Effects of intake port structures and valve timings on the scavenging process in a two-stroke poppet valve diesel engine 2019-01-1169
The two-stroke operation is one of the most effective approaches to significantly increase the torque and power of a 4-stroke engine without the necessary requirement of intensifying the engine. Scavenging process is one of the key factors determine the performance of the two-stroke engine. In order to improve the scavenging process, a structure of top entry intake ports with poppet valves was employed on the 2-stroke single cylinder engine with the conventional horizontal intake ports replaced. The reversed tumble flows in the cylinder were formed during the intake process. In addition, the effect of intake port structures and valve timings on scavenging processes was estimated through the 3D simulation of the gas exchange process.
Results show that by advancing the exhaust valve opening the exhaust gas exits more sufficiently and the intake backflow was reduced significantly. Therefore, the charging efficiency and scavenging efficiency were improved. The reversed tumble flow led to a lower air short-circuiting rate and a higher scavenging efficiency compared to the conventional flat intake port case. It was also found that in the case of the reversed tumble intake ports structure, when exhaust valve timing was advanced by 20°CA, the scavenging efficiency increased from 74% to 86% ，and the trapping efficiency increased from 72% to 76%.
Wei Liu, Yan Zhang, Bo Yu, Yaozong Li, Ziyu Wang