A numerical model for predicting the smoldering behavior of bio-based insulation materials: Model theory and validation

Bio-based insulation materials are prone to self-sustained smoldering after ignition. While empirical studies highlight key factors influencing smoldering initiation and spread, a comprehensive understanding of the mechanisms remains incomplete. This study introduces a smoldering model for bio-based insulation materials, integrating flow, heat, and moisture transfer with a 3-step reaction model. Material parameter quantification is demonstrated using wood fiber insulation as a reference, with methodologies applicable to other materials. Experimental setups for fluid mechanical, thermal, and moisture transport properties are described, supplemented by data from literature. The modeling framework couples flow, heat, and moisture transport mechanisms with reaction rates dependent on temperature and concentration. A diffusion-limiting approach accounts for particle-surface transport constraints. Implementation is performed using COMSOL Multiphysics (R) 6. Validation tests in a 1.5 m tube furnace with controlled heating zones and inflow conditions demonstrate the model's ability to accurately predict smoldering velocity. Further optimization is required to improve ignition time predictions. While some inhomogeneity effects are not fully captured, the model provides a solid foundation for further refinement and scaling to component levels.