Ignition of various wood species by radiant energy

The ignition of various wood species by exposure to the radiation of a DKsR-10000 xenon lamp was investigated. Time dependences of ignition delay on the radiant energy intensity were obtained for various wood species: cedar, larch, pine, birch, and aspen. The effect of the initial temperature and moisture content of wood on the ignition time was studied. The ignition temperature of pine and birch wood for various radiant energy intensities was determined by an optical method. It is shown that the ignition time of pine wood decreased by a factor of 1.5–2 as the initial temperature of samples was increased by 100 degrees. It was found that the ignition temperature of wood increased with increasing radiant flux density and depended on the wood species. Increasing the wood moisture content by a factor of 10 increased its ignition time by more than 50%.     

Effect of Radiant Heat Transfer on the Minimum Spark–Ignition Energy of Gas Suspensions

A mathematical model of spark ignition of a gas suspension is constructed on the basis of a two–temperature thermal diffusion model of gas–suspension combustion and the radiant heat transfer is modeled in a diffusion approximation. The dependences of the minimum ignition energy on the parameters which describe the disperse phase and the domain of the disperse–phase parameters in which the radiant heat transfer affects greatly the minimum spark–ignition energy is determined by solving the problem numerically. The analytical formula that was obtained for determination of the critical spark–ignition energy of the gas suspension and that takes into account the radiant heat transfer in the gas suspension gives values different from numerical results by not more than 30% in a broad range of determining parameters of the problem. The theoretically obtained values of the minimum spark–ignition energy of a gas suspension of coal dust agree satisfactorily with experimental data.     

Thermal Explosion of Powder Mixtures: Numerical Approach

A numerical approach to investigate the heating and the ignition of powder mixtures by radiant energy is presented. The ignition study is based on the possibility of separating the initiation transient from the propagation process, by operating in thermal explosion mode.     

The use of the ISO/TC92 test for ignitability assessment

The ignitability of solids, including fire-retardant-containing polystyrene, is reported using results of a small-scale thermal radiation exposure test (a modified ISO ignitability test procedure). Additional information is provided from the results of exposure to convective heating and from oxygen index determinations. The use of a permanent sample mask and smaller samples than described in the ISO procedure proved convenient. The ISO procedure was found useful for determining the response of ignition time to changes in radiant flux. Good agreement was found with the analysis of Quintiere and Harkleroad for most samples but not with polystyrene, with and without halogen fire retardant. The increase in ignition resistance with fire retardant concentration suggested by the oxygen index is not always consistent with the ignition delay times under radiative or convective assault.     

Experimental study on ignition and combustion characteristics of typical oils

The impact of radiant heat flux on ignition and combustion behavior of typical oils (diesel, lubricating oil, and aviation kerosene) was conducted in a cone calorimeter. A circular steel pan with a diameter of 10 cm was used to contain diesel, lubricating oil, and aviation kerosene without water sublayer. Using the standard oxygen consumption method, we obtained ignition time, heat release rate, mass loss rate, extinction coefficient, CO, and CO₂ yield, and average specific extinction area was calculated from the extinction coefficient. Janssens' method was adopted in this study to deal with ignition time and radiant heat flux under a 0.55 power rule. Results show that the fitting through Janssens' method is good for ignition time of diesel, lubricating oil, and aviation kerosene and radiant heat flux. Moreover, heat release rate, mass loss rate, and CO/CO₂ ratio appear to positively correlate with radiant heat flux, whereas average specific extinction area varies in a certain range. Copyright © 2013 John Wiley & Sons, Ltd.     

A theoretical basis for flammability properties

Theoretical formulations are presented for the fire growth processes under external radiant heating. They included ignition, burning and energy release rate, and flame spread. The behaviour of these processes with external heating is described along with the critical conditions that limit them. These include the critical heat fluxes for ignition, flame spread and burning rate. It is shown how these processes and their critical conditions depend on a limited number of properties measurable by a number of standard test methods. The properties include heat of combustion, the heat of gasification, ignition temperature and the thermal properties of the material. Alternatively, the properties could be related to parameters easily found from data; namely: (1) the critical heat flux (CHF) for ignition; (2) the slope of the energy release rate with externally imposed flux, defined as heat release parameter (HRP); and (3) the ignition parameter, defined as thermal response parameter (TRP). It is further shown that the flame heat flux differences between small laminar flame ignition sources and larger turbulent flames can affect flame spread due to heat flux and ignition length factors. Finally, it is found that the critical energy release rates theoretically needed for ignition, sustained burning, and turbulent upward flame spread are roughly 13, 52, and 100 kW/m², respectively, and independent of material properties. Copyright © 2005 John Wiley & Sons, Ltd.     

