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Past work focused on energy release measurements for lithium-ion and other batteries during runaway. This energy can be considered in two forms: (1) that of decomposition exothermic energy and (2) combustion energy. Results generally show for 18650 batteries that decomposition energy tends to increase with the SOC and can exceed its stored electric energy by 2-times. Combustion energy can reach 6-times the stored electric energy. Water is demonstrated as having the best potential means for dissipating these energies. Experiments have been conducted to examine the behavior of capillary flows in a water-saturated cellulosic sponge to mitigate battery runaway. An 18650 lithium-ion battery with a high decomposition energy was punctured to initiate runaway in the water experiments. It was demonstrated that a prototype cardboard box package containing nine 18650 batteries at 100% SOC produced violent fire and explosion for a cardboard separator matrix, but no propagation of battery damage in a water-saturated sponge separator matrix. It is suggested, by analysis that the mechanism for water in mitigating runaway and subsequent propagation to surrounding batteries is it's very high coefficient of heat transfer during boiling that considerably reduces the temperature during runaway. [ABSTRACT FROM AUTHOR]

Abstract: A combined analytical and experimental study was performed to determine the length and width of a candle flame. Measurements were made of laminar steady flames from photographs of straight-wick candles composed of n-tetracosane and normal paraffin waxes. The wicks studied ranged in diameter from about 1 to 9mm, and in height from about 2 to 10mm, with aspect ratios (diameter to length) of 0.1 to 2. The flame length from the pool surface and the flame width at the top of the wick were found. It was also noted and recorded that the flame attachment point along the vertical wick varied. The attachment point was found to depend on the aspect ratio of the wick. A model based on stagnant layer burning for a finite cylinder was used, along with the Roper laminar burner model for flame height. With slight adjustment to a constant, the width of the flame was well predicted, and the prediction for the flame height was about 60% too high and offset. In addition, the model gave insight to produce an accurate simple correlation for flame height in terms of wick aspect ratio and Rayleigh number. [ABSTRACT FROM AUTHOR]

Abstract: A new formula for fire-induced wall vent flow rate is developed based upon a theoretical derivation and mathematical fit to data. Previous research had developed a formula of mass flow rate for fire-induced doorway flows only. Here it is extended to include window flows. A theoretical model based on an ideal point source fire plume is used to guide the form of the empirical correlation. A thorough examination concerning the difference between the window and doorway flow modes is conducted. Both sill height and width of the windows pose key influence on the formula. The two vent configurations are merged into one equation. The results were compared to available flow data and shown to be within 15% accuracy for a wide range of fire conditions. [Copyright &y& Elsevier]

Abstract: A theoretical model for wood pyrolysis including char surface oxidation is presented. The main objective is to expose the physical mechanisms governing glowing ignition. By “glowing ignition,” we mean the onset of surface combustion. The char surface oxidation, which can lead to glowing ignition, is considered at the surface boundary condition. Two regimes of char surface oxidation, namely, kinetic and diffusion-controlled, are distinguished. Depending on the char surface oxidation resistances, the char surface oxidation as either kinetic- or diffusion-controlled can be identified. A criterion for glowing ignition is developed based on a surface energy balance. A numerical result shows that according to the present glowing ignition criteria, an inflection point of the surface temperature history can indicate glowing ignition. Generally, a good agreement between theoretical and experimental results at glowing ignition is obtained. [Copyright &y& Elsevier]

The objective of this work was to determine the accuracy and limitations of a new version of Fire Dynamics Simulator (FDS), developed by McGrattan et al., on axi-symmetric fire plumes. The current version uses LES for turbulence, a mixture-fraction-based infinitely fast chemistry model for combustion, and a constant radiative loss fraction. These sub-models have been tested for unconfined fires of different sizes, based on a dimensionless heat release rate QD* in the range of 0.1 to 10.0, which covers most natural fire scenarios. No adjustment of constants or algorithms in the model FDS2.0 have been made. An examination of plume theory is made first to find the benchmark correlations. This shows a generalization for a collection of correlations based on theory, and which might be “the best”. Using the characteristic length as the scaling factor, it is found that the optimum resolution of a pool fire simulation is around 0.05. With this resolution, the flame height prediction is found to fit well with flame height correlations. Some other parameters such as temperature and mixture fraction are found to be close to the empirical estimations at flame tips. The Froude number, which describes the relative strength of momentum and buoyancy, falls within the measurement range of many researchers. The simulation also reveals that the temperature near the burner is over-predicted, while the centerline temperature and velocity in the non-combusting region is predicted well. [Copyright &y& Elsevier]

