The propagation behavior of high-speed divergent deflagrations in a thin gap chamber

Abstract

Investigating the combustion characteristics of fuel mixtures in thin channels enhances the understanding of the combustion process and safety in various applications. Previous studies of flame propagation behavior in thin gap chambers focused on low-speed flames and detonations, with a lack of research on high-speed deflagrations with flame propagation velocity (FPV) of hundreds of meters per second. This study investigated the propagation behavior of such high-speed divergent deflagration in a thin gap chamber by using a stoichiometric ethylene–oxygen mixture. FPV fluctuations during the propagation were observed for the first time. The effects of the initial pressure (6–20 kPa) and the chamber radius (60 mm, 75 mm, 90 mm) were analyzed. The results show that higher initial pressures amplify FPV fluctuations, increase the maximum FPV, and enhance flame front wrinkling, while smaller chamber radii shift fluctuation positions earlier in time and absolute position. The relative position of the critical FPV deceleration point in the first fluctuation in the near-wall stage exponentially converges to 0.825 as pressure increases, independent of the chamber radius. Key mechanisms for FPV fluctuations in the two propagation stages were identified: 1) In the initial FPV fluctuation stage, reflected pressure waves from the chamber wall interact with the flame front, reversing local flow and causing deceleration. 2) In the near-wall fluctuation stage, competition between outward deflagration propagation and pressurization of unburned gas leads to cyclic acceleration-deceleration patterns, including temporary contraction. These findings provide fresh insights into the behavior of high-speed deflagrations in thin chambers and have practical significance for combustion system design and safety measures.