Dimethyl Ether (DME) Spary Charcteristics in a Common-rail Fuel Injection System

Abstract

Fundamental spray characteristics of DME (Dimethyl Ether) 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 3MPa chamber pressures) and three different injection pressures (25MPa, 40MPa and 55MPa) under room temperature condition. A CCD (Charge Coupled Device) 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 ICCD (Intensified Charge Coupled Device) camera was adopted, in conjunction with Mie-scattering imaging technique for single-hole spray. Intermittent hesitating DME spray was observed depending upon injection conditions and might be due to unstable force balance inside the common-rail nozzle during injection period. Macroscopic spray characteristics of the DME in the atmospheric chamber conditions proved intrinsic physical properties of the DME, while became diesel-like under 3MPa ambient pressure. Higher injection pressure produced wider vapour phase area while it decreased with higher chamber pressure conditions.