Parameter investigation of the pilot fuel post-injection strategy on performance and emissions characteristics of a large marine two-stroke natural gas-diesel dual-fuel engine

This study aimed to conduct a parametric study to investigate the effect arising from pilot fuel post-injection strategy on engine combustion, performance, and emissions of a large two-stroke natural gas-diesel dual-fuel engine for marine applications. The one-dimensional and three-dimensional simulation models were built in AVL-BOOST and CONVERGE, respectively, and validated according to experimental results. The effects of post-injection strategies on post-injection timing and mass ratio on engine combustion, performance, and emissions were investigated. As revealed by the results, an appropriate pilot fuel post-injection strategy could achieve lower NOx emissions with less loss of performance. As post-injection timing was delayed, the NOx emission first decreased and then increased. Subsequently, it decreased to the lowest and finally increased. With the increase in the post-injection mass ratio, the NOx emission was kept decreasing. Compared with the original engine, the NOx emission decreased by 81.85 ppm with a post-injection timing of 18 deg after top dead center and with a mass ratio of 0.7. However, the indicated power only decreased by 4.82 kW, and the indicated specific fuel consumption only increased by 0.2 g/kWh. This study can provide some theoretical guidance for the injection strategy optimization of the marine two-stroke natural gas-diesel dual-fuel engines and provide technical suggestions for practical application.