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Alternative fuels are gaining acceptance globally because of the limited availability of petroleum resources and the stringent environmental pollution regulations. Since compression ignition engines are more widely used when compared to spark ignition engines, greater attention is being paid to develop an alternative source of fuel for the diesel engines. In the present investigation, hybrid fuel blends of diesel-ethanol-vegetable oil (pungamia methyl ester) are selected for testing in a multi-cylinder transport bus engine (HINO-6D) and its suitability as an alternative fuel is studied. Different combinations of the hybrid fuel blends are prepared and tested. Chemical surfactants are used to overcome the problem of phase separation of alcohol. The brake thermal efficiency of the engine operated with hybrid fuel blends are calculated and found to be slightly higher than that of diesel. The smoke and oxides of nitrogen are found to be reduced while using hybrid fuel blends as fuel.

The problem of cyclic variation in combustion has been investigated by measuring 2000 continuous in-cylinder pressure traces. The experimental work was carried out in a single cylinder two-stroke SI engine loaded by an eddy current dynamometer. The air-fuel ratio was varied form rich to lean by a modified carburetor. The pressure traces were recorded by a piezo-electric pressure pickup and PC based data acquisition system. Cyclic variation in combustion was identified by the variation in peak pressure (Pmax) and indicated mean effective pressure (IMEP). The results show that cyclic variation increases when the air-fuel mixture becomes lean. It also indicates the existence of combustion phasing and different modes of combustion. The combustion variation and its effect on the performance of the engine is more severe in two-stroke engine as compared to a four-stroke engine.

This paper presents the results of experimental work conducted on a catalytically activated two stroke spark ignited engine, to investigate the cyclic variation of combustion parameters. A comparative study was carried out with the base engine for finding out the effect of catalytic activation. The catalyst selected was copper and coated on the inside surface of combustion chamber walls and piston crown by plasma spraying technique. Cylinder pressures were recorded for 2000 continuous cycles using a piezoelectric pressure pickup and PC based data acquisition system. The covariance (COV) were calculated for the 2000 cycles and compared with base engine. The results show that the catalyst coating accelerates the pre-flame reaction and shortens the combustion duration. The cyclic variation of combustion parameters were less than the base engine and there is a group of cycles which deviate from the normal cycles.