An Assessment of a Stratified Scavenging Process Applied to a Loop Scavenged Two-Stroke Engine

Stratified scavenging has been applied to two-stroke engines to improve fuel consumption and reduce exhaust emissions. To evaluation how this is achieved a stratified scavenging process was simulated using a three-gas single-cycle scavenging apparatus. The experiment simulated the fuel stream entering the rear transfer port of a five port cylinder and air streams entering the remaining ports. The scavenging efficiency and fuel trapping are calculated after the cycle by examining the cylinder contents. The design of the apparatus is particularly suited to investigating cylinder design changes during the prototype stage of engine development.

A simulation of the stratified scavenging experiment using the Computational Fluid dynamics (CFD) code VECTIS, showed good correlation with measured results. The simulation provides a real insight into the cylinder flow behaviour of the separate fuel and air streams entering the cylinder. Various cylinder designs were simulated to investigate improvements in fuel trapping.