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Conditions for suppressing the flaming combustion and thermal decomposition of model forest and peat fire by exposure to water, foaming agent emulsion (5%), solution (10%), FR-Les 01 solution (20%), flame retardant solution (5 vol.%), OS-5 solution (15%), and bentonite slurry (5%) were determined. Temperatures during the buildup of model fires and extinguishing of the latter by specialized water-based compositions were measured. Minimum volumes of the extinguishing compositions and the time necessary and sufficient to suppress the pyrolysis of plant biomass were established. Minimum densities of irrigation of model forest and peat fires using water-based compositions with specialized additives were determined. [ABSTRACT FROM AUTHOR]

Background. The physical processes governing flame behaviour are key elements for a better understanding of forest fires. Aims. To study the combustion properties of several dead Mediterranean forest fuels. Method. Samples of straw, eucalyptus, shrubs and Pinus Pinaster with the same load were placed in circular containers of the same size, and ignited in the absence of wind. Key results. The combustion parameters (burning rate, flame height, temperature and gas velocity) evolved according to the same trend regardless of the fuel type. A new law is proposed to account for the anomalous relaxation processes occurring in the growth and decay phases of the flame. The dynamic exponent depends on the vegetation type only in the growth phase (highest for Pinus Pinaster and lowest for straw). The relaxation times are shortest for shrubs and largest for straw. The maximum flame height and burning rate are largest for shrubs and lowest for straw. Froude modelling suggests that the scaling behaviour of the flame may depend on the fuel type. Conclusions. The observed relaxation parameters driving fire dynamics and the combustion characteristics depend on the nature of the fuel. Implications. Further investigation of the vegetation region's influence on these properties is necessary. [ABSTRACT FROM AUTHOR]

Electrical cables are a potential source of ignition and fire hazards in various types of buildings and industrial installations, as well as in all modes of transportation, including aircraft. Fires in buildings pose the greatest threat to human life and health. The composition of thermal degradation products depends mainly on the type of combustible materials and the type of combustion process—flaming or smoldering. The purpose of this paper was to determine, based on experimental studies, the effects of flaming and smoldering combustion on the response times of fire smoke detectors. In addition, the concentrations of fire gases formed in the process of duct combustion, including CO, SO2, NO2, NO, HCN, HCl, HBr and HF, were measured using an FTIR spectrometer. The results presented confirm the significant effect of the way the cable samples burned on detector tripping time. The highest concentration of smoke (Y) in the test chamber was obtained during flame combustion. It was further found that the characteristics of the cable insulation material used, such as the type of PVC, had a significant effect on the toxicity of the emitted gases. The largest amounts of toxic gases were emitted during the smoldering combustion of a cable with a plasticized PVC sheath. [ABSTRACT FROM AUTHOR]

To utilize various types of biomass as raw materials for briquette fuel, the influence of raw material on combustion behavior should be clarified. This study aimed to confirm the influence of biomass raw materials on flaming and char combustion, particularly on the duration of combustion. Cypress, bamboo, rice husk, and paper were used as raw materials for the briquettes. Several sizes of briquettes were burned in a hot airflow setup, and the mass loss (for individual samples) and the durations of flaming and char combustion were obtained. It was found that the duration of flaming combustion for each raw material is proportional to the product of the inverse square of the specific surface area and briquette density. It is suggested that these proportional constants are correlated with the mass percentage of holocellulose in the biomass, which is estimated via ultimate analysis. However, the duration of char combustion for each biomass raw material is almost proportional to the product of the inverse square of the specific surface area and the fixed carbon content of the briquette. It is suggested that these proportional constants are correlated with the mass percentage of ash content in the biomass. Thus, in our study, we were able to predict the combustion characteristics of briquettes made from various raw materials individually. [ABSTRACT FROM AUTHOR]

Electrical cables are a potential source of ignition and fire hazards in various types of buildings and industrial installations, as well as in all modes of transportation, including aircraft. Fires in buildings pose the greatest threat to human life and health. The composition of thermal degradation products depends mainly on the type of combustible materials and the type of combustion process—flaming or smoldering. The purpose of this paper was to determine, based on experimental studies, the effects of flaming and smoldering combustion on the response times of fire smoke detectors. In addition, the concentrations of fire gases formed in the process of duct combustion, including CO, SO2, NO2, NO, HCN, HCl, HBr and HF, were measured using an FTIR spectrometer. The results presented confirm the significant effect of the way the cable samples burned on detector tripping time. The highest concentration of smoke (Y) in the test chamber was obtained during flame combustion. It was further found that the characteristics of the cable insulation material used, such as the type of PVC, had a significant effect on the toxicity of the emitted gases. The largest amounts of toxic gases were emitted during the smoldering combustion of a cable with a plasticized PVC sheath.

Composition of pyrolysis gases for wildland fuels is often determined using ground samples heated in non-oxidising environments. Results are applied to wildland fires where fuels change spatially and temporally, resulting in variable fire behaviour with variable heating. Though historically used, applicability of traditional pyrolysis results to the wildland fire setting is unknown. Pyrolytic and flaming combustion gases measured in wind tunnel fires and prescribed burns were compared using compositional data techniques. CO2 was dominant in both. Other dominant gases included CO, H2 and CH4. Relative amounts of CO, CO2 and CH4 were similar between fire phases (pyrolysis, flaming combustion); relatively more H2 was observed in pyrolysis samples. All gas log-ratios with CO2 in pyrolysis samples were larger than in flaming combustion samples. Presence of live plants significantly affected gas composition. A logistic regression model correctly classified 76% of the wind tunnel samples as pyrolysis or flaming combustion based on gas composition. The model predicted 60% of the field samples originated from pyrolysis. Fire location (wind tunnel, field) and fire phase affected gas composition. The compositional approach enabled analysis and modelling of gas compositions, producing results consistent with the basic characteristics of the data. [ABSTRACT FROM AUTHOR]

This paper explores the behaviors of piloted ignition of fresh broadleaf foliage under external radiant heat flux. A total of 12 plant species were adopted, with volatile matter content varying from 15.4 to 41.4%. Measurements were conducted using a cone calorimeter with the radiant heat flux set at 35, 55, 70, and 85 kW m−2. Under the same radiant heat flux, the samples underwent combustion in two major modes. Some of the samples appeared short time flame and followed by smoldering, whereas the others maintained smoldering throughout the measurements. With an increase in the radiant heat flux or volatile matter content of a sample, the combustion mode of the samples may shift from smoldering to flaming combustion at initial stage of measurement. The critical heat release rate of a sample to form flaming combustion is between 20.9 and 22.5 kW m−2. Further analysis confirmed that the flaming combustion formed at initial stage of measurement mainly relies on the pyrolysis process of the sample surface layer. The initial volatile matter content of a sample and the rate of temperature rise at the surface layer are major factors governing the mass flux of volatiles generated and subsequently determining whether the sample undergoes flaming combustion. [ABSTRACT FROM AUTHOR]

An approach to the mathematical modeling of the suppression of thermal decomposition and flaming combustion of forest fuels (FFs) is proposed which differs from the well-known approaches in that the pyrolyzed FF layer is represented