Ignition of Combustible Forest Materials by a Radiant Energy Flux

The paper reports results of experimental ignition of litter layers consisting of needles of cedar, pine, and fir-tree, birch leaves, lichen (Cladonia), and moss (Pleurozium shreberi). It is established that the moss is ignited faster than the other combustible forest materials. It is shown that with equal moisture contents, the ignition times of needle litter from different trees are identical within the experimental error, and for litter of birch leaves, the ignition time is shorter than that for litter of coniferous trees. This difference is found to be due to differences in the interaction of the radiant flux with litter layers of needles and leaves. Minimum values of the ignition heat pulses for needle and leaf litter layers are estimated for various heat-flux densities. These values tend to a minimum for a heat-flux density of 0.5–0.8 MW/m².     

Comparison of cone and OSU calorimetric techniques to assess the flammability behaviour of fabrics used for aircraft interiors

Two test methods for measuring the heat release rate, HRR have been compared on fabric composites used for aircraft interior materials as side‐wall panels. These methods are based on the principles of direct measurement of the convective and radiant heat by thermopiles using an Ohio State University (OSU) calorimeter, and oxygen consumption using a cone calorimeter. It has been observed when tested by standard procedures, cone results at 35 kW/m² incident heat flux do not correlate with OSU results at the same heat flux. This is because in the cone calorimeter, the sample is mounted horizontally whereas the OSU calorimetric method requires vertical sampling with exposure to a vertical radiant panel. A further difference between the two techniques is the ignition source—in the cone it is spark ignition, whereas in the OSU it is flame ignition; hence, samples in the OSU calorimeter ignite more easily compared to those in the cone under the same incident heat fluxes. However, in this paper we demonstrate that cone calorimetric exposure at 50 kW/m² heat flux gives similar peak heat release results as the 35 kW/m² heat flux of OSU calorimeter, but significantly different average and total heat release values over a 2 min period. The performance differences associated with these two techniques are also discussed. Moreover, the effects of structure, i.e. type of fibres used in warp/weft direction and design of fabric are also analysed with respect to heat release behaviour and their correlation discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Ignition of composite propellant at subatmospheric pressures by means of carbon dioxide laser

Ignition behavior of solid propellant composed of 25 wt% polybutadiene and 75% ammonium perchlorate under subatmospheric conditions has been studied using a carbon dioxide laser whose radiant flux is uniformalized. Data of ignition time in Ar, N₂ and He atmospheres, and critical radiant flux and pressures over which ignition might be achieved, were obtained. Moreover, the data were compared with theoretical values, taking account of variable heat conductivity for the ambient gases with a surface ignition hypothesis. It is concluded that these ambient gases participate in the pre- and post-ignition reactions and the ignition preventive behavior of He atmosphere is not predictable merely based on its high transport properties. The detailed observation of the ignition transient near the critical pressure revealed that the ignition in Ar atmosphere occurs in gas phase under less than 100 torr whereas in He atmosphere it occurs always at the condensed phase surface.     

Absorption and reflection of infrared radiation by polymers in fire‐like environments

In large‐scale fires, the input of energy to burning materials occurs predominantly by radiative transfer. The in‐depth (rather than just surface) absorption of radiant energy by a polymer influences its ignition time and burning rate. The present investigation examines two methods for obtaining the absorption coefficient of polymers for infrared radiation from high‐temperature sources: a broadband method and a spectral method. Data on the total average broadband transmittance for 11 thermoplastics are presented (as are reflectance data), and the absorption coefficient is found to vary with thickness. Implications for modeling of mass loss experiments are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Ignition of porous, solid radiation source

Asymptotic analysis of the ignition of a semiinfinite porous body by a radiant heat flux yields a critical condition dividing ignition from inert heating. For the case of ignition, the temperature field in the body prior to ignition and the time characteristics of the process are determined. The dependence of the ignition time on the system parameters is analyzed. Tomsk State University, Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 6, pp. 5–13, November–December, 1995.     

