Abstract
Experimental study on combustion instability of lean premixed swirl flame was conducted for methane-hydrogen mixtures, and the influence mechanism of hydrogen content (0%, 10%, 20%, and 40%) on the combustion instability under different acoustic frequencies (110–240 Hz) was investigated. A forced acoustic field created by a loud speaker was to simulate the complex and variable acoustic environment of unstable combustion. The flame transfer function was used to characterize the combustion instability. The morphologies of the flame, the evolution of vortex in the flame flow field, intensity of OH* chemiluminescence of flame front structure, and the degree of local thermo-acoustic oscillation of flame were also investigated to facilitate this study. The results show that the increase in hydrogen content weakens the combustion instability of lean premixed swirl flame in the acoustic frequency ranges of 170–240 Hz, while the combustion instability is enhanced for the acoustic frequency ranges of 110–160 Hz. The main reason for this phenomenon is the increase in the hydrogen content changes development of the vortex in the flame flow field, the evolution of the flame surface and the intensity of OH* chemiluminescence of flame front structure. This study provides an important reference for mastering the mechanism of the combustion instability of mixed gas flames and for developing technologies to inhibit combustion instability.
Highlights
Under lean premixing conditions, the relationship between the sound pressure in the combustion chamber of the gas turbine and the amount of heat released is close to the thermo-acoustic oscillation condition, which can lead to excitation and an unstable combustion state
The change of the flame front, vortex in the flame flow field, intensity of OH∗ chemiluminescence of flame front structure, and the degree of local thermo-acoustic oscillation of flame are investigated to give us insights into the inhibition of combustion instability
The influence mechanism of hydrogen content on combustion instability of lean premixed swirl flame under different acoustic frequencies for methane-hydrogen mixtures was investigated by experiments, and the obtained results show that the influences of hydrogen content are related to evolution of vortex in the flame flow field, the evolution of the flame surface and the intensity of OH∗ chemiluminescence of flame front structure, which in turn affect the heat-release fluctuation eventually enhancing or weakening flame instability
Summary
Lean premixed combustion is widely applied in gas turbines to effectively suppress NOX emissions. under lean premixing conditions, the relationship between the sound pressure in the combustion chamber of the gas turbine and the amount of heat released is close to the thermo-acoustic oscillation condition, which can lead to excitation and an unstable combustion state. Unstable combustion in gas turbines cause flashback and blowout resulting in high-decibel noise. The high heat-release rate and strong mechanical vibration can result in structural damage of the combustion chamber and the turbine; this can be a safety hazard. This is an important technical problem facing the gas turbine industry worldwide. Researchers have studied the influencing factors of combustion instability in terms of acoustic-flame surface interactions, hydrodynamic instability-vortex shedding, equivalence ratio fluctuation, and entropy wave fluctuation.11 These four mechanisms occur for different reasons, the essence is to change the pulsation of the heat-release rate via the influence of flow mixing on the flame. The flame transfer function was used to quantify the effects of hydrogen content on the combustion instability of swirl flame under different acoustic frequencies These studies of flame dynamics investigated the effects of hydrogen content change on the morphology of the flame, the evolution of vortex in the flame flow field, intensity of OH∗ chemiluminescence of flame front structure, and local thermo-acoustic oscillation of the flame. The results offer insight into the mechanism of hydrogen content on combustion instability
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