Investigations into the Influence of Dimethyl Ether Micro Flame Ignition on the Combustion and Cyclic Variation Characteristics of Flame Propagation/Auto-Ignition Hybrid Combustion in an Optical Engine

Abstract

ABSTRACTIn order to enhance combustion phasing control and reduce cyclic variations in flame propagation/auto-ignition hybrid combustion, a concept of dimethyl ether (DME) micro flame ignition (MFI) hybrid combustion is proposed and studied in an optical engine. Three-stage heat release characteristics can be observed in its main combustion period, which are the rapid but short DME auto-ignition in the first stage, followed by slower flame propagation observed from the outer rim of the DME auto-ignition zone, and, at last, the intense heat release of the end-gas auto-ignition. The DME injection timing can be used to effectively control the combustion phasing and the early stage heat release characteristics. Compared to the spark ignition-controlled auto-ignition (SI-CAI) hybrid combustion, the DME MFI hybrid combustion shows great benefits in stabilizing combustion, which is caused by the accelerated flame formation and propagation speed due to larger area of ignition source and higher ignition energy.