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

Determination of the Heat Release Distribution in Turbulent Flames by a Model Based Correction of OH* Chemiluminescence

[+] Author and Article Information
Martin Lauer

Lehrstuhl für Thermodynamik, Technische Universität München, Boltzmannstraße 15, 85748 Garching, Germanylauer@td.mw.tum.de

Mathieu Zellhuber, Thomas Sattelmayer

Lehrstuhl für Thermodynamik, Technische Universität München, Boltzmannstraße 15, 85748 Garching, Germany

Christopher J. Aul

Department of Mechanical Engineering, Texas A&M University, 3123 TAMU, College Station, TX 77843

1 Also other criteria for the macroscopic isotropy of the turbulence, like $〈uiui〉t=〈ujuj〉t, i≠j$ and the independence of the integral length scale on direction, have been checked with comparable results and conclusions.

2 First published in Russian in Kolmogorov, A.,1941, Dokl. Akad. Nauk SSSR, 30 (4).

3 In a detailed study Bradley et al.  found that the strain rate distributions show a continuous transition between the distributions of randomly oriented and material surfaces, depending on the ratio of Kolmogorov velocity and laminar flame speed. They defined empirical exponential forms for $〈a〉$ and $σa$ to take this transition into account [32]. Since in the present study the condition $νη>ul$ is clearly satisfied, the simpler relationship defined by Yeung et al.  [18] is used.

J. Eng. Gas Turbines Power 133(12), 121501 (Sep 01, 2011) (8 pages) doi:10.1115/1.4004124 History: Received April 09, 2011; Revised April 12, 2011; Published September 01, 2011; Online September 01, 2011

Abstract

Imaging of OH* or CH* chemiluminescence with intensified cameras is often employed for the determination of heat release in premixed flames. Proportionality is commonly assumed, but in the turbulent case this assumption is not justified. Substantial deviations from proportionality are observed, which are due to turbulence-chemistry interactions. In this study a model based correction method is presented to obtain a better approximation of the spatially resolved heat release rate of lean turbulent flames from OH* measurements. The correction method uses a statistical strain rate model to account for the turbulence influence. The strain rate model is evaluated with time-resolved velocity measurements of the turbulent flow. Additionally, one-dimensional simulations of strained counterflow flames are performed to consider the nonlinear effect of turbulence on chemiluminescence intensities. A detailed reaction mechanism, which includes all relevant chemiluminescence reactions and deactivation processes, is used. The result of the simulations is a lookup table of the ratio between heat release rate and OH* intensity with strain rate as parameter. This lookup table is linked with the statistical strain rate model to obtain a correction factor which accounts for the nonlinear relationships between OH* intensity, heat release rate, and strain rate. The factor is then used to correct measured OH* intensities to obtain the local heat release rate. The corrected intensities are compared to heat release distributions which are measured with an alternative method. For all investigated flames in the lean, partially premixed regime the corrected OH* intensities are in very good agreement with the heat release rate distributions of the flames.

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Figures

Figure 1

Left hand side: Sketch of the test rig. Right hand side: Typical axial equivalence ratio profile due to ambient air entrainment [7].

Figure 2

Typical chemiluminescence spectrum of an atmospheric, turbulent methane-air flame. The dashed lines is an approximation for the broadband emission from CO2*. The dotted line is the transmission curve of a typical OH* filter. The gray area represents the desired measurement signal.

Figure 3

Measured two-point correlation, fitted with the exponential function defined in Eq. 3 and the determined integral length scale

Figure 4

Energetic sketch of a finite flame volume. The heat losses are negligible in this study [26].

Figure 5

Comparison of the time-averaged product of the radial and axial component of the velocity fluctuation (right hand side) with 〈ux'2〉 t (left hand side)

Figure 6

Sketch of the two-point correlation function and the parabola defining the Taylor length scale

Figure 7

Comparison of the Kolmogorov velocity vη (left hand side) and the laminar flame speed ul (right hand side). Since the laminar flame speed is obtained from chemiluminescence measurements, it can be determined only in regions where chemiluminescence is emitted, whereas the Kolmogorov velocity, determined from PIV measurements, can be calculated in the complete flame midplane.

Figure 8

Result of the intensity correction procedure for the φ=0.67 operation point. In the upper part the local heat release rate, the measured OH* intensities, and the corrected OH* intensities are shown. The lower part shows the corresponding axial profiles.

Errata

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