Lamb, Joseph
(2022)
Advanced characterisation of internal diesel injector deposit molecular compositions.
EngD thesis, University of Nottingham.
Abstract
Diesel engines remain widely used in a range of applications throughout the world, the clean operation of which is imperative for minimising their environmental impact during the transition towards a decarbonised energy system. The negative impact of insoluble internal diesel injector deposit (IDID) formation on emissions is well documented, and their incidence and severity has increased over the past two decades due to reasons thought to include the higher temperatures and pressures of newer injector systems and the uptake of biodiesel blending. Prevention and mitigation of such deposit formation requires an understanding of the formation process which requires the identification of detrimental fuel and additive components, their mechanisms of contributing to deposit formation, and how new mitigation strategies could prevent them.
Previous investigations have characterised IDIDs with a range of techniques, with ToF-SIMS proving itself effective for the analysis of insoluble carbonaceous deposit components and its ability to depth profile demonstrating a layered structure. However, characterisation with this technique was limited to non-diagnostic assignments due to high fragmentation of sputtered ions and low mass resolving power. This thesis builds on these studies with the recently developed technique of OrbiSIMS, which combines SIMS’s ability to access insoluble material with the high mass resolving power of the OrbitrapTM mass analyser and preservation of chemistry through the softer Ar3000+ GCIB. Through this technique, detailed characterisation of deposit components is achieved, including chemistries not seen before that provide new insights into IDID formation processes. Examples include species originating from lubricant oil additives such as alkylbenzene sulfonates (C18H29SO3-) and polyaromatic hydrocarbons derived from the carbonisation of fuel such as circumovalene (C66H20+). In view of SIMS’s limitation in being semi-quantitative, XPS is applied in support for elemental quantification that validates and provides context to the OrbiSIMS data, finding deposits that are generally over 70 relative atomic percent carbon but with significant contributions from other elements, including inorganic salts of sodium and calcium.
With OrbiSIMS and XPS depth profiling, the location of the detailed deposit chemistries of interest as well as elemental quantification with depth is observed all the way down to the needle substrate. The IDIDs showed an increase in inorganic content in the sub-surface, however XPS shows that carbon is the dominant element throughout the full thickness of the IDIDs analysed. Using a multivariate analysis approach, depth profile trends were identified and each sample characterised as four pseudo-layers. Each sample’s organics and polyaromatics are found towards the surface, above inorganic and carbonaceous material, the latter suggesting a carbonisation of the surface organic material over time. Finally, the substrate is identified in all samples. This method achieves the most comprehensive IDID characterisation to date and the chemistries responsible for the nascent deposit formation can be suggested from the lower pseudo-layers’ characterisations, for example indicating lubricant oil contamination or sodium contamination with a source of sulfate and carbonate.
To assess the effects of fuel, additive and contaminant chemistries in a controlled environment on diesel deposit formation, a laboratory bench test (the JFTOT) was applied to generate samples of known origin that can be analysed using the same methods. The deposit composition formed from a range of fuel, additive and contaminant components, including biodiesel, additives of interest and lubricant oil. The same chemistries identified are present in the IDIDs from real-world failures, and the JFTOT investigations demonstrate the possible origins of these components. For example, biodiesel and lubricant oil are indicated as a source of sulfur and phosphorus while LMW PIBSI is indicated as a source of nitrogen, all of which become integrated into carbonaceous material that is seen in both JFTOTs and real-world IDIDs. The findings from these investigations can inform the industry and future investigations to help mitigate deposition and ensure the efficiency and longevity of diesel engines.
| Item Type: |
Thesis (University of Nottingham only)
(EngD)
|
| Supervisors: |
Scurr, David
Snape, Colin
Barker, Jim |
| Keywords: |
Diesel fuels, Diesel motor, Fuel injection systems, Injectors, Surface analysis, OrbiSIMS, XPS |
| Subjects: |
T Technology > TJ Mechanical engineering and machinery > TJ751 Internal combustion engines. Diesel engines |
| Faculties/Schools: |
UK Campuses > Faculty of Engineering |
| Item ID: |
71631 |
| Depositing User: |
Lamb, Joseph
|
| Date Deposited: |
04 Nov 2022 04:40 |
| Last Modified: |
29 Jul 2025 04:30 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/71631 |
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