The effect of two different kinds of vegetable oil on combustion and emission characteristics of a vehicle dimethyl ether engine

Dimethyl ether (DME) is one of the promising fuels for a compression ignition engine. However, pure DME cannot be used on internal combustion engines directly owing to its low viscosity and poor lubricity. Experimental investigation of the performance of a DME engine with two different kinds of vegetable oil is carried out. Results prove that a certain proportion of rapeseed oil or castor oil dissolves well in DME fuel at the engine's normal operating condition. The lubricity of DME fuel can be improved by adding a proportion of vegetable oil to it, and the plunger surface of the fuel pump has no large wear scars. Also the plunger surface of the fuel pump with DME-rapeseed oil is a little smoother than that with DME-castor oil. The power outputs of a DME engine with these two kinds of vegetable oil are comparable with that of a diesel engine and even exceed that of a diesel engine at low speeds and loads. However, the power output of the engine with DME-castor oil is a little lower than that with DME-rapeseed oil. Smokeless combustion can be realized in a DME engine with these two kinds of vegetable oil, and NO, emission is about 40 per cent of that of a diesel engine. The peak pressure of a DME engine with these two kinds of vegetable oil is lower than that of a diesel engine, which indicates lower noise and ballistic load. Furthermore, the peak cylinder pressure for DME-castor oil operation is a little lower than that for DME-rapeseed oil operation. Experiments prove not only that the drawback of low viscosity and poor lubricity of DME fuel can be overcome but also that high efficiency and clean and low-noise combustion can be realized with the addition of vegetable oil to a DME engine.