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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

# Spatial Analysis on Forced Heat Release Response of Turbulent Stratified Flames

[+] Author and Article Information
Zhiyi Han

Department of Engineering,
University of Cambridge,
Trumpington Street,
Cambridge CB2 1PZ, UK
e-mail: zh253@cam.ac.uk

Saravanan Balusamy, Simone Hochgreb

Department of Engineering,
University of Cambridge,
Trumpington Street,
Cambridge CB2 1PZ, UK

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 18, 2014; final manuscript received August 19, 2014; published online December 9, 2014. Assoc. Editor: Song-Charng Kong.

J. Eng. Gas Turbines Power 137(6), 061504 (Jun 01, 2015) (8 pages) Paper No: GTP-14-1410; doi: 10.1115/1.4029056 History: Received July 18, 2014; Revised August 19, 2014; Online December 09, 2014

## Abstract

The local equivalence ratio distribution in a flame affects its shape and response under velocity perturbations. The forced heat release response of stratified lean-premixed flames to acoustic velocity fluctuations is investigated via chemiluminescence measurements and spatial Fourier transfer analysis. A laboratory scale burner and its boundary conditions were designed to generate high-amplitude acoustic velocity fluctuations in flames. These flames are subject to inlet radial equivalence ratio distributions created via a split annular fuel delivery system outfitted with a swirling stabilizer. Simultaneous measurements on the oscillations of inlet velocity and heat release rate were carried out via a two-microphone technique and OH* chemiluminescence. The measurements show that, for a given mean total power and equivalence ratio ($φg=0.60$), the flame responses vary significantly on the equivalence ratio split, forcing frequency, and velocity fluctuation amplitude, with significant nonlinearities with respect to forcing amplitude and stratification ratio (SR). The spatial Fourier transfer analysis shows how the dependence is affected by the underlying changes in the rate of heat release, including the direction and speed of the perturbation within the flame.

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## Figures

Fig. 1

Schematic of the stratified swirl burner. Dimensions in millimeters, not to scale. Centerbody diameter Dc = 6.35 mm, inner tube diameter Di = 155 mm, outer tube Do = 26.64 mm, and quartz tube Dqt = 94.00 mm. Area ratio of inner channel to outer channel, Ai/Ao = 0.512.

Fig. 2

CH* and OH* chemiluminescence emission intensity versus input power for uniformly premixed and stratified combustion. Lines for SR = 1.0 and 0.5 overlap. Dashed lines show the operating points for velocities of 5 and 10 m/s, respectively.

Fig. 3

Time-averaged OH* chemiluminescence images (top half of each figure) and Abel-deconvoluted, radius-weighted OH* chemiluminescence images (bottom), for different SR = 1.0, 0.5, and 2.0. The color scales are self-normalized. Inlet conditions: SR = 1.0, 0.5, and 2.0, U = 5 and 10 m/s, φg=0.60, TI = 20 ± 2 °C, PI = 1 ± 0.02 bar. (a) SR = 1.0, U = 5, (b) SR = 0.5, U = 5, (c) SR = 2.0, U = 5, (d) SR = 1.0, U = 10, (e) SR = 0.5, U = 10, and (f) SR = 2.0, U = 10.

Fig. 4

Flame transfer function of premixed and stratified flame: gain (a) and phase difference in multiples of π (b). SR = 1.0, 0.5, and 2.0, U = 5 and 10 m/s, φg=0.60, Ti = 20 ± 2 °C, and pi = 1 ± 0.02 bar.

Fig. 5

Normalized heat release response as a function of forcing amplitude at forcing frequencies of 60, 160, and 380 Hz. SR = 1.0 (top), 0.5 (middle), and 2.0 (bottom), φg=0.60, Ti = 20 ± 2 °C, pi = 1 ± 0.02 bar. (a) U = 5 m/s and (b) U = 10 m/s.

Fig. 6

High speed image FFT of OH* chemiluminescence. Each image set contains the magnitude (top) the FFT intensities, normalized to the overall FFT peak, and the phase (bottom), in multiples of π. Columns (a)–(c) obtained for 5 m/s, column (d) for 10 m/s. Inlet conditions: φg=0.60, Ti = 20 ± 2 °C, and pi = 1 ± 0.02 bar.

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