Setting Up A Comprehensive CFD Model of A Small two Stroke Engine for Simulation

Short circuiting of fresh charge during the scavenging process of a two-stroke engine has been an object of technological innovation for many decades resulting in many solutions based on studies of in-cylinder flow pattern during scavenging process. Computational Fluid Dynamics (CFD) has emerged as a tool for simulation of internal combustion engine processes and many commercial software codes are now available to accomplish this study. CFD models for studying the behavior of two-stroke engines under different operating conditions and fuels have been developed. The effects of changes in fuel supply systems, ignition and influence of fuel injection on engine performance characteristics have been developed. CFD codes are extensively used to arrive at preliminary and indicative solutions for many aspects of port design like opening and closing timings, orientations, sizes and other design parameters. The major advantage of CFD study is its ability to predict the spatial and temporal values of fluid properties throughout the domain of interest of the whole 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 in this work since it has been established that the crankcase pressure plays a major role in the effective delivery of fresh charge to the cylinder. Few analysis results of the model for the velocity and crankcase pressure in the scavenge port have also been included in the paper to demonstrate the broad agreement with the results obtained by Yuji Ikeda et al from FLDV experiments on a SUZUKI 100 cc crankcase scavenged two stroke engine. The limitations of the CFD software and the shortcomings of the model have been discussed along with suggestions for perfecting the model.