Computational fluid dynamics investigations of the effect of water injection timing on thermal stratification and heat release in thermally stratified compression ignition combustion

Advanced combustion concepts, like homogeneous charge compression ignition, are limited by their narrow operating range, which stems from a lack of control over the heat release process. This study explores a new advanced combustion mode, called thermally stratified compression ignition, which uses a direct water injection event to control the heat release process in low-temperature combustion. A three-dimensional computational fluid dynamics model coupled with detailed chemical kinetics is used to better understand the effects of direct water injection on thermal stratification in the cylinder and the resulting heat release process. Previous results showed that increasing the injection pressure results in a significantly broader temperature distribution due to increased evaporative cooling. In this way, direct water injection can control low-temperature combustion heat release and extend significantly the operable load range. In this study, simulations were performed over a range of start of injection timings in order to determine its effect on thermal stratification and heat release. The results show that for both low and high injection pressures advancing the start of water injection results in increased thermal stratification and reduced peak pressure and heat release rate for injections occurring after -60 degrees CAD. Before -60 degrees CAD, advancing the water injection has a varied effect on thermal stratification and heat release depending on the injection pressure and mass of the injected water.