Determination of the heat release distribution in turbulent flames by chemiluminescence imaging

Imaging of OH or CH chemiluminescence with intensified cameras is often used for the determination of heat release in turbulent flames. Proportionality is commonly assumed, but was never proven. This study investigates which information about turbulent flame heat release rate can be obtained from chemiluminescence. It is found that although the integral heat release rate can be obtained from the integral chemiluminescence intensity, no information about the local heat release rate is provided by chemiluminescence due to turbulence-chemistry interactions. A model based correction method is introduced 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, and is linked with one-dimensional simulations of strained counterflow flames. In this way the non-linear effect of turbulence on chemiluminescence intensities and heat release rate is taken into account and corrected, heat release rate proportional OH intensities are obtained. 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.