On the Adequacy of Chemiluminescence as a Measure for Heat Release in Turbulent Flames With Mixture Gradients

Abstract

The determination of the heat release in technical flames is commonly done via bandpass filtered chemiluminescence measurements in the wavelength range of OH∗ or CH∗ radicals, which are supposed to be a measure for the heat release rate. However, these indirect heat release measurements are problematic because the measured intensities are the superposition of the desired radical emissions and contributions from the broadband emissions of CO2∗. Furthermore, the chemiluminescence intensities are strongly affected by the local air excess ratio of the flame and the turbulence intensity in the reaction zone. To investigate the influence of these effects on the applicability of chemiluminescence as a measure for the heat release rate in turbulent flames with mixture gradients, a reference method is used, which is based on the first law of thermodynamics. It is shown that although the integral heat release can be correlated with the integral chemiluminescence intensities, the heat release distribution is not properly represented by any signal from OH∗ or CH∗. No reliable information about the spatially resolved heat release can be obtained from chemiluminescence measurements in flames with mixture gradients.

A numerical study on the ability to predict the heat release rate using CH* chemiluminescence in non-sooting counterflow diffusion flames

“…As a result, in particular from a practical application point of view, total chemiluminescence information would be a more convenient and realistic method to diagnose the total heat release rate status in practical combustors system. Therefore, in the following section, based on Lauer et al [16], the applicability of total chemiluminescence, emitted by CH*, to predict the total heat release rate of flames is examined.…”

Impact of the heat release distribution on high-frequency transverse thermoacoustic driving in premixed swirl flames

“…It is known that OH*-chemiluminescence is not strictly proportional to the heat release, but OH*-chemiluminescence correlates with the heat release in turbulent premixed systems. 13 …”

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

“…Recording the natural emission from the flame is the simplest diagnostic yielding time-resolved estimates of heat release rate fluctuations [4,5]. Effects of the turbulence intensity, strain rate, flame front curvature, mixture composition, temperature and pressure need however to be included to obtain quantitative heat release rate data [6][7][8][9][10][11][12][13][14]. These studies stress out the need of alternative techniques to measure heat release rate disturbances.…”