An analysis is presented that calculates the temperature of the steel truss rods in the World Trade Center towers subject to a fire based on the building ventilation factor. The CIB correlation is used for the fire. Conduction analyses are made taking into account variable properties for the steel and the insulation. A structural failure model is described based on compression buckling of the truss rods due to a reduction in the Young''s modulus. The computed times for the estimated failure or incipient collapse of the floors in both towers has been computed as 105±20 min for WTC 1 (north) and 51±9 min for WTC 2 (south), compared to the collapse times from the aircraft impact of 104 and 56 min, respectively. The insulation thickness and the difference of 19.1 mm (3/4″) and 38.1mm (11/2″) and 38.1 mm (11/2″) between the two towers appear to have been the root cause of the collapses. [Copyright &y& Elsevier]

Experiments have been conducted on a variety of lithium ion batteries to measure their energy output in thermal runaway. Techniques were developed to measure the internal energy release as decomposition of the battery takes place, and combustion energy that can arise from ignited battery gases released in runaway. A nitrogen bomb calorimeter was designed, constructed and utilized to measure the internal energy in runaway. Three techniques were examined for measuring the combustion energy: (1) the Cone Calorimeter, (2) the Oxygen Bomb, and (3) the using a Gas Chromatograph to measure combustion species. The results from these measurement techniques are discussed and compared to the literature for similar batteries. Results generally show for 18650 batteries that the energies in runaway depend on chemistry, decomposition tends to increase with the SOC and can exceed its electric energy by 2-times, while combustion energy can reach 6-times. [ABSTRACT FROM AUTHOR]

Methods are described for measuring the energy released by a Li-ion battery in thermal runaway. A calorimetry technique is described to measure the exothermic energy released during thermal runaway. The technique uses the battery as a calorimeter with temperature and mass loss measurements to analyze the energetics. Runaway is induced by heating of the battery. Only one battery is investigated over a range of heating power and state of charge (SOC). The dynamics of the battery are investigated including time events, temperature, mass lost and energies. The total energy in runaway is manifested by the internal energy stored in the battery and the enthalpy of the ejected mass. Combustion of the ejected gases is described by a technique using the Cone Calorimeter. Results are reported. Both of these techniques are considered less desireable because of the rapid release of energy therefore two new techniques are proposed. The technique of Lyon&Walters using a standard Bomb Calorimeter with nitrogen instead of oxygen to measure the runaway exothermic energy, and measurement of the resulting ejected gas composition to measure the combustion energy. [ABSTRACT FROM AUTHOR]

A model is presented that dynamically predicts the mass loss rate of fuel in a compartment as a function of ventilation, thermal feedback, fuel type and scale. Without a loss of generality, a floor-based fuel is considered. The effect of ventilation is included in the model through the ambient oxygen concentration in the ambient surrounding the fuel at the floor. A mixing model associated with the inlet airflow at the vent is developed to determine this oxygen concentration. An extinction criterion for the flame is based on a critical flame temperature for a diffusion flame associated with the ambient conditions surrounding the flame at the floor. The model is executed in BRI2002, a zone model, capable of computing species and thermal conditions in the upper and lower compartment gas layers. Computations show good agreement with small-scale compartment data for heptane pool fires. The results can accurately portray many regimes of burning including extinction, combustion oscillations, reduction in the flaming area, and quasi-steady burning. [ABSTRACT FROM AUTHOR]

A gas-fueled burner with heat flux gages embedded in its porous surface is used to emulate condensed fuel flames. The measured heat flux, the flow rate of the fuel/inert mixture, and the burner surface temperature allow the emulation of the burning characteristics of condensed fuels. The burner is named the Burning Rate Emulator (BRE). It can burn a gaseous fuel at an effective heat of gasification matching the actual heat of gasification of condensed-phase fuels. It also can match other characteristics of the condensed-phase fuel by careful selection of certain properties of the gaseous fuel. These properties are the heat of combustion, the effective heat of gasification, the surface temperature, and the laminar smoke point. The BRE is shown to reasonably emulate steady burning of methanol, heptane, polyoxymethylene (POM) and polymethylmethacrylate (PMMA) burning in 50 mm diameter pools. It also can be used to emulate ignition and extinction. The results can be used to predict behavior at other conditions, such as burning with external radiant heating. The BRE can be extended to emulate steady burning under diverse conditions. The plausibility of the BRE is demonstrated and its limitations and difficulties are discussed. In particular, the difficulty of dealing with the actual surface heat flux distribution is examined. In general, the paper intends to demonstrate the attributes of a BRE. [ABSTRACT FROM AUTHOR]