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Author (up) Carmignani, L.; Garg, P.; Thomsen, M.; Gollner, M.J.; Fernandez-Pello, C.; Urban, D.L.; Ruff, G.A.
Title Effect of sub-atmospheric pressure on the characteristics of concurrent/upward flame spread over a thin solid Type
Year 2022 Publication Combustion and Flame Abbreviated Journal Combust. Flame
Volume 245 Issue Pages 112312
Keywords Upward flame spread; Heat release rate; Acrylic fuel; Pressure modeling
Abstract The variation of ambient pressure is a potential tool for studying the driving parameters of fire dynamics and heat release in low-pressure environments such as high-altitude locations, aircraft, and spacecraft. The study of upward flame spread over a solid fuel has direct implications on material flammability and fire development, and low pressure environments have recently gained more attention for the possible comparison with the reduced gravity conditions encountered during space missions. In this work, we consider upward spreading flames over thin acrylic sheets in ambient pressures between 30 and 100 kPa. A forced flow velocity of 20 cm/s is added to the naturally-driven buoyant flow, creating a mixed flow field (natural and forced) that varies with pressure. Flame characteristics such as spread rate and standoff distance are measured from the video analysis of the experiments. It is observed that the former decreases with pressure while the latter increases. The larger flame stand-off distance at low pressures partially explains the decrease of the flame spread rate since the convective heat flux from the flame to the solid decreases. Additionally, volumetric concentrations of the combustion products are measured during the experiments. The results show lower O-2 consumption and CO2 production rates at lower pressures. Based on these rates, we could calculate the heat release rate from upward spreading flames at low pressure, providing fundamental information for better understanding pressure-gravity correlations. According to the results, the volumetric heat release rate is proportional to pressure, which is consistent with previous studies on pressure modeling of fires. This suggests that chemical kinetics is not a constraint for the conditions tested in this study, which could help make future flammability tests comparable to low gravity ones.
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0010-2180 ISBN Medium
Area Expedition Conference
Notes WOS:000861453100006 Approved
Call Number UAI @ alexi.delcanto @ Serial 1688
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Author (up) Cruz, J.J.; Escudero, F.; Alvarez, E.; da Silva, L.F.F.; Carvajal, G.; Thomsen, M.; Fuentes, A.
Title Three-wavelength broadband soot pyrometry technique for axisymmetric flames Type
Year 2021 Publication Optics Letters Abbreviated Journal Opt. Lett.
Volume 46 Issue 11 Pages 2654-2657
Keywords VOLUME FRACTION; DIFFUSION FLAMES; TEMPERATURE; ABSORPTION; ETHYLENE
Abstract Soot temperature measurements in laminar flames are often performed through two-color broadband emission pyrometry (BEMI) or modulated absorption/emission (BMAE) techniques, using models to relate the ratio between flame intensities at two different wavelengths with soot temperature. To benefit from wider spectral range and increase the accuracy of experimental estimation of soot temperature, this work proposes a new approach that uses three-color broadband images captured with a basic color camera. The methodology is first validated through simulations using numerically generated flames from the CoFlame code and then used to retrieve soot temperature in an experimental campaign. The experimental results show that using three-color and BEMI provides smoother reconstruction of soot temperature than two-color and BMAE when small disturbances exist in the measured signals due to a reduced experimental noise effect. A sensitivity analysis shows that the retrieved temperature from three-color BEMI is more resilient to variations on the ratio of measured signals than BMAE, which is confirmed by an error propagation analysis based on a Monte Carlo approach.
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0146-9592 ISBN Medium
Area Expedition Conference
Notes WOS:000658132700025 Approved
Call Number UAI @ alexi.delcanto @ Serial 1413
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Author (up) Thomsen, M.; Carmignani, L.; Rodriguez, A.; Scudiere, C.; Liveretou, C.; Fernandez-Pello, C.; Gollner, M.; Olson, S.; Ferkul, P.
