Dimethyl ether (DME) spray characteristics in a common-rail fuel injection system

The fundamental spray characteristics of dimethyl ether (DME) and conventional diesel were investigated in a constant-volume vessel pressurized by nitrogen gas. A common-rail fuel injection system was adopted with a sac-type injector. DME and diesel were injected into the chamber at two different chamber pressures (atmospheric and 3 MPa) and three different injection pressures (25, 40 and 55 MPa) under room temperature condition. A charge coupled device (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. For evaluation of the evaporation characteristics, shadowgraphy of the DME spray using an Ar ion laser and an intensified charge coupled device (ICCD) camera was adopted, in conjunction with the Mie scattering imaging technique for single-hole spray. Intermittent hesitating DME spray was observed, depending on the injection conditions, and might be due to the unstable force balance inside the common-rail nozzle during the injection period. The macroscopic spray characteristics of the DME in the atmospheric chamber conditions proved. to be intrinsic physical properties of the DME, and they became diesel-like under 3 MPa ambient pressure. A higher injection pressure produced a wider vapour phase area while it decreased with higher chamber pressure conditions.