Numerical Study on the Effects of Multiple-Injection Coupled with EGR on Combustion and NOx Emissions in a Marine Diesel Engine

Abstract

In this work, the potential of multi-injection strategies coupled with EGR to improve the trade-off relationship of NOx-BSFC (Brake specific fuel consumption) is carefully studied by multi-dimensional simulation using CONVERGE in a low-speed two-stroke diesel engine. The present study reveals that by introducing high EGR rate, the reduction of NOx emissions, the peak heat release rate and the peak pressure can be observed. But the effective fuel consumption rate is increased. We investigate the effects of various multiple-injection strategies on the engine performance, that is, single pilot-injection, single post-injection, single pilot-injection combined with single post-injection, and double pilot-injections, coupled with 39% EGR. The results show that low BSFC can be effectively achieved by a single pilot-injection strategy of small interval and large quantity. However, with a comprehensive consideration of low NOx emissions and BSFC, a strategy of 25 °CA pilot-main interval and 20% quantity should be chosen to obtain the best performance. The analysis of post-injection reveals that it is beneficial to reducing NOx emissions, but BSFC can be deteriorated. Moreover, it can be concluded that it is possible to achieve low NOx emissions and fuel consumption simultaneously by using the pilot-injection combined with post-injection. It also can be found that NOx emissions are deteriorated remarkably when using double pilot-injections.