Closed-Loop Active Control of Combustion Instabilities Using Subharmonic Secondary Fuel Injection

1999 ◽  
Vol 15 (4) ◽  
pp. 584-590 ◽  
Author(s):  
C. M. Jones ◽  
J. G. Lee ◽  
D. A. Santavicca
Keyword(s):  
Active Control ◽  
Closed Loop ◽  
Fuel Injection ◽  
Combustion Instabilities ◽  
Secondary Fuel

Active Control of Combustion Instabilities in Gas Turbine Burners

2006 ◽  
Author(s):  
Christian Oliver Paschereit ◽  
Ephraim Gutmark
Keyword(s):  
Gas Turbine ◽  
Active Control ◽  
Closed Loop ◽  
Fuel Injection ◽  
Nox Emissions ◽  
Modulation Amplitude ◽  
Symmetric Mode ◽  
Instability Mode ◽  
Secondary Fuel ◽  
Symmetric Instability

This paper gives an overview of open and closed loop active control methodologies used to suppress symmetric and helical thermoacoustic instabilities in an experimental low-emission swirl-stabilized gas turbine combustor. The controllers were based on fuel (or equivalence ratio) modulations in the main pre-mixed combustion or alternatively in secondary pilot fuel. For the main premix fuel supply two methods of fuel injection modulations were tested: symmetric and asymmetric injection. The tests showed that the closed loop asymmetric modulations were more effective in the suppression of the symmetric mode instability than symmetric fuel excitation. Symmetric excitation was quite efficient in abating the symmetric mode as well, however, at a certain range of phase shift the combustion was destabilized to an extent that caused blow out of the flame. Using premixed open loop fuel modulations the symmetric instability mode responded to symmetric excitation only when the two frequencies matched. The helical fuel injection affected the symmetric mode only at frequencies that were much higher than that of the instability mode. The asymmetric excitation required more power to obtain the same amount of reduction as that required by symmetric excitation. Unlike the symmetric excitation which destabilized the combustion when the modulation amplitude was excessive, the asymmetric excitation yielded additional suppression as the modulation level increased. The NOx emissions were reduced to a greater extent by the asymmetric modulation. Secondary fuel injection in a pilot flame was used to control low frequency symmetric instability and high frequency helical instability. Adding a continuous flow of fuel into the pilot flame controlled both instabilities. However, modulating the fuel injection significantly decreased the amount of necessary fuel. The reduced secondary fuel resulted in a reduced heat generation by the pilot diffusion flame and therefore yielded lower NOx emissions. The secondary fuel pulsation frequency was chosen to match the time scales typical to the central flow recirculation zone which stabilizes the flame in the burner. Suppression of the symmetric mode pressure oscillations by up to 20 dB was recorded.

Suppression of Instabilities in Gaseous Fuel High-Pressure Combustor Using Non-Coherent Oscillatory Fuel Injection

2003 ◽  
Author(s):  
D. Shcherbik ◽  
E. Lubarsky ◽  
Y. Neumeier ◽  
B. T. Zinn ◽  
K. McManus ◽  
...  
Keyword(s):  
High Pressure ◽  
Active Control ◽  
Fuel Injection ◽  
Injection Rate ◽  
Open Loop ◽  
Combustion Instabilities ◽  
Open Loop Control ◽  
Pressure Oscillations ◽  
Loop Control ◽  
Fuel Injection Rate

This paper describes the application of active, open loop, control in effective damping of severe combustion instabilities in a high pressure (i.e., around 520 psi) gas turbine combustor simulator. Active control was applied by harmonic modulation of the fuel injection rate into the combustor. The open-loop active control system consisted of a pressure sensor and a fast response actuating valve. To determine the dependence of the performance of the active control system upon the frequency, the fuel injection modulation frequency was varied between 300 and 420 Hz while the frequency of instability was around 375 Hz. These tests showed that the amplitude of the combustor pressure oscillations strongly depended upon the frequency of the open loop control. In fact, the amplitude of the combustor pressure oscillations varied ten fold over the range of investigated frequencies, indicating that applying the investigated open loop control approach at the appropriate frequency could effectively damp detrimental combustion instabilities. This was confirmed in subsequent tests in which initiation of open loop modulation of the fuel injection rate at a non resonant frequency of 300Hz during unstable operation with peak to peak instability amplitude of 114 psi and a frequency of 375Hz suppressed the instability to a level of 12 psi within approximately 0.2 sec (i.e., 75 periods). Analysis of the time dependence of the spectra of the pressure oscillations during suppression of the instability strongly suggested that the open loop fuel injection rate modulation effectively damped the instability by “breaking up” (or preventing the establishment of) the feedback loop between the reaction rate and combustor oscillations that drove the instability.

