Effect of Compression Ratio on Performance of a Four-Stroke Spark-Ignition Engine - A Theoretical and Experimental Study

Abstract

Researchers strive to improve the performance characteristics such as power, thermal efficiency, mean effective pressure etc. of automotive engines. As the emission norms are becoming stringent day by day, the car manufacturers try their best to decrease the emissions and improve the performance without major compromise on performance. Improvements in the performance of an engine are can be achieved by increasing the compression ratio below detonating values. In this study influence of compression ratio on cylinder peak pressure, power, efficiency, and work for a four-stroke spark-ignition engine is reported. Both experimental and theoretical studies have been undertaken. Theoretical work is carried out using thermodynamic modelling techniques. Compression ratios ranging between 6.3 and 10.3 are considered in the speed range of 1200 and 2800 rpm. Experiments have been carried out on a single cylinder engine for a compression of 8.3 over the above speed range. The investigation is carried out particularly at such low speeds since in city driving the vehicles run only at part throttle in the above range of engine speed. The general conclusion is that the increase in compression ratio increases the performance.