DiMethyl Ether (DME) has been known to be an outstanding fuel for combustion in diesel cycle engines for nearly twenty years. DME has a vapour pressure of approximately 0.5MPa at ambient temperature (293K), thus it requires pressurized fuel systems to keep it in liquid state which are similar to those for Liquefied Petroleum Gas (mixtures of propane and butane). The high vapour pressure of DME permits the possibility to optimize the fuel injection characteristic of direct injection diesel engines in order to achieve a fast evaporation and mixing with the charged gas in the combustion chamber, even at moderate fuel injection pressures.
To understand the interrelation between the fuel flow inside the nozzle spray holes tests were carried out using 2D optically accessed nozzles coupled with modelling approaches for the fuel flow, cavitation, evaporation and the gas dynamics of 2-phase (liquid and gas) flows. And to understand the spray characteristics tests were carried out using constant volume vessel. For a spray observation, two methods were used a shadowgraph and a diffuse forward scatter method to obtain both gaseous phase and liquid phase of DME. Tests were then run on a single cylinder engine to determine the differences in combustion with the differing hole shapes as well as extra high injection pressure.
Results showed that the different nozzle hole shapes changed the flow and the cavitation tendency. And these characteristics be utilized for an optimaization of the spray and combustion