Title Downward Flame Spread Rate Over PMMA Rods Under External Radiant Heating Type
Year 2022 Publication Fire Technology Abbreviated Journal Fire Technol.
Volume 58 Issue 4 Pages 2229-2250
Keywords Flame spread; Radiant heating; PMMA rod; Solid burning; SoFIE
Abstract There are multiple situations in which fires may occur at environmental conditions that are different than standard atmospheric conditions. Changes in ambient pressure, oxygen concentration, flow velocity, the presence of an external heat source or gravity may change the flammability and fire dynamics of materials. The objective of this work is to study the effect of external radiant heating on downward flame spread over cylindrical samples of polymethyl methacrylate (PMMA). In this work, experiments under normal gravity and atmospheric ambient conditions are conducted using a variable heat flux with peak values up to 13.2 kW/m(2). A forced flow of air with a mass-mean velocity of 10 cm/s is used during the experiments. Flame spread rates were measured from video processing of the experiments at different conditions. Results show that the flame spread rate measured depends strongly on the amount of radiant heating provided. An analysis is presented to correlate the flame spread rate with the energy applied to the surface of the sample and the surface temperature. The results provide a baseline for comparison with future microgravity experiments to be performed by NASA as part of the SoFIE/MIST project aboard the International Space Station. It is expected that the results will provide insight for what is to be expected in different conditions relevant for fire safety in future space facilities.
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0015-2684 ISBN Medium
Area Expedition Conference
Notes WOS:000789722000001 Approved
Call Number UAI @ alexi.delcanto @ Serial 1568
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Author (up) Thomsen, M.; Cruz, J.J.; Escudero, F.; Fernandez-Pello, C.; Fuentes, A.
Title Sooting behavior on a spreading flame over PMMA rods under different oxygen concentrations Type
Year 2023 Publication Fire Safety Journal Abbreviated Journal Fire Saf. J.
Volume 141 Issue Pages 103967
Keywords Diffusion flame; Solid fuel burning; Flame spread; Line of sight attenuation; Axisymmetric flame
Abstract The flame spread process over the surface of a solid combustible material is highly influenced by the radiative feedback from the flame, and the conditions under which the process takes place. Soot particles generated during the burn are a big contributor to flame radiation and can play a critical role in the radiative exchange between the flame and the solid. Thus, increased knowledge of the soot production processes involved in the spread of a flame can further promote the understanding of growth and development of fires. The main purpose of this work is to study the effect of oxygen concentration on the sooting behavior of cylindrical samples of polymethyl-methacrylate (PMMA) in an opposed flow configuration. Measured data shows that during downward/opposed flame spread the mass burning rate and soot volume fractions increase with higher oxygen concentrations. The data presented is correlated using a scaling analysis that provides correlations for the maximum soot volume fraction, and the maximum integrated soot volume fraction as a function of the oxygen concentration using similar residence times to establish comparable conditions. The data shows the correlations introduced here provide useful information of the sooting behavior of spreading flames in environments of varied oxygen concentrations that could be used to guide potential fire safety applications.
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Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0379-7112 ISBN Medium
Area Expedition Conference
Notes WOS:001083427400001 Approved
Call Number UAI @ alexi.delcanto @ Serial 1893
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Author (up) Thomsen, M.; Cruz, J.J.; Escudero, F.; Fuentes, A.; Fernandez-Pello, C.; Gollner, M.; Urban, D.L.; Ruff, G.A.
Title Determining flame temperature by broadband two color pyrometry in a flame spreading over a thin solid in microgravity Type
Year 2023 Publication Proceedings Of The Combustion Institute Abbreviated Journal Proc. Combust. Inst.