Damping of Combustion Instabilities Through Pseudo-Active Control

2018 ◽  
Author(s):  
Jesús Oliva ◽  
Ennio Luciano ◽  
Javier Ballester
Keyword(s):  
Combustion Chamber ◽  
Active Control ◽  
Gas Turbines ◽  
Fuel Injection ◽  
Pressure Oscillation ◽  
Practical Reasons ◽  
Fuel Injector ◽  
Secondary Fuel ◽  
Pilot Fuel ◽  
Instability Control

Active instability control techniques have demonstrated very good capabilities to correct combustion oscillations but, due to high costs and other practical reasons, have not achieved the success expected in gas turbines engines. A different approach, named here as ‘pseudo-active instability control’, has been explored and the first results are presented in this work. In this case, the flow of non-premixed pilot fuel is modulated by passive methods: the pressure oscillation in the combustion chamber induces a velocity fluctuation at the secondary fuel injector. In principle, damping of the instability may be achieved if the heat release oscillations due to the secondary fuel are out of phase with those of the main flame. This work reports a first exploration of this strategy, aimed mainly at performing a proof of the concept. An experimental study has been carried out in a laboratory premixed combustor with pilot fuel injection. The relationship between the fluctuations of pressure in the combustion chamber and those of velocity at the injector was studied both experimentally (hot wire anemometry) and theoretically (1-D acoustic model of the injection line). Combustion tests in limit cycle conditions demonstrated that modifications in the geometry of the secondary injection affected the pressure fluctuations inside the combustion chamber. Depending on the geometry (and, hence, acoustic impedance), the instability was enhanced or damped. This demonstrates that the proposed ‘pseudo-active control’ can produce similar effects (at least, qualitatively) to those of active control, but only using passive means, as initially postulated.

Influence of the Interaction of Equivalence Ratio and Mass Flow Fluctuations on Flame Dynamics

2005 ◽  
Author(s):  
M. P. Auer ◽  
C. Hirsch ◽  
T. Sattelmayer
Keyword(s):  
Heat Release ◽  
Active Control ◽  
Mass Flow ◽  
Equivalence Ratio ◽  
Feedback Loop ◽  
Combustion Instabilities ◽  
Flame Dynamics ◽  
Secondary Fuel ◽  
Flow Oscillations ◽  
Mass Flows

Modern lean combustion systems are often prone to combustion instabilities — an interaction of acoustic waves, fluid dynamics and heat release oscillations. Mass flow oscillations are one important part of the feedback loop of combustion instabilities. Therefore, modulated mass flows of fuel or/and combustion air are main objectives in many studies on combustion instabilities and their active control (AIC, Active Instability Control). Flame response and flame transfer matrices are often determined by excitation of combustion air at various frequencies by sirens or loudspeakers. For the purpose of active control modulated secondary fuel is usually injected to the mass flow to dampen heat release fluctuations of the flame in order to de-couple the thermoacoustic feedback loop. This paper demonstrates the influence of modulated mass flows on the flame dynamics in an atmospheric test rig with a natural gas fired swirl burner. In the investigated cases the modulation of combustion air also result in equivalence ratio fluctuations due to choked main fuel injection. This combination has a tremendous effect on the flame dynamics. A model was developed to describe the interaction of equivalence ratio fluctuations and total mass flow oscillations and their influence on combustion instabilities. In experiments these equivalence ratio fluctuations were generated by injecting modulated secondary fuel. The derived model provides a deep insight into the driving mechanisms of combustion instabilities.

PI Control of HSFDs for Active Control of Rotor-Bearing Systems

1997 ◽  
Vol 119 (3) ◽  
pp. 658-667 ◽  
Author(s):  
J. P. Hathout ◽  
A. El-Shafei
Keyword(s):  
Vibration Control ◽  
Active Control ◽  
Closed Loop ◽  
Rotating Machinery ◽  
Loop System ◽  
Pi Control ◽  
Closed Loop System ◽  
Transient Vibration ◽  
Critical Speeds ◽  
Rotor Bearing

This paper describes the proportional integral (PI) control of hybrid squeeze film dampers (HSFDS) for active control of rotor vibrations. Recently it was shown that the automatically controlled HSFD based on feedback of rotor speed can be a very efficient device for active control of rotor vibration when passing through critical speeds. Although considerable effort has been put into the study of steady-state vibration control, there are few methods in the literature applicable to transient vibration control of rotor-bearing systems. Rotating machinery may experience dangerously high dynamic loading due to the sudden mass unbalance that could be associated with blade loss. Transient run-up and coast down through critical speeds when starting up or shutting down rotating machinery induces excessive bearing loads at criticals. In this paper, PI control is proposed as a regulator for the HSFD system to attenuate transient vibration for both sudden unbalance and transient runup through critical speeds. A complete mathematical model of this closed-loop system is simulated on a digital computer. Results show an overall enhanced behavior for the closed-loop rotor system. Gain scheduling of both the integral gain and the reference input is incorporated into the closed-loop system with the PI regulator and results in an enhanced behavior of the controlled system.

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