Davies, Hywel;
(2025)
Experimental characterisation of evaporating and non-evaporating sprays using planar laser diagnostics and Lagrangian tracking.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
This thesis focusses on the measurement of parameters relevant to droplet evaporation in polydispersed sprays using planar optical techniques. A range of applications are addressed, from automotive to energy generation and epidemiology. These fields stand to benefit from improved understanding of droplet evaporation mechanisms within turbulent sprays. Interferometric Droplet Sizing (IDS) is a planar method that provides spatially resolved measurements of droplet diameter and velocity over a large volume. To explore the suitability of the IDS method in performing measurements on turbulent sprays a series of experiments were performed using an automotive fuel injector to observe effects of ethanol content within ethanol-gasoline fuel blends. Results showed an increase in mean droplet diameter and homogeneity of droplet concentration distribution with increasing ethanol content. Several limiting factors were observed, restricting the ability of IDS to determine droplet volumetric concentrations. To improve performance a Lagrangian tracking processor was developed, using high-speed imaging and IDS principles. The Lagrangian tracking was shown to increase the number of droplet measurements and allowed the spatially resolved tracking of droplet position and diameter over time. The Lagrangian tracker was capable of directly measuring the evaporation of methanol droplets entrained within a heated air flow. Droplet evaporation rates were compared with a single droplet evaporation model, showing good agreement. The Lagrangian tracker was used to relate droplet diameter and droplet-gas slip velocity in an acoustic flow field. Close agreement was observed between data and modelled relations between stokes number and slip velocity. Evaporation rate enhancement of droplets from increasing acoustic amplitudes was observed to be considerable in comparison to enhancement with increasing ambient temperature. During this work, the relevance of aerosol characterisation to the spread of infectious, diseases became apparent with the outbreak of COVID-19. Using highspeed imaging human expiration of droplets was monitored. The information recorded, such as typical droplet velocities, concentrations, inter-person variation and the impact of face coverings will help to improve research into the propagation of human produced aerosols and the impact this has on the spread of diseases.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Experimental characterisation of evaporating and non-evaporating sprays using planar laser diagnostics and Lagrangian tracking |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering UCL |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10209927 |
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