Computational fluid dynamics approach to study the gas exchange process in small two stroke engines

Abstract

Climatic conditions favour use of two wheelers, which possess the advantages of low cost, simplicity, lightweight and ease of maintenance, almost throughout the year in countries like India. Also economically weaker sections of the society of many developing countries having agriculture as their major occupation prefer these two wheelers. Computational Fluid Dynamics (CFD) has emerged as a powerful and alternate tool for simulation of internal combustion engine processes and many commercial software codes are now available to study in-cylinder flow pattern. CFD models have been developed (e.g.) for studying the effects of changes in fuel supply systems and ignition and influence of fuel injection on engine performance characteristics. The first part deals with the CFD analysis on the turbulence intensity and its enhancement near spark discharge area in a model with a flat top piston using construction details adopted from available data. The second part deals with the development of a comprehensive simulation model for a two-stroke engine. A unique model to simulate simultaneous expansion and compression of crankcase contents of a small two stroke engine during the compression and expansion strokes respectively has been developed. The third part deals with a CFD model of a 70cc XL Super engine. Based on the procedures and methodology adopted for the simulation of the Suzuki model, predictions of the port passage velocity and crankcase pressure in the scavenge port are obtained for this engine. In spite of the uncertainties in the geometric model of the Suzuki engine, broad agreement is noticed between experimental results and CFD predictions. It is reasonable to assume that the predictions for the XL Super engine can be relied upon since the model has been prepared with all the construction details. As an extension of the third part, the influence of a modification carried out on the existing XL SUPER model is also studied. It is seen that advancing the exhaust port opening produced the expected results.