The formation of injector deposits in gasoline and diesel engines has been identified as a problem since the late 2000s. A build-up of these deposits leads to diminished engine performance, fuel economy and emissions quality. The addition of deposit-control additives to fuels is thought to mitigate this issue through their interactions with the internal metal surfaces of engines. This thesis pursues a fundamental understanding of the adsorption behaviour of model fuel additives in hydrocarbon solutions.

Substrates representative of engine surfaces, including low-carbon and stainless steels, were characterised. It was found that the steel surfaces consist of iron oxide and a mixture of iron and chromium oxide respectively. Depth profiling experiments on the stainless steel revealed a Cr-enriched region not directly at the surface, but in a region just below. However, it is clear that the principle exposed surface for adsorption is iron oxide.

The adsorption of a model alkyl phenol additive onto iron oxide from various alkane solvents was investigated using a variety of surface techniques. It was found that adsorption proceeds to monolayer formation where the molecules are essentially ‘upright’. Spectroscopic measurements indicated that the binding to the surface takes place through a phenolate anion, despite the non-polar and non-aqueous solvent. The alkyl chain has significant conformational disorder and the terminal methyl groups are directed away from the surface. At high relative concentrations, ethanol, which is often present in gasoline blends, successfully out-competes the additive for the iron oxide surface. Subsequent investigation of ethanol adsorption showed evidence for a liquid phase multilayer structure on the iron oxide surface.

The complexity of both additive and solvent was increased through adsorption studies of a multi-functional phenol and amine surfactant (PH-01) in various mixtures of a four component model gasoline. The adsorption behaviour of PH-01 is similar to that of the alkyl phenol as it forms ‘upright’ monolayer surface structures where the head-group interacts with the surface and the alkyl tail extends into the solvent. Quantitative ¹H NMR was developed for use in adsorption experiments, new to this field, which facilitated the observation of trends in adsorption behaviour with solvent polarity and composition. Experiments were conducted at up to 160 ° C, where significant spectral changes were observed, suggesting the reaction of PH-01 with autoxidation products of the solvent has taken place.