Single-Shot Temperature Measurements in a Scramjet Combustor Using Thermally Assisted Laser-Induced Fluorescence

The knowledge of the temperature in the flowfield of the scramjet is critical to the understanding of its performance. This study represents the application of an optical diagnostic technique, thermally assisted laser-induced fluorescence, to the temperature measurements in the combustor of a supersonic combustion engine. The experiments were conducted in the T4 shock tunnel using a scramjet model. Experimental data were obtained by focusing a laser beam into the combustor and exciting the OH radical. A detailed numerical model that simulates all radiative and collisional processes of relevance with the appropriate system of differential equations was developed for the analysis of the influence of energy transfer processes on the fluorescence signal. The population distributions achieved with numerical modeling of the LIF process validated the approach proposed to deduce temperatures. By evaluating the scramjet LIF spectra with a full spectral fit, a temperature distribution across the combustor width was obtained. The experimental results were compared with the computational fluid dynamics simulations of the combustion process.