Effect of engine parameters on in-cylinder flows in a two-stroke gasoline direct injection engine

This paper deals with the in-cylinder flow field analysis in a two-stroke engine under motoring conditions by particle image velocimetry (PIV) and computational fluid dynamics (CFD). The main objective is to analyze the effect of engine parameters viz., engine speed, compression ratio (CR) and port orientation on the in-cylinder flows in a loop-scavenged two-stroke gasoline direct injection (GDI) engine, with an aim to help researchers to design fuel efficient and less polluting two-stroke engines. In this study, a single-cylinder 70 cm3 two-stroke engine which is very commonly used for the two-wheeler application, is considered. The engine cylinder is modified to provide optical access into the in-cylinder region. The PIV experiments are conducted at various engine speeds viz., 500, 1000 and 1500 rev/min, and the plane averaged velocity vector fields obtained, are analyzed to understand the in-cylinder flow behavior. The CFD study is also carried out using the commercial CFD code, STARCD, to study and compare the in-cylinder flow parameters at various engine operating conditions. The CFD results are compared with the experimental results to the extent possible. The CFD predictions are found to be in good agreement with the experimental results. Therefore, the CFD analysis has been extended further to understand the effect of various engine parameters on the in-cylinder flows. We found that the turbulent kinetic energy and tumble ratio increased by about 25% and 20% respectively, when the engine speed was increased from 1000 to 1500 rev/min. Also, we found that the turbulent kinetic energy and tumble ratio decreased by about 13% and 26% when the compression ratio was increased from 7 to 8. In addition, we found that the port orientation, rather than port areas had a greater influence on the in-cylinder flow parameters.