Experimental research on detonation impulse measurements in micro-scale smooth tubes using a ballistic pendulum

In order to research on the possibility of using micro-scale detonation for space propulsion and energy utilization, the detonation impulse/specific impulse of ethylene-oxygen mixtures in micro-scale tubes with a length of 1 m and various inner diameters (4~10 mm) under different equivalence ratios were measured for the first time using a ballistic pendulum. The measured impulses were compared and validated with Wintenberger's analytical model which is based on direct detonation initiation. The results show that, the deflagration to detonation transition (DDT) distance had a major effect on impulse. As the DDT distance shortened, the impulse became greater. The maximum impulse occurred at the equivalence ratio of 1.4 for all different tubes under the current experimental condition. The impulses calculated by the analytical model were in good agreement with the experimental values as long as the DDT effect was ignored. On the other hand, the detonation impulse was proportional to the tube inner diameter. However, smaller inner diameter could reduce the deviation of the impulses among different equivalence ratios.