Enhancing the lubricity of gas-to-liquid (GTL) paraffinic kerosene: impact of the additives on the physicochemical properties

Abstract

Synthetic paraffinic kerosene (SPK) is an ultra-clean fuel with low aromatic content and negligible quantities of sulfur compounds. Although, SPK has a good potential to replace the conventional fuel Jet A-1, it also has some deficiencies. One of them is the low lubricity compared to its conventional counterpart Jet A-1. To improve the lubricity of SPK, three selected additives have been mixed with SPK at different concentrations. The lubricity of the samples was determined experimentally and the samples that meet the industry specifications have been studied further. The effect of the additives on the physicochemical properties, such as, density, flash point, freezing point, viscosity, and heat content, were investigated. Linoleic acid was found to be an excellent lubricity improver even at a very low concentration and its negative impact on the other physicochemical properties was found to be insignificant. Ethyl oleate also demonstrated significant improvement in lubricity at low concentrations but had a negative impact on the fuel's freezing point at high concentrations. Quinoline, at high concentrations, elevated the blend's freezing point above the acceptable limits. In parallel to the experimental campaign, a pre-existing mathematical modelling tool was utilized to predict the properties of interest. The lubricity model was successfully introduced into the mathematical model in order to improve the capabilities of the model. Linoleic acid sample showed the best improvement in lubricity of SPK with wear scar diameter of 417 μm; well below the ASTM D7566 maximum limit of 850 μm. The dual nature of this study facilitated the optimization of the physicochemical properties of the fuel samples.

A Review on the Impact of Bio-Additives on Tribological Behavior of Diesel Fuels

“…According to earlier research, the primary components of biodiesel, such as fatty acid methyl ester, and a few other chemicals, such as glycerides, antioxidants, and sterols, which can improve the lubricity of the fuels, are responsible for improved lubricity [36]. This finding can be attributed to the existence of oxygen-type heteroatoms, which provide the molecule polarity and, as a result, increase its adhesion to metal surfaces.…”

“…Conventional high-sulfur content diesel fuel often has sufficient lubricating capacity to meet these active parts' requirements [30]. In the process of removing sulfur compounds, due to rigorous rules, techniques such as hydrodesulfurization and many others to reduce the quantity of diesel fuel's sulfur content are particularly beneficial for environmental protection, but they also eliminate lubricity-imparting chemicals such as polyaromatics and oxygen-containing compounds [31] which results from the decline in fuel lubricity [32,33].…”

“…The use of low lubricity poses some serious problems. Diesel fuel-related problems include faster wear, erosion or corrosion of the injection nozzles, instability of engine rpm, hard start, engine smoke, and limited power [36]. In the USA and Europe, it has been found that utilizing highly refined fuels can decrease distributor pump lifespans by up to 95% [34,37].…”

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

“…9 On the properties side, the main handicap for GTL is its poor lubricity compared to fossil diesel due to the null aromaticity, and some authors have focused their research to find a solution via additives. 10,11 Also, the GTL production reactions can be adjusted to yield longer alkanes, which are characterized by a better lubricant capacity, 12 but at the expense of worsening the cold flow properties. Contrarily to GTL, esters (the components of biodiesel fuels), as other fatty acid compounds, are magnificent lubricants since it possesses a polar end in their molecule which is adsorbed on surfaces and a long non-polar chain that provides a thin liquid film that prevents wear.…”