Lubricity of Volatile Fuels for Compression Ignition Engines 2000-01-1804
While standardized laboratory-scale wear tests are available to predict the lubricity of liquid fuels under ambient conditions, the reality is that many injection systems operate at elevated temperatures where fuel vaporization is too excessive to perform the measure satisfactorily. Alternative fuels such as Dimethyl Ether (DME) are gaseous at ambient conditions and must be pressurized to form a lubricating liquid. The present paper describes an apparatus purposely designed to evaluate fuel lubricity in a pressurized environment at temperatures of up to 30°C. The remaining test parameters are identical to those of the widely standardized High Frequency Reciprocating Rig (HFRR), which allows use of previously developed correlations to full-scale injection equipment. Results obtained using the High Pressure High Frequency Reciprocating Rig (HPHFRR) indicate that DME, as well as other volatile fuels evaluated, have very poor lubricity. The lubricity of DME was restored to an acceptable level by high concentrations of additive. The synthetic fuels were particularly sensitive to additive chemistry. Non-acidic additives were ineffective in dimethoxy methane (DMM) and some additives that were effective in conventional diesel were ineffective in Fischer Tropsch diesel. Simple mathematical models were used to predict the effects of kinematic-viscosity on full-scale equipment wear. It is concluded that lubricity additives for use in synthetic fuels must be selected with care and it is unlikely that they will render the volatile low viscosity synthetic fuels suitable for use in all injection equipment designs.