Combustion behaviour of polyurethane flexible foams under Cone Calorimetry test conditions

The first part of this study focuses on the effect of cone calorimeter test variables on polyurethane flexible foam properties such as ignitability, heat release rate, effective heat of combustion and mass loss. Three of the main commercial foam types were used, i.e. conventional slabstock foams, high-resilience slabstock foams and all-MDI (methylene diphenyldiisocyanate) moulded foams. A decrease in heat flux (down to 40%) with increasing distance from the conical heater was measured. As a consequence, results were found to depend to a large extent on the thickness and the melting behaviour of the foam samples. To achieve a sufficiently constant and uniform heat flux exposure, sample thickness had to be limited to 25 mm. In addition, repeatability was found to be good under various conditions, with percentage standard deviations for effective heat of combustion, peak rate of heat release and mass loss below 10%. Levels of radiant flux above 25 kW m^?2 were found to be very severe to test flexible polyurethane foams. Under such conditions, foams that show large differences in combustion performance in small-scale flammability tests performed almost identically in the cone calorimeter. In the second part of this study the effects of foam variables, such as foam type, density and melamine content, are defined. These effects were clearly pronounced at radiant flux levels of 15–25 kWm^?2. Density was found to be the key variable in controlling ignition resistance. In addition, high-resilience slabstock foams and all-MDI moulded foams performed better than conventional slabstock foams of the same density. Melamine addition resulted in a delay of ignition for all three foam types and an incomplete combustion, decreased heat release and effective heat of combustion in HR-slabstock and all MDI moulded foams. However, melamine is not effective as a heat sink in conventional slabstock foams. The different performance of the foam types under study can be explained by a different melting behaviour.     

Ignition of a thin film by a beam of radiant energy

The problem of destruction of a thin polymer film due to heating by a beam of radiant energy is studied. The multistage nature of chemical conversion and dependence of optical properties on depth of decomposition is considered. Analytical estimates are given for the time characteristics of film ignition and its dependence on beam thickness and heating intensity. Optical phenomena related to the chemical reactions are observed by a numerical method.Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 6, pp. 3–10, November–December, 1991.     

Ignition and Combustion of Condensed Systems with Energy Fillers

This paper describes the results of an experimental study of ignition and combustion of condensed systems, containing energy fillers, i.e., powders of aluminum, boron, aluminum borides, and titanium. Compositions on a hydrocarbon or active fuel binder with a combined oxidizer (ammonium perchlorate and/or ammonium nitrate) are considered. Thermodynamic estimates for the ballistic characteristics of the compositions under study are given. It is shown that a unit pulse increases by 3.5% with the replacement of aluminum by boron in the compositions considered. It is experimentally determined that the time delay of ignition of boron-containing compositions decreases in conductive and radiant heat transfer and that the stationary burning rate of boron and aluminum boride containing compositions increases. The efficiency of the impact of energy fillers on the characteristics of condensed systems as a function of the composition of a combined oxidizer is determined.     

Optical Pyrometry of Fireballs of Metalized Explosives

Fast‐response optical diagnostics (a time‐integrated spectrometer and two separate fast‐response three‐color pyrometers) are used to record the transient visible radiation emitted by a fireball produced when a condensed explosive is detonated. Measurement of the radiant intensity, in several narrow wavelength bands, is used to estimate the temperature of the condensed products within the fireball. For kg‐scale conventional oxygen‐deficient homogeneous TNT and nitromethane explosive charges, the radiant intensity reaches a maximum typically after tens of milliseconds, but the measured fireball temperature remains largely constant for more than 100 ms, at a value of about 2,000 K, consistent with predictions using equilibrium thermodynamics codes. When combustible metal particles (aluminum, magnesium or zirconium) are added to the explosive, reaction of the particles enhances the radiant energy and the fireball temperature is increased. In this case the fireball temperatures are lower than equilibrium predictions, but are consistent with measurements of particle temperature in single particle ignition experiments.     

