HIGH INJECTION PRESSURE DME IGNITION AND COMBUSTION PROCESSES: EXPERIMENT AND SIMULATION

With nearly smokeless combustion, Dimethyl Ether (DME) can be pressurized and used as a liquid fuel for compression-ignition (CI) combustion. However, due to its lower heating value and liquid density compared with diesel fuel, DME has a smaller energy content per unit volume. To obtain an equivalent energy content of diesel, approximately 1.86 times more quantity of DME is required. This can be addressed by a larger nozzle size or higher injection pressure. However, the effect of high injection pressure on DME spray combustion characteristics have not yet been well understood. In order to fill this gap, spray and combustion processes of DME were studied extensively via a series of experiments in a constant-volume and optically accessible combustion vessel. In the current study, a hydraulic electric unit injector (HEUI) with a 180 µm single-hole nozzle was driven by an oil-pressurized fuel injection (FI) system to achieve injection pressure of 1500 bar. The liquid and vapor regions of DME jet were visualized using a hybrid Schlieren/Mie scattering at non-reacting conditions. At reacting conditions, high-speed natural flame luminosity of DME combustion was used to capture the flame intensity, and planar laser-induced fluorescence (PLIF) imaging was used to characterize CH2O evolution. Spray and combustion characteristics of DME were compared with diesel in terms of rate of injection (ROI), liquid/vapor penetration and, ignition delay. Flame lift-off length (LOL), flame structure, and formaldehyde (CH2O) formation of DME were also studied through high-speed imaging. The RANS Converge CFD simulation was validated against the experimental and used as a powerful tool to explore the DME spray characteristics under various conditions. Further insights into DME spray and flame structure were obtained through experimentally validated Large Eddy Simulations (LES) simulations