Dimethyl Ether (DME) is a promising new alternative fuel for compression ignition DI engines. However, some problems arise from the poor lubricity of DME. Breakdown of the film bearing between needle and sleeve of the injector can lead to mechanical wear and leakage, a problem that is not mitigated easily. For example, the application of returning the leakage to fuel tank could raise a back pressure on the injection needle. This pressure can affect injection rate and consequently engine performance.
In this study, fuels based on various DME to gas oil (diesel fuel) ratios were investigated, in part. Physical and chemical properties of DME and gas oil are shown to lead to mutual solubility at any ratio. Blended fuels have a higher lubricity compared with pure’ DME and a better injection spray compared with pure gas oil.
Blends including zero weight percent DME (neat gas oil operation), and nominal blend percentages of 2.5, 5, 10, 20, 40, 60, 80 and straight DME were evaluated in a single cylinder research test engine. Performance, emissions and other features of blended fuel operation yielded the following results:
By taking relative advantages of DME and gas oil, the DME blended gas oil achieved satisfactory properties in lubricity and atomization, which contributed to improvements in leakage and spray characteristics.
Engine performances were found to be comparable among the test fuels which contains a proportion of DME of up to about 10%.
As much as 30% soot emission reductions could be achieved with about 10% DME blended fuel operation, however, no significant reductions in and unburned hydrocarbon emissions were observed.