Study of deposit formation chemistry in gasoline fuels and gasoline direct injection systems using chromatography and mass spectrometry

Abstract

New UHPSFC-MS methods have been developed to separate and detect components in gasoline and gasoline gum samples that were undetectable by GC-MS. The gum is the residue that remains after the evaporation of the gasoline and contains semi- and non-volatile components. The gasoline gum content is under investigation to identify suspect molecules with low abundance within the fuel that can be related to deposit formation in gasoline direct injection engines, which can lead to decrease of engine performance, increased emissions or failure of engines parts. Concentration protocols need to be applied to produce gums, which enable speciation and concentration of different deposit precursor molecules, enabling their subsequent analysis by mass spectrometry. The gum samples were prepared following two different approaches that serve different purposes; the industrial standard method IP 131 / ASTM D381-12 ^[28] (industry test method – ITM gum) and a cold nitrogen gas evaporation method which was named Soton gum ^{[Chapter 3.2]} . The ITM gum contains any oxidation products formed in the gasoline sample prior or during the relatively mild conditions of the test procedure and serves a complimentary role to the analysis of fuels that correlates to the quality of the gasoline. The Soton gum removes the volatiles and concentrate semi- and non-volatile components with low abundance within the fuel. The analysis of EI/ASTM and Soton gum by GC-MS had revealed hydrocarbons and homologous that were also observed in the fuel analysis. However, when the same samples were analysed by UHPSFC positive ion ESI MS, polymeric material (e.g. carrier oils, detergents) were detected. In addition, the analysis of ITM and Soton gum by UHPSFC positive ion APPI MS has revealed differences on the polymeric profile between the two types of gum that was not observed in the past. The Soton gum contained homologous series with aromatic and olefinic content that were not observed in the ITM gum. These materials are described by the General Motors Reference fuel composition patent - US 8,764,854 B1 ^[27] and are suspected to be related to deposit forming chemistries. The combination of both GC-MS and UHPSFC-MS analysis of gasoline and gasoline gum content is providing a holistic picture of the composition of the fuel which could allow deeper understanding for the cause of deposit formation in gasoline direct injection engines.

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ORCID for Graham Langley: orcid.org/0000-0002-8323-7235

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