Effects of multitype intake structures on combustion performance of different opposed-piston engines

The uniflow scavenging opposed-piston (USOP) engine has more potential for performance improvement than the conventional engine. The combustion performance of the USOP engine is greatly affected by the uniflow scavenging process. However, the uniflow scavenging process fluctuates greatly. In addition, the opposed free piston linear generator (OFPLG) and the opposed-piston two-stroke (OP2S) belonging to the USOP engine have different piston motion laws, so the influence of intake structure on different USOP engines should be explored. This study established and verified a CFD simulation model and selected three optimization directions (intake swirl, scavenging performance, and exhaust gas backflow inhibition). The effects of intake wall thickness, intake port shape, intake port offset, and the number of intake ports were investigated by an orthogonal test. Last, three optimum schemes that respond to the three optimization directions were used to compare the combustion performance of different USOP engines. Results showed that the intake wall thickness, intake port shape, and intake port offset significantly affect the combustion performance. Improving the intake swirl and scavenging performance are effective methods to optimize comprehensive performance. Intake swirl regulation improves combustion performance by accelerating the uniform distribution of oil spray. Scavenging performance optimization improves combustion performance by increasing the in-cylinder fresh air mass. Intake wall thickness and intake port offset can simultaneously improve the intake swirl and scavenging performance.