Assessment of Lubricity Properties of Dimethyl Ether Using the Medium Frequency Reciprocating Rig

Adequate lubricity of a fuel is an important issue when the wear in diesel engine injection equipment is to be minimised. For conventional diesel oils, there exist methods capable of measuring the lubricity of the fuels. These methods cannot handle Dimethyl Ether (DME), as it has to be pressurised in order to stay liquid.

In this paper, the development and test of a method capable of measuring the lubricity of DME is described: The Medium Frequency Pressurised Reciprocating Rig (MFPRR). The apparatus was designed so that it can cope with both the physical and the chemical properties of DME. The calibration was achieved by using both the standard method for diesel oil and the MFPRR, to test three liquid fuels of varying lubricities.

The result was that the MFPRR discriminated just as well between the fuel lubricities as did the standard method. The lubricity of DME was measured and was found exceptionally low. By mixing the DME with very small quantities of additives the lubricity can be redressed. Only one additive was capable of giving DME a lubricity higher than the one of diesel oil.

Even at such high lubricities it cannot be concluded that wear in the diesel injection pumps will be sufficiently reduced. Data from full-scale tests and the literature indicate that the very low viscosity of DME relative to the one of diesel oil will afflict the wear extent in existing pumps when fuelled by DME.