Dimethyl Ether (DME) Spray Characteristics Compared to Diesel in a Common-Rail Fuel Injection System 2002-01-2898
Dimethyl Ether (DME) has been considered as one of the most attractive alternative fuels for compression ignition engine. Its main advantage in compression-ignition engine application is high efficiency of diesel cycle with soot free combustion though conventional fuel injection system has to be modified due to the intrinsic properties of the DME. Experimental study of the DME and conventional diesel spray employing a common-rail type fuel injection system with a sac type injector was performed in a constant volume vessel pressurized by nitrogen gas. A CCD camera was employed to capture time series of spray images, so that spray cone angles and penetrations of the DME spray were characterized and compared with those of diesel. Intermittent hesitating DME spray appeared at injection pressures of 25MPa and 40MPa in both atmospheric and 3MPa chamber pressures. Under atmospheric pressure condition, regardless of injection pressure, spray cone angles of the DME were wider than those of diesel and penetrations were shortened due to flash boiling effect. Tip of the DME spray was formed in mushroom like shape at atmospheric condition but it disappeared in higher chamber pressure. On the contrary, spray characteristics of the DME became similar to diesel under 3MPa ambient pressure. Hole-to-hole variation of the DME was lower than that of diesel in both atmospheric and 3MPa chamber pressures.