Dimethyl Ether (DME) - Development and Test of the New Volatile Fuel Tribo-Tester VFTT

Over the past few years, dimethyl ether (DME) has been recognised as an excellent fuel for diesel engines. The characteristics of engines fuelled with this advantageous fuel, DME, are low noise and clean emissions with virtually no particulate matter. The toxicity of DME is low. This issue has been thoroughly investigated as DME is commonly used as an aerosol propellant. A significant problem when fuelling diesel engines with DME is that the injection equipment breaks down rapidly due to extensive wear. Two main parameters are the causes for these insufficient lubrication qualities of DME: The lubricity and the viscosity. In former works these properties of DME were established to be very low. They can be raised by additising DME so that it acquires the same physical properties as diesel oil. In this case the DME blend is mainly composed of additive though. This means that the emission advantage of DME is significantly reduced then. As a result of the above, the work described in this paper was initiated. It introduces the search for materials that can cope with the properties of pure DME. In order to do so, a method capable of testing materials in DME was developed: The new volatile fuel tribo-tester (VFTT). This apparatus can cope with the physical properties of DME as it can be pressurised. The test rig has a block on ring configuration with the possibility of varying the pressure between the test specimens. During a test the load, the friction coefficient and the wear amount are measured. These parameters are then compared with those obtained for diesel oil lubricating two steel surfaces in order to establish whether the chosen materials will ensure full lifetime of the injection equipment.