A Stratified Charging Two-Stroke Engine for Reduction of Scavenged-Through Losses

Svavenged-through losses of fresh charge in two-stroke engines are known to be the major causes for high specific fuel consumption (sfc) and hydrocarbon (HC) emissions. This paper describes one of the concepts of stratified-charging in which initial charging is carried out by air or leaner mixtures, and this is followed by rich mixtures. The distinguishing feature of the concept is that the loss-contribution of the initial fractions of incoming charge is higher, which consists more of air. For this, a practical dual-intake system was developed. The experimental evaluation showed that the sfc and HC of the new engine version were consistently lower, however, the level of reduction depended upon the flow-ratio of the two circuits of the dual-intake system and the load. It did not practically depend upon the trapped air-fuel ratio.