Experimental investigations on biodiesel-water emulsion as a potential fuel for early and late injection based premixed lean combustion

[Display omitted] •Raw Karanja oil is used as surfactant to produce stable biodiesel-water emulsion.•18% water emulsion is produced with 2% surfactant.•Mechanical injection system is replaced with a flexible electronic system.•Modified injector nozzle mimicked production nozzle characteristics.•Early and late injection strategies employed to attain premixed lean combustion.•Water-emulsion with late injection mitigated NOx, smoke, and improved engine performance. Low temperature combustion strategies are a suitable alternative to conventional diesel combustion to simultaneously reduce oxides of nitrogen and smoke emissions while maintaining engine performance. However, limited load range and increased unburned hydrocarbon and carbon monoxide emissions are challenges posed by these strategies. The present investigation aims to address these limitations using biodiesel-water emulsion as a potential fuel for low temperature combustion in a light-duty diesel engine. Biodiesel derived from non-edible Karanja oil and its emulsion containing 18% water was used. The surfactant employed to stabilize the biodiesel-water emulsion was the raw Karanja oil itself. Two different fuel injection strategies were explored to achieve lean premixed combustion: early/advanced injection and late injection just after the top dead centre. To implement these strategies, the mechanical fuel injection system in the production engine was replaced with an electronic injection system having complete flexibility over the injection schedule. The results are compared with conventional diesel combustion under production settings. For the early injection strategy, up to 40% load, the brake specific fuel consumption and brake thermal efficiency were on par with conventional diesel combustion for biodiesel and the emulsion. However, there was a decline in the performance for both fuels at 60% load, which was the maximum achievable load with an early injection strategy. With the late injection, the engine could be operated across its entire load range with similar reductions in oxides of nitrogen and smoke emissions. While the brake thermal efficiency and brake specific fuel consumption for biodiesel were on par with conventional diesel combustion, there was an improvement of 8 and 6%, respectively, with biodiesel-water emulsion. The emission results showed that with either injection strategies, with biodiesel and its emulsion, 85 and 80% reduction in oxides of nitrogen and smoke emissions, resp