Experimental study of DDT run-up distance and detonation wave velocity deficit for stoichiometric hydrogen-oxygen mixture in micro spiral channels

Abstract

The determination of the deflagration-to-detonation transition (DDT) run-up distance LDDT is crucial in both the design of pulse detonation engines (PDEs) and safety protection. In this paper, the LDDT of stoichiometric hydrogen–oxygen premixed mixtures in millimeter-scale spiral channels were studied experimentally and high-speed photography was employed to capture the flame propagation process. The mixtures in three different rectangular cross-sectional channel widths and various initial pressures were tested. The present results show that the LDDT decreases with increasing the initial pressure, and with increasing the channel width, the larger LDDT is observed. When fitted with the LDDT ∝ P0−m relationship, the values of m obtained in this study ranged from 0.997 to 4.222. The critical value of 0.1 for the equivalent area divergence induced by the boundary layer ξ is proposed to distinguish the behaviors between micro and macro channels, regardless of the type of mixture and channel configuration. Additionally, an empirical formula considering the influence of the boundary layer is obtained, which allows for the quantitative prediction of LDDT. Because of the influence of curvature effect, the smaller the channel width, the greater the prediction deviation. Due to the boundary layer effect, the momentum and heat dissipation are more pronounced in smaller tubes, resulting in a loss of velocity for the detonation wave. It is suggested that the detonation wave velocity increases as the channel width and initial pressure increase. Fay's model was employed to estimate the theoretical velocity deficit, and the experimental results were in good agreement with the theoretical predictions. The current findings are valuable for the field of micro PDE and may help the assessment of the potential risk of hydrogen detonation in micro systems.