Scalar measurements in a flickering flame using high-speed rainbow schlieren deflectometry

Abstract

Rainbow schlieren apparatus was integrated with a high-speed digital imaging system to quantify the scalar structure of steady and flickering jet diffusion flames of gaseous hydrogen. The rainbow schlieren technique utilizes a continuously graded color filter placed at the focal point of the decollimating lens to quantify the transverse displacement of light rays passing through the media. Excellent agreement was reached between steady flame shapes determined from the schlieren technique and direct visualization. For the flickering flame at jet exit Reynolds number of 300, the rainbow schlieren images were taken at acquisition rates of up to 1000 frames per second. The image data were analyzed to determine full-field distributions of refractive index, and hence, temperature and oxygen concentration assuming chemical equilibrium in the flame. The contour plots of instantaneous temperature and oxygen concentration are shown to quantitatively describe the flow structure during a flicker cycle. Results show that the capability to quantitatively describe the temporal evolution of the temperature field is greatly improved by using the high-speed imaging system.