Mahmood, Adnan;
(2023)
A multi-physics simulation approach to Investigating the underlying mechanisms of Low-Speed Pre-Ignition.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
As part of the effort to improve thermal efficiency, engines are being significantly downsized. A common issue in gasoline engines which limits thermal efficiency and is further exacerbated by downsizing, is low speed pre ignition (LSPI). This thesis uses a Multiphysics approach, initially using a validated 1D engine performance model of a GTDI engine, to define realistic boundary conditions. A strong emphasis on validating each simulation methodology as much as possible is maintained at each stage. A hydrodynamic model of the ring-liner and Lagrangian CFD model are used to investigate the impact of engine oil fluid properties on the mass of oil transported from the crevice volume to the combustion chamber. A heat transfer and evaporation model of a single droplet inside an engine environment was developed for alkanes of chain lengths representing the extremes of the chain lengths present in engine oil. It was found the droplet generally evaporates at a crank angle which is close to the point where LSPI is observed. The hydrocarbon study ends with a CFD constant volume simulation to understand why engine oil like hydrocarbons ignite in rig tests but not in an engine. This research then proceeds to develop a single particle detergent model in an engine environment, to initially understand why ignition occurs when a calcium Ca based detergent is present but not in the case of a magnesium Mg detergent. It was found from simulation that the common theory of calcium oxide CaO resulting from thermal degradation from the previous cycle then reacting with Carbon dioxide CO2 late in the compression stroke is unlikely. There is a stronger case for the CaO particle causing ignition as it is present in fresh engine oil sprayed onto the liner. As predicted by the hydrocarbon evaporation model the oil will cover and protect the CaO particle until late in the compression stroke when the oil will evaporate, exposing the CaO particle to CO2.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | A multi-physics simulation approach to Investigating the underlying mechanisms of Low-Speed Pre-Ignition |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) Licence (https://creativecommons.org/licenses/by-nc-nd/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 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 |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10168822 |
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