Volume 39 Issue 3 Pages 3909-3918
Keywords Broadband pyrometry; Soot temperature; Boundary layer diffusion flame; Concurrent flame spread; Sibal material
Abstract Fire spread inside a spacecraft is a constant concern in space travel. Understanding how the fire grows and spreads, and how it can potentially be extinguished is critical for planning future missions. The conditions in-side a spacecraft can greatly vary from those encountered on earth, including microgravity, low velocity flows, reduced ambient pressure and high oxygen, and thus affecting the combustion processes. In microgravity, the contributions of thermal radiation from gaseous species and soot can play a critical role in the spread of a flame and the problem has not been fully understood yet. The overall objective of this work is to address this by studying the soot temperature of microgravity flames spreading over a thin solid in microgravity. The ex-periments presented here were performed as part of the NASA project Saffire IV, conducted in orbit on board the Cygnus resupply vehicle before it re-entered the Earth's atmosphere. The fuel considered is a thin fabric made of cotton and fiberglass (Sibal) exposed to a forced flow of 20 cm/s in a concurrent flow configuration. Reconstruction of the flame temperature fields is extracted from two color broadband emission pyrometry (B2CP) as the flame propagates over the solid fuel. A methodology, relevant assumptions and its applicability to other microgravity experiments are discussed here. The data obtained shows that the technique provides an acceptable average temperature around similar to 1300 K, which remains relatively constant during the spread with an error value smaller than 117 K. The data presented in this work provides a methodology that could be applied to other microgravity experiments to be performed by NASA. It is expected that the results will provide insight for what is to be expected in different conditions relevant for fire safety in future space facilities. (c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 1540-7489 ISBN Medium
Area Expedition Conference
Notes WOS:001058486000001 Approved
Call Number UAI @ alexi.delcanto @ Serial 1879
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Author (up) Thomsen, M.; Fernandez-Pello, A.C.; Williams, F.A.
Title On the Growth of Wildland Fires from a Small Ignition Source Type
Year 2023 Publication Combustion Science and Technology Abbreviated Journal Combust. Sci. Technol.
Volume Early Access Issue Pages
Keywords Wildfire; spot ignition; fire growth; rate of spread; fire model
Abstract Wildland and Wildland-Urban-Interface (WUI) fires are an important problem that may have major consequences in terms of safety, air quality, and damage to buildings, infrastructure, and the ecosystem. It is expected that with climate change, the wildland fire and WUI fire problem will only intensify. Wildland fires are often initiated by small ignition sources caused either by human intervention (hot metal fragments or burning biomass) or by natural events (lighting or sun heating). Once the wildfire or structural fire has been ignited and grows, it can spread rapidly through ember spotting, where pieces of burning materials are lifted by the plume of the fire and then transported forward by the wind, landing where they can start spot fires downwind. The ignition mechanisms for all of these fires have the common characteristic of a small and localized area of origin, with the subsequent spread of the fire to wider and larger areas. Because of the three-dimensional characteristics of this type of propagating fire, its rate of spread has an initial acceleration phase leading to an equilibrium rate of spread when the fire reaches a certain size, which is referred to as a “line-fire” type of spread. Most of the studies on wildland fire propagation have been conducted with line fires and have been concerned with characterizing the equilibrium rate of spread rather than the initial spread from a small ignition source. In this paper, some of the studies conducted to date on the subject of wildland fire growth from a small ignition source, and the physics supporting the mathematical expressions that are used to describe the growth of the fire are discussed. An attempt is also made to provide support for these works through a more fundamental approach to model the problem.
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0010-2202 ISBN Medium
Area Expedition Conference
Notes WOS:001034393700001 Approved
Call Number UAI @ alexi.delcanto @ Serial 1845
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Author (up) Thomsen, M.; Fernandez-Pello, C.; Urban, D.L.; Ruff, G.A.
