Dimethyl Ether Injection Studies

A series of preliminary investigations has been performed in order to investigate the behavior of DME in a diesel injection environment. These studies have in-cluded visual observations of the spray penetration and angles for high pressure injection into Nitrogen using conventional jerk pump injection equipment. It was shown that the penetration of the DME spray can be predicted with the methods developed for diesel fuel by Hiroyasu and co-workers. Some anomalies in spray shape, such as rapid lateral spreading at the base of the spray and spray bifurcation have been observed.The compressibility effects of DME in high pressure injection have also been observed. DME has a higher compressibility than diesel fuel, resulting in larger pressure oscillations in the injection system during the injection process. The oscillations with DME also have a slower delay rate than those of diesel fuel in the same system. As a first attempt to simulate combustion of DME in Diesel engines, the results of the spray studies have been incorporated into a simplified spray combustion model. A turbulent jet structure was adjusted to fit the penetration rates of the observed sprays. The observed spray widths agreed with the model. This spray model was then adapted to a combustion model similar to that of Hiroyasu and co-workers. In the DME model, the chemical reactions were assumed to be much faster than the mixing related processes. Combustion rates calculated on the basis of the spray correlations were found to agree well with the experimentally observed combustion rates during the mixing controlled portions of the combustion in a naturally aspirated direct injection diesel engine.