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

Abstract

Imaging of OH* or CH* chemiluminescence with intensified cameras is often employed for the determination of heat release in premixed flames. Proportionalitx is commonly assumed, hut 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 peiformed 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.1.2 Purpose of the Study. The nonlinear influence of turbulence on chemiluminescence intensities has to be considered to Journal of Engineering for Gas Turbines and Power

On the Use of OH* Radiation as a Marker for the Heat Release Rate in High-Pressure Hydrogen Liquid Rocket Combustion

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“…2 This theoretically defined quantity is difficult to obtain in experiments. 3 Especially under the harsh conditions in realistic liquid rocket demonstrators, where access to the combustion chamber is limited, the direct determination of the volumetric heat release rate is practically impossible.…”

Analysis of chemiluminescence, density and heat release rate fluctuations in acoustically perturbed laminar premixed flames

“…These studies stress out the need of alternative techniques to measure heat release rate disturbances. Measurements are then often limited to flame images for qualitative analysis except in a few studies where the signal is calibrated using specific post-processing procedures to map the heat release rate on two-dimensional images [15,16]. Another limitation is that the chemiluminescence emission yields a signal integrated in the line-of-sight and it is difficult to obtain spatially resolved data without additional hypothesis on the system symmetry.…”

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