Scavenging port based injection strategies for an LPG fuelled two-stroke spark-ignition engine

Conventional two-stroke, spark-ignition engines exhibit poor fuel economy and emit high hydrocarbon (HC) emissions due to short-circuiting of the fuel-air mixture. Literature suggests that the use of LPG in two-stroke engines poses further problems in terms of higher HC emissions. In this work, timed compressed air injection into the transfer ducts with LPG induction through the manifold (AI-LPG-IND) was adopted to reduce short-circuiting losses in a two-stroke spark-ignition engine. The engine was fully instrumented for performance, emission and combustion related measurements. Gaseous LPG injection through one of the boost ports (LPG-BPI) of the engine was also attempted. Experimental results at 25% and 100% throttle were compared with manifold injection of LPG (LPG-MI) and gasoline at the best spark timing. The AI-LPG-IND system resulted in 40% reduction in HC emissions as compared to the LPG-MI system with a simultaneous increase in the power output at 25% throttle. It was also better than the LPG-BPI system in terms of emissions at this condition. However, due to the relatively small quantity of injected air at 100% throttle, the AI-LPG-IND system was similar in performance to the LPG-MI. The LPG-BPI system reduced HC emissions at 100% throttle, but the thermal efficiency was lower than other systems.