Investigation of the injection process and combustion of a dimethyl ether engine with different nozzle flow areas

Abstract

Dimethyl ether (DME) is a promising alternative fuel, which can be used as a substitute for fossil diesel fuels, with a smaller lower heating value. When used in diesel engines, the nozzle flow area (i.e. the number of nozzle holes × nozzle hole diameter) of the engine is normally increased to maintain the engine power. In this study, three kinds of nozzle (with nozzle flow areas of 5 × 0.30 mm, 5 × 0.35 mm, and 5 × 0.40 mm respectively) were prepared. With a two-cylinder diesel engine, the effects of the nozzle flow area on the DME injection process and combustion characteristics were investigated. The experimental results indicate that the DME acoustic velocity shows no variation with the change in the nozzle hole diameter and that the DME injection timing is not affected. However, as the nozzle hole diameter increased, the DME line pressure (and, in particular, the second peak of the line pressure on the nozzle side) is greatly decreased. Meanwhile, the fall of the needle valve lift is advanced, resulting in a decrease in the injection duration. Further, the engine ignition delay is slightly increased, the total combustion duration is slightly shortened, and the engine brake thermal efficiency is slightly elevated.