HCCI engine is a form of internal combustion engine which inherits high thermal efficiency of CI engines and low PM emissions of SI engines. However, high pressure rise rates in high load operation and lack of controllability, limit HCCI practical application. An approach to tackle these issues is injecting water in the combustion chamber. In the present work, 3D CFD model coupled with the KH/RT spray model was developed to simulate the effect of water injection on HCCI engines. Advanced grid handling techniques were adopted to increase computational accuracy while balancing computational cost.