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Coherent structures and their effects on processes occurring in swirl combustors

Valera Medina, Agustin 2009. Coherent structures and their effects on processes occurring in swirl combustors. PhD Thesis, Cardiff University.

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Abstract

Access to energy is fundamental to civilisation, both as economic and social yTL development. This is fuelling a growing demand for reliable, affordable and clean energies. The current problems related to climate change have made imperative the search of technologies that can produce higher amounts of energy at lower emission rates. Therefore, technologies such as swirling flows with premixed lean injection have been characterized as one of the most reliable to achieve this objective. However, the use of this technology implicates the appearance of phenomena that have been barely studied such as the manifestation of coherent structures that are crucial for the stability and high efficiency of the combustion process, and which have been assumed from indirect measurements. Moreover, these structures have been recognised as major players in the generation of instabilities such as pressure and heat transfer variations, internal vibrations and flashback into the mixing chambers. Therefore, a better understanding of these structures will allow the design of better burners and a greater control over the former, permitting a more efficient process. This project is intended to reveal some of the characteristics of these structures, showing their high 3 dimensionality and high dependence on geometrical parameters, equivalence ratio, Swirl and Reynolds numbers, amongst other factors. It is recognised how under isothermal conditions the system produces strong Precessing Vortices that are fundamental in the final shape of the flow field, while the Central Recirculation Zones are dependent on the pressure decay ratio inside of the combustion chamber. Combustion conditions showed the high dependence on the method of fuel injection used, with the appearance of stronger structures at lower equivalence ratios when high amounts of premixed gas were pumped into the system and the change in shape of the recirculation zones by using different injectors. Flashback demonstrated to be a factor highly related to the strength of the Central Recirculation Zone for those cases where a Combustion Induced Vortex Breakdown was allowed to enter the swirl chamber, whilst cases where a bluff body impeded its passage showed a considerable improvement to the resistance of the phenomenon. The use of nozzle constrictions also reduced flashback at high Re. All these results were aimed to contribute to better designs of future combustors.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Engineering
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
ISBN: 9781303214301
Date of First Compliant Deposit: 30 March 2016
Last Modified: 04 Jun 2017 05:55
URI: http://orca-mwe.cf.ac.uk/id/eprint/54815

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