Investigation On The Gas Exchange Process Of An Opposed-piston Two-stroke Diesel Engine

With the advantages such as high efficiency, high power density and excellent balance,Opposed-piston two-stroke Diesel Engine (OP2S) caused the attentions at home and abroad.Based on the scavenging theory, the gas exchange process of OP2S folded crank-trainengine was investigated with a method of numerical simulation and experiments.According to the structural characteristics and working principle of the scavengingprocess, the features were obtained, such as the shortage of the scavenging duration and themixture of fresh gas and burned gas. The gas motion was analyzed and the tangential angleand elevation angle were designed for the gas organization. The1D and CFD model of theOP2S engine were established.1D simulation was applied in the affection investigation of the port height and width.Results showed that the delivery ratio and scavenging efficiency increased by theincreasing of the intake ports height and width, while the trapping efficiency decreased bythe increasing of the intake ports height and width. The delivery ratio increased by theincreasing of the exhaust ports height and width, while the trapping efficiency andscavenging efficiency decreased by the increasing of the exhaust ports height and width.The influence of scavenging quality and gas motion caused by the tangential and tumbleangle was investigated based on the CFD simulation. Results showed that the tangentialangle can improve the swirl level, but the scavenging efficiency dropped when thetangential angle was too large. When the tangential angle was larger than10°, the exhaustgas retention area was existed in the middle of the exhaust side of the cylinder. The areabecame large as the tangential angle increased, which was bad for the scavenging process.The elevation angle can improve the tumble level, but led to the decrease of the scavengingefficiency. Therefore, the tangential angle and tumble angle can organize the in cylinder gasmotion, which were benefit for the mixture and combustion, but worsen the scavengingquality.Based on the scavenging characteristics of OP2S engine and the tracer gas principle,the inlet tracer gas method was employed on the OP2S engine and the influence of theoperating condition on the OP2S engine was investigated by using this method. Resultsshowed that as the increasing of difference between intake and exhaust pressure at the sameengine speed, the delivery ratio and scavenging efficiency increased, while the trapping efficiency decreased. As the increasing of engine speed at the same difference betweenintake and exhaust pressure, the delivery ratio and scavenging efficiency decreased, whilethe trapping efficiency increased.