Comparison of the Lubricity of Gasoline and Diesel Fuels

The High Frequency Reciprocating Rig (HFRR) commonly used to measure the friction and wear properties of diesel fuels has been modified to study gasoline lubricity.Wear tests have been carried out on a range of gasoline and diesel fuels. The non-additised gasolines tested all give higher wear than severely-refined Class I diesel fuels. The effect of relative humidity on the wear properties of both gasoline and diesel fuels has been compared. Both types of fuel give wear behavior which is almost independent of water vapour pressure down to 0 8 kPa, but show a reduction of wear below this humidity level.In practice most gasoline fuels contain detergent additives. The influence of two commercial gasoline detergent additives of different structure on gasoline lubricity has been studied. Both additives reduce wear, to an extent which is dependent upon additive concentration and also upon the base fuel. Wear tends to remain high up to a detergent additive concentration of about 200-300 ppm but then falls above this level. This concentration is of the same order as that used in practice in commercial gasolines.Wear tests have been carried out using a commercial diesel fuel lubricity additive. This has been found to be equally effective in reducing wear and friction coefficient in gasolines as in diesel fuel