Ignition Of Wood Research Articles

Effects of sample orientation on pyrolysis and piloted ignition of wood

In this work, the pyrolysis and piloted ignition behavior of thermally thick paulownia wood brick for different orientations has been experimentally investigated, by using the conical heater. Three typical orientations were adopted, that is, upward, downward, and vertical cases with the incident heat flux ranging from 12 to 39 kW/m2. A numerical approach was used to test the effect of heat convection and radiation blockage on pyrolysis. The ignition time was observed to be strongly dependent on orientation. In detail, the shortest ignition time turns to be for downward orientation, but longest ignition time for vertical orientation. Total mass loss at ignition is weakly dependent on orientation. Meanwhile, critical mass flux increases with external heat flux rising and varies somewhat with orientation.

Thermal Behavior of Wood Slab Under a Truncated-Cone Electrical Heater: Experimental Observation

With regard to the significance of thermal decomposition and ignition of wood, a set of experiments were carried out to investigate the influence of the key factors on its thermal performances. The in-depth temperature rise, solid conversion, ignition time, and ignition temperature of wood were examined when the wood slab was subjected to the radiation from a truncated-cone electrical heater. Thermal decomposition of different species performs similarly under high heat fluxes. The vertically distributed vessels in an along-grain sample facilitate the evolution of produced volatiles, and the formed char skeleton could be easily damaged to cause “cracking” among the conjunctions of vessels. The horizontal vessels in the across-grain sample give a thermally stable structure, while more energy should be consumed to break the wall of vessels. This gives rise to the shorter endurance of flaming combustion for the along-grain samples. The lag effect of moisture content on temperature rise and ignition time is observed, producing the increasing ratio of 3 s/% for ignition time against moisture content.

Checks on Possibilities for the Spontaneous Combustion of wood : Part II Critical Conditions and Anisotropy Effect for the Spontaneous Ignition of Wood Spheres Followed up by Computer Simulation.

Checks on Possibilities for the Spontaneous Combustion of wood : Part II Critical Conditions and Anisotropy Effect for the Spontaneous Ignition of Wood Spheres Followed up by Computer Simulation.

Modelling spontaneous ignition of wood, char and RDF in a lab-scale packed bed

Many municipal waste combustors use preheated primary air in the first zone to dry the waste. In most cases the preheat temperature does not exceed 140°C. In previous experiments it is found that at temperatures around 200°C, in some circumstances, self- or spontaneous ignition can be achieved. Using preheated air can be a powerful tool to control the ignition and combustion processes in a waste combustion plant. To use this tool effectively, the influence of the preheated air on the fuel bed needs to be well understood. The present work is done to develop a model that predicts the spontaneous ignition temperature of the fuel bed and the critical temperature of the primary air at which the fuel bed ignites. The influence of primary air flow rate and addition of inert are modeled for a packed bed of wood. From the model a dimensionless parameter is derived in which all investigated parameters (fuel type, air flow rate and inert fraction) are combined. This parameter appears to be sufficient to describe both the spontaneous ignition and the critical air temperature. The results from the model are validated with experiments presented in previous work [1]. The model slightly over-predicts the temperatures by 6–7°C, and the trends are predicted well. Besides calculations for the temperatures, the ignition time and location are calculated as well. The ignition time is under-predicted due to the assumption of a uniform temperature distribution inside the particles. The location of ignition is predicted well. For char, a minimum spontaneous ignition temperature is derived from DSC measurements. The temperature at which the interaction of char and oxygen switches from endo- to exothermic seems to coincide with the spontaneous ignition temperature.

Thermal-balanced integral model for pyrolysis and ignition of wood

The pyrolysis and ignition of wood is of great importance to understand the initial stage of combustion, helping control the occurrence and spread of unwanted building and forestry fires. The development of a thermal-balanced model is introduced for examining the analytical relationship between the ignition time and external heat flux. The critical heat flux, one of the important fire-retardant characteristics of combustible solid, is determined from a correlation study between the ignition time and external heat flux. One of the thermal-balanced integral models, considering the effect of surface heat losses, average absorptivity and moisture content, is employed to give the prediction of surface temperature rise, ignition time and ignition temperature of the Aspen. The results show that the model readily and satisfactorily predicts ignition temperature and ignition time of wood with different moisture contents.

