Effect of in-cylinder air-water interaction on water evaporation and performance characteristics of a direct water injected GDI engine

Abstract

Water injection is one of the promising strategies for modern downsized GDI engines to meet performance and emission requirements under wide operating conditions. However, the benefits of water injection strongly depend upon water evaporation and distribution of water vapours inside the combustion chamber. In this regard, water injector location and orientation are two significant geometrical parameters which decide the in-cylinder positioning of the water spray, evaporation, and vapour distribution. Therefore, this CFD study presents the effects of water injector location, and orientation on the in-cylinder air-water interaction, water evaporation, vapour distribution, performance and emission characteristics of a wall-guided GDI engine. It also presents the effects of water injector location and orientations on water evaporation rate, water droplet distribution, heat release rate, IMEP, and exhaust emissions. In this study, the spark-plug is considered as located in the middle of the cylinder head, and the water injector is mounted in between the exhaust valves. Four locations of the water injector (21 mm, 25 mm, 29 mm, and 33 mm from the spark-plug) are considered for the investigation. Also, the injector orientation is varied from 12° to 28°, in the step of 4°. The engine is operated under naturally aspirated and full-load conditions at an engine speed of 2000 rev/min. Analysis of results shows that the water evaporation rate increases when more amount of water is sprayed in the region where the velocities of water droplets are in the opposite direction of that of the in-cylinder air. It is found that the water injector located at 29 mm with the orientation of 24° is found to be optimum configuration, where the IMEP improved by about 9.2%, while NOx and soot emissions reduced by about 48.2% and 22.6% respectively compared to those of the case of no_water.