Flammability of plastics I: Ignition temperatures

The Piloted ignition of six common thermoplastics has been studied by exposing horizontal samples (65 times; 65 times; 6 mm thick) to irradiance levels in the range 10–40 kw m^?2. Fine thermocouples were attached to the exposed face and allowed the surface temperature to be monitored continuously. Times to sustained ignition from a small pilot flame and the corresponding surface temperature were recorded. Within experimental error, ignition temperatures showed no systematic dependence on surface area when this was reduced to ca 20 mm square. Times to ignition were dependent not only on radiant intensity but also on the spectral characteristics of the source.     

Ignition of a radiating gas by an incandescent surface

Conclusions The fundamental regularities of ignition of a radiating and absorbing gas by an incandescent surface are examined. In the case of an optically thin medium characteristic for high-temperature ignition, the problem is solved in the traditional stationary and nonstationary formulations [8]. It is shown that radiant heat transfer plays an essential part in the gas ignition process, in particular, the process can be accelerated and retarded in an optically thin gas medium because of radiant heat exchange. The case of an optically dense gasl _kb/l _o corresponds to radiant heat conduction, and therefore, does not result in a change in the ignition time but only to an increase in the scale of the lengthl _o. For intermediate values ofl _kb/l _o the dependence of on parameters governing the energetics of radiant heat transfer is complex in nature and can only be analyzed numerically in each specific case. The development of a suitable model of radiation heat exchange is the fundamental difficulty here.Minsk. Translated from Fizika Goreniya i Vzryva, Vol. 26, No. 1, pp. 15–21, January–February, 1990.     

Evaluating ignition data using the flux time product

A protocol based on the flux time product (FTP)¹ is used to analyze ignition data obtained from the Cone Calorimeter under an impressed flux in the range 20–70 KWm^?2 for different orientations and modes of ignition for conditioned cellulosic materials. The mean, maximum and minimum ignition times are depicted graphically by orientation and mode of ignition. Flux time products, FTP indices, critical irradiances and estimates of the convective heat loss associated with a change in specimen orientation are derived using the mean time-to-ignition data. It is demonstrated that consideration of the thermal thickness of a specimen may not be necessary when the proposed FTP methodology is utilized to determine valid correlations between the time-to-ignition and the incident radiant flux.     

Composite Propellant Ignition and Extinction by CO2 Laser at Subatmospheric Pressure

Aspects of the heating, ignition and extinction of an AP/HTPB(86/14) composite propellant, induced by means of a CO₂ laser energy pulse, are investigated in the subatmospheric pressure range to determine the influence of the operating conditions on these processes. Measurements of the ignition delay time and ignition temperature for any operating condition have been done by microthermocouples able to record the temperature history of the irradiated surface and of the gas phase. Determinations of the boundaries location, defining the propellant behavior after the external energy removal, by the go-nogo techniques, have permitted to evaluate the minimum exposure time which assures to avoid the propellant extinction after the propellant ignition. Combustion transients have been studied to determine the burning propellant response to the laser energy pulse and to define the pulse features which yields the propellant extinction for different working pressure. Laser Doppler Velocimetry(LDV)technique, able to measure the velocity of the gas coming out from the burning propellant surface, was used to follow the whole combustion transient giving a precise picture of the phenomenon. Comparisons between data obtained studying the ignition and extinction by laser energy pulse phenomena show that the operating pressure has opposite effects on the propellant response to the external energy input having the same characteristics.     

Approximate estimates of the characteristics of propellant ignition using radiant flux through shields with various properties

An analytical solution to the problem of propellant ignition using radiant flux is presented in a conjugate statement. The solution generalizes and supplements the results obtained earlier. The cases of ignition through absolutely transparent and opaque shields are considered. Approximate formulas for estimation of the time and temperature of the chemical-reaction onset and the time and temperature of the loss of quasi-stationary equilibrium in different limiting cases are obtained. Estimates of the influence of heat transfer into the environment (by the conductive mechanism) on the ignition characteristics are given. A comparison of the ignition characteristics of the propellant and shields is made.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 1, pp. 26–41, January–February, 1996.