Chemical Effect of DME on the Combustion and Heat Release of SI-CAI Hybrid Combustion Based on Micro Flame Ignition Strategy

Abstract

ABSTRACT Gasoline SI-CAI combustion has shown its advantages in expanding the operating range of high-efficiency combustion. However, the high cyclic variation occurs since the presence of exhaust gas limits the spark ignition and its controllability by auto-ignition. To further improve the stability and reliability of hybrid combustion, MFI (Micro Flame Ignition) strategy has been proposed. Although the phenomenon of MFI hybrid combustion was learned before, the chemical effect of high-activity fuel DME (Dimethyl Ether) and its inter-reaction with gasoline to the combustion process has yet to be studied. In this paper, the carbon tracer method was used to separate the reaction of DME and gasoline in CFD (Computational Fluid Dynamics) simulation, and chemical reaction kinetic analysis was carried out. The congregate DME could produce formaldehyde by 2-step oxidation of DME spontaneously, which led to a high flame speed than the spark ignition. The discrete MFI strategy showed a two-times flame speed ignited by the spark plug, which led to the mid-product of gasoline enhancing the first step of DME oxidation. Although the discrete DME showed high chemical activity in the whole cylinder, the high temperature and pressure caused by DME’s auto-ignition led to a shorter ignition delay for the auto-ignition process in the congregate MFI strategy.