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A novel flame retardant, tetraethylene pentamine heptamethylene tetraphosphonate dimethyl ester ammonium triphosphorus acid (TPHTDEAT), was synthesized and characterized by NMR. TPHTDEAT-treated cotton fabrics showed excellent flame retardancy tested by the limiting oxygen index (LOI) of 43.3% of cotton fabrics treated with 40 mass% TPHTDEAT and excellent durability tested by LOI of 29.6% of cotton fabrics after 50 laundering cycles according to AATCC 61-2013 2A standard. Most phosphorus existed as phosphonates, which did not combine with metal ions to reduce the flame retardancy during the washing process. P and N atoms were tested by X-ray photoelectron spectroscopy on the treated cotton fibers. The SEM and XRD results implied that flame retardants entered the cotton fiber interiors. The FTIR and durability results suggested that TPHTDEAT was grafted with -OH of cellulose molecules of cotton fibers. The TG analysis suggested that TPHTDEAT promoted char formation during heating process. The cone calorimetry results indicated that the heat release rate and total heat release of TPHTDEAT-treated cotton were much lower than those of untreated cotton. These results indicated that excellent flame retardancy of treated cotton and the durability of treated cotton were increased by introducing phosphonate groups into flame retardant molecules. [ABSTRACT FROM AUTHOR]

• Impinging flame structures and thermal characteristics in ceiling flow quantified in a corner. • Corner angle effects on the ceiling flow behaviors revealed. • Characteristic length scale for the flame length proposed. • Models of ceiling flame length and thermal characteristics established. This paper presents an experimental investigation and analysis of impinging flame structures as well as thermal characteristics in ceiling flow generated by fuel jet diffusion combustion with air entrainment constraint in a corner of various angles, which had not been quantified in the literature. The impinging flame length, as well as the temperature and heat flux profile along the ceiling centerline were measured for various corner angles (from 30° to 150°), heat release rates (HRRs) and source-ceiling heights, with a total of 183 experimental conditions considered comprehensively. Experimental results show that the impinging flame behaviors have a complex variation nature with the change of corner angles. The impinging flame under the ceiling presented a particular V-shape structure. The measured impinging flame length decreases monotonously with the increasing corner angles. Then, a new global formula was proposed to predict the impinging flame length by considering the effect of corner angles and source-ceiling height on air entrainment and fuel combustion, including both before- and after- impingement stages. The temperature rise and total heat flux at a given position also decreased with the increasing of corner angles. Previous correlations based on a characteristic plume radius are not in agreement with the data for different corner angles. Then, the normalized formulas for the temperature and total heat flux decay profiles along the centerline were proposed using the total flame length as the characteristic length scale and the experimental data were better represented. The present work provides, for the first time, a general model for describing the impingement flame behavior and thermal characteristics in the ceiling flow produced by a jet diffusion combustion with air entrainment constraint in a corner of various angles. [ABSTRACT FROM AUTHOR]

• Flame side sag behavior of elevated diffusion flames under cross wind studied. • The evolutions of flame side sag lengths of the upstream and downstream analyzed. • Four phases of flame side sag behavior distinguished and analyzed. • Mechanism of side sag behavior revealed with characteristic length scales proposed. • Models of flame sag length and turning points of different phases established. The present study provides an experimental investigation and scaling analysis of diffusion flame side sag behavior. This phenomenon happens as a result of the elevated flame (above the ground) under cross wind conditions, and manifest as the flame sinks both upstream and downstream along the burner sides. Experiments are carried out by employing four square burners of various dimensions (10, 15, 20, 25 cm) with the burner exit surface raising 0.3 m above the ground to simulate an elevated diffusion flame. Propane is used as fuel to regulate various heat release rates (HRRs). The cross winds are provided by a wind tunnel with speed in the range of 0.54 ∼ 2.77 m/s. The flame side sag lengths of the upstream (H u) and downstream (H d) are measured for a total of 216 test conditions. It is found that the evolution of flame side sag can be clearly distinguished as four phases and the turning points of different phases are related to the crosswind speed, burner size and HRR. Both H u and H d increase with the increasing of wind speed and HRR, and H d is larger than H u at lower wind speeds while reverse along with the increasing of wind speed. CFD simulation (FDS) is performed to interpret the flow field, from that, the flame side sag can be attributed to interaction between the induced vortex and the sinking flame. Three characteristic length scales are proposed by considering the controlling physics involved in this phenomenon. Finally, general dimensionless functions are derived based on these characteristic length scales, which correlate the experimental results of H u and H d well. The transition of four phases can also been quantified in these formulas. [ABSTRACT FROM AUTHOR]

• Flame heights of free-, wall- and corner buoyant flames quantified. • Effects of wall and corner on flame height revealed. • Flame height has a 2-D to 3-D transition and critical dimensionless HRR is proposed. • Flame height correlations of free-, wall- and corner buoyant flames established. • Characteristic length scale for the flame height proposed. This paper investigates buoyant turbulent diffusion flame height of gaseous fuel combustion in various air entrainment conditions: free-, wall- and corner flames. Experiments are carried out using five square burners with side lengths of 0.3 m, 0.25 m, 0.2 m, 0.15 m and 0.1 m, and five rectangular burners with side dimensions of 0.15 m × 0.3 m, 0.125 m × 0.25 m, 0.1 m × 0.2 m, 0.075 m × 0.15 m, 0.05 m × 0.1 m, to produce corner-, wall- and free flames. The heat release rates (HRR) are in the range of 6.62–26.46 kW for the rectangular burners and 2.21–35.28 kW for the square burners to have 172 experimental conditions comprehensively. It is found that for the same HRR and burner size, the flame height (ℓ f) of corner restriction is larger than the flame height of wall flame, and ℓ f of wall flame is larger than that of free flame. For a given HRR and air entrainment condition, the flame height decreases with the burner dimension increase. Results also show that the effect of wall or corner on the air entrainment can be represented by the "mirror-approach" with an acceptable deviation (−12.5%~13.5%). At the same time, for free and wall flames, there is a transition of dimensionless flame heights from two-dimensional air entrainment to three-dimensional air entrainment. For corner flame, most of the data fall in the two-dimensional air entrainment condition. Combined with comprehensive data of previous reports together, flame height formulas and critical non-dimensional heat release rates for the transition points are proposed for these three types of air entrainment conditions globally by using the perimeter as the characteristic length scale based on "mirror-approach". [ABSTRACT FROM AUTHOR]