Modelling piloted ignition of wood and plastics

To gain insight in the startup of an incinerator, this article deals with piloted ignition. A newly developed model is described to predict the piloted ignition times of wood, PMMA and PVC. The model is based on the lower flammability limit and the adiabatic flame temperature at this limit. The incoming radiative heat flux, sample thickness and moisture content are some of the used variables. Not only the ignition time can be calculated with the model, but also the mass flux and surface temperature at ignition. The ignition times for softwoods and PMMA are mainly under-predicted. For hardwoods and PVC the predicted ignition times agree well with experimental results. Due to a significant scatter in the experimental data the mass flux and surface temperature calculated with the model are hard to validate. The model is applied on the startup of a municipal waste incineration plant. For this process a maximum allowable primary air flow is derived. When the primary air flow is above this maximum air flow, no ignition can be obtained.

Experimental and numerical study of the effect of sample orientation on the pyrolysis and ignition of wood slabs exposed to radiation

The effect of sample orientation (vertical and horizontal) on the pyrolysis and ignition of wood exposed to radiation has been studied with experimental and numerical methods in the present article. Experimental results show that the pyrolysis rate of vertically oriented wood exposed to radiation is higher than for horizontally oriented wood exposed to radiation. Pyrolysis gas significantly dominates the process of pyrolysis of wood exposed to radiation. Accounting for radiation absorption by pyrolysis gas, a numerical model has been developed to simulate the pyrolysis and ignition of wood in horizontal and vertical orientations exposed to radiation.

Experimental study of the effect of spark power on piloted ignition of wood at different altitudes

Generally, a continuous spark is used in piloted-ignition experiments on combustible materials. However, the potential effect of the spark’s power in such experiments, has been ignored in previous studies. In this article, experiments are carried out to assess the effect of spark power on the ignition characteristics of fir at different altitudes characterized by atmospheric pressures of 0.77 and 1.0 atm. It is concluded that ignition time becomes shorter with an increase of spark power. With a rise in spark power, the mass flux at ignition and the critical heat flux decline in the ignition process. Ignition time is found to be more sensitive to spark power in lower altitudes.

Experimental Study of the Influences of Orientation and Altitude on Pyrolysis and Ignition of Wood

On account of limited attention paid to the influence of orientation and altitude in previous research, the pyrolysis and ignition characteristics of wood in different orientations and altitudes were investigated experimentally. Two orientations were explored: vertical and horizontal. In addition, experiments were conducted in Lhasa and in Hefei, which are at very different altitudes. Ignition time, mass loss rate, and surface temperature are discussed. Compared with those in the horizontal orientation, shorter ignition times, faster mass loss rates, and lower surface temperatures were observed in the vertical orientation. In addition, there are shorter ignition times, faster mass loss rates, and higher surface temperatures in Lhasa (high altitude) than in Hefei (low altitude).

Spontaneous ignition of wood, char and RDF in a lab scale packed bed

Many municipal waste combustors use preheated primary air in the first zone to dry the waste. In most cases the preheat temperature does not exceed 140 °C. In previous experiments it is found that at temperatures around 200 °C, in some circumstances, self- or spontaneous ignition can be achieved. Using preheated air can be a powerful tool to control the ignition and combustion processes in a waste combustion plant. To use this tool effectively, the influence of the preheated air on the fuel bed needs to be well understood. The present work is done to investigate in a systematically way the spontaneous ignition behaviour of a packed bed heated with a preheated air stream. Experiments on a lab scale packed bed reactor are carried out for various fuel types. Because MSW is an highly inhomogeneous fuel, wood and char are used as model fuels. To include the inhomogeneous character of MWS, also experiments are carried out with RDF. Parameters such as primary air flow velocity and temperature, addition of inert material, moisture content of the fuel (wood chips) and particle size (char) have been changed to see their effect on the spontaneous ignition temperature and on the minimum air temperature needed for ignition. The spontaneous ignition temperature is defined as the bed temperature at which a transition takes place from a negligible or slow fuel reaction rate to a rapid oxidation of either the volatiles or the solid fuel without an external source such as a spark or a flame. The minimum or critical air temperature is defined as the lowest air temperature at which ignition can be obtained. It is found that the type of fuel has influence on the ignition temperatures. Besides both the critical air temperature needed for the spontaneous ignition and the spontaneous ignition temperature increase with an increase in the primary air velocity (between 0.1 and 0.5 m/s) and increasing the added inert fraction (between 0 and 40 wt%), irrespective of the fuel type. The effect of air flow velocity and temperature and also the effect of inert on both the critical air temperature and the spontaneous ignition temperature can be explained qualitatively by using Semenov’s analysis of thermal explosions. Semenov’s theory is quantitatively applied to predict the spontaneous ignition and the critical air temperatures for wood.

