Methodology of Lubricity Evaluation for DME Fuel based on HFRR 2011-32-0651
The methodology of lubricity evaluation for DME fuel was established by special modified HFRR (High-Frequency Reciprocating Rig) such as Multi-Pressure/Temperature HFRR (MPT-HFRR). The obtained results were summarized as follows: The HFRR method is adaptable with DME fuel. There is no effect of the test pressure (up to 1.8 MPa) and the test temperature (up to 100°C) of MPT-HFRR on wear scar diameter. The results with MPT-HFRR can be applied at the sliding parts of the injection needle and the fuel supply pump's plungers which are secured lubricity by the boundary lubrication mode mainly and the mixed lubrication mode partially. Using the fatty-acid-based lubricity improver in amounts of approximately 100 ppm, the lubricity of DME, which has a lack of self-lubricity, is ensured as same as the diesel fuel equivalent level. There is a big deviation of measured wear scar diameter when the LI concentration is not enough. It is caused that the amount of LI is not enough for the surface area of the material on which polar lubricant must be absorbed. The reason of securing lubricity is that the fatty acid, which is a main component of test LI, absorbs chemically on the sliding metal surface of fuel injection parts, and it forms metallic soap. Over adding fatty-acid-based LI doesn't give any advantage on lubricity.