Study on performances and combustion characteristics of DME fueled light duty direct injection diesel engine

摘要

This paper presents the results of experimental studies carried out on a light duty direct injection diesel engine operating on dimethyl ether (DME). The effects of main parameters of combustion system such as plunger diameter, nozzle type, fuel delivery advance angle, vertical distance of nozzle tip into cylinder, injection pressure and swirl ratio on performances and emissions of DME engine are investigated. The indicator diagrams and needle valve lifts are taken after optimization of the parameters of combustion system and the characteristics of combustion and emissions are measured and calculated and compared with those of the engine operating on diesel fuel. The results show that by adding a pressure pump, a pressure regulator and a buffer in the fuel supply system, the vapor lock of DME in the fuel system is eliminated and the engine runs smoothly on DME over the wide range of speeds and loads. The average thermal efficiency of DME engine shows 2～3% higher than those of diesel operation. DME operation can reduce NO{sub}x emission significantly and achieve smokeless combustion. The combustion characteristics: injection and ignition delays, the rate of pressure rise and the maximum cylinder pressure, the rate of heat release are measured and calculated and compared with those of diesel operation. The experimental and calculating results show that the injection delay (in crankangle) is longer than that of diesel engine because of the lower acoustic velocity in liquid DME. The ignition delay of DME shows much shorter than that of diesel engine. The peak pressure of DME operation is far lower than that of diesel engine due to less premixing combustion, the maximum rate of pressure rise is equivalent to that of gasoline engine, resulting in lower combustion noise and lower NO{sub}x emission. The diffusion combustion of DME operation is much faster than that of diesel engine and DME contains oxygen which result in the reduction of smoke, PM, hydrocarbon and carbon monoxide emissions. The study demonstrates that DME is an excellent alternative fuel for compression ignition engines.