Experimental Investigations on the Effects of Water Injection in a Light-Duty Diesel Engine Operated with Biodiesel Fuel

In-cylinder emission control methods for simultaneous reduction of oxides of nitrogen (NO_x) and particulate matter (PM) are gaining attention due to stringent emission targets and the higher cost of after-treatment systems. In addition, there is a renewed interest in using carbon-neutral biodiesel due to global warming concerns with fossil diesel. The bi-directional NO_x-PM trade-off is reduced to a unidirectional higher NO_x emission problem with biodiesel. The effect of water injection with biodiesel with low water quantities is relatively unexplored and is attempted in this investigation to mitigate higher NO_x emissions. The water concentrations are maintained at 3, 6, and 9% relative to fuel mass by varying the pulse width of a low-pressure port fuel injector. Considering the corrosive effects of water at higher concentrations, they are maintained below 10% in the present work. The effects of water injection on a light-duty diesel engine's performance and emission characteristics operated with Karanja biodiesel are investigated in the present work. The experiments were conducted at a constant rated speed of 1500 rpm under varying load conditions. The engine characteristics are first compared between diesel and biodiesel. Furthermore, the results obtained with water injection are compared with neat biodiesel as a reference fuel. There are no significant differences in the peak pressure and peak heat release rates between biodiesel and the water-injection cases. It is observed that there is a marginal improvement in brake thermal efficiency of the engine with a maximum increase of 1.5%. The brake specific fuel consumption increases at low load by nearly 6%, but it decreases by 3% at high load. A maximum of 19% reduction in the NO_x emissions with 9% water injection is obtained at full load. The smoke emission does not seem to be affected at low loads, but there is a decrease at high loads of nearly 25% with 9% water injection. Overall, the present study shows that water injection can simultaneously reduce NO_x and smoke emissions and improve engine performance.