Characteristics of the Spray and Combustion Process of DME under Engine Conditions(CNG and Alternative Fuels, Oxygenated Fuels)

Abstract

The characteristics of spray, auto-ignition and combustion process of DME (Dimetyl ether) were investigated by 3-D simulation in a combustion vessel under high temperature and pressure conditions and engine conditions. Spray impingement and non-premixed combustion model have been developed and incorporated into the computational fluid dynamics code, STAR-CD. Laminar flamelet concept was used to simulate non-premixed combustion. In order to reduce the enormous computational time, fitted function of the integration of pre-assumed PDF (Probability density function) was introduced. For the chemical mechanism of DME, a skeletal chemical kinetics mechanism which consists of 28 species and 45 reactions was deduced by approximation of detailed mechanisms by means of sensitivity analysis and steady-state with addition of generic species or global reactions. To verify this combustion model, autoignition and combustion processes were investigated in a pre-combusted vessel. The simulation results were well matched with experimental results of the spray tip penetration of liquid and vapor phase, and ignition delay time of DME spray. In comparison with the trends observed experimentally, the flamelet-concepted combustion model predicted the essential feature of combustion processes and the autoignition characteristics of DME spray reasonably well on the various initial conditions. The combustion process of DI engine fueled by DME was simulated with moving grid of a commercial diesel engine.