Performance of a direct-injection natural gas engine with multiple injection strategies

This paper presents the experimental results for the performance of a direct-injection natural gas marine engine with different multiple injection strategies. In order to investigate the effects of natural gas post injection proportion and natural gas injection separation, a series of tests were performed at five different injection proportions (8%, 10%, 15%, 20%, 25%) and injection separation from 100 mu s to 700 mu s at every 100 mu s. The averaged cylinder pressure traces and combustion parameters (MFB50%, MFB90% and MFB5-90%) of each test point were calculated for combustion analysis. HC, CO and NOx emissions were collected to reveal the emissions characteristics. The results showed that the peak values of cylinder pressure and heat release rate will be lower than that of natural gas single injection strategy when multiple natural gas injection strategies are applied. Though the phase angle of 50% mass fraction burned is advanced at medium natural gas injection separations, the phase angle of 90% mass fraction burned is more likely to occur early at longer natural gas injection separations. With regard to emissions, HC and NOx emissions can benefit from using shorter natural gas injection separations while CO can only be reduced with small post injection proportions with certain natural gas injection separations. (C) 2019 Elsevier Ltd. All rights reserved.