Uncovering the molecular compositions, origins and formation pathways of engine deposits using OrbiSIMS

Internal combustion powered vehicles will be used in road, rail, marine and aviation applications for the foreseeable future, particularly in developing nations. Formation of insoluble deposits on key engine components, such as fuel injectors and filters, affect all these vehicle types to cause increased emissions and fuel consumption. Despite years of research, little is known of the molecular composition, origin of contributing species and formation pathways of deposits, especially of their carbonaceous matrix. This is due to their insolubility and layered nature, meaning traditional solvent-based analysis techniques are unsuited to probe their composition and structure. This thesis first details previous attempts of characterizing deposits and shows the need for high resolution mass spectrometry (MS) techniques to analyse deposits in-situ (i.e., on the component itself). To address this knowledge gap, 3D Orbitrap secondary ion mass spectrometry (3D OrbiSIMS) Ar3000+ gas cluster ion beam (GCIB) depth profiling and chemical imaging is applied to deposits from gasoline and diesel vehicles. Molecular species are accurately identified and confirmed using MS/MS for the first time, with supporting X-ray photoelectron spectroscopy (XPS) data. Key species identified include trace levels of lubricating oil derived alkyl benzyl sulfonates, inorganic salts (up to 16 %) in diesel samples and nitrogen containing species (up to 5 %) in the gasoline deposit. Finally, high amounts (> 80 %) of carbon in all samples, which are attributed to polycyclic aromatic hydrocarbon (PAH) type species, previously only speculated to exist in deposits