Abstract The paper presents a novel approach to determine charring of wood exposed to standard and natural fire that is based on a new numerical model named PyCiF. The new model couples an advanced 2D heat-mass model with a pyrolysis model. A new charring criterion based on a physical phenomenon is implemented in the PyCiF model to determine charring of wood. This presents the main advantage of the new PyCiF model in comparison to common modelling approaches, which require an empirical value of the charring temperature that is often called the char front temperature. The fact that the char front temperature is not an explicit value as assumed by the isotherm 300 °C is advantageously considered in the presented approach where an assumed empirical value of the char front temperature is not directly required to determine the thickness of char layer. The validation of the PyCiF model against experimental results showed great model accuracy, meaning that the model is appropriate for the evaluation of charring depths of timber elements exposed to the standard fire as well as the natural fires. Additionally, as shown in the case study, the presented approach also enables to determine the char front temperature for various natural fire exposures. This will be especially important for the upgrade of the new design methods for fire safety of timber elements exposed to natural fire given in the various design codes such as Eurocode 5.

中文翻译：

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一种在热-质量-热解耦合模型中实施的确定天然火中木材炭化的新方法

摘要 本文提出了一种新的方法来确定暴露于标准和自然火的木材的炭化，该方法基于名为 PyCiF 的新数值模型。新模型将先进的 2D 热质量模型与热解模型相结合。在 PyCiF 模型中实施了一种基于物理现象的新炭化标准，以确定木材的炭化。与常用建模方法相比，新 PyCiF 模型的主要优势在于，后者需要炭化温度的经验值，通常称为炭前沿温度。在所提出的方法中有利地考虑了炭前沿温度不是如等温线300°C所假设的明确值的事实，其中不直接需要炭前沿温度的假设经验值来确定炭层的厚度。PyCiF 模型与实验结果的验证表明模型的准确性很高，这意味着该模型适用于评估暴露于标准火灾和自然火灾的木材元素的炭化深度。此外，如案例研究所示，所提出的方法还能够确定各种自然火灾暴露的炭锋温度。这对于升级各种设计规范（例如欧洲规范 5）中暴露于自然火灾的木材构件的防火安全的新设计方法尤为重要。如案例研究所示，所提出的方法还能够确定各种自然火灾暴露的炭锋温度。这对于升级各种设计规范（例如欧洲规范 5）中暴露于自然火灾的木材构件的防火安全的新设计方法尤为重要。如案例研究所示，所提出的方法还能够确定各种自然火灾暴露的炭锋温度。这对于升级各种设计规范（例如欧洲规范 5）中暴露于自然火灾的木材构件的防火安全的新设计方法尤为重要。