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This study describes the effect of spark plug location on NO and HC emissions from a single-cylinder engine with a specially modified combustion chamber. The effects of changes in combustion duration caused either by spark location, dual spark plugs, or charge dilution on NO and HC emissions were also examined. Experiments were run at constant speed, constant load, and mbt spark timing. Nitric oxide emissions were the same with the spark plug located either near the intake or exhaust valve, but were higher with the spark plug midway between the valves or with dual ignition. Hydrocarbon emissions were lowest with the spark plug nearest the exhaust valve and increased with the distance of the spark plug from the exhaust valve. With charge dilution the decrease in NO emission was isolated into a pure dilution effect and a combustion duration effect. The combustion duration effect was minimal at rich mixtures and increased with air-fuel ratio.

A method to stratify the fuel-air mixture along the cylinder axis of engines is described. Axial stratification, with the richest mixture near the top of the combustion chamber and the leanest mixture near the piston top, was obtained by imparting swirl to the intake air and by injecting fuel into the inlet port just before the end of the intake stroke. Axial stratification was developed in both single and multi-cylinder engines over the range of operating conditions tested. A production four-cylinder engine modified to operate with axially-stratified-charge, showed: increased combustion stability and tolerance to dilute mixtures; decreased fuel consumption; similar HC and CO emissions; lower NO emissions and octane requirement when compared with the unmodified engine operated at the same overall equivalence ratio.

The axially stratified-charge (ASC) concept was demonstrated in a compact production car by modifying the engine and developing the required control system and calibration. Two production 1.8 L four-cylinder engines were modified to operate as ASC engines by adding shrouded inlet valves to produce swirl, and by providing timed-sequential port fuel injection. One of these engines was calibrated for minimum fuel consumption in the laboratory using a computer-controlled engine and dynamometer. The second engine was installed in a vehicle equipped with an oxidizing catalyst. A complete control system was developed for this engine to implement the minimum fuel consumption calibration in the vehicle. The fuel economy of the ASC vehicle was six percent better than that of the base vehicle. It had acceptable driveability, and had a 91 Research octane requirement on the fuel.