Simulation Model for a Crankcase-Compression Two-Stroke Spark-Ignition Engine Including Intake and Exhaust Systems

Abstract

A model is presented to simulate the power cycle and gas exchange process in a crankcase-compression two-stroke spark-ignition engine which includes intake and exhaust systems. Chemical equilibrium and a two-zone combustion model with a spherical flame front are assumed for the power cycle and generalized non-steady gas dynamic expressions, including variable composition, variable specific heats, friction and heat transfer, are assumed for the gas exchange process in the intake and exhaust systems. For the scavenge process in the cylinder, a thermal mixing model is used to calculate the pressure changes. Experiments with a small high-speed engine showed that the model gave good predictions of the pressure changes during the gas exchange process and the air flow rate. The power predictions followed the experimental trend, but the quantitative results were not so good as the air flow predictions. Despite the limitations of the power predictions, the method offers the designer a tool for improving the performance of the crankcase-compression engine.