Revealing the orientation threshold and optimum contact surface in flame formation, thermal processes, and combustion behaviour of moisturized solid fuel
| Authors: | Ali Edalati-nejad, Sara S. McAllister, Maryam Ghodrat, Jason J. Sharples |
| Year: | 2026 |
| Type: | Scientific Journal |
| Station: | Rocky Mountain Research Station |
| DOI: | https://doi.org/10.1016/j.icheatmasstransfer.2026.110582 |
| Source: | International Communications in Heat and Mass Transfer |
Abstract
The ignition of small fuel elements plays a crucial role in fire propagation. These fine fuels are often the first to ignite and serve as a bridge for fire spread to larger scenarios. The moisture content of these fuels significantly affects their flammability and thermal behaviour. In this study, the effect of fuel moisture content (FMC) and orientation on the drying, pyrolysis, ignition, and thermal processes of a cellulose solid fuel is investigated through a series of numerical simulations. In addition, experimental ignition-time measurements were conducted at the U.S. Forest Service Missoula Fire Sciences Laboratory to provide an independent assessment of model performance. The simulations represent a leaf-scale fuel element allowed to heat up and ignite in a hot upwards-directed (convective) airflow. The leaf is considered in three different orientations of vertical, horizontal, and inclined at a 45° angle, and with five different FMC values between 4% and 63%. The simulations are conducted with FireFOAM, using Large Eddy Simulation (LES). Simulation results are validated against available experimental measurements, using the time evolution of the fuel mass loss. The results indicate the inclined orientation has the highest temperature increase among the three orientations, suggesting a critical angle exists for optimal convective heat transfer. Furthermore, the inclined orientation exhibited the highest drying and pyrolysis rates. This suggests that the angle between the airflow direction and the leaf surface normal critically influences the boundary layer development around the leaf.