DME is the simplest ether and consists of oxygen and methyl. Because of its chemical and physical properties it is thought that DME could be one of the candidates as an alternative fuel in the internal combustion engine. The authors have been investigating the combustion characteristics of the mixed fuel comprising of Dimethyl ether and Marine Diesel Oil (JIS A-heavy oil). In the experiments, DME is mixed at the liquefied state with MDO inside a high pressure fuel tank pressured with nitrogen gas. Fuel supply lines are replaced with pressure resistant tubes, and the mixed fuel is supplied to the small direct injection diesel engine. We obtained the effect on the fuel injection characteristics to the mixed fuel combustion, in the diesel engine. The two different fuel injection rates are obtained by changing the injection nozzle opening pressure, that for the relatively lower case (9.0MPa) and higher (24.0MPa). The fuel injection pressure histories and the combustion characteristics, such as the combustion pressure and the exhaust emission, are examined for both the injection conditions. The average injection pressure increased with increased engine load in the lower nozzle opening pressure case. Whilst it is almost constant with the higher nozzle opening pressure case. It was concluded that ignition delay could be shortened by DME mixing. And NOx emissions were reduced in the higher engine load case, and with mixing DME for both nozzle opening pressure cases.
