Effect of Layered-Port VVT on Performance of Opposed-Piston Two-Stroke Diesel Engine

Variable valve timing (VVT) technology effectively improves the performance of diesel engines. The technology is widely used in traditional four-stroke diesel engines. They use a valve-type mechanism to realize VVT. The valve-type mechanism is not suitable for opposed-piston two-stroke (OP2S) diesel engines, so VVT technology was never before applied in OP2S diesel engines. However, this study aims to resolve this problem; A layered-port VVT mechanism was developed for an OP2S engine and its performance was investigated. A simulation model of an OP2S diesel engine was established by the equivalent two-stroke method. The effect of port parameters on the indicated mean effective pressure (IMEP) and scavenging efficiency was studied. It was observed that the optimal port heights varied at different speeds, and the layered-port scheme significantly improves the performance of the diesel engine compared with the fixed port scheme. The IMEP increased by 2.2%. The indicated specific fuel consumption (ISFC) decreased by 3.4%. Soot emissions decreased by 2.3%. The power and fuel economy characteristics of the double-layer port were generally better than the power and fuel economy characteristics of the triple-layer port. The soot emissions of the double-layer port were lower than the soot emissions of the triple-layer port. (C) 2019 American Society of Civil Engineers.