Combustion and emission characteristics of a diesel engine fuelled with biodiesel/dimethyl ether blends

Biodiesel and dimethyl ether (DME) are two promising alternative fuels. The use of their blends in direct-injection (DI) engines seems beneficial since the blending could not only compromise the viscosity between biodiesel and DME but also could improve atomization by initiating flash boiling. Therefore in this work the combustion and emission characteristics of a DI engine fuelled with biodiesel/DME blends were investigated with DME per centage varying from 0 to 100 (wt.%). The experiment was carried on a modified diesel engine. The results show that the increased DME per centage results in retarded ignition time and reduced peak value of heat release rate of premixed combustion, but has little effect on the overall combustion duration. With increasing DME blend ratio, the maximum pressure rise rate is depressed linearly, but the exhaust gas temperature rises for all loads. Also a remarkable decrease in power occurs because of the low heat value of DME. Oxides of nitrogen (NOx) and smoke emissions decreased simultaneously with increasing DME per centage in the blend fuel. Similar behaviour can be seen with different engine speed. Owing to the improved atomization, high DME blend fuel generates more fine particles. In addition, the increase of DME ratio in the blend fuel also leads to decreased carbon monoxide (CO) emission at high loads but increased HC emissions at low loads.