Mitigating instability by actuating the swirler in a combustor

Abstract

The present disclosure relates to a method and apparatus to mitigate thermo-acoustic instabilities in combustor of gas turbine engines using a lean premixed flame; and provides a dynamic control strategy for mitigating thermo-acoustic instability in a swirl stabilized, lean premixed combustor by rotating the otherwise static swirler meant for stabilizing the lean premixed flame. The swirler is subjected to a controlled rotation for imparting increased turbulence intensity and higher tangential momentum to the premixed reactants towards mitigating thermo-acoustic instability. The rotating swirler induces vortex breakdown and increased turbulence intensity to decimate periodic interactions found during a particular phase of the instability cycle on account of periodic collision of diverging flame base with the flame segment above the dump plane in the combustor. This prevents flame-flame interactions and emergence of strongly positive Rayleigh indices which contribute as sources of acoustic energy to drive the self-excited instability.

Description

FIELD OF THE INVENTION[0001]The present disclosure relates generally to the field of gas turbines. In particular it relates to a method of reduction of thermo-acoustic instabilities in a lean premixed combustor of a gas turbine.BACKGROUND[0002]Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.[0003]Enhanced periodic pressure fluctuations that result from a positive feedback between the unsteady heat release rate and the acoustic pressure fluctuations in a confined combustion chamber is referred to as thermo-acoustic instability. In case of combustion chambers of gas turbines, high oscillation amplitudes can occur which lead to undesirable effects, such as, for example, a high mechanical / thermal load on the combustion chamber, flash...

AI Technical Summary

Benefits of technology

The objective of this patent is to reduce the problem of unstable flame condition in gas turbine combustors, allowing for the use of lean premixed combustion technology. This is achieved by implementing a closed loop control mechanism that detects unstable flame condition, computes the fastest route to achieve stable condition, and actuates means to rotate the swirler at the desired speed. Using this mechanism, the combustor acts as a smart combustor and automatically maintains stable flame condition free from thermo-acoustic instability.

Problems solved by technology

In case of combustion chambers of gas turbines, high oscillation amplitudes can occur which lead to undesirable effects, such as, for example, a high mechanical / thermal load on the combustion chamber, flashback or the flame being extinguished.

Specifically, lean premixed gas turbine combustor operation is frequently plagued by intense thermo-acoustic oscillation at nearly discrete, narrow band frequencies leading to structural damage and possible failure of the engine parts.

This is the major obstacle in using lean premixed combustion technology in gas turbine combustors despite its other remarkable benefits in terms of reduced pollutant emission, negligible soot production to name a few.

Systematic mitigation of thermo-acoustic instability is thus an important challenge.

However, instability mitigation using mechanisms like Helmholtz resonators are difficult to realize in realistic combustor systems mainly due to space and power constraints.

Liquid-fuelled rockets and gas turbine combustors are often equipped with acoustic dampers like Helmholtz resonators, perforated liners, quarter and half-wave tubes and baffles; but the addition of such components affects the combustor performance, weight and heat loads.

Furthermore, increasing blade angle for achieving higher swirl number introduces blockage in the flow path resulting in enhanced pressure drop.

Therefore, a variable blade angle swirler offers limited change in swirl number at the cost of pressure drop.

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