Study on the efficiency of a spark-ignition variable displacement and compression ratio engine

Abstract

A variable stroke engine was proposed as a promising solution for improving the efficiency of flex-fuel engines by adjusting the compression ratio; this prevents knock onset for fuels with different octane numbers. Similarly, the displacement was adjusted by varying stroke length with the objective of mitigating cylinder pumping losses. This article compares the efficiency of a spark-ignition, port-fuel injection engine, with variable displacements and compression ratios; a conventional engine with a fixed compression ratio; and an engine with variable compression ratios. A simulation-based calibration was performed for each engine, using the results from a phenomenological model to predict the engine performance. The calibration maps were obtained by maximising efficiency through determining the optimal combination of available engine parameters such as spark timing, compression ratio, displacement, and throttle actuation. A comparison of the efficiencies of the different types of engines showed an improvement of approximately 15% for the engine under partial load conditions and with variable displacement and compression ratio, compared to a conventional engine.