A study on flexible dual-fuel and flexi combustion mode engine to mitigate NO, soot and unburned emissions

•Flexible dual-fuel engine could be a potential option for future mobility.•Through flexible dual-fuel engine, current emission norms can be achieved without relying on the after-treatment systems.•Different fossil and renewable fuel combinations are used for experimentation.•Dimethyl ether and Polyoxymethylene dimethyl ether provide better thermal efficiency and near zero emissions. In the present study, an existing commercial light-duty automotive diesel engine is modified to a flexible dual-fuel engine (FDFE). The FDFE operates with different low and high reactivity dual fuel combinations under low temperature combustion (LTC) mode using combined multipoint fuel injection and common rail direct injection systems. The FDFE can smoothly transit between LTC and conventional diesel combustion (CDC) mode. FDFE combines SI and CI benefits and stands as a potential internal combustion engine for future hybrid electric options. In this study, the modified engine was operated in flexi fuel mode with methanol/diesel, methanol/biodiesel, methanol/dimethyl ether (DME), methanol/polyoxymethylene dimethyl ether (PODE), (methanol + Isobutanol blends)/diesel and (methanol + PODE blends)/diesel in LTC strategy at a different speed and torque conditions. This approach improved the brake thermal efficiency by 8%, decreased NO and soot emissions by more than 90% compared to CDC mode. The improvement in brake thermal efficiency reduced CO2 emissions compared to CDC mode. In the FDFE engine, combustion phasing and fuel energy input are maintained as same as in CDC mode to investigate the dual-fuel effects in LTC mode over a neat diesel mode. Experimental study with energy and exergy analysis was carried out to assess the technical suitability of the FDFE as compared to the conventional diesel engine. The results proved that without relying on the after- treatment systems and fossil fuels, it is possible to reduce the NO, soot, unburnt hydrocarbon, carbon monoxide and CO2 emissions from the diesel engine, paving the way for extending the life of the diesel engine.