Effect of the addition of ethanol on the combustion and emission characteristics of a common-rail dimethyl ether engine

The effect of the addition of ethanol on the combustion and emission characteristics of dimethyl ether combustion were investigated in this study using an electronically controlled common-rail dimethyl ether engine. The ignition delay, the crank angle for 50% mass fraction burned, the combustion duration, the nitrogen oxide emissions, the hydrocarbon emissions and the carbon monoxide emissions of the fuel blends with the addition of different percentages of ethanol were analysed for different loads and for different injection timings separately. The results suggest that the effect of ethanol on the dimethyl ether combustion mainly prolongs the ignition delay and inhibits the combustion rate. The ignition delay is prolonged significantly with increasing percentage of ethanol added for low loads or retarded injection timings. A reduction in the combustion rate and an increase in the combustion duration are associated with a higher percentage of ethanol added for high loads or advanced injection timings, leading to lower nitrogen oxide emissions. On the addition of 15% ethanol, the nitrogen oxide emissions are reduced by about 17% for a brake mean effective pressure of 1.2 MPa, and by 32% when the start of injection is at -7 degrees crank angle after top dead centre. Premixed combustion with a sharply prolonged ignition delay and a shortened combustion duration can be achieved by the addition of 15% ethanol when the start of injection is at 5 degrees crank angle after top dead centre. The carbon monoxide emissions show a tendency to increase with increasing amount of ethanol added, whereas the hydrocarbon emissions remain nearly the same until the percentage of ethanol reaches 15%.