The Stretch for Better Passenger-Car Fuel Economy

Since the earliest days of the automobile, improved fuel economy has been an objective of passenger-car manufacturers. The original market paced fuel-economy phase gave way to the CAFE-regulated phase in the late 1970s. September 1993 marked the start of a third fuel-economy phase, the Partnership for a New Generation of Vehicles (PNGV). PNGV has as its objective the development of a mid-size “Supercar” achieving an EPA combined-schedule fuel economy of 80 mpge (80 mi/gal gasoline equivalent = 34 km/L = 2.94 L/100 km) without sacrificing other attributes of the current U.S. mid-size car. The PNGV program is differentiated from the two previous phases by its cooperative research effort between industry and government. A review of past automotive phases sets the stage for future PNGV projections. After considering three of the several methods that have been used for predicting fuel economy in vehicles that have yet to be designed, a fourth method, the “building block” approach, is chosen to explore the relative influences of key parameters responsible for vehicle fuel economy. These include powertrain efficiency; vehicle mass, aerodynamic drag and rolling resistance; accessory load; and the recovery of braking energy. A more detailed examination of implications for the PNGV engine is then undertaken. It is found that for reasonable levels of the other parameters, the engine efficiency required to achieve the 80 mpge PNGV fuel-economy target will be a difficult challenge.