microgravity diffusion flames spreading over a thick solid fuel in low-velocity flows
- Paper number
IAC-17,A2,3,11,x38095
- Author
Prof. Shuang-Feng Wang, NML, Institute of Mechanics, Chinese Academy of Sciences, China
- Coauthor
Ms. Feng Zhu, NML, Institute of Mechanics, Chinese Academy of Sciences, China
- Year
2017
- Abstract
The problem of flame spread over solid fuel in microgravity is practically important for fire safety in spacecraft. With few exceptions, however, research on microgravity flame spread has been focused on thermally thin fuels due to the constraint on available test time. In this paper, experimental results for flame behaviors over thick PMMA in microgravity are reported. The microgravity experiments were conducted aboard the SJ-10 satellite of China in 2016. Oxygen concentrations for the four tests were 40\%, 35\%, 30\%, and 25\%, respectively. The ignition of each test sample resulted in a diffusion flame opposing the flow, and the flame spread was observed when the flow velocity was decreased from 9 cm/s to 6 cm/s, then to 3 cm/s, and at last to 0. For the thermally-thick fuel, the entire flame spread and extinction processes in low-speed gas flow are revealed by the present microgravity experiments. Particularly, flame behaviors in response to a step change of flow velocity are analyzed. At high oxygen concentration with high flow speed, uniform flame can sustain, while at lower oxygen concentration and flow speed, only flamelet can survive. When the flow velocity is slowed down, flame keeps uniform or flamelet, and it can adapt to a new environment within 1 s. As a uniform flame shrinks into flamelet or flamelet goes to extinction, visible flame standoff distance and flame position vary dynamically, and the process lasts several tens of seconds. It is found that, for steady flame spread, gas conductive heat flux and solid in-depth conduction increase with flame spread rate, while surface radiative flux keeps constant. When the flame breaks into flamelet, gas conductive heat flux oscillates with time. Before extinction, flamelet standoff distance oscillates with increasing amplitude, and heat loss ratio almost reaches 100\%.
- Abstract document
- Manuscript document
(absent)