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High-Speed Observation and Modeling of Dimethyl Ether Spray Combustion at Engine-Like Conditions
Abstract:
Dimethyl Ether (DME) is one of the major candidates for the alternative fuel for compression ignition (CI) engines. However, DME spray combustion characteristics are not well understood. There is no spray model validated against spray experiments at high-temperature and high-pressure relevant to combustion chambers of engines. DME has a lower viscosity and lower volumetric modulus of elasticity. It is difficult to increase injection pressure. The injection pressure remains low at 60 MPa even in the latest DME engine. To improve engine performance and reduce emissions from DME engines, establishing the DME spray model applicable to numerical engine simulation is required.
In this study, high-speed observation of DME sprays at injection pressures up to 120 MPa with a latest common rail DME injection system was conducted in a constant volume combustion vessel, under ambient temperature and pressure of 6 MPa-920 K. The spray penetration, evaporation, liquid length and ignition delay were investigated and compared with those of diesel sprays. Based on the observed results, the spray model of DME was developed. A reduced chemical kinetic model for the oxidation of DME, that included 27 species and 52 reactions, was made and coupled with the spray model. Calculated results showed good overall agreement with experimental data, such as spray tip penetration, faster evaporation, and short liquid length. Ignition delay time was slightly longer compared with experiment. Using this model, engine simulation was performed. The results showed a reasonable agreement with the experiments.