Enhancement of ethylene-air continuous rotating detonation in the cavity-based annular combustor

Abstract

To investigate enhancement effects of cavity on continuous rotating detonation (CRD), extensive ethylene-air CRD tests are conducted in the cavity-based annular combustor. By varying the length-to-depth ratio (L/D) of cavity, five modes are distinguished and classified into three operating zones, I: Excessive Impact (deflagration and sawtooth wave); II: Proper Impact (single wave and co-rotating two-wave); III: Deficient Impact (counter-rotating two-wave). In the cavities with small L/D in zone I, excessive deflagration could inhibit the accumulation of combustible mixture, making detonation degenerate into deflagration. While the cavities with proper L/D in zone II could intensify CRD, resulting in a propagation mode transformation from counter-rotating two-wave to co-rotating mode. The added circumferential contact surface between the cavity-stabilized flame and combustible mixture is a key factor of cavity enhancement, which can pre-heat combustible mixture and reduce the detonation inducing time. Through the distribution of chemiluminescence intensity ratio, the intensity ratio peaks of deflagration and detonation are estimated to be in 40-50 mm and 20-30 mm downstream from the inlet respectively, indicating that detonation with proper cavities is accomplished in shorter distance. Overall, L/D=5.5 with the depth of 20 mm may be an optimized selection based on the evaluations of mode, reaction zone, and pressure.