Evaluating the scavenging process by the scavenging curve of an opposed-piston, two-stroke (OP2S) diesel engine

Due to its inherent advantages of superior manufacturability, power density, and thermal efficiency, the opposed-piston, two-stroke (OP2S) diesel engine has great potential in alleviating energy consumption and improving fuel economy. The scavenging process is the key factor affecting the performance of OP2S diesel engines; however, because there are many evaluation parameters for the scavenging process, there are also many difficulties in matching and optimizing the scavenging system. To bridge this knowledge gap, this study established a three-dimensional model of an OP2S diesel engine to optimize the port height by the scavenging curve. The model was verified and validated through a steady flow experiment. The scavenging performance indicators, including distribution of residual gas, scavenging efficiency, trapping efficiency, and delivery ratio, were investigated under different port heights. The scavenging model method and the scavenging curve method were employed to evaluate the scavenging process. The results show that, when analyzing the factors that affect scavenging performance, the scavenging curve can be used to evaluate not only the optimization potential of the scavenging system but also the development of the scavenging process. After optimizing the port height by the scavenging curve, the actual scavenging curve appeared in the zone enveloped by the scavenging curve of the maximum port (34 mm/34 mm) and the scavenging curve of the minimum port (12 mm/14 mm). In this greater zone, there is a preferred zone where the port height to stroke ratio is from 0.11 to 0.15, which is the optimal value. This study reveals the influence of different port heights on scavenging performance and provides design insights for evaluating and optimizing the scavenging process of an OP2S diesel engine.