Microgravity flame extinction induced by a moving air vortex ring

With the growth of outer space exploration missions, a safe, effective and clean fire extinguishing in microgravity spacecraft environment is critical. This paper explores the microgravity flame extinction dynamics induced by a moving air vortex ring. Tests were conducted both on the ground and in microgravity by a drop tower for comparison. An electromagnetic piston-tube system was designed to produce well-controlled air vortex ring to extinguish candle flames with different heat release rates (HRRs). We found a linear extinction boundary correlating the flame HRR with the Reynolds number and characteristic thickness of vortex ring. The flame extinguishing efficiency of air vortex ring in microgravity is 30 % higher than that on the ground. To explain the underlying mechanism, the flame stretch rate that accounts for the unsteady effect, i.e., the competition between external disturbance and flame self-stabilization, was examined. The absence of gravity and buoyancy has a minimum effect on the vortex ring but reduces the oxygen supply and flame diffusion, thereby the flame in microgravity is more vulnerable to vortex ring disturbance. The power of generating a vortex ring is 2–3 orders of magnitude lower than the HRR of flame that it can extinguish, and such a power requirement can be further reduced by 20–30 % in microgravity. This work reveals limiting conditions of vortex ring-induced flame extinction in microgravity and helps design future clean firefighting system for space travel.