Investigation of forced flow orientations on the burning behaviours of wooden rods using a synchronised multi-imaging system

Abstract

The burning behaviour of a wooden rod under various forced flow conditions was investigated by employing a synchronised multi-imaging system integrating visible wavelength, short-wavelength infrared (SWIR), and Schlieren techniques. The wood samples were fixed horizontally and at an inclined angle to study the effect of the surface orientation under forced flow. A small-scale wind tunnel was developed to supply three types of forced flow: concurrent, opposed and cross flow. Each imaging technique helps to gain different physical insights of different aspects of the phenomenon. The combined data provides a comprehensive understanding of the flow effect on fire propagation. It was found that the forced flow strongly influences the often-invisible hot gas flow surrounding the burning rod. The heat feedback from the attached hot flow layer helped to maintain the surface temperature, which further influenced the burning behaviour. The mechanisms that the various flow orientation caused, affected the heated gas differently. Additionally, a method was proposed to monitor the burning process, which used thermal imaging to quantitatively calculate the area of pyrolysis zone on the surface. With the visualisation of the Schlieren images at the critical timings, it was found the thick hot gas flow underneath the wooden rod was a crucial factor that determined the intensity of burning, which may provide important guidance on effective wooden beam fire suppression and control.