Investigation into engine performance of a hydrogen-dimethyl ether spark-ignition engine under various dimethyl ether fractions

Spark-ignition combustion mode could be used to widen the operation range of homogeneous charge compression ignition combustion mode on a hydrogen-dimethyl ether (DME) engine. To improve power output and reduce nitrogen oxides emissions, this study investigated the combustion and emissions properties of a hydrogen-DME spark-ignition engine under various DME fractions (alpha(DME)). The result showed that flame development and propagation periods were extended after DME blended. The increases of both periods were 1.7 and 2.0 degrees CA when alpha(DME) various from 1.4% to 3.0%, respectively. However, when alpha(DME) increased to 3.4%, flame propagation period had a 1.7 degrees CA reduction because of the spontaneous high-temperature oxidation of a few end unburned mixtures. Blending DME could improve power output of the neat hydrogen engine. The maximum improvement of indicated mean effective pressure could achieve 18.3%, after DME addition. Because of the weakened flame kernel and flame propagation process, when alpha(DME) lower than 3.0%, blending DME increased cyclic variation yet the variations were in 0.13%. Nitrogen oxides emissions could be reduced significantly, when DME was added into the neat hydrogen engine. The maximum reduction could achieve 49.9%, based on neat hydrogen fuel-supply mode. Hydrocarbon and carbon monoxide emissions were increased after DME addition. When alpha(DME) increased from 1.4% to 3.4%, the enhancement of hydrocarbon emissions was about two-third lower than that of carbon monoxide emission.