Fatty acids, from fuel refining

To avoid these problems, refiners commonly use additives called detergents" (Hall et al., 1976), (Bert et al., 1983). These are in reality surfactants made from molecules having hydrocarbon chains long enough to ensure their solubility in the fuel and a polar group that enables them to be absorbed on the walls and prevent deposits from sticking. The most effective chemical structures are succinimides, imides, and fatty acid amines. The required dosages are between 500 and 1000 ppm of active material. 

It is important to emphasize that all conventional motor fuels—petroleum gasolines and diesel—are produced by complex refining processes. These fuels are mixtures and contain hundreds of organic compounds. None is a single, pure substance. Similarly, almost all biomass-based liquid motor fuels contain numerous organic compounds, but in some cases can consist of relatively few compounds, as in the case of the methyl esters of fatty acids in biodiesel. The exceptions are the lower molecular weight alcohols and a few derivatives that can be used directly as neat motor fuels. They can easily be manufactured from biomass feedstocks as individual compounds. 

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