NDLI: Measurement and Analysis of Flame Transfer Function in a Sector Combustor Under High Pressure Conditions

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Cheung, W. S. Sims, G. J. M. Copplestone, R. W. Tilston, J. R. Wilson, C. W. Simon, R. Stow Ann, P. Dowling
Copyright Year	2003
Abstract	Lean premixed prevaporised (LPP) combustion can reduce NOx emissions from gas turbines, but often leads to combustion instability. A flame transfer function describes the change in the rate of heat release in response to perturbations in the inlet flow as a function of frequency. It is a quantitative assessment of the susceptibility of combustion to disturbances. The resulting fluctuations will in turn generate more acoustic waves and in some situations self-sustained oscillations can result. Flame transfer functions for LPP combustion are poorly understood at present but are crucial for predicting combustion oscillations. This paper describes an experiment designed to measure the flame transfer function of a simple combustor incorporating realistic components. Tests were conducted initially on this combustor at atmospheric pressure (1.2 bar and 550 K) to make an early demonstration of the combustion system. The test rig consisted of a plenum chamber with an inline siren, followed by a single LPP premixer/duct and a combustion chamber with a silencer to prevent natural instabilities. The siren was used to induce variable frequency pressure/acoustic signals into the air approaching the combustor. Both unsteady pressure and heat release measurements were undertaken. There was good coherence between the pressure and heat release signals. At each test frequency, two unsteady pressure measurements in the plenum were used to calculate the acoustic waves in this chamber and hence estimate the mass-flow perturbation at the fuel injection point inside the LPP duct. The flame transfer function relating the heat release perturbation to this mass flow was found as a function of frequency. The same combustor hardware and associated instrumentation were then used for the high pressure (15 bar and 800 K) tests. Flame transfer function measurements were taken at three combustion conditions that simulated the staging point conditions (Idle, Approach and Take-off) of a large turbofan gas turbine. There was good coherence between pressure and heat release signals at Idle, indicating a close relationship between acoustic and heat release processes. Problems were encountered at high frequencies for the Approach and Take-off conditions, but the flame transfer function for the Idle case had very good qualitative agreement with the atmospheric-pressure tests. The flame transfer functions calculated here could be used directly for predicting combustion oscillations in gas turbine using the same LPP duct at the same operating conditions. More importantly they can guide work to produce a general analytical model.
Sponsorship	International Gas Turbine Institute
Starting Page	187
Ending Page	194
Page Count	8
File Format	PDF
ISBN	0791836851
DOI	10.1115/GT2003-38219
e-ISBN	0791836711
Volume Number	Volume 2: Turbo Expo 2003
Conference Proceedings	ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference
Language	English
Publisher Date	2003-06-16
Publisher Place	Atlanta, Georgia, USA
Access Restriction	Subscribed
Subject Keyword	Silencers Atmospheric pressure Oscillations Instrumentation Combustion Acoustics Fuels Waves High pressure (physics) Flames Gas turbines Turbofans Hardware Signals Combustion systems Ducts Transfer functions Pressure Flow (dynamics) Emissions Heat Fluctuations (physics) Nitrogen oxides Pressure measurement Combustion chambers
Content Type	Text
Resource Type	Article

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