Phase Resolved Analysis of Flame Structure in Lean Premixed Swirl Flames of a Fuel Staged Gas Turbine Model Combustor

Abstract

A scaled model of a gas turbine (GT) burner with coaxially mounted swirlers has been used to study the effects of fuel staging on the behavior of lean premixed methane air flames. Lean flames are known to be susceptible to instabilities that can lead to unsteady operation, flame extinction, and thermo-acoustic oscillations. High speed (10 kHz) laser and optical diagnostic techniques have been used to investigate the fuel staging effect on the mechanisms involved in such instabilities. Methane air flames at atmospheric pressure have been investigated at a constant thermal power of 58 kW. The global equivalence ratio was kept constant, while the fuel staging was varied. The bulk flow velocity at the exit plane was kept constant at 20 m/s. Simultaneous high speed OH PLIF, OH * CL, and acoustic measurements were performed at kHz repetition rate to characterize the flames and determine the operability limits of the combustor. The characterization measurements reveal significant changes in flame shape for various staging ratios as well as onset of self-excited thermo-acoustics in flames with more than 55% fuel injection in the outer swirler. The phase resolved analysis of the OH * CL revealed pulsation in the heat release due to acoustics in flames with higher percentage of fuel in the outer swirler. Comparison of the pressure oscillation in the combustion chamber with the heat release yielded a clear picture regarding the feedback mechanism that sustains the self-excited thermo-acoustic pulsations. The variation of local equivalence ratio of the mixture seems to be the driving force that initiates the onset of acoustics pulsations.

Experimental analysis of thermo-acoustic instabilities in a generic gas turbine combustor by phase-correlated PIV, chemiluminescence, and laser Raman scattering measurements

“…Those measurements include OH* and CH* chemiluminescence to identify heat release variations, OH, CH 2 O and CH PLIF to determine fluctuations in the flame surface density or local Rayleigh index and laser Raman measurements to assess changes in the thermo-chemical state of the flame [Bellows 2007, Biagioli 2008, Giezendanner 2003, Hubschmid 2008, Ishino 2001, Lee 2003, Schildmacher 2006. More recently, high-speed imaging techniques in combination with acoustic pressure tracing have been applied to study thermo-acoustic instabilities in GT-relevant combustors , Caux-Brisebois 2014, Durox 2013, Galley 2011, Gounder 2014, Steinberg 2010, Steinberg 2012, Steinberg 2013, Worth 2012, yielding deeper insight into the feedback mechanisms.…”

The Effects of Strong-Weak Swirling Interaction on Emissions in a Multi-Nozzle Combustor

“…However, some parameters can be adjusted at any time according to the combustion state, such as fuel staging and swirl number [9]. Fuel staging affected the local flame structure and heat release rate by changing the interaction of adjacent flame fronts and thereby controls combustion stability and pollutant emissions [10,11]. However, the research on fuel staging mainly focuses on the combustion stability [12][13][14].…”