Technological Evaluation of Fuel Efficiency Improvement Concepts to Meet Future Regulatory Requirements in the North American Market 2002-01-2809

As fuel economy and emissions regulations increase in stringence, automakers face ever increasing difficulty in meeting government imposed standards. In this paper a study of fuel economy improving techniques used to meet these regulations, notably Corporate Average Fuel Economy (CAFE), and the upper limit on the effectiveness of these techniques is presented. The effects of external vehicle improvements, such as lightweighting, rolling resistance and aerodynamic improvements were investigated to illustrate the limitations of these methods to dramatically improve overall vehicle efficiency. Engine efficiency improvements, including the effects of compression ignition (unthrottled) versus spark ignition (throttled) engine types were examined. Other engine efficiency areas that were investigated were the implementation of cylinder deactivation and gasoline direct injection engines. Powertrain efficiency concepts, including manual transmissions and continuously variable transmissions were evaluated as well. Final areas of investigation were those of hybridization, from light, i.e. start-stop systems, to more moderate, motive power adding systems, and finally, fuel cell powered systems. Challenges to the implementation of these techniques, both technical and legislative were examined and discussed. A computer model was selected for the analysis and uses a backward simulating approach to compute predicted fuel economy. Areas of thermal efficiency, energy management, energy recovery, and energy reduction were analyzed. Simulation results show that application of any single technology fleet-wide will not meet a targeted 36mpg standard. Diesel, fuel cell, and hybrid vehicle powertrain technologies are needed in order to meet this standard.