Experiment study of the altitude effects on spontaneous ignition characteristics of wood

This paper has studied the influence of ambient pressure and oxygen content on spontaneous ignition of wood by conducting contrastive experiments with wood slab exposed to high temperature radiation at two different altitudes. The measurement of mass loss, time to ignition, and surface temperature of wood are carried out. Results show that mass loss rate of wood at high altitudes (3650 m) is higher than the one at low altitudes (50 m), while ignition delay time of the sample at high altitude is shorter. The surface temperatures at the time of ignition in the two different places are both close to each other, which indicates that the pressure did not affects the ignition temperature. The theoretical analysis on the phenomenon of different ignition behavior of wood in these two altitude environments has been presented.

Forensic Engineering Analysis Of Low Temperature Ignition Of Wood

The Phenomena Of Wood Igniting When Exposed For Extended Periods Of Time To Temperatures Below Woods Published Ignition Temperature Value Has Been Of Considerable Interest In Recent Years. The Interest Spans The Fire Investigative, Engineering, And Fire Science Communities All The Way To The Legal System. A Recent Federal Court Ruling Has Introduced Aggravated Controversy On The Subject, Casting Doubt On The Phenomena. While There Are Presently No Scientific Formulas To Reliably Predict The Occurrence, There Is Substantial Empirical Data Which Demonstrates That It Does In Fact Occur. The Purpose Of This Paper Is To Report On Certain Empirical Case Studies, Research Activities, And Experiments Undertaken Which Clearly Demonstrate That Wood Will Ignite When Exposed For An Extended Period Of Time To Temperatures Well Below Its Commonly Recognized Published Ignition Temperature Of Approximately 482 F (250 C). In Particular, It Was Concluded For The Conditions Studied That Ignition Of Wood Occurred Under Exposure Temperatures Of As Low As 256 F When Exposed 12 To 16 Hours Per Day In As Little As 623 Days Or Approximately 21 Months. Data From Three Well-Documented Restaurant Kitchen Fires And Observations Of Wood Located Behind Heated Wall Mounted Appliances In Three Operating Restaurants, Combined With Laboratory And Manufacturer Testing Are Used To Demonstrate That Low Temperature Ignition Of Wood Clearly Occurs.

Paleomagnetic evidence for low-temperature emplacement of the phreatomagmatic Peperino Albano ignimbrite (Colli Albani volcano, Central Italy)

The Peperino Albano (approximately 19–36 ka old) is a phreatomagmatic pyroclastic flow deposit, cropping out along the slopes of the associated Albano maar (Colli Albani volcano, Italy). The deposit exhibits lateral and vertical transitions from valley pond to veneer facies, as well as intracrater facies. We present the results of a paleomagnetic study of thermal remanent magnetization (TRM) of the lithic clasts of the Peperino Albano ignimbrite that provide quantitative estimates of the range of emplacement temperatures across the different facies of the ignimbrite. Emplacement temperatures estimated for the Peperino Albano ignimbrite range between 240° and 350°C, with the temperatures defined in the intracrater facies being generally lower than in the valley pond and veneer facies. This is possibly due to the large size of the sampled clasts in the intracrater facies which, when coupled with low temperature at the vent, were not completely heated throughout their volume during emplacement. The emplacement temperatures derived from the paleomagnetic results are in good agreement with the presence of un-burnt plants at the base of the ignimbrite, indicating that the temperature of the pyroclastic flow was lower than the temperature of ignition of wood. Paleomagnetic results from the Peperino Albano confirm the reliability of the paleomagnetic approach in defining the thermal history of pyroclastic flow deposits.

Modelling the pyrolysis of wet wood – I. Three-dimensional formulation and analysis

A three-dimensional mathematical model for the pyrolysis of wet wood is developed with detailed consideration of moisture evaporation, anisotropic and variable properties, and pressure driven internal convection of gases. Multiple competing reactions are formulated; a single first-order Arrhenius reaction is however applied herein. Transient pyrolysis of a beech wood cube with different initial moisture contents is investigated under various furnace temperatures. Influences of anisotropic properties due to the grain structure on heat and mass transfers are discussed. This model serves as a precursor for Part II: Simulation of piloted ignition of wood in a cone calorimeter of this two-part study.

