Quantitative measurement of soot volume fraction using LII behind an aeroengine flame stabilizer in an atmospheric pressure model test rig

This study addresses the complexities of measuring the soot volume fraction in large combustion chambers of aeroengines, where achieving uniform saturation excitation and mitigating intense background light interference are necessary for accurately determining two-dimensional distributions—a critical aspect for optimizing engine design. We present an advanced laser-induced incandescence (LII) method specifically developed for aeroengine afterburners. This method incorporates a total-reflection-based beam-homogenizing cavity to ensure uniform laser energy distribution across the measurement area. By calculating the threshold laser fluence for two-dimensional saturation excitation, our approach minimizes laser absorption and path integral effects, achieving uniform saturation excitation. A 1000 mm focusing mirror is used to maintain a consistent light-sheet thickness. Our LII system was calibrated in situ, showing 95% consistency and enabling the use of single-band LII signals to capture precise two-dimensional soot volume fraction distributions. To counteract intense background interference, filtering algorithms were applied to the LII images, resulting in a high signal-to-noise ratio of 78.3 dB. Our analysis provides crucial insights into how the overall and axial distributions of soot volume fraction in recirculation areas correlate with global equivalence ratios and incoming air flow rates, offering critical data for enhancing combustion efficiency and reducing emissions.