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Abstracts from Combustion and Flame
Contents of Related Journals / Fire Safety Journal 37 (2002) 803–805
805
Transition from Smoldering to Flaming Combustion of Horizontally Oriented Flexible Polyurethane Foam with Natural Convection C.Y.H. Chao and J.H. Wang Department of Mechanical Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong To understand the mechanism of the transition from smoldering to flaming combustion of a flexible polyurethane foam, experiments were conducted with horizontally oriented foam layers under natural convection; this is a common scenario for a real fire. Temperature measurement, gas sampling, and thermal analysis were used to explore the transition’s mechanism. It is seen that, the exothermicity of the oxidation of the residual char left by the passage of the smolder wave front is much larger than that of the oxidation of the original foam material. The transition is determined mainly by the exothermic oxidation of the residual char and the availability of oxygen inside the foam. Futhermore, from the aspect of fire safety during the use of flexible polyurethane foam in upholstered furniture, a series of experiments was done on how the foam length, ignition power, moisture content in the foam and flame retardant influence the transition in the flexible polyurethane foam. The results show that these factors can affect the occurrence of transition from smoldering to flaming and also the transition time because of the oxidation of the residual char left by the smoldering. PII: S 0 3 7 9 - 7 1 1 2 ( 0 2 ) 0 0 0 1 5 - 2
The Role of Particles in the Inhibition of Counterflow Diffusion Flames by Iron Pentacarbonyl Marc D. Rumminger and Gregory T. Linteris Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA Laser light scattering and thermophoretic sampling have been used to investigate particle formation in counterflow diffusion flames inhibited by iron pentacarbonyl Fe(CO)5. Three CH4–O2–N2 reactant mixtures are investigated, with Fe(CO)5 added to the fuel or the oxidizer stream in each. Flame calculations that incorporate only gas-phase chemistry are used to assist in interpretation of the experimental results. In flames with the inhibitor added on the flame side of the stagnation plane, the region of particle formation overlaps with the region of high H-atom concentration, and particle formation may interfere with the inhibition chemistry. When the inhibitor is added on the non-flame side of the stagnation plane, significant condensation of metal or metal oxide particles is found, and implies that particles prevent active inhibiting species from reaching the region of high radical concentration. As the inhibitor loading increases, the maximum scattering cross section increases sharply, and the difference between the measured and predicted inhibition effect widens, suggesting that particle formation is the cause of the deviation. Laser-based particle size measurements and thermophoretic sampling in low strain rate flames show that the particles have diameters between 10 and 30 nm. Thermophoresis affects the nanoparticle distribution in the flames, in some cases causing particles to cross the stagnation plane. The scattering magnitude in the counterflow diffusion flames appears to be strongly dependent on the residence time, and relatively independent of the peak flame temperature. PII: S 0 3 7 9 - 7 1 1 2 ( 0 2 ) 0 0 0 1 7 - 6
805
Transition from Smoldering to Flaming Combustion of Horizontally Oriented Flexible Polyurethane Foam with Natural Convection C.Y.H. Chao and J.H. Wang Department of Mechanical Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong To understand the mechanism of the transition from smoldering to flaming combustion of a flexible polyurethane foam, experiments were conducted with horizontally oriented foam layers under natural convection; this is a common scenario for a real fire. Temperature measurement, gas sampling, and thermal analysis were used to explore the transition’s mechanism. It is seen that, the exothermicity of the oxidation of the residual char left by the passage of the smolder wave front is much larger than that of the oxidation of the original foam material. The transition is determined mainly by the exothermic oxidation of the residual char and the availability of oxygen inside the foam. Futhermore, from the aspect of fire safety during the use of flexible polyurethane foam in upholstered furniture, a series of experiments was done on how the foam length, ignition power, moisture content in the foam and flame retardant influence the transition in the flexible polyurethane foam. The results show that these factors can affect the occurrence of transition from smoldering to flaming and also the transition time because of the oxidation of the residual char left by the smoldering. PII: S 0 3 7 9 - 7 1 1 2 ( 0 2 ) 0 0 0 1 5 - 2
The Role of Particles in the Inhibition of Counterflow Diffusion Flames by Iron Pentacarbonyl Marc D. Rumminger and Gregory T. Linteris Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA Laser light scattering and thermophoretic sampling have been used to investigate particle formation in counterflow diffusion flames inhibited by iron pentacarbonyl Fe(CO)5. Three CH4–O2–N2 reactant mixtures are investigated, with Fe(CO)5 added to the fuel or the oxidizer stream in each. Flame calculations that incorporate only gas-phase chemistry are used to assist in interpretation of the experimental results. In flames with the inhibitor added on the flame side of the stagnation plane, the region of particle formation overlaps with the region of high H-atom concentration, and particle formation may interfere with the inhibition chemistry. When the inhibitor is added on the non-flame side of the stagnation plane, significant condensation of metal or metal oxide particles is found, and implies that particles prevent active inhibiting species from reaching the region of high radical concentration. As the inhibitor loading increases, the maximum scattering cross section increases sharply, and the difference between the measured and predicted inhibition effect widens, suggesting that particle formation is the cause of the deviation. Laser-based particle size measurements and thermophoretic sampling in low strain rate flames show that the particles have diameters between 10 and 30 nm. Thermophoresis affects the nanoparticle distribution in the flames, in some cases causing particles to cross the stagnation plane. The scattering magnitude in the counterflow diffusion flames appears to be strongly dependent on the residence time, and relatively independent of the peak flame temperature. PII: S 0 3 7 9 - 7 1 1 2 ( 0 2 ) 0 0 0 1 7 - 6