Effect of swirl-spray impact on the comprehensive performance of uniflow-scavenging opposed-piston engines

Uniflow-scavenging opposed-piston (USOP) engines exhibit high thermal efficiency and power density. However, the USOP engine has a continuous in-cylinder airflow state between different cycles, which affects direct injection oil spray distribution. The USOP engine nozzles were mounted on a cylinder liner. The forward and reverse impacts of the in-cylinder swirl differed in the asymmetric orifice layout. A dual-intake channel USOP simulation model was established. The key parameters of the simulation model were verified, and the effects of forward and reverse impacts under different nozzle layouts and swirl strengths were analysed by simulation. The results show that all swirl-spray impacts benefit the combustion. Swirl-spray impacts can effectively improve the oil spray distribution and atomisation. In addition, reducing the swirl in the next cycle concentrates the exhaust gas in the cylinder centre, improving the scavenging efficiency. Forward and reverse impacts enhance and weaken the in-cylinder swirl, respectively. However, the effect of the reverse impact was more pronounced than that of the forward impact.