For nearly twenty years, DiMethyl Ether has been known to be an outstanding fuel for combustion in diesel cycle engines. Not only does it have a high Cetane number, it burns absolutely soot free and produces lower NOx exhaust emissions than the equivalent diesel.However, the physical properties of DME such as its low viscosity, lubricity and bulk modulus have negative effects for the fuel injection system, which have both limited the achievable injection pressures to about 500 bar and DME's introduction into the market. To overcome some of these effects, a common rail fuel injection system was adapted to operate with DME and produce injection pressures of up to 1000 bar.To understand the effect of the high injection pressure, tests were carried out using 2D optically accessed nozzles. This allowed the impact of the high vapour pressure of DME on the onset of cavitation in the nozzle hole to be assessed and improve the flow characteristics. CFD simulation was also used to assist in the interpretation of the 2D test results.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. Initial screening of the injection nozzles using DoE methods was carried out at various injection timings, pressures, air flows and EGR rates. The tests were carried out using a simplified WHSC and JE05 cycle to investigate the effects of these changes on fuel consumption and emissions at engine out NOx levels between 0.4g/kW.h and 9.0g/kW.h and to judge how the resulting emissions would affect aftertreatment system choices.Results showed that the higher injection pressure combined with high EGR rates could bring an improvement in DME combustion, while the different nozzle hole shapes changed the flow characteristics and the cavitation tendency of the sprays which also can be utilized for an optimization of the mixture preparation and combustion.