Effect of the sample width and concurrent airflow velocity on heat and mass transfer behaviors in steady flame spread stage

This paper presents an experimental study on the joint effects of concurrent airflow and sample width on the steady flame spread behaviors. Flame spread parameters, including flame height, preheating length, heat flux distribution, flame spread rate (FSR) and pyrolysis length, were measured and analyzed comprehensively. Results show that the FSR and pyrolysis length increase with sample width and concurrent airflow velocity. For wider samples, FSR and pyrolysis length are more sensitive to the changes in airflow velocity. The flame height and preheating length increase with sample width, due to the enhanced fuel burning rate and limited air entrainment. The average heat flux in preheating zone is independent to the airflow velocity and sample width. In pyrolysis zone, the convective heat flux is the dominant heat transfer term under concurrent airflow. Theoretical analysis indicates that in steady spread stage, FSR and the pyrolysis length are proportional to the concurrent airflow velocity. Additionally, FSR increase with the 1/3rd power of sample width, whereas the pyrolysis length increases with the 2/3rd power of sample width. Pyrolysis length can be well predicted based on the energy balance at the pyrolysis front.