A Mechanism of Combustion Instability in Lean Premixed Gas Turbine Combustors
- 2 April 2000
- journal article
- Published by ASME International in Journal of Engineering for Gas Turbines and Power
- Vol. 123 (1), 182-189
- https://doi.org/10.1115/1.1339002
Abstract
There has been increased demand in recent years for gas turbines that operate in a lean, premixed (LP) mode of combustion in an effort to meet stringent emissions goals. Unfortunately, detrimental combustion instabilities are often excited within the combustor when it operates under lean conditions, degrading performance and reducing combustor life. To eliminate the onset of these instabilities and develop effective approaches for their control, the mechanisms responsible for their occurrence must be understood. This paper describes the results of an investigation of the mechanisms responsible for these instabilities. These studies found that combustors operating in a LP mode of combustion are highly sensitive to variations in the equivalence ratio (ϕ) of the mixture that enters the combustor. Furthermore, it was found that such ϕ variations can be induced by interactions of the pressure and flow oscillations with the reactant supply rates. The ϕ perturbations formed in the inlet duct (near the fuel injector) are convected by the mean flow to the combustor where they produce large amplitude heat release oscillations that drive combustor pressure oscillations. It is shown that the dominant characteristic time associated with this mechanism is the convective time from the point of formation of the reactive mixture at the fuel injector to the point where it is consumed at the flame. Instabilities occur when the ratio of this convective time and the period of the oscillations equals a specific constant, whose magnitude depends upon the combustor design. Significantly, these predictions are in good agreement with available experimental data, strongly suggesting that the proposed mechanism properly accounts for the essential physics of the problem. The predictions of this study also indicate, however, that simple design changes (i.e., passive control approaches) may not, in general, provide a viable means for controlling these instabilities, due to the multiple number of modes that may be excited by the combustion process.Keywords
This publication has 7 references indexed in Scilit:
- Acoustic control of combustion instabilities and emissions in a gas-turbine combustorPublished by Institute of Electrical and Electronics Engineers (IEEE) ,2002
- Effect of Fuel Nozzle Configuration on Premix Combustion DynamicsPublished by ASME International ,1998
- Measurement of Air-Fuel Ratio Fluctuations Caused by Combustor Driven OscillationsPublished by ASME International ,1998
- The Role of Unmixedness and Chemical Kinetics in Driving Combustion Instabilities in Lean Premixed CombustorsCombustion Science and Technology, 1998
- An experimental study of combustion dynamics of a premixed swirl injectorSymposium (International) on Combustion, 1998
- The role of equivalence ratio oscillations in driving combustion instabilities in low NOx gas turbinesSymposium (International) on Combustion, 1998
- Thermoacoustic oscillations in combustion chambers of gas turbinesAIAA Journal, 1995