Abstract
The scavenging process for opposed-piston folded-cranktrain (OPFC) diesel engines can be described by the time evolution of the in-cylinder and exhaust chamber residual gas rates. The relation curve of in-cylinder and exhaust chamber residual gas rate is called scavenging profile, which is calculated through the changes of in-cylinder and exhaust chamber gas compositions determined by computational fluid dynamics (CFD) simulation. The scavenging profile is used to calculate the scavenging process by mono-dimensional (1D) simulation. The tracer gas method (TGM) is employed to validate the accuracy of the scavenging profile. At the same time, the gas exchange performance under different intake and exhaust state parameters was examined based on the TGM. The results show that the scavenging process from 1D simulation and experiment match well, which means the scavenging model obtained by CFD simulation performs well and validation of its effectiveness by TGM is possible. The difference between intake and exhaust pressure has a significant positive effect on the gas exchange performance and trapped gas mass, but the pressure difference has little effect on the scavenging efficiency and the trapped air mass if the delivery ratio exceeds 1.4.
Highlights
The opposed piston two stroke (OP2S) engine concept can be traced back to late 1800s
20th century, OP2S engines were developed in multiple countries for a wide variety of applications, modern emissions regulations stopped the widespread development of most two-stroke engines in the latter half of the 20th century [1]
Ternel and Thiriot used the synthetic scavenging model to study the influence of intake and exhaust pressure on the scavenging process in their preliminary design of a two-stroke uniflow diesel engine for passenger cars [18]
Summary
The opposed piston two stroke (OP2S) engine concept can be traced back to late 1800s. A synthetic scavenging model for the overall characterization of the scavenging process of two-stroke engines was widely used. It gives the mass fraction of burned gases exhausted as a function of the mass fraction of burned gases in the cylinder. Ternel and Thiriot used the synthetic scavenging model to study the influence of intake and exhaust pressure on the scavenging process in their preliminary design of a two-stroke uniflow diesel engine for passenger cars [18]. The cylinder is divided into different zones and a combination of the perfect displacement model, perfect mixing model and short circuiting model is used to simulate the scavenging process. On the one hand the TGM validates the scavenging model, on the other hand it shows the rules influencing the scavenging process
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