Flashback analysis and avoidance in swirl burners

Hatem, Fares 2017. Flashback analysis and avoidance in swirl burners. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This study is aimed to investigate and demonstrate the feasibility and validity of various flame flashback resistance techniques for premixed fuel conditions. It presents a series of experiments to determine the impact of different configurations on flame flashback mechanisms. Experiments were performed using a 150 kW tangential swirl burner working on premixed mode with various swirl numbers; the flow field characteristics were measured by 1D LDA. The first part of the project targeted the effect of central fuel injector geometries on flame flashback mechanisms, especially combustion induced vortex breakdown (CIVB). It was found that changing the central fuel injector outside diameter can significantly alter the flame flashback mechanism. Large injector diameters result in boundary layer flashback (BLF), contrary, the use of small injectors diameter led to CIVB. Thus a dimensionless number (χ) which represent the ratio between the injector outside diameter and the nozzle inside diameter was introduced. Using this dimensionless number the critical value of transition from CIVB to BLF has been defined, the value being χ= 0.280 for Sg=1.12 and χ= 0.320 for Sg= 0.9. The second part was about the effect of using axial air injection instead of central fuel injectors. It was found that axial air jets have a considerable potential for flame stability requirements, they producing wider stability operation than that of central injectors. Moreover, the stability limits increase regarding both equivalence ratio and inlet tangential velocity. It appeared that using such air jets could reduce the combustor maintenance cost that arises due to a continuous harsh environment. However, it was found that axial air jets could enforce flame propagation during flashback via wall boundary layer. Thus, the third part of the study was about the validity of using micromeshes to improve BLF resistance in addition to axial air injection. It was found that using both techniques produced high flashback resistance for both mechanisms, i.e. CIVB and BLF.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Engineering
Uncontrolled Keywords:	Flame Flashback; Swirl Burners; Central Fuel Injectors; Axial Air Injection; Turbulence Intensity; CIVB & BLF.
Date of First Compliant Deposit:	17 August 2017
Last Modified:	23 Apr 2021 09:34
URI:	https://orca.cardiff.ac.uk/id/eprint/103700

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