Experimental investigation for optimum compression ratio of single cylinder spark ignition engine

Abstract

The present experimental investigation is intended to find the optimum compression ratio (CR) of single cylinder-spark ignition engine (SIE). In order to improve the performance characteristics of SIE includes improving brake thermal efficiency (BTE) and reducing brake specific fuel consumption (BSFC) which represents the main targets of this study. The volume of combustion chamber was altered by changing the thickness of cylinder head gasket, and keeping other components, that form the geometry shape of combustion chamber, constant to obtain various clearance volume and consequently variable compression ratios (VCRs). This altering permitted to have different values of CRs of 7, 7.5, 8, 8.5, and 8.7 at engine speeds of 2600 and 2800 rpm at different loads. The results showed that BTE was increased by an average of 13 % with increase of CR from 8.5 to 8.7 and it was decreased by an average of 7.5 % with decrease of CR from 8.5 to 7 at an average speed. Also, it was found that BSFC was decreased with an average of 11 % as CR was increased from 8.5 to 8.7, whereas BSFC was increased with an average of 4.5 % as CR was decreased from 8.5 to 7 at an average speed. Based on these results, it is clearly obvious that the optimum CR is 8.7.