The influence of different external heating ways on pyrolysis and spontaneous ignition of some woods

A considerable amount of research has been conducted on the pyrolysis, ignition of wood under constant heat flux. However, the heat flux accepted by materials during the fire is increasing with time. This paper describes the theoretical and experimental investigation on pyrolysis and spontaneous ignition of wood exposed to heat fluxes linearly increasing with time. A one-dimensional model that describes the pyrolysis of wood subject to a linearly increasing heat flux is presented. Experiments are conducted for different wood species subjected to several increasing rates of heat fluxes. Some special characteristics of wood pyrolysis and spontaneous ignition have been proposed based on those investigations.

Experimental Study on Spontaneous Ignition of Wood Exposed to Variable Heat Flux

The ignition of combustible materials is an important process in a fire incident. In this work, an experimental study on the ignition process of wood exposed to a variable heat flux has been carried out. Increasing heat flux is adopted and adjusted to simulate a practical fire environment. The time to ignition, temperature distribution, and mass loss are measured for two species of wood. Both, the increasing rate of incident heat flux and the properties of wood, especially density, obviously affect the results. A conduction model is developed to calculate the surface temperature. A compound ignition criterion is brought out for a variable heat flux.

Glowing ignition of wood: the onset of surface combustion

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.

Ignition threshold for impact‐generated fires

Widespread fires can be generated after large impact events by atmospheric heating caused by the reaccretion of high‐energy, vapor‐rich plume material. We examine the threshold irradiance levels necessary for spontaneous and pilot ignition of various types of vegetation and define three specific cases for investigation: (1) 51 kW/m2 for a period of at least 2 min to spontaneously ignite wood; (2) 20 kW/m2 for a period of at least 20 min to ignite wood in the presence of an ignition source; and (3) 28 kW/m2 for a period of at least 1 min to ignite foliage, rotten wood, and forest litter. The threshold ejected plume mass for continent‐wide spontaneous ignition of wood is ∼2 to 6 × 1015 kg, independent of impact location but dependent on the details of the ejecta speed distribution. The threshold ejected plume mass for global spontaneous ignition of wood is in the range ∼1 to 2 × 1016 kg. The threshold plume masses for continent‐wide and global fires are very nearly the same for piloted ignition of wood, while the threshold plume masses for continent‐wide and global ignition of leaves and forest litter are significantly lower, by a factor of ∼2 to 3. Impact craters of at least 85 km diameter are needed to produce continental‐scale fires, and craters of ∼135 km diameter are needed for global‐scale fires.

Ignition of Wood: A Review of the State of the Art

This review encompasses the available practical and experimental data on the ignition of solid wood. Only solid, natural wood is considered, not sawdust, chips, or products that have been treated with fire retardants or other substances, nor is the ignition of living trees. Panel products such as plywood or particleboard have ignition properties very similar to solid wood, so the solid-wood results will generally be applicable to them. Wood may ignite by flaming directly, or it may ignite in a glowing mode, which may or may not be followed by flaming. It is shown that the ignition temperature is around 250oC for wood exposed to the minimum heat flux possible for ignition, and that it invariably ignites, at least initially, in a glowing mode under these conditions. The ignition temperature rises rapidly as the heat flux is increased. Piloted ignition at heat fluxes sufficient to cause a direct-flaming ignition normally occurs at surface temperatures of 300 – 365oC. Autoignition temperatures at fluxes higher than minimum are essentially unknown. No theory is available which encompasses the possibility of glowing, glowing followed by flaming, or direct-flaming ignition modes. Most published studies have dealt with radiant or radiant+convective heating, and knowledge is extremely poor for ignition from direct contact by hot bodies or by flames. A speciesindependent correlation is derived for the radiant, piloted ignition of thermally-thick wood, but the fit is only fair. The minimum flux for ignition is 4.3 kW m -2 , based on a single study; most reported tests have been much too brief to produce useful data on this point.

A model for the prediction of the thermal degradation and ignition of wood under constant and variable heat flux

The ignition of combustible materials is an important aspect of the processes taking place in an unwanted fire. In this work, an experimental and theoretical study of the ignition process of wood has been carried out. Experiments of both spontaneous and piloted ignition have been performed. Constant and decreasing variable heat fluxes have been tested. A mathematical model has been used to predict the time to ignition of wood for the different operating conditions used. The solution of the model provides the temperature at each point of the solid, the local solid conversion and the time to ignition of the material. In general, a good agreement between experimental and theoretical results is obtained.