Schlieren visualization of detonation diffraction and initiation in B/C2H4/O2 heterogeneous mixtures using a variable-initial pressure pre-detonator tube

Solid powder detonation engines hold significant potential for enhancing aerospace propulsion performance, owing to the high volumetric energy density of solid fuels and the high thermal efficiency of the detonation cycle. These engines are typically ignited by a pre-detonator tube, and the initiation characteristics of the heterogeneous mixtures directly determine their reliable start-up. However, current studies on detonation wave diffraction and initiation have primarily focused on homogeneous detonations, while the discrete nature of powder fuels results in significant differences in heterogeneous systems. To investigate the initiation characteristics of B/C 2 H 4 /O 2 gas–solid two-phase hybrid detonations ignited by a pressure-variable pre-detonator tube, this study therefore conducted experiments in an in-house detonation bomb with schlieren visualization. Results show that the heterogeneous nature of powder fuels enables re-initiation far from the expansion cone and tube axis, fundamentally differing from gaseous detonations, which are confined within the expansion cone. Moreover, compared with gaseous detonation ( φ C 2 H 4 = 0.6), the slight addition of boron particles ( φ C 2 H 4 = 0.6, φ b o r o n = 0.1) can reduce the detonation onset difficulty, whereas an excessive particle concentration ( φ C 2 H 4 = 0.6, φ b o r o n = 0.7) hinders it. Furthermore, as the initial ambient pressure inside the detonation bomb increases from 48 kPa to 96 kPa, the initiation difficulty of the B/C 2 H 4 /O 2 mixture decreases, and the distance from the tube outlet to the re-initiation location also shortens from 91.8 mm to 39.35 mm. These findings provide a theoretical basis for the reliable onset of powder-fueled detonation engines and contribute to a deeper understanding of gas–solid two-phase hybrid detonation initiation.