“…Historically, fouling of fuel filters and injectors has been attributed to many different factors including adulteration with low cost hydrocarbon products such as used lubricating oil [27], poorly processed vegetable oils [28,29,30], contamination of the fuel with such agents as dirt and rust [31,32], microbial growth [33,34,35], impurities from the refining process (particularly where biodiesel is involved [36]) and also as a result of thermal and oxidative degradation of the fuel [37,38] which may be exacerbated by the presence of contaminants. Metal contaminants have been shown to catalyse the oxidation of fuel [39] and in one widely used test the fuel is deliberately adulterated with an organic zinc compound in order to promote injector deposit formation [40].…”