Document Type
Article
Publication Date
7-1-2025
Abstract
The SoFIE-GEL (Solid Fuel Ignition and Extinction-Growth and Extinction Limit) microgravity combustion experiment was recently conducted aboard the International Space Station (ISS). In these tests, diffusion flame extinction limits of 4-cm diameter PMMA (polymethacrylate) spheres were determined as a function of forced flows (0.2 to 80 cm/s), oxygen concentrations (13 % to 34 %) and pressure (0.15–1.1 atm). In particular, the effect of sample heat-up is investigated. The sample surface layer is preheated by the ignitor and the diffusion flame itself before the extinction procedure (e.g. flow velocity decrease or increase or oxygen decrease) is implemented. The degree of sample heat-up is inversely related to the gas flame heat loss to the solid which is quantified by embedded thermocouples inside the sample sphere near the flow forward stagnation point. This region controls the flame extinction process. In this paper, the extinction boundary in one atmosphere is presented in a map using oxygen percent and flow velocity (and stagnation flow strain rate) as coordinates. The oxygen-velocity (strain rate) boundary is a truncated U-shaped band when plotted with a log x axis. The data at high flow velocity (80 cm/s) is truncated because of the limitation of the test facility. The boundary contains data with different degrees of sample preheating inside the band. More preheat widens the flammable domain. Two modes of extinction are distinguished: quenching at low flow speeds or small stagnation flow strain rates, stagnation and wake blowoffs at high flow velocities or high flow strain rates. Merging between the two branches occurs at a flow strain rate of 7.5 s−1. The minimum oxygen percentage is slightly <14 %. This long duration, remotely controlled microgravity experiment enables us to study the effect of purely forced flow on the burning of bulk solids, especially in the low velocity regime, not easily achievable in normal gravity. In total, 7 hours of microgravity PMMA burning time is recorded. Several examples from recorded test runs are shown to illustrate the special features of the experiment.
Keywords
low oxygen limits, microgravity, preheating, quenching and blowoff, solid fuel extinction
Language
English
Publication Title
Combustion and Flame
Grant
80NSSC23M0035
Rights
© 2025 The Authors. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/), which permits non-commercial copying and redistribution of the material in any medium or format, provided the original work is not changed in any way and is properly cited.
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
James, S., Li, C., Ferkul, P. V., Olson, S. L., & Johnston, M. C. (2025). Experimental determination of diffusion flame extinction boundaries over a PMMA sphere: The effect of sub-surface solid heating. Combustion and Flame, 277, 114244.
Manuscript Version
Final Publisher Version