Experimental study of burner geometry effect on the coherent structures, flashback, and flame front dynamics of unconfined and confined partially premixed swirling methane flames
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Date
2020-02-12
Authors
Ahmed, Mahmoud M.A.
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Abstract
The effect of burner geometry (central fuel nozzle, mixing tube length, and flame confinement) on the ensuing flowfield’s coherent structures (precessing vortex core and vortex shedding) and their relationship with some combustion stability parameters, such as flashback and flame front dynamics of a swirling partially premixed methane flame, is experimentally studied. In this investigation, several measurement techniques are employed. These include particle image velocimetry (PIV), Mie scattering, laser Doppler velocimetry (LDV), Bruel & Kjaer microphone, high-speed Schlieren imaging technique, and high-speed luminescence imaging. In addition, proper orthogonal decomposition (POD) is used as a post processing technique to capture the flow-field coherent structures. In the first part of the study, the effect of central nozzle geometry on coherent structures’ strength and frequency is examined inside a relatively long mixing tube. Furthermore, the relationship between the strength and frequency of coherent structures and the mean flashback region inside the mixing tube is studied. In the second part, the central nozzle geometry is modified based on the conclusions reached in the first part of the study, and its effect on the suppression of the coherent structures is investigated using a relatively short mixing length. Finally, the effect of nozzle geometries, which exhibit the highest and lowest coherent structures’ amplitude, on coherent structures and acoustics modes is studied using different mixing tube lengths in the presence of a flame confinement. The results showed that the central nozzle geometry significantly affects coherent structures’ strength and amplitude inside the mixing tube. Moreover, the results revealed a strong relationship between coherent structures’ strength and the mean flashback region inside the mixing tube. Furthermore, the central nozzle geometry is found to significantly affect the amplitude of coherent structures for both confined and unconfined swirling partial premixed flames, and acoustics for the confined flames. All in all, it can be concluded that passive techniques can be a viable strategy for mitigating combustion instabilities of partially premixed flames.
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Keywords
Partially premixed flame, Coherent structures, Swirl, Flashback, Burner geometry
Citation
Ahmed, M. M. A., and Birouk, M. (January 29, 2020). "Effect of Fuel Nozzle Geometry on Swirling Partially Premixed Methane Flames." ASME. J. Eng. Gas Turbines Power. March 2020; 142(3): 031009. https://doi.org/10.1115/1.4045477
Ahmed, M. M. A., and Birouk, M. (August 4, 2018). "Effect of fuel nozzle geometry and airflow swirl on the coherent structures of partially premixed methane flame under flashback conditions." Experimental Thermal and Fluid Science. December 2018; 99: 304-314. https://doi.org/10.1016/j.expthermflusci.2018.08.003
Ahmed, M. M. A., and Birouk, M. (March 22, 2019). "Burner geometry effect on coherent structures and acoustics of a confined swirling partially premixed methane flame."Experimental Thermal and Fluid Science. July 2019; 105: 85-99. https://doi.org/10.1016/j.expthermflusci.2019.03.011
Ahmed, M. M. A., and Birouk, M. (August 4, 2018). "Effect of fuel nozzle geometry and airflow swirl on the coherent structures of partially premixed methane flame under flashback conditions." Experimental Thermal and Fluid Science. December 2018; 99: 304-314. https://doi.org/10.1016/j.expthermflusci.2018.08.003
Ahmed, M. M. A., and Birouk, M. (March 22, 2019). "Burner geometry effect on coherent structures and acoustics of a confined swirling partially premixed methane flame."Experimental Thermal and Fluid Science. July 2019; 105: 85-99. https://doi.org/10.1016/j.expthermflusci.2019.03.011