Numerical modelling of flame spread over thin circular ducts

Abstract: This paper presents a numerical investigation into the phenomenon of flame spread over thin circular ducts in normal gravity and microgravity environments. Flame spread over such geometry is of significant interest due to its relevance in various practical applications, including tubes for flow purpose in medical system, fire safety in spacecrafts, ducts as well as wiring tubes. This study comprises of a comprehensive investigation of key parameters affecting flame spread rate, including fuel radius and opposed flow speed in normal gravity and microgravity environments. A 2-D axisymmetric flame spread model accounted for char and numerical simulations were performed which revealed valuable insights into the underlying mechanisms governing flame spread over such geometry. The results computed from the numerical model is compared with the experimentally observed flame spread rate to validate the numerical model which can be used to gain a comprehensive understanding of the underlying physical phenomena. As the radius of circular duct increases the flame spread rate increases both in normal gravity and microgravity environments. The conduction heat feedback and radiation heat gain coming from hot char through gas phase at inner core region are the two major mechanisms which controls the flame spread phenomena over the circular duct fuels. The flame spread rate at different flow ranging from quiescent (0 cm/s) to 30 cm/s is also evaluated and 21 % oxygen and found a non-monotonic increasing decreasing trend of flame spread rate at different opposed flow speed in both normal gravity and microgravity environments.