic proton-exchange membrane (PEM) fuel-cell vehicles, methane and iso-octane in spark-ignition (SI) engine vehicles, and diesel fuel (from methane or petroleum) in direct-injection (DI) diesel engine vehicles.
Technical Paper

Impacts of Diverse Driving Cycles on Electric and Hybrid Electric Vehicle Performance

1997-08-06
972646
A vehicle's energy consumption and emissions are extremely sensitive to the operating modes of that vehicle. The LA4 test cycle in the Federal Test Procedure (FTP) is the current basis for evaluating a vehicle's energy consumption and emissions, but it was developed more than 20 years ago and does not represent today's typical driving patterns. In this paper, we describe a set of computer simulation models to evaluate energy consumption and emissions of internal combustion engine (ICE) vehicles, electric vehicles (EVs), and hybrid-electric vehicles (HEVs) under a variety of driving cycles. Using these models, two real-world vehicles -- a 92 Ford Taurus and a 97 GM EV1, -- and a hypothetical rangeextender type HEV, are modeled and analyzed under five different driving cycles. We focus our analysis on vehicle performance characteristics such as driving range, equivalent fuel economy, EV and HEV system efficiency, pure electric drive range, and tailpipe emissions.
Technical Paper

Evaluating Commercial and Prototype HEVs

2001-03-05
2001-01-0951
In recent years, vehicle manufacturers have made great progress in developing and demonstrating commercially available and prototyped hybrid electric vehicles (HEVs). These vehicles include commercially available gasoline hybrid cars (Toyota Prius and Honda Insight) and Partnership for the Next Generation Vehicle (PNGV) diesel hybrid prototypes (Ford Prodigy, GM Precept, and DaimlerChrysler ESX3). In this paper, we discuss tested and claimed fuel benefits and performance of these commercial and prototyped HEVs relative to conventional vehicles (CVs) that are otherwise similar to these HEVs, except for hybridization. We also describe a reverse-engineering approach to de-hybridize or “conventionalize” these five existing commercial and prototyped HEVs. Because these commercial and prototyped HEVs represent a variety of technological choices, configurations, and development stages, this analysis gives us in-depth knowledge about how each of these vehicles achieves high efficiency.
Technical Paper

Near-Term Fuel Economy Potential for Light-Duty Trucks

2002-06-03
2002-01-1900
This paper assesses the technical potential, costs and benefits of improving the fuel economy of light-duty trucks over the next five to ten years in the United States using conventional technologies. We offer an in-depth analysis of several technology packages based on a detailed vehicle system modeling approach. Results are provided for fuel economy, cost, oil savings and reductions in greenhouse gas emissions. We examine a range of refinements to body, powertrain and electrical systems, reflecting current best practice and emerging technologies such as lightweight materials, high-efficiency IC engines, integrated starter-generator, 42 volt electrical system and advanced transmission. In this paper, multiple technological pathways are identified to significantly improve fleet average light-duty-truck fuel economy to 27.0 MPG or higher with net savings to consumers.
Technical Paper

Meeting Both ZEV and PNGV Goals with a Hybrid Electric Vehicle - An Exploration

1996-08-01
961718
This paper is written to provide information on the fuel efficiency, emissions and energy cost of vehicles ranging from a pure electric (ZEV) to gasoline hybrid vehicles with electric range varying from 30 mi (50km) to 100 mi (160km). The Federal government s PNGV and CARB s ZEV have different goals, this paper explores some possibilities for hybrid-electric vehicle designs to meet both goals with existing technologies and batteries. The SAE/CARB testing procedures for determining energy and emission performance for EV and HEV and CARB s HEV ruling for ZEV credit are also critically evaluated. This paper intends to clarify some confusion over the comparison, discussion and design of electric- hybrid- and conventional- vehicles as well.
Technical Paper

Hybrid Options for Light-Duty Vehicles

1999-08-17
1999-01-2929
Hybrid electric vehicles (HEVs) offer great promise in improving fuel economy. In this paper, we analyze why, how, and by how much vehicle hybridization can reduce energy consumption and improve fuel economy. Our analysis focuses on efficiency gains associated solely with vehicle hybridization. We do not consider such other measures as vehicle weight reduction or air- and tire-resistance reduction, because such measures would also benefit conventional technology vehicles. The analysis starts with understanding the energy inefficiencies of light-duty vehicles associated with different operation modes in U.S. and Japanese urban and highway driving cycles, with the corresponding energy-saving potentials.
Technical Paper

Modeling the Effect of Engine Assembly Mass on Engine Friction and Vehicle Fuel Economy

1995-02-01
950988
In this paper, an analytical model is developed to estimate the impact of reducing engine assembly mass (the term engine assembly refers to the moving components of the engine system, including crankshafts, valve train, pistons, and connecting rods) on engine friction and vehicle fuel economy. The relative changes in frictional mean effective pressure and fuel economy are proportional to the relative change in assembly mass. These changes increase rapidly as engine speed increases. Based on the model, a 25% reduction in engine assembly mass results in a 2% fuel economy improvement for a typical mid-size passenger car over the EPA Urban and Highway Driving Cycles.
Technical Paper

Critical Issues in Quantifying Hybrid Electric Vehicle Emissions and Fuel Consumption

1998-08-11
981902
Quantifying Hybrid Electric Vehicle (HEV) emissions and fuel consumption is a difficult problem for a number of different reasons: 1) HEVs can be configured in significantly different ways (e.g., series or parallel); 2) the Auxiliary Power Unit (APU) can consist of a wide variety of engines, fuel types, and sizes; and 3) the APU can be operated very differently depending on the energy management system strategy and the type of driving that is performed (e.g., city vs. highway driving). With the future increase of HEV penetration in the vehicle fleet, there is an important need for government agencies and manufacturers to determine HEV emissions and fuel consumption. In this paper, several critical issues associated with HEV emissions and fuel consumption are identified and analyzed, using a sophisticated set of HEV and emission simulation modeling tools.
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