Abstract
The main characteristics of pool fire flames are flame height, air entrainment, pulsation of the flame, formation and properties of soot particles, mass burning rate, radiation feedback to the pool surface, and the amount of pollutants including soot released to the environment. In this type of buoyancy controlled flames, the soot content produced and their subsequent thermal radiation feedback to the pool surface are key to determine the self-sustainability of the flame, their mass burning rate and the heat release rate. The accurate characterization of these flames is an involved task, specially for modelers due to the difficulty of imposing adequate boundary conditions. For this reason, efforts are being made to design experimental campaigns with well-controlled conditions for their reliable repeatability, reproducibility and replicability. In this work, we characterized the production of soot in a surrogate pool fire. This is emulated by a bench-scale porous burner fueled with pure ethylene burning in still air. The flame stability was characterized with high temporal and spatial resolution by using a CMOS camera and a fast photodiode. The results show that the flame exhibit a time-varying propagation behavior with a periodic separation of the reactive zone. Soot volume fraction distributions were measured at nine locations along the flame centerline from 20 to 100 mm above the burner exit using the auto-compensating laser-induced incandescence (AC-LII) technique. The mean, standard deviation and probability density function of soot volume fraction were determined. Soot volume fraction presents an increasing tendency with the height above the burner, in spite of a local decrease at 90 mm which is approximately the position separating the lower and attached portion of the flame from the higher more intermittent one. The results of this work provide a valuable data set for validating soot production models in pool fire configurations.
Highlights
Pool fires are a common form of fire in industrial applications, representing a big concern in terms of fire science research
To the best of the authors’ knowledge, this work presents for the first time results of soot volume fraction measured by the auto-compensating laser induced incandescence technique applied to a surrogate pool fire flame
The decay of the incandescence signal over time was measured at two wavelengths to determine an effective soot temperature, which was used to estimate the soot volume fraction
Summary
Pool fires are a common form of fire in industrial applications, representing a big concern in terms of fire science research. By decoupling the problem of liquid fuel vaporization and fuel combustion, soot production and soot radiation can be studied in detail with significantly reduced uncertainty, seeking to reveal the process of soot formation and quantify the soot volume fraction distribution as well as radiative heat transfer This approach largely alleviates the 3R challenge in any experimental studies: Repeatability, Reproducibility, and Replicability. The investigated flames were not bench-scale surrogate pool fires, it is still worth mentioning the studies of Zeng et al (2019) and Kearney and Grasser (2017) conducted in large scale buoyant flames These researchers applied the line-of-sight spectral intensity measurement with a pair of fast-infrared spectrometers and simultaneous PLII/CARS techniques, respectively, to obtain simultaneous soot volume fraction and soot/flame temperature. In this study the auto-compensating laser-induced incandescence (AC-LII) technique is applied to measure the local soot volume fraction from an ethylene flame burning in still air, emulating a small-scale pool fire. To the best of the authors knowledge, this is the first time the AC-LII technique is applied to a buoyancycontrolled diffusion flames
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