Thermoacoustic limit cycles in a premixed laboratory combustor with open and choked exits

Journal Article · Tue Sep 15 04:00:00 EDT 2009 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2009.05.011· OSTI ID:21223025

Hield, Peter A; Brear, Michael J; Jin, Seong Ho ^[1]

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1. Department of Mechanical Engineering, The University of Melbourne, Melbourne (Australia)

This paper presents an experimental and theoretical investigation of the response of a turbulent premixed flame during thermoacoustic limit cycle in a simple, laboratory combustor. The flame dynamics are examined using high-speed pressure transducers and CH* chemiluminescence. The so-called 'interaction index' and time delay between the acoustic velocity fluctuations at the flame holder and the flame's overall heat release fluctuations are then determined. A wide range of operating conditions, traversing the combustor's flammability limits in Mach number and equivalence ratio, are studied for four different combustor exits, including one where the exit is choked. In all cases the time delay correlates very well with the amplitude of the velocity fluctuations. There is also some correlation between the interaction index and these velocity fluctuations, but this is less clear. These results suggest a novel, nonlinear flame model, derived entirely empirically. An existing low-order thermoacoustic model is then extended to include convection and dispersion of entropy fluctuations downstream of the flame, enabling the effect of the choked nozzle to be examined. The novel nonlinear flame model is integrated into the low-order thermoacoustic model, and used to investigate the experimentally observed thermoacoustic limit cycles. The model correctly simulates the observed switch to a low-frequency, entropically driven instability observed when the combustor exit is choked. (author)

• OSTI ID: 21223025
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 9 Vol. 156; ISSN CBFMAO; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ACOUSTICS
AMPLITUDES
COMBUSTION KINETICS
CONVECTION
CORRELATIONS
ENTROPY
FLAMES
FLUCTUATIONS
HEAT
INSTABILITY
LIMIT CYCLE
NONLINEAR PROBLEMS
NOZZLES
Premixed combustion
TIME DELAY
TURBULENCE
Thermoacoustic instability
VELOCITY