Effects of Injection Pressure on Combustion of a Heavy Duty Diesel Engine With Common Rail DME Injection Equipment

Recently there has been much interest in Dimethyl Ether (DME) as a new fuel for diesel cycle engines. DME combines the advantages of a high cetane number with soot-free combustion, which makes it eminently suitable for compression engines. According to the latest engine test results, however, DME engine energy consumption was inferior to a diesel engine's under a heavy load. DME probably requires strong air-fuel mixing and short fuel injection. Some tests have reported that DME engine performance almost equals a diesel engine's by injecting high rail pressure DME into standard or slightly modified diesel common rail injection equipment. The effect, however, of higher injection pressure on the rates of heat release and spray distribution is unclear. In this study the rail pressure levels examined included 20, 25, 30, and 35 MPa. The results obtained from a single cylinder heavy-duty engine test show that the rate of heat release increases during the premixed combustion phase. A lower BSEC is obtained under higher injection pressure, which is also lower than that of a diesel engine. In addition, a visualization of spray behavior in a high-temperature and high-pressure chamber shows that DME evaporation is active under higher injection pressure. Conversely, the higher rail pressure increases NOx concentration. These effects were due to the large amount of fuel injected during the ignition delay period.