Investigation on ignition and flame propagation of pyrolyzing fuel in a cylindrical combustor is accomplished. The pyrolyzing fuel of cylindrical shape is concentrically located in a combustor sustained at high temperature. Due to gravity, the buoyancy motion is inevitably incurred in the combustor and this affects the flame initiation and propagation behavior. The radiative heat transfer due to absorption gas plays an important role since it absorbs and emits radiative energy. Numerical studies have been performed over various parameters relevant to gas radiation as well as overheat ratios. The ignition criterion is decided on experimental basis. For the case of relatively small overheat ratio, the gas absorption reduces the flow intensity by the far-reaching effect of radiation. Visible blue flame hence does not evolve. For a high overheat ratio, the strong visible blue flame is generated and self-propagates. The gas radiation makes the considerable effect on ignition delay and flame thickness as well as thermal and reactive nature of visible blue flame. (C) 2004 Elsevier Ltd. All rights reserved.