In this article, flame spread phenomena over cylindrical fuel geometry are studied in spacecraft environments and contrasted with those on Earth. An in-house 2D axisymmetric computational fluid dynamics model is used to study the flame spread phenomena. Experimental flame spread results, in normal gravity and microgravity conditions, are used for model validation. The effect of uniform external opposed flow (0–25 cm/s) and surrounding oxygen concentrations (17.5–35%) is investigated in detail for a thin fuel rod of diameter 1 mm. The flow fields around the flame spreading in normal gravity and microgravity are very different. In normal gravity, buoyancy accelerates the flow and entrains surrounding air into the flame. In microgravity, the flow velocities increase only moderately due to thermal expansion. The change in the flow field results in significantly larger flames in microgravity, which spreads faster than the normal gravity flames. A detailed heat transfer analysis is carried out for the solid fuel. In general, the radial heat conduction of heat from the flame to fresh fuel ahead of the flame is the most prominent mode of heat transfer that controls the flame spread rate. However, in normal gravity conditions, near the low oxygen extinction limit, the contribution of axial heat conduction through the solid fuel also becomes significant and may contribute to about 20% of the total heat input to the fresh solid fuel. In normal gravity, the flame spread rate decreases with the increase in external flow speed. On the other hand, in microgravity, an increasing and decreasing trend in flame spread rate is observed with the increase in external flow speed. The flame spread rate increases with the increase in oxygen in normal gravity and microgravity environments.
Basavaraju et al. (Thu,) studied this question.