Detonation cell size estimation via chemiluminescence imaging in an optically accessible linear detonation tube

An optically based experimental approach for estimating detonation cell size of premixed gas phase fuel–oxidizer mixtures in an optically accessible linear detonation tube is presented. Detonation wave fronts propagating through undiluted near-stoichiometric ethylene–oxygen mixtures in the circular detonation tube were visualized and recorded using CH* chemiluminescence imaging near 430 nm at 100 kHz for initial mixture pressures up to 22 kPa. The chemiluminescence imaging, coupled with high-speed videography, is shown to capture cellular detonation structures as small as 1.6 mm in width. The measured cell sizes increase as the initial fill pressure decreases, corroborating well-established relationships between detonation cell sizes and initial reactant pressures. The optically based method is validated against conventional soot foil measurements performed simultaneously with multiple detonations at various initial fill conditions. Both chemiluminescence images and soot foil measurements are compared to previously published cell size trends for undiluted fuel–oxygen detonations, demonstrating reasonable agreement with the established methods. Paired with the optically accessible detonation channel, the high-speed chemiluminescence imaging technique offers a passive estimation of detonation cell size for the range of conditions investigated with a faster experimental turnaround time relative to conventional methods.