Characterizing low-frequency flame-front oscillations – An investigation into their origin and possible mitigation

Madhavan, A.K.

Characterizing low-frequency flame-front oscillations – An investigation into their origin and possible mitigation

Master thesis (2023)

Authors

A.K. Madhavan Aerospace Engineering

Contributors

G. A. Bohlin Flight Performance and Propulsion - Aerospace Engineering (mentor)

Leonardo Castellanos Flight Performance and Propulsion - Aerospace Engineering (graduation committee member)

Faculty

Aerospace Engineering, Aerospace Engineering

Combustion diagnostics Flame-front oscillations Low-frequency oscillations Premixed conical flame Bunsen flame Flame plumes Oscillation reduction Buoyancy variations Flow rate fluctuations Chemiluminescence CARS spectroscopy Flame front edge detection algorithms Instability amplitudes Mitigation strategies Flame holder design

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Published Date

13-06-2023

Language

English

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Faculty

Aerospace Engineering

Abstract

This investigation focuses on the premixed conical flame, a mainstay of combustion diagnostics. While extensive studies have explored high-frequency oscillations in the canonical Bunsen flame, little attention has been given to low-frequency oscillations affecting flame fronts. This thesis aims to explain the origins of these oscillations and proposes mitigation strategies. The goal is to improve high-accuracy diagnostics of standard conical flames by generating stable flame plumes through oscillation reduction.
The thesis explores two theories for low-frequency oscillations: buoyancy variations and flow rate fluctuations. Image chemiluminescence and CARS spectroscopy validate these hypotheses. Spatial oscillations are detected using flame front edge detection algorithms, while CARS analysis indirectly confirms fluctuations. Preliminary experiments establish reference data sets, followed by a primary experimental campaign spanning Reynolds numbers from 500 to 1000 for constant equivalence ratios. This isolates the effect of buoyancy variations. The report concludes by suggesting simple design changes for the flame holder to reduce instability amplitudes.

Files

MSc_Thesis_Report_Official.pdf

(pdf | 11.5 Mb)

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