Analysis of energy release and NOx emissions of a CI engine fuelled on diesel and DME

Combustion and NO_x emissions from a dimethyl ether (DME) fuelled compression ignition engine were investigated. The test engine used consisted of an unmodified two-cylinder direct injection four-stroke air cooled type. The injection timing and injector opening pressure were left unaltered from their diesel fuelling settings. Analysis of the fuel line pressure shows that due to the compressibility of DME the rate of pressure rise was lower, resulting in injection occurring later when compared to diesel injection. The maximum combustion chamber pressure was found to be higher in the case of diesel fuelling. In terms of energy release it was found that with DME this occurs later than in the case of diesel fuelling with the larger proportion occurring just after top dead centre. A comparison of NO_x emissions revealed that, at all loads tested, these were higher in the case of DME fuelling and decreased steadily with increasing speed. At the higher speeds however, the levels of NO_x monitored were noted to be less than those of their diesel counterpart. Some of the factors influencing the promotion of NO_x emissions with DME fuelling are discussed and analysed.