Fire Inception in Microgravity: Orbital Experiment BRE-Flamenco Onboard the International Space Station, 2019-2021

A possible scenario of fire inception in microgravity is ignition and burning of solid or liquid materials followed by the flame growth and spread. In this scenario, as well as in normal gravity, flammability of the material is directly coupled with the stability of gaseous flame. Until recently, transient dynamics and stability of the low momentum diffusion flames emanating at the flat surface into the stagnant atmosphere in microgravity has not been investigated. To date, we even could not predict whether this kind of flame can attain its steady state. This poster presents an overview of the orbital experiment BRE-Flamenco performed onboard the International Space Station in 2019-2021, jointly with the theoretical and numerical analysis of the experimental results.

The key findings of this work disclose the major effects of the reduced gravity on laminar diffusion flames, including dramatic increase of the radiative fraction in the energy balance casing flame extinction. This flame extinction is identified as the radiative one, which is opposed to the strain-induced blow-off occurring in normal gravity. The flame is shown to be inherently unstable: the initial phase of steady flame growth is interrupted by local flame extinction followed by flame oscillations (of toroidal, spiral, capuchin type) and complete extinguishment. It has been established, that a steady flame can only exist at high oxygen concentration and low fuel supply rate (characteristic of solid or liquid combustibles), and the critical condition for the steady flame to exist has been proposed. Approximate theory developed in this work is shown to predict the critical pre-extinction flame size, while the transient flame dynamics including formation of triple flames is favorably replicated in detailed CFD simulations.