Observations of Flame Behavior in a Laboratory-Scale Pre-Mixed Natural Gas/Air Gas Turbine Combustor From PLIF Measurements of OH

Abstract

The objective of this study was to obtain instantaneous planar laser induced fluorescence (PLIF) images of OH in a laboratory-scale, gas-turbine combustor (LSGTC) with a premixed, swirl-stabilized, natural gas flame. Instantaneous PLIF images of OH were obtained at each of four operating conditions (high swirl and medium swirl at fuel equivalence ratios of 0.80 and 0.65). Comparison of the instantaneous images illustrates the stochastic nature of the flame structure. Pixel by pixel statistical analysis of each collection of images allowed both mean and standard deviation images to be generated, and analysis at selected locations has allowed probability density functions to be obtained in various regions of the flame structure. PLIF images of OH, along with visual photographs and video recordings, showed a wide variation in flame structure for the different operating conditions. The variations in flame shapes are primarily a result of the effect of the swirl intensity and fuel equivalence ratio. Changes in the airflow rate over an order of magnitude do not seem to affect the visual flame structure in this experiment. Operation at φ = 0.80 produced the most stable flames with both injectors. The flame with the high swirl injector was more coalesced and closer to the injector than with the medium swirl injector. At φ = 0.65, the flame was quite unstable for both swirl injectors. With the medium swirl injector, the flame would oscillate between two different flame structures, one that was more or less attached to the vortex funnel, and one that was lifted well above the vortex funnel. The MS case at φ = 0.65 was at the very edge of the lean flammability limit, and would on occasion extinguish.

Effect of Fuel Particle Size on the Stability of Swirl Stabilized Flame in a Gas Turbine Combustor

“…Before the lean blowoff, the flame tends to oscillate between extinction and reignition phases [25]. It is very similar to the large scale pulsations observed by other researchers in bluff body flame as well as in swirl stabilized combustor as lean blowoff was approached [26][27][28][29]. High heat loss and the presence of large trans verse and axial velocity gradients were believed to be the reasons.…”

Lean Blow-out Studies in a Swirl Stabilized Annular Gas Turbine Combustor

“…Hertzberg et al [26] also observed this kind of oscillation, and claimed that blow-out was a result of increased ignition times, longer re-circulation zones and local extinction resulting from high instantaneous strain rates. Hedman et al investigated blow-out in a swirl stabilized combustor and observed intense flame oscillations and temporary loss of flame near the lean blow-out [27]. CFD studies by Norton in micro-burners also observe periodic oscillations near extinction [28].…”

Observations of Flame Behavior in a Laboratory-Scale Pre-Mixed Natural Gas/Air Gas Turbine Combustor From LDA Velocity Measurements

“…The combustion facility used for this study is the same as that used by Hedman and coworkers [1][2][9][10][11]. Pyper [12] constructed the laboratory-scale gas turbine test facility, and assisted Warren and Hedman [11] in installing a single Stokes CARS (coherent anti-Stokes Raman Spectrometer) instrument.…”

“…This study was part of a series of laser-diagnostic experiments performed on a common combustion apparatus. Companion studies were performed to measure gas velocities using two-component laser Doppler anemometry (LDA) [3] and to obtain instantaneous planar laser induced fluorescence (PLIF) images of OH [1]. These data were obtained principally for evaluation of comprehensive gas turbine combustion models [4][5][6][7].…”