Investigation of scavenging performance in an OP2S engine with a novel EGR-air stratified strategy

In this study, the scavenging process in an opposed-piston two-stroke (OP2S) engine is numerically investigated under the EGR-air stratified scavenging strategy. The effects of geometric features and boundary conditions, such as exhaust port height (EPH), piston phase (PP), and intake pressure, on scavenging parameters were examined. The results indicate that the EGR–air stratified scavenging strategy effectively improves trapping efficiency of air (TE of air) and maintains high scavenging efficiency (SE). Furthermore, it contributes to reducing NOx emissions by optimizing the operating conditions of the three-way catalyst. The proper matching of the EPH and PP could mitigate the scavenging short-circuiting problem. An increase in EPH could improve the delivery ratio (DR), thereby increasing both SE and TE of air. However, extra-large EPH could reduce TE of air. Furthermore, adjusting the air intake pressure could slightly improve TE of air, although the impact on reducing the scavenging short-circuiting problem is quite limited. High SE could be sustained while TE of air could be significantly elevated by maintaining the pressure differential constant and decreasing both EGR and air intake pressures.