An unsteady one-dimensional model for the solid phase is applied to simulate the spontaneous ignition and burning of thick wood samples with grain orientation parallel or perpendicular to incident heat fluxes in the range 18–40 kW/m², that is, in the absence of flame. The description of heat and mass transfer processes, at constant gas pressure, is combined with global volumetric rates of wood decomposition and char oxidation. Surface regression occurs for a limit value of char density while a critical surface temperature describes ignition. Good quantitative predictions are obtained for the ignition times and the surface temperature and mass loss rate profiles during burning. Conversion always consists of three main stages. The first short transients correspond to the formation of a relatively thin charred surface layer and glowing ignition. The second much longer stage represents a pseudo-steady-state burning, where the rates of advancement of the decomposition and oxidation zones are approximately constant as well as the surface temperature and the global rate of mass loss. Finally, the last short stage, resulting from the adiabatic bottom condition, is the enlargement of the decomposition zone to the entire sample. The first transient stage and the ignition times are noticeably affected by the external heating conditions whereas the characteristics of the pseudo-steady-state burning are mainly dependent on the char oxidation rate, which is controlled by the oxygen diffusion rate.

中文翻译：

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木材点火和燃烧固相模型的实验验证

应用固相的非稳态一维模型来模拟厚木样品的自发着火和燃烧，其颗粒取向平行于或垂直于入射热通量，范围为18-40 kW / m ^2。即没有火焰。对在恒定气压下的传热和传质过程的描述与木材分解和炭氧化的总体体积速率结合在一起。当炭表面密度极限值描述着火时，表面退化发生在炭黑密度的极限值上。对于燃烧时间，燃烧过程中的表面温度和质量损失率曲线，可以获得良好的定量预测。转换始终包括三个主要阶段。第一短瞬变对应于相对薄的焦化表面层的形成和发光的点火。第二个更长的阶段代表伪稳态燃烧，其中分解区和氧化区的前进速率以及表面温度和整体质量损失速率近似恒定。最后，由于绝热底部条件而导致的最后一小段时间是整个样品分解区的扩大。第一过渡阶段和点火时间明显受外部加热条件的影响，而拟稳态燃烧的特性主要取决于炭的氧化速率，炭的氧化速率由氧的扩散速率控制。