Combustion Characterization of DME-Fueled Dual Fuel Combustion with Premixed Ethanol

The heterogeneous nature of direct injection (DI) combustion yields high combustion efficiencies but harmful emissions through the formation of high nitrogen oxide (NOx) and smoke emissions. In response, extensive empirical and computational research has focused on balancing the NOx-smoke trade-off to limit diesel DI combustion emissions. Dimethyl ether (DME) fuel is applicable in DI compression ignition engines and its high fuel oxygen produces near-smoke-free emissions. Moreover, the addition of a premixed fuel can improve mixture homogeneity and minimize the DI fuel energy demands lessening injection durations. For this technique, a low reactivity fuel such as ethanol is essential to avoid early autoignition in high compression ratio engines.

In this work, empirical experiments of dual fuel operation have been conducted using premixed ethanol with high-pressure direct injection DME. The engine performance was characterized with DI diesel fuel as a baseline, and the matching operation of DME was compared. The ethanol content was tested from 35% to 65% on an energy basis. The enhanced volatility and reactivity of DME fuel showed an improved ability to withstand earlier injection timings. The high reactivity of DME showed early and rapid combustion up to 65%. Enhanced combustion efficiency was achieved at early injection timings rather than near-TDC as the high reactivity of DME had a longer period to mix with premixed ethanol. In fact, nearly zero DME species were measured in the exhaust gases while the majority were unburned ethanol.