Study on the injection process of a direct-injection diesel engine fuelled with dimethyl ether

Abstract

The injection process of dimethyl ether (DME) was tested on a naturally aspirated, direct- injection (DI) diesel engine with a pump-line-nozzle fuel system. In order to eliminate vapour leakage, DME was pressurized into the injection pump by nitrogen. In view of its low calorific value and liquid density, the pump plunger diameter and nozzle orifice area were enlarged to achieve the rated power. As DME is easy to atomize and evaporate, the nozzle opening pressure was lowered. The study demonstrates that the injection delay with DME is much longer than that with diesel fuel, due to the lower sound velocity in DME liquid, resulting from its higher compressibility and lower density. When a diesel engine operates on DME instead of diesel fuel, the advance angle of fuel supply should be increased. The fluctuations of line pressure, nozzle needle lift, opening time, and closing time for DME are larger than those for diesel fuel.