Effect of increase in the transfer-duct volume on the performance of a stratified scavenged two-stroke SI engine

Reed valves can be provided at the top of the transfer ducts of a two-stroke SI engine for stratified scavenging. This modification permits fresh air to be trapped in the transfer ducts during the induction process and used in the initial scavenging phase. This results in a considerable reduction in short-circuiting of the fresh charge. In the present work, a small two-stroke SI engine was modified to use this system. Experiments indicated a considerable improvement in performance particularly when air is fed under pressure through the reed valves at the transfer ducts. Subsequently, the volume of the transfer ducts was enlarged so that they can trap more fresh air. This modification led to a significant improvement in brake thermal efficiency and reduction in HC and CO emissions even when air was not sent under pressure through the reed valves. There was a good improvement in the combustion process and also a reduction in cyclic fluctuations of indicated mean effective pressure.