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Abstract

The growing demand for efficient and environmentally sustainable internal combustion engines has highlighted the vital role of fuel injectors in achieving cleaner combustion. This thesis offers a detailed analysis of in-nozzle flow, near-nozzle spray dynamics, combustion behaviour, and soot emissions across a diverse range of fuels under realistic conditions. Advanced imaging techniques, including high-speed schlieren imaging and diffuse backlight illumination (DBI), were used to visualise in-nozzle and near-nozzle flow dynamics. Combustion parameters and soot emissions were quantified using OH* chemiluminescence and DBI extinction imaging, providing insights on phenomena such as cavitation, spray formation, and flame lift-off length, and revealing the influence of fuel properties on injection and combustion processes.

Engine Combustion Network (ECN) single-hole injectors Spray C and Spray D, along with ECN multi-hole injector Spray M, were tested under realistic conditions. Findings show that Quaternary Ammonium Salt (QAS) additives suppress geometric cavitation while enhancing longitudinal vortices in diesel fuels, thereby also increasing spray cone angles. The effect of viscoelasticity was pronounced in tapered nozzles, where vortical cavitation dominated over geometric cavitation, significantly shaping spray morphology.

Experiments with conventional diesel, Jet-A, and Sustainable Aviation Fuels (SAFs), such as Bicyclohexyl (BCH) and C-4 using Spray C and Spray D nozzles elucidated cavitation and spray characteristics under variable injection-pulse durations. BCH exhibited pronounced vortical cavitation in Spray D, leading to wider spray cone angles and improved air-fuel mixing. Combustion experiments showed QAS-treated fossil-derived diesel fuels had extended ignition delays, reduced lift-off lengths, and significant soot reduction. However, these benefits were less pronounced in bio-derived fuels due to complex interactions between molecular structure, additives, and viscoelastic micelle formation.

This research underscores the effects of injector geometry, fuel and additive properties, as well as injection timing on cavitation, spray dynamics, and combustion. It highlights the potential of viscoelastic additives to optimise spray formation and suppress emissions in fossil-derived fuels while offering crucial insights into the unique behaviour of SAFs, especially BCH, in advanced injection systems. The findings contribute to the broader development of sustainable, efficient fuel injection strategies for cleaner combustion and reduced environmental impact.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > T Technology (General) T Technology > TJ Mechanical engineering and machinery T Technology > TL Motor vehicles. Aeronautics. Astronautics T Technology > TP Chemical technology
Departments:	School of Science & Technology > Department of Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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