Effect of Water Injection and Spatial Distribution on Combustion, Emission and Performance of GDI Engine-A CFD Analysis

Water injection in diesel engines is a successful way to reduce NO_x emissions and enhance brake power output. The advantages of water injection are because of its high enthalpy of vaporization and high specific heat capacity by which it absorbs heat from the in-cylinder mixture. The benefits of water injection depend on the rate of water vaporization and its spatial distribution in the combustion chamber. However, detailed effects of these parameters are very rarely studied in the past. Therefore, in the present study, an attempt has been made to assess the effect of water injector configuration on performance of a GDI engine by CFD analysis. Here, the analysis is done mainly to study and enhance the evaporation and spatial distribution characteristics of the water injection inside the combustion chamber. Water is directly injected into the cylinder of a naturally aspirated, four-stroke GDI engine. Various water injection configurations formed by different spray patterns and injector orientations are considered for the study and compared with a no water case. The analysis is done under full-load conditions with a constant engine speed of 2000 rev/min. The CFD models used in this study are validated from the available data in the literature. From the results, it is found that the water spray pattern in a shape of the regular hexagon at an injector orientation of 25^˚ produces higher IMEP with lower NO_x and soot emissions.