Abstract: A fuel additive composition useful for incorporation in or admixture with fuels, particularly fuels containing vanadium and/or sodium as a contaminant such that upon combustion of the fuels containing or in the presence of said additive composition metal surfaces in contact with the resulting hot gaseous fuel combustion products are subject to less corrosion, contains one or more compounds providing the elements or elemental components magnesium, silicon, chromium and chlorine, these elements Mg, Si plus Cr, Cl being present in the additive composition in the weight ratio 1/>0.5/>1.0, respectively, the amount of Si to Cr being in the ratio 1:0.1-10.

Abstract: Gas turbine fuels, either ash-containing fuels having a high alkali metal content, such as greater than 5 ppm by weight sodium and/or potassium, or substantially ash-free fuels which are burned or combusted under conditions that alkali metal appears in the combustion products, are advantageously combusted in the presence of additive components consisting essentially of compounds of silicon and magnesium which form SiO.sub.2 and MgO at fuel combustion temperatures, the proportions of said compounds being such as to provide a combined SiO.sub.2 and MgO equivalent wherein the SiO.sub.2 :MgO ratio is greater than 2:1, the quantity of said additive components present during the combustion of said fuel being such as to provide a magnesium to vanadium weight ratio of at least 2:1 and a weight ratio of silicon to alkali metal of at least 2:1, preferably greater than 6:1.