Image-Based Diagnostic System for the Measurement of Flame Properties and Radiation

Abstract

Data collection in the field is fundamental in providing relevant information during fire spread across vegetation or in industrial environments. Considering the challenge and costs of obtaining measurements in the presence of a fire at such a large scale, the development of non-intrusive optical methods is a good alternative. As part of an ongoing effort to improve the understanding of wildfire spread and provide useful tools for fire management, an image-based diagnostic system is being developed for the three-dimensional reconstruction of the turbulent flame in the field. The method allows the time-resolved measurement of the geometric flame features (height, surface area and volume). This paper presents the application of two synchronized stereovision systems to static line of fire scenarios. Each stereovision system, with 1 m inter-camera distance, was located at 12 m from the fire and captured complementary images from front and rear views. Dual spectral band (visible-NIR) cameras were used to enhance fire pixel detection. A series of experiments were carried out on 5 m long and 2 m wide beds of excelsior in the open with fuel loads of 2, 4 and 8 kg/m2. The maximum flame heights were in the range of 1.2–2.4 m. Measurement of the heat flux densities was performed at several positions using thermopile-type sensors. Peak heat fluxes of 6.4–15.7 kW/m2 were measured at 3 m from the fire. The thermal radiation impinging ahead of the flame front was characterized according to its geometric properties. The results exhibit not only a linear relationship between the flame volume and radiant heat flux but also high correlations between their temporal fluctuations. The image processing technique enables measurements of flame volume to be a reliable substitute for the usual fire thermal properties.