Diagnosis of combustion with water injection using high-speed visualization and CFDs

Direct water injection (DWI) was newly introduced as a promising NOx reduction method for ma-rine diesel engines thanks for its easy installation requiring no major engine modification. Its true potential, however, remains uncertain for lack of both numerical and experimental investigations. In this study, the ef-fect of DWI on decreasing flame temperature was objectively examined by two simulation codes of different combustion models and by flame temperature measurement in a visual engine based on the two-colour method using CMOS type camera. Simulation results were in good agreement with the measurement results in both flame propagation and flame temperature so that NOx reduction of DWI could be clearly explained. Moreover, it was found that DWI could result in more complicated combustion process than expected since preceding water vapour greatly affected the propagation and the air entrainment of the fuel spray. 1. Introduction