Fuels

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.

Orange oil was extracted by steam distillation from the peels of oranges produced as waste in the orange juice factories. This raw orange oil, a potential source for biojet fuel, was analysed by FT-IR and GC-MS, and compared with distilled orange oil and pure d-limonene, which is its main chemical constituent. Both distilled orange oil and d-limonene were hydrogenated under reaction conditions (from 3 to 18 bar) which are mild enough to be industrially feasible, to improve its properties, especially to reduce their sooting tendency. Some important properties such as density, viscosity, heating values, lubricity, flash point, crystallization onset temperature, and smoke point were measured for hydrogenated orange oil and d-limonene (as a reference for comparison) at different conversions. These hydro-biofuels were blended with Jet A1 to check their suitability as biobased blending components for aviation. Based on the results obtained for the main aviation fuel properties, it is concluded that up to 15 vol% of partially hydrogenated orange oil could be blended with Jet A1 without any significant drawback for the performance of the actual airplanes. Flammability reduction systems would be needed to further increase the blend proportion of this drop-in biofuel in Jet A1.