Exploring the potential of water injection (WI) in a high-load diesel engine under different fuel injection strategies

Abstract

Water injection (WI) is a promising technology in diesel engines. However, the joint effects of WI and fuel injection strategy have not been investigated well. Furthermore, the comparison between WI and exhaust gas recirculation (EGR) requires further clarification. This study aims to identify the optimal way of WI and its benefits for a high-load diesel engine operated with various fuel injection strategies. Therefore, four schemes, i.e., diesel single injection strategy with/without WI and diesel double injection strategy with/without WI, were optimized by employing numerical simulation. The optimal water injection timing for single injection strategy is near −108°CA ATDC, while it is 8–20°CA before the first diesel injection for double injection strategy. Water mass is the most decisive parameter, and the optimal water masses are 10%–35% and 29%–51% of the fuel mass, respectively. When WI is employed alone without introducing EGR, NOx can be reduced by 30% and 90% respectively. Compared with EGR, the main superiority of WI is reduced NOx emissions without sacrificing fuel economy until the water mass reaches 50% of the fuel mass. For single injection strategy, the cooling effect of WI is the dominant factor, while for double injection strategy, the dilution effect becomes prominent.