Fire disaster, as an unavoidable threat around the world, caused millions of loss of living beings and properties. To minimise the damage that fire disaster causes, the prediction of fire spread is significant. Due to the burning of wood is a series of complicated processes, the study of fire spread along the wood surface is far from complete. To comprehensively understand the mechanism of wood combustion as well as the fire spread, a systematically study is necessary.
With the development of digital cameras and computer science, the vision systems based on the digital camera become a useful tool for measurement and visualisation.
In this work, the fire spread on inclined wooden rod surface is systematically studied based on the vison systems. An original designed imaging system that synchronises visible, schlieren, and thermal imaging systems is developed. The various diagnostical techniques, including the temperature measurements by two-colour method and thermal imaging, optical flow motion estimation, and selective enhancement technique are developed along with the imaging system. Rely on the imaging system that developed in this study, the burning ability, temperature of the wooden surface and flame, the dim blue flame and the invisible hot gas flow can be visualised simultaneously.
The first contribution of this work is the developed pyrometers which are based on two methods: the first one is the two-colour method, which relies on the response ratio between two selected wavelengths. This method is used for measuring the soot flame temperature. The second pyrometer is based on thermal imaging, which uses a narrow band wavelength thermal image with known emissivity. It is used for reading the temperature of the wood surface. With the instruments developed in this work, the flame temperature and surface temperature of the burning wood can be monitored at the same time.
Based on the imaging system and diagnostical techniques, the fire spread on wooden rods surface that inclined at various angles is investigated. It is first found in this work both the flame and fire plume would have geometry change at the inclination surface. Besides, with the help of the optical flow method, the minor fluctuate (<2mm/s) of the flame and hot flow can be detected and used to analyse the burning phenomena.
Another finding is the essential role of underneath preheating on sustaining the burning and spreading the fire. The pyrolysis zone, as well as the preheating zone, have been illustrated and visualised by synchronising the blue flame with the schlieren image by the first time. Furthermore, with involving the thermal imaging system, the preheating length underneath the burning rod is calculated and shows a monotonically increase with the increasing angle. Moreover, this work introduces a novel method to measure the flame attachment phenomenon quantitatively by using enhanced thermal image.
The effects of cross-wind on the burning of wood are investigated systematically with the imaging system. The main finding is that under the low speed of cross-wind, the burning and fire spread are enhanced, while they are decreased under the high speed of the wind. With the help of the multiple spectrum imaging, the mechanisms of the wood combustion under wind condition has been studied and visualised.
This new imaging system with developed diagnostical techniques is a useful tool for investigating the burning of wood and fire propagation. The findings in this works could help enhance the understanding of the fire protection and optimise the strategy both in fire protection and fire extinction.
