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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.

Improving the fuel economy of a passenger car by installing a small-displacement low-power engine is a methodology long recognized, but the accompanying loss in vehicle performance is a tradeoff unacceptable to the customer. Recovering the power deficiency by boosting the engine with a turbocharger or an engine-driven supercharger has often been suggested as a remedy. Turning back the pages of history, about thirty years ago an unusual supercharging scheme was evaluated that involved injection of high-pressure air from a storage reservoir directly into the cylinders of a downsized engine. Makeup air was provided by a pair of 21-MPa (3000 psi) engine-driven compressors. Large gains in fuel economy were measured when the compressors were not required to recharge the storage reservoir, as might be expected, but in simulated city and highway driving, those gains were greatly diminished by the need to replace stored supercharging air.

Leading contenders in the search for a superior alternative powerplant for light-duty automotive use include the steam and Stirling engines, the gas turbine, and the diesel. In this paper the status of each of those alternative engines is reviewed and i its prognosis considered. The steam engine is unsuitable because of poor fuel economy. Obstacles blocking acceptance of the Stirling and gas turbine engines are sufficient so that even if they are surmountable, significant-use in light-duty vehicles is unlikely before the 1990s. The light-duty diesel is here today but faces some difficult regulatory hurdles in the near future.

The evolution of increasingly stringent standards for passenger-car exhaust emissions has increased the need for more sophisticated engine controls. In the era prior to emissions control, the dependent variables were fuel economy, driveability, and convenience and cost to the customer. The principal independent variables were spark advance and air-fuel ratio. With the tailpipe emissions of unburned hydrocarbons, carbon monoxide, and oxides of nitrogen now added to the list of dependent variables, a number of additional concepts have been introduced on production automobiles. Among these are exhaust-gas recirculation (EGR), the oxidizing catalytic converter, and the three-way catalytic converter. These developments, in combination with tighter emission standards and new fuel-economy mandates, have complicated the engine control problem. This presentation focuses on the definition of that problem.

The intensive search for an alternative low-emission powerplant for passenger cars has led to a re-evaluation of the gas turbine for this type of service. The GT-225 engine was designed as a research tool to aid in making such an evaluation. Factors which received special consideration in making design decisions included exhaust emissions, fuel economy and drivability. An extensive combustor development effort was undertaken to achieve low emissions. The engine has been installed in a test-bed vehicle to permit evaluation of emissions and other factors under actual driving conditions. Vehicle tests of the engine fitted with a low-emission combustor demonstrated the following emissions: 0.11 g/km (0.18 g/mile) HC; 1.2 g/km (2.0 g/mile) CO; and 0.23 g/km (0.38 g/mile) NOx.

Eliminating the conventional liquid cooling system of a diesel engine to conserve energy normally rejected to that heat sink offers promise as a means for improving fuel economy. Such low-heat-rejection (LHR) diesels have generally been advanced for heavy-duty vehicles. In this study, application of the concept is analyzed for a light-duty indirect-injection diesel of the type used in passenger cars. The naturally aspirated LHR diesel is found to offer no fuel economy advantage, principally because of the deteriorated volumetric efficiency arising from hot cylinder walls. It is found that most of the energy conserved by deleting the cooling system is diverted to the exhaust gas. Methods examined for recovering the lost volumetric efficiency and/or harnessing the increased energy content of the exhaust include supercharging, adding a bottoming cycle, and combining the diesel with turbomachinery. The latter option is judged superior for the passenger-car application.

The average American driver wants a comfortable, stylish, reliable and durable vehicle that offers brisk performance, reasonable fuel economy, and is pleasing to drive - all at an affordable cost. Current regulations reinforce the need for good fuel economy and also mandate limits on exhaust emissions. For this set of attributes, the spark-ignition reciprocating engine promises to dominate well into the 21st century. Among on-going developments showing potential to extend its domination are multivalve cylinders, advanced induction systems, and variable valve actuation. Among the alternative powerplants undergoing development are the two-stroke spark-ignition engine, the low-heat-rejection diesel, the Stirling engine and the gas turbine. Because of several special qualities of ceramics, this class of materials is being considered for broadened application to engines. Environmental concerns are leading to consideration of alternative fuels and to concern about carbon dioxide emissions.