The present study provides an experimental characterization of cellular flame structures and thermal characteristics of axi-symmetric ceiling fires. Experiments were carried out employing circular gaseous burners of various diameters at the ceiling facing downward using methane and propane as fuel. For this configuration, a hot buoyant diffusion flame burning beneath the cold fuel gas issuing from the ceiling above was naturally resulted in. A cellular flame structure, due to the inherent "Rayleigh-Taylor" instability of this buoyant flow configuration, was formed beneath the ceiling. The flame length (radius), temperature and heat flux distribution along the ceiling as well as characteristic inner cell size evolution of this special cellular flame were quantified experimentally for such ceiling fire of various conditions. Scaling analysis was performed to analyze the obtained parameters of the cellular flame structure and thermal characteristics of the ceiling fire. Results showed that the overall length (radius) of the cellular flame has a 2/5 power dependence on heat release rate and is independent of burner sizes and fuel types. Temperature profile and heat flux distribution for various conditions can be universally expressed as a function of L / R f , the distance from the burner center normalized by the flame length. The characteristic cell size of the cellular flame was related to temperature, which can be well represented by a 2.33 power function based on the "Rayleigh-Taylor" instability scaling analysis. The cell size spatial evolution inside the cellular flame was self-similar corresponding to the dependence of temperature on relative position, and a non-dimensional function was obtained. This study provides fundamental data and a scaling analysis into the basic physics of the cellular flame behavior and thermal characteristics of ceiling fires. [ABSTRACT FROM AUTHOR]

This paper investigates the flame morphological characteristics (flame height, flame horizontal length and flame tilt angle) of diffusion combustion with or without near-wall constraint in cross-wind. Experiments are carried out using propane as fuel for 10, 15, 20 cm square burners at various heat release rates. Two air entrainment conditions are performed: with near-wall (simulated by a mica board) constraint or in free space (without near-wall). The cross-wind is provided by a wind tunnel up to 3.5 m/s. The evolution of flame height, flame horizontal length and flame tilt angle are measured for a total of 240 test conditions. It is found that the flame height of near-wall condition is higher while the flame tilt angle is lower than that of free condition, both changing monotonously with cross-wind speed. The flame horizontal length is first relatively smaller then larger for near-wall condition than that of free condition with increase in cross-wind speed, however, for both air entrainment conditions it increases first then decreases with cross-wind speed. Three independent length scales are proposed based on the analysis of competition of combustion buoyancy and cross-wind momentum and the inherent physics. General formulas are proposed, based on dimensionless parameters derived according to the derived length scales, to represent the flame morphological characteristics for both with or without near-wall conditions in cross-wind. [ABSTRACT FROM AUTHOR]

Fire hazards in outdoor environmental conditions cause huge damage to process safety in fuel transportation and pipeline leakage. Few literatures are reported about the combustion behaviors and instability characteristics of dual jet flames under cross wind, which are important to risk assessment and manufacturing design. In this work, a series of propane fire source with nozzle diameters of 3 mm, 4 mm and 5 mm are designed for different nozzle separation distances under cross wind. Results showed the tilt angle of rear jet flame was smaller than front jet flame due to the vitiated effective wind towards the rear jet flame by the blockage of the front jet flame. Furthermore, it's found that the blow-out cross wind velocity of the rear jet flame is smaller than that of the corresponding single jet flame. The combustion of the front jet flame will restrict the rear jet flame to a certain extent. Finally, dimensional analysis and correlations are established, where the blow-out cross wind velocity of rear jet flame as well as that of the single jet flame can be well represented by Froude number. These new observations and correlation are helpful for further understanding combustion behaviors of dual tandem jet flames under cross wind. [ABSTRACT FROM AUTHOR]

• Flame pulsation frequencies of free-, wall- and corner buoyant flames quantified. • Effect of wall on flame pulsation frequency revealed. • Correlation for flame pulsation frequency established. • Characteristic length scale for the flame pulsation frequency proposed. This work studies the flame pulsation frequency f of free-, wall- and corner buoyant turbulent diffusion flames. Five square gaseous burners with the burner side length of 10, 15, 20, 25 and 30 cm are used to produce the three types of flames. In addition, five rectangular gaseous burners with dimensions of 30 cm × 15 cm, 25 cm × 12.5 cm, 20 cm × 10 cm, 15 cm × 7.5 cm, 10 cm × 5 cm (aspect ratio of 2:1 with half surface area of the square burners) are also used to produce wall flames. Propane is used as fuel. Results show that heat release rates have no significant effect on f. The flame pulsation frequency of free flames is larger than that of wall flames, which is further larger than that of corner flames. For all types of flames, the flame pulsation frequency decreases with the increasing of the burner size. The classic 1/2 power law correlation, i.e., f ~(g / D)0.5 for flame pulsation frequency of free flame can well describe the data of all types of flames (square, rectangular; free flame, wall flame and corner flame) on the basis of the "mirror" approach, and the perimeter-equivalent diameter is used as the appropriate length scale. [ABSTRACT FROM AUTHOR]