Flame spread studies over solid fuel have gained importance from decades and has been ongoing research for many investigators because of its importance in fire safety applications. Fire safety concern plays important role in both, normal gravity and microgravity environments due to increasing manned mission program in space. This work presents experimental study on opposed flow flame spread over thin hollow cylindrical cellulosic fuel of diameters varying from 10 mm to 49 mm in normal gravity and microgravity environment. To understand the effect of flow and geometry on flame spread, experiments are conducted in low convective opposed flow conditions ranging from 10 cm/s to 30 cm/s for both hollow cylindrical and planar fuels in normal gravity and microgravity at oxygen concentration of 21% and 1 atm pressure. All the microgravity test were conducted using the 2.5 s drop tower available at the National Centre for Combustion Research and Development (NCCRD), IIT Madras, India. A simplified analysis is also carried out to arrive at an expression for flame spread rate over thin hollow cylindrical fuels.

An inhouse axisymmetric numerical model is also modified to understand the physical phenomena of flame spread over hollow cylindrical geometry. The gas phase is described by two dimensional governing equations comprising of full Navier-Stroke equations for laminar flow as well as mass, energy and species conservation equations. For thin solid fuel, continuity equation and two-dimensional energy equation along with pyrolysis of solid fuel is implemented. A single step second order finite rate Arrhenius reaction between oxygen and fuel vapor is assumed. The fuel is assumed as thermally thin which implies the temperature across the thickness of fuel is remains constant.