New application to reduce NOx emissions of diesel engines: Electronically controlled direct water injection at compression stroke

•Engine performance and emissions are examined for direct water injection.•A 1 L naturally aspirated DI diesel engine has been used for the experiments.•The optimum start of injection for water was 270°CA at the compression stroke.•The optimum water ratio was determined to be 60% for performance emissions.•With direct water injection, engine power increased and SFC decreased. In this study, the effect of Direct Water Injection (DWI) on the performance, emissions and combustion was experimentally investigated on a light-duty water-cooled direct injection, diesel engine. Water was injected into the combustion chamber under full load conditions with a dedicated water injector placed on the cylinder head at 10%, 20%, 40%, 60%, 80% and 100% of the fuel by mass, namely W10, W20, W40, W60, W80, W100, respectively. The injection quantity and start of injection in degrees crank angle (°CA) for water injector were controlled by an electronic control unit. Initially, standard engine values were obtained by fueling the engine with diesel fuel for full load condition, and then experiments were repeated at different DWI ratios. Reductions in NOx emissions up to 61% were obtained after applying DWI to the engine during the compression stroke. In addition, considerable improvements were observed in engine performance parameters. It was found out that, engine power increased by 3.7% and specific fuel consumption (SFC) decreased by 4.1%. There were not significant changes in exhaust gas emissions, CO and smoke, while hydrocarbon (HC) emissions increased. Considering all parameters, the optimum condition was obtained forW60-DWI ratio. It was determined that, the water injection performed during compression stroke decreased negative compression and increased cumulative heat release.