Title On simulating the effect of gravity on concurrent flame spread over thin paper through variations in ambient pressure Type
Year 2021 Publication Combustion and Flame Abbreviated Journal Combust. Flame
Volume 232 Issue Pages 111538
Keywords Flame spread rate; Low pressure; Environmental conditions; Partial gravity
Abstract The environment inside a spacecraft, or a space habitat, can greatly differ from those on earth, affecting the burning behavior of solid fuels. Because in a gravity field there is a flame-induced buoyancy, it is very difficult to reproduce on Earth the environmental conditions of a spacecraft, or a habitat in the Moon or Mars, thus making fire testing and burning predictions harder. A potential alternative approach to overcome this problem is to reduce buoyancy effects by using reduced ambient pressure in normal gravity. The objective of this work is to explore the possibility of simulating the effect of gravity, and in turn buoyancy, through changes in ambient pressure, on upward/concurrent flame spread over a thin combustible solid. Comparisons with available data at different gravity levels are used to determine the extent to which low-pressure can be used to replicate flame spread characteristics at different gravities. Experiments of the upward/concurrent flame spread over thin Kimwipe paper sheets were conducted in normal gravity inside a pressure chamber with ambient pressures ranging between 100 and 30 kPa and a forced flow velocity of 10 cm/s. Results show that reductions of pressure slow down the flame spread over the paper surface, and also reduces flame intensity. Comparison with published partial gravity data shows that as the pressure is reduced, the normal gravity flame spread rate approaches that observed at different gravity levels. The data presented is correlated in terms of a mixed convection non-dimensional number that describes the convective heat transferred from the flame to the solid, and that also describes the primary mechanism controlling the spread of the flame. The correlation provides information about the similitudes of the flame spread process in variable pressure, flow velocity and gravity environments, providing guidance for potential ground-based testing for fire safety design in spacecraft. (c) 2021 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0010-2180 ISBN Medium
Area Expedition Conference
Notes WOS:000686901100008 Approved
Call Number UAI @ alexi.delcanto @ Serial 1451
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Author (up) Thomsen, M.C.; Fuentes, A.; Demarco, R.; Volkwein, C.; Consalvi, J.L.; Reszka, P.
Title Soot measurements in candle flames Type
Year 2017 Publication Experimental Thermal And Fluid Science Abbreviated Journal Exp. Therm. Fluid Sci.
Volume 82 Issue Pages 116-123
Keywords MAE; Modulated Absorption/Emission; Soot volume fraction; Soot temperature; Wick effects
Abstract Soot volume fractions and soot temperatures have been measured for the first time on candle flames. Measurements on laminar steady flames were carried out using candles with wick diameters of 2, 3 and 4 mm. Wick length was varied between 4 and 10 mm. The shape of the candle flame was obtained from CH* spontaneous emissions. Measured flame heights show an increase with wick dimensions, approaching an asymptotic value for increasing wick lengths. Soot volume fractions were obtained from laser extinction measurements with the Modulated Absorption/Emission (MAE) technique. A deconvolution technique and a regularization procedure were applied to the data. Radial profiles of soot volume fractions increase when varying the wick dimensions; this effect is produced by the greater amount of fuel released by the wick. Radially integrated soot volume fractions were also calculated, presenting a similar behavior to the soot volume fraction radial profiles. The peak integrated soot volume fraction was found at approximately half the flame height, independent of the wick dimensions and burning rates. Soot temperature was obtained from emission measurements at two different wavelengths considering the attenuation of the soot particles in the optical path length. A deconvolution and regularization procedure was carried out in order to obtain temperature profiles for different heights in the flame. The observed increase in soot production and soot temperature profiles was directly related to the higher burning rate experienced by the candle. The results show that peak integrated soot volume fractions are proportional to both the mass loss rates and the flame heights. (C) 2016 Elsevier Inc. All rights reserved.
Address [Thomsen, M. C.] Univ Calif Berkeley, Dept Mech Engn, Berkeley, CA 94720 USA, Email: pedro.reszka@uai.cl
Corporate Author Thesis
Publisher Elsevier Science Inc Place of Publication Editor
Language English Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0894-1777 ISBN Medium
Area Expedition Conference
Notes WOS:000392769400012 Approved
Call Number UAI @ eduardo.moreno @ Serial 696
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