Improving the Performance of a Small Spark-Ignition Engine by Using Oxygen-Enriched Intake Air

In order to improve the performance of a small gasoline engine, a part of oxygen is added to the intake air when the engine is operated at wide open throttle. The combustion process can be enhanced by using an oxidant that contains a higher proportion of oxygen than that in normal air. This paper studies the combustion characteristics and engine performance of such engine. Engine testing is performed on a 50 cc four-stroke spark-ignition engine with the oxygen concentration of intake air ranging from 21% to 25% by volume. The engine torque is increased with increasing oxygen concentration. The HC and CO emissions are decreased with oxygen enrichment, but the NOx emission is increased.