Lubricity of paraffinic fuels additivated with conventional and non-conventional methyl esters

Fuel lubricity prevents wear between metallic parts in relative motion inside the injection system of combustion engines. Among diesel fuels, paraffinic (gas-to-liquid or hydrotreated oils) and biodiesel (methyl esters) fuels are emerging since some of them are renewable and, in the case of paraffinic fuels, present excellent properties that can be exploited in compression ignition engines. However, the lubricant properties of raw paraffinic fuels are poor. This work explores the potential of individual methyl esters, found in different biodiesel fuels derived from a wide variety of sources, as lubricity additives for paraffinic fuels. Blends at 1% and 2% ester content in a surrogate of paraffinic fuel were tested under the standardized high-frequency reciprocating rig test for lubricity determination. Results confirm the extremely poor lubricity of the surrogate and that the wear scar diameter measured (the higher this, the lower the fuel lubricity) can be significantly reduced with any of the tested esters just at 1% concentration. Higher ester concentration (2%) does not always improve the lubricity further. The number of double bonds in the ester was revealed very significant, but to boost the lubricity of the blend and fulfill the limits set in fuel quality standards, two or more polyunsaturated esters are necessary.

Lubricity additives for motor fuels

The paper describes the origin of insufficient lubricity properties of motor fuels, the essence of the problem and laboratory test methods applied to determine fuel lubricity. Ways applied by fuel industry to enhance lubricity are presented. There was also carried out a patent analysis concerning lubricity additives and fuel compositions. The anti-wear behaviour of lubricity enhancers, their types and possible undesirable effects were described.

THE INFLUENCE OF THE CHEMICAL STRUCTURE OF SYNTHETIC HYDROCARBONS AND ALCOHOLS ON THE LUBRICITY OF CI ENGINE FUELS AND AVIATION FUELS

The paper covers the mechanism of lubrication layer formation by fuels containing synthetic hydrocarbons and alcohols. Development of alternative fuels containing FAME, alcohols, and synthetic hydrocarbons has increased the interest in the mechanism of lubrication of fuelling systems parts. Fuel lubricity tests have been conducted using the HFRR and BOCLE testing rigs. Fuels under testing, both for CI engines and for aviation turbine ones, contained synthetic components: saturated hydrocarbons both of even and odd number of carbon atoms, and butanol, isomers. These components have been added to conventional fuels, such as diesel fuel and Jet A-1 fuel at the concentration of 0–20% (V/V). All fuels under testing contained commercially available lubricity improvers (carboxylic acid). Test results were analysed using model αi described in [L. 6, 7]. As a result of the analysis, it has been found that the liquid phase, which is a lubricating film, should contain agglomerates or molecular clusters responsible for the transport of energy introduced into lubricating film by electrons emitted from metal surface. The mechanism enabling a description of the effect of base fuel without lubricity improvers on efficiency of such additives has been suggested.