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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.

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.

Information is readily available on how a vehicle model's emissions system performs under certification conditions, but it is not widely known how it performs after years of use. This study predicts the odometer dependence of in-use car emissions, in grams per mile (gpm), over many model years. To do this, model years are analyzed starting in the mid 1980's until the mid 1990's. High emitters are eliminated from the study using a vehicle probability distribution technique. Emissions data was obtained from EPA's long-term Federal Test Procedure (FTP) survey, AAMA, CARB's Light Duty Vehicle Surveillance Program (LDVSP 14), and University of California Riverside CMEM database. The UCR data includes second-by-second engine-out and tailpipe-out emissions. Emissions system durability was found by comparing the emissions of vehicles of the same model year at different odometer readings.

An analytical model that describes SI engine fuel consumption and friction with basic engine physical parameters as inputs has been developed and evaluated in this study. Fundamental characteristics of SI engine indicated efficiency, heat loss and friction have been captured by the model. Despite the approximations made in arriving at the final formula of the model, the proposed fuel–rate equation has been shown to represent both the SI engine fuel consumption and WOT friction reasonably well with a base set of parameters. If both the engine performance data and motored WOT friction data are available, the proposed model can be used to obtain a more precise set of parameters that describe both the engine friction and fuel consumption accurately (fuel rate differences within ±5%) at any speed and load combinations (omitting enrichment points).

Modeling tailpipe NOx emissions has always been difficult due to the complexity of the numerous factors involved in the catalytic conversion of the pollutant. Most emissions modeling has been based on steady state driving. A parameterized algebraic model for second-by-second tailpipe emissions of NOx for a composite Tier 1 car is presented employing data from the Federal Test Procedure Revision Project (FTPRP). Calculating fuel rate from measured engine out values, the catalytic converter is physically modeled based on the fuel rate history and a few fitted parameters. Under certain conditions, the changes in fuel rate are related to trends in the air to fuel ratio. The model accurately predicts the time dependence of hot stabilized tailpipe NOx emissions in the FTP bag 3 and US06 driving cycles. Modeling of low power driving, as in bag 2, is not as successful.

In-use vehicles which are high emitters make a large contribution to the emissions inventory. It is not known, however, whether high-emitting vehicles share common emissions characteristics. We study this by first examining laboratory measurements of second-by-second engine-out and tailpipe emissions from a small number of MY90-97 high-emitting vehicles. We distinguish high-emitter types by the behavior of six ratios in low- and moderate-power driving: the engine-out emissions indices (engine-out pollutant to fuel-rate ratios) and the catalyst pass fractions (tailpipe to engine-out ratios) for CO, HC, and NOx. Four general types of high emitter are observed: 1) fuel-air ratio excessively lean, 2) fuel-air ratio excessively rich, 3) partial combustion such as misfire, and 4) severe deterioration in catalyst performance in vehicles where malfunctions of Types 1, 2 or 3 are not predominant. We also find that these behaviors may be chronic, or may only occur transiently.

Due to their inherent high efficiency and the ease of starting once the engine is hot, turbocharged direct injection (TDI) diesel engines have emerged as one of the contending powerplants for PNGV hybrid vehicles. The interest in applying diesel engines in hybrid vehicles has prompted the modeling of direct injection diesel engine fuel consumption. The empirical equation developed in this study, which models engine friction and indicated efficiency as functions of engine operating speed and load, shows excellent agreement with test data gathered from public sources. The engine speed dependence of the friction and indicated efficiency are determined by fitting available data. Several assumed load dependences are considered. (If public data were available on engine cylinder pressure by crank angle as a function of engine speed and load, the load dependence could be determined empirically.)

Simulation models for second-by-second fuel rate, and engine-out and tailpipe emissions of CO, HC, and NOx from a “composite” car in hot engine and catalyst conditions are presented and tested using Federal Test Procedure Revision Project (FTPRP) data from 15 1991-1994 cars. The models are constructed as a combination of simple science and curve fitting to the FTPRP data. The models are preliminary, the simplest models being presented to illustrate how much can be predicted with very few parameters. Fuel rate and engine out emissions of all three pollutants are accurately predicted. The tailpipe emissions models are only moderately successful, largely because we are only moderately successful in predicting catalyst pass fractions during low power driving. Nevertheless, the composite car shows regular emissions behavior, and these are modeled effectively.

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.

The paper describes a new hybrid vehicle design option having very low energy storage capability, and in particular, a parallel hybrid with hydraulic storage and reapplication of braking energy. The operating efficiency of the propulsion system at light loads is substantially improved by splitting the engine into two segments, and finding ways of shutting down one or both engine segments whenever possible. The hybrid vehicle utilizes primarily current technologies. A diesel powered parallel hybrid as described demonstrates a reduction in fuel consumption of 53.9% on a volume basis when compared with an equivalent baseline vehicle.

Malfunctioning emission controls continue to be a major source of emissions from in-use vehicles. We analyze two sources of data on cars with malfunctioning emissions controls: remote sensing surveys and dynamometer tests of cars in the condition they were received. Our analysis indicates that roughly 8 percent of relatively new (2- to 5-year old), modern technology (fuel-injected) cars have malfunctioning emission controls. There is a wide range in the probability of malfunction of specific models, from zero to over 20 percent. Possible causes of high model-specific malfunction probability are poor initial design and/or manufacture.

A methodology is established to assess total life-cycle exhaust emissions for light-duty motor vehicles. The focus is to model a vehicle's carbon monoxide (CO), hydrocarbon (HC), and oxides of nitrogen (NOx) exhaust emissions over its lifetime in the state of California. The data used for this analysis is based on California Air Resources Board's (CARB) Light-Duty Vehicle Surveillance Program (LDVSP), series 12, from March 1993 to March 1994. Bag-based emission data of 165 light duty vehicles from model years (MY) 1984 - 1992 driven under the LA4 and Unified Cycles are analyzed. Vehicle exhaust emissions are estimated based on the following operating conditions: hot-stabilized operation, cold and hot starts, enrichment conditions, and emission control device deterioration/malfunctions.

A hybrid car is conceptually described and analyzed which meets the goal of a factor of three improvement in fuel economy set by the government-industry collaboration, Partnership for a New Generation of Vehicles, announced Sept. 29, 1993. This car combines an internal combustion engine with a low-energy, but high-power capacity, storage unit, such as a capacitor or flywheel. The storage capacity is one-half kWh. All energy requirements are ultimately met from the fuel tank. Essentially all the performance achievements of current conventional cars are met by this hybrid. Two versions of the hybrid are considered: one in which the vehicle loads are the same as those of the average 1993 car, but the drive train is replaced with a hybrid system, and one, where, in addition, the vehicle loads are reduced, at fixed performance and interior volume, to levels slightly beyond the best achievements in current production vehicles.

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.

Fuel consumption per revolution is approximately a linear function of work output per revolution, for power levels less than about two-thirds of the power at wide-open throttle. Thus where N is engine speed, Pf is fuel energy rate (kW), and Pb is power output (kW). The approximation is relatively good for engine speeds typical of regulatory driving cycles. The parameters α and b are studied using engine measurements conducted in the late 1970s. The parameter values are rather uniform, with averages α = 0.29V, where a is in kJ/rev and V is displacement in liters, and b = 2.45 (dimonsionless). Engine maps for more modern engines show, that the parameter a has declined. Several applications are discussed: especially simulation of vehicle fuel use, and creation of a figure of merit for fuel use by engines.