An investigation into the characteristics of DISI injector deposits using advanced analytical methods

There is an increasing recognition of injector deposit (ID) formation in fuel injection equipment as direct injection spark ignition (DISI) engine technologies advance to meet increasingly stringent emission legislation and fuel economy requirements. While it is known that the phenomena of ID in DISI engines can be influenced by changes in fuel composition, including increasing usage of aliphatic alcohols and additive chemistries to enhance fuel performance, there is however still a great deal of uncertainty regarding the physical and chemical structure of these deposits, and the mechanisms of deposit formation. In this study, a mechanical cracking sample preparation technique was developed to assess the deposits across DISI injectors fuelled with gasoline and blends of 85% ethanol (E85). The deposits were analysed with SEM-EDS, FTIR Microscopy, TD-GCMS and an Alicona Infinite Focus 3D micro-coordinate system to assess the chemical composition and topography of the deposits for insights into their formation mechanisms. The location and topography of the deposits in this study indicate that they form in the region of the injector tip, and reduce in size and quantity as distance increases away from the combustion chamber. Elemental analysis results indicate that the dominant deposit compositions are C, O, S and Ca, of which S and Ca decrease but C increases with the locations closer to the combustion chamber. The topography results can be used to develop more sophisticated CFD analysis whilst also leading to a deeper understanding of deposit formation.