Detonation Cell Size Estimation via Chemiluminescence Imaging in an Optically-Accessible Linear Detonation Tube

An experimental approach for estimating detonation cell size for gas phase fuel-oxidizer mixtures in an optically-accessible linear detonation tube is presented. Detonation wave fronts of ethylene-oxygen mixtures propagating through the circular channel of the detonation tube were visualized and recorded using CH* chemiluminescence imaging near 430 nm. Chemiluminescence imaging, coupled with high-speed videography capabilities, is shown to obtain time-averaged size and shape of the detonation wave structure. The measured cell sizes increase as the initial fill pressure decreases, corroborating long-known relationships between detonation cell sizes and initial reactant pressures. The nonintrusive method is validated against conventional soot foil measurements performed simultaneously with multiple detonations at various initial pressure conditions. Both chemiluminescence images and soot foil measurements are compared to previously known cell size trends for the ignited fuel-oxidizer mixtures. Paired with the optically-accessible detonation channel, the chemiluminescence technique offers a nonintrusive estimation of detonation cell size with a faster experimental turnaround time relative to conventional methods.