This paper presents the combustion characteristics of a light-duty direct-injection diesel engine operating on dimethyl ether (DME). The indicated pressure diagrams and injector needle lifts are recorded and the combustion characteristics are demonstrated and compared with those of an engine operated on diesel fuel. The experimental and calculated results show that the DME engine has a longer delay of injection and duration of injection, a lower maximum cylinder pressure and rate of pressure rise, as well as a shorter ignition delay compared with those of a diesel engine. The DME engine has a low mechanical load and combustion noise, a fast rate of diffusion combustion and a shorter combustion duration than that of a diesel engine. It has the ideal pattern of compression ignition engine heat release.

Investigations of emission characteristics were carried out on a compression ignition, dimethyl ether engine (DME) with exhaust gas recirculation (EGR) and on a diesel engine with a dimethyl carbonate (DMC) additive. The experimental results show that the DME engine with EGR can simultaneously reduce smoke and NO x emissions. The NO x can be reduced by about 20 per cent for every 10 per cent of EGR introduction, while smoke remains at zero. The diesel equivalent brake speci®c fuel consumption (b.s.f.c.) shows a slight decrease when DMC is added, while the eective thermal eciency shows a slight improvement. It is found that the smoke reduction rate and smoke show a linear relationship with DMC percentage or oxygen mass percentage in the diesel fuel. For the speci®c brake mean eective pressure (b.m.e.p.), smoke will be reduced by 20 per cent for every 10 per cent DMC added and by 40 per cent when the oxygen mass percentage in the fuel reaches 10 per cent. The CO decreases when DMC is added, while NO x shows an increase. This dierence is pronounced at a high b.m.e.p. For the speci®c b.m.e.p., CO and NO x show a linear relationship with DMC mass percentage in the fuel; CO will be reduced by 20 per cent while NO x will be increased by 20 per cent for every 10 per cent DMC added.

The paper presents the research results of a light-duty direct injection diesel engine operating on dimethyl ether (DME). The eects of the main parameters of the combustion system, such as plunger diameter, nozzle type, fuel delivery advance angle, protruding distance of the nozzle tip from the bottom plane of the cylinder head and swirl ratio, on the performance of the DME engine are investigated. The indicator diagrams are taken after optimizing the combustion system and characteristics of combustion and emissions are measured for DME and diesel operation. The results show that, by adding a pressure pump in the fuel supply system, the vapour lock of DME in the fuel system is eliminated. The engine runs smoothly on DME over a wide range of speeds and loads. The eective thermal eciency of the DME engine is 3 per cent higher than that of the diesel engine, and a low rate of pressure rise, low combustion noise, smokeless combustion and low NO x emissions of the DME engine can be achieved. The results demonstrate good characteristics in reducing emissions for a diesel engine operating on DME.

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