Influence of equivalence ratio on flame acceleration and detonation transition of ethylene/oxygen mixture in a narrow channel

High-speed schlieren and chemiluminescence visualizations were utilized to resolve the influence of equivalence ratio () on the evolvements of reaction and shock waves in a transparent channel filled with ethylene/oxygen mixtures initially at ambient temperature and pressure. Equivalence ratios of the mixtures ranged from 0.5 to 1.6. Cross-section of the square channel was 1 mm × 1 mm, and the total length was 730 mm. Reaction propagation in = 0.5 mixture terminated with low-speed detonation, while the reaction fronts in other cases eventually propagate at near Chapman-Jouguet velocities. The timings of leading shock formation, shock cluster formation as well as detonation transition were the earliest in the = 1.3 mixture. Leading shock velocity and peak acceleration rate of reaction front were the highest for the mixture. Schlieren visualizations also showed that the shock cluster structures, emerged when the reaction wave propagating velocity exceeds 1100 m/s and before detonation transition, are identical to the pattern of a low-speed detonation wave front.