Stratified-charge two-stroke stepped-piston engine

Abstract

A two-stroke stepped-piston prototype engine, in carbureted version was designed and developed. It incorporates a unique three-port transfer system with an accumulator for high induction efficiency, so as to perform very much like a two-stroke engine but equipped with a four-stroke crankcase lubrication system. GT-Power software was used in the development stage to predict the engine output. The data predicted was then compared with the experimental results. A computational fluid dynamic software, COSMOS/Floworks, was used to develop a computational model to investigate the scavenging and compression processes of the prototype engine.The prototype was subjected to a series of laboratory trials for engine performance and emissions tests. Emission characteristics were established for regulated and unregulated gases. From the engine performance test, maximum pressures attained from GT-Power simulation and prototype engine were 54.62 bars at 5000 rpm and 26.12 bars at 4500 rpm respectively. Maximum indicated power produced is 11.25 kW at 8000 rpm and 3.86 kW at 4500 rpm for GT-Power simulation and prototype engine respectively. Torque, brake power and brake fuel consumption were also determined. For comparative reason, a Yamaha 125Z engine was selected as the cylinder capacity with similar working principle as the prototype engine. Torque produced by Yamaha 125Z was highest, followed by GT-Power simulation and prototype engine. The average difference of torque between Yamaha 125Z and GT-Power simulation was about 13.06%. The minimum values of brake specific fuel consumption for Yamaha 125Z, GT-Power simulation and prototype engine were 280.42 g/kWh at 3500 rpm, 351.08 g/kWh at 5000 rpm and 510 g/kWh at 3500 rpm respectively. The maximum peaks differences were attributed to the differences of combustion chamber design used and assumptions made in GT-Power.