Research On Influence Of Flowing Characteristics Of Pyrolysis Gas On Pyrolysis And Ignition Process Of Charring Materials

The process of pyrolysis and ignition of combustible solid are an important stage for the occurrence and growth of fire. The process is also a complex physical and chemistry, containing every aspect of thermal dynamics: radiation, convection, conduction and mass transfer. The pyrolysis and ignition of charring materials heat radiation is a major subject which the numerous scholars research on. In the process, two key factors are concentration of combustible gas and temperature (or other energies, e. g. pilot), in which the concentration is affected by several factors, for example external radiation and density of solid. However, in some special conditions, for example the low ambient pressure environment, the flow characteristics of pyrolysis gas is different from the one in the normal condition; furthermore, the rule of pyrolysis process of solid to have the change. Researcher before in field of this, the research work is not deep enough and sufficient. In addition, the research on the pyrolysis and ignition of charring material by the majority of researchers before supposes the heating surface of solid horizontal and the radiation heat flow vertical downward, but in actual fire process, many other typical operating modes, for example solid heating surface vertical, receives the horizontal incident heat flow, this kind of operating mode is similar with the construction fire the wall surface combustible substance receives the situation which outside other heat source (for example: flame) radiates.The present article analyzed the pyrolysis and ignition of charring materials under radiation in different ambient pressure condition and under the different radiation orientation experimentally and theoretically. The flowing characteristics of pyrolysis gas under the different condition have been conducted deep analysis and the discussion.According to the contrastive experiment in Hefei and Lhasa, the pyrolysis and ignition characteristics of wood under radiation at different altitude have been obtained. The mass loss rate, surface temperature and ignition time have been measured during experiment. It is observed that the mass loss rate is higher, the surface temperature before ignition is higher and the ignition time is shorter in the environment of low pressure and oxygen of Lhasa. It is analyzed that the low pressure benefits the releasing of combustible gas, which can easily reach to a critical condition. It is concluded that the occurrence of ignition of wood is easier in low pressure condition. The surface temperatures at the moment of ignition are the same in the two places.Pyrolysis and ignition of wood under horizontal and vertical radiation has been conducted with experimental method. Under the horizontal radiation, the mass loss rate and surface temperature are both higher than the one under vertical radiation, and the ignition time with pilot is shorter. The absorption of external radiation by pyrolysis gas is the factor causing the difference under the two conditions.The absorption of radiation by pyrolysis gases under horizontal and vertical radiation are different, according which and former model by researcher before, a model considering the influence of pyrolysis gas flowing on the boundary condition has been developed. The experiment data validated the accuracy of model. The difference between model and experiment has been analyzed.