Study on the synthetic scavenging model validation method of opposed-piston two-stroke diesel engine

The scavenging process of two stroke engines is a complex phenomenon. In two stroke engines, each outward stroke of the piston is a power stroke. This means the operation of clearing the burned gas in cylinder and obtaining fresh air for next cycle must accomplish at same time. The combined intake and exhaust process in two stroke engine is called scavenging. Nowadays, a synthetic scavenging model is widely used to describe the scavenging process of two stroke engines. It represents the time evolution of the in-cylinder residual gas rate and the exhaust residual gas rate. An opposed two stroke diesel engine's (OP2S) synthetic scavenging profile is calculated through the changes of gas compositions in-cylinder and exhaust pipe by CFD simulation. To validate the accuracy of this profile, a validation method based on tracer gas technique is proposed. First, scavenging parameters including scavenging efficiency and trapping efficiency are calculated by 1D software using the synthetic scavenging profile as a vital boundary condition. The results reveal that the delivery ratio of the OP2S diesel engine should below 140%. Second, use tracer gas technique to measure the scavenging parameters of OP2S diesel engine. In the experimental process, we find the OP2S diesel engine operates steady only if the delivery ratio is higher 50%. The scavenging parameters from 1D simulation and experiment match well which means the synthetic scavenging model received by CFD simulation performs well and validating its effectiveness through tracer gas technique is available.