Internal combustion engines are used heavily in diverse applications worldwide. Achieving the most efficient operation is key to improving air quality as society moves to a decarbonized energy system. Insoluble deposits that form within internal combustion engine components including fuel injectors and filters negatively impact CO2 and pollutant emissions. Understanding the composition, origins, and formation mechanisms of these complex materials will be key to their mitigation however, previous attempts only afforded nondiagnostic chemical assignments and limited knowledge toward this. Here, we uncover the identity and spatial distribution of molecular species from a gasoline direct injector, diesel injector, and filter deposit in situ using a new hyphenation of secondary ion mass spectrometry and the state-of-the-art Orbitrap mass analyzer (3D OrbiSIMS) and elemental analysis. Through a high mass resolving power and tandem MS we unambiguously uncovered the identity, distribution, and origin of species including alkylbenzyl sulfonates and provide evidence of deposit formation mechanisms including formation of longer chain sulfonates at the gasoline deposit’s surface as well as aromatization to form polycyclic aromatic hydrocarbons up to C66H20, which were prevalent in the lower depth of this deposit. Inorganic salts contributed significantly to the diesel injector deposit throughout its depth, suggesting contamination over multiple fueling cycles. Findings will enable several strategies to mitigate these insoluble materials such as implementing stricter worldwide fuel specifications, modifying additives with adverse reactivity, and synthesizing new fuel additives to solubilize deposits in the engine, thereby leading to less polluting vehicles.

Modern mass spectrometry techniques produce a wealth of spectral data, and although this is an advantage in terms of the richness of the information available, the volume and complexity of data can prevent a thorough interpretation to reach useful conclusions. Application of molecular formula prediction (MFP) to produce annotated lists of ions that have been filtered by their elemental composition and considering structural double bond equivalence are widely used on high resolving power mass spectrometry datasets. However, this has not been applied to secondary ion mass spectrometry data. Here, we apply this data interpretation approach to 3D OrbiSIMS datasets, testing it for a series of increasingly complex samples. In an organic on inorganic sample, we successfully annotated the organic contaminant overlayer separately from the substrate. In a more challenging purely organic human serum sample we filtered out both proteins and lipids based on elemental compositions, 226 different lipids were identified and validated using existing databases, and we assigned amino acid sequences of abundant serum proteins including albumin, fibronectin, and transferrin. Finally, we tested the approach on depth profile data from layered carbonaceous engine deposits and annotated previously unidentified lubricating oil species. Application of an unsupervised machine learning method on filtered ions after performing MFP from this sample uniquely separated depth profiles of species, which were not observed when performing the method on the entire dataset. Overall, the chemical filtering approach using MFP has great potential in enabling full interpretation of complex 3D OrbiSIMS datasets from a plethora of material types.

Insoluble carbonaceous deposits were grown in internal combustion engine components and interrogated by OrbiSIMS depth profiling, and we uncovered the composition and proposed time resolved growth mechanisms of these materials.

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A new ultra-high performance supercritical fluid chromatography -mass spectrometry (UHPSFC-MS) method has been developed using electrospray ionisation (ESI) to detect and quantify a new fiscal fuel marker, ACCUTRACE™ S10 that was introduced into fuel in the UK and Ireland from April 1st 2015. S10 is synthesised by the Dow Chemical Company and is used as a replacement for UV-visible fuel markers, such as quinizarin, Euromarker and Solvent Red 24. It is UV invisible, is doped at a low level (2.5 ppm) and was designed for detection using modern gas chromatography -mass spectrometry (GC-MS) instrumentation. All currently proposed methods for the determination of ACCUTRACE™ S10 fuel marker in diesel fuel [automotive diesel oil, current specifications EN 590 and U.S. ASTM D975] use gas chromatography-mass spectrometry (GC-MS), and 2-dimensional GC-MS (2-D GC-MS) is necessary to detect the marker at tank dilutions. However the lower limit of detection (LLOD) and lower limit of quantification (LLOQ) for S10 are severely compromised using legacy GC-MS instrumentation and measurement at tank dilutions is not feasible. ACCUTRACE™ S10 exhibited unusual ionisation characteristics when analysed by atmospheric pressure ionisation techniques, the ionisation is modelled and discussed and the strong ionisation response utilised to develop a new approach to detection and quantitation of the new fuel maker. The novel UHPSFC-MS method utilises this phenomenon, allows injection of undiluted fuels and affords detection and quantitation at doping and tank dilution levels.