A Ramesh

Gasoline and liquefied petroleum gas (LPG) were injected into the manifold of a 145 cc two stroke engine using a specially developed electronic circuit to have a close control over the air fuel ratio. Experiments were carried out at 3000 rev min-1 and fixed throttle positions of 10, 15, 25, 40, 50 and 100% of full opening. The amount of fuel injected (air fuel ratio), injection timing and injection pressure were varied. The maximum brake thermal efficiency with LPG was 25% and that with gasoline was 23%. The engine could generally operate with much leaner mixtures with LPG due to its good mixture formation capability. HC levels and exhaust gas temperature were slightly higher with LPG while NO levels were comparable. It was found that the injection pressure had to be reduced at part throttle conditions in order to get better engine stability and performance. The maximum power output with LPG was lesser than that with gasoline. © 2007 Energy Institute.

Abstract Improvements in a two-stroke, spark-ignition (2S-SI) engine can be realized by curtailing short-circuiting losses effectively through direct injection of the fuel. Liquefied petroleum gas (LPG) is an alternative transportation fuel that is used in several countries. However, limited information is available on LPG fuelled direct injected engines. Hence, there is a need to study these systems as applied to 2S-SI engines in order to bring out their potential benefits. A manifold injected 2S-SI engine is modified for direct injection of LPG, in gaseous form, from the cylinder head. This engine is evaluated for performance, emission and combustion. Evaluation at various throttle positions and constant speed showed that this system can significantly improve the thermal efficiency and lower the hydrocarbon (HC) emissions. Up to 93% reduction in HC emissions and improved combustion rates are observed compared to the conventional manifold injection system with LPG. CO emissions are higher and peak NO emissions are lower with this system due to the presence of richer in-cylinder trapped mixtures and charge stratification. This system can operate with similar injection timings at different throttle positions which make electronic control simpler. It can work with low injection pressures in the range of 4-5 bars. All these advantages are attractive for commercial viability of this engine.