Ignition of the solid fuel in a confined rectangular enclosure was numerically studied for the two dimensional unsteady natural convective case by taking account of non-participating radiation. The pressure field was evaluated using a compressible form of the SIMPLER algorithm, while QUICK scheme was adopted for finite difference formulation of the convective term. Radiation exchange was calculated by direct matrix inversion.
The flow field was strongly governed by the radiation. In particular, the rapid heating of the adiabatic floor due to radiation made the flow therein unstable, and the very complicated fluid motion was incurred during the initial period. As a result of this effect, the fluid dynamic and thermal fields were developed very fast. Radiation was found to reduce the heating time required for the pyrolysis of solid fuel.
The volatile gas pyrolyzing from the solid fuel was mixed by convection and diffusion, and then ignited at any position where an appropriate thermal condition was satisfied. The ignition phenomenon was found to be controlled by such mechanisms as the heating and pyrolysis of solid fuel, the convection and diffusion characteristics of fuel and oxidizer, and gas phase heating process. In case that the hot wall temperature was lower than 900K, no ignition occurred. On the other hand, the hot wall temperature ranged between 950K ~ 1100K, the ignition was controlled by the mixing of fuel and oxidizer, and occurred in the hot wall boundary layer. It was also observed that the thermally controlled ignition took place in vicinity of the adiabatic ceiling when the hot wall temperature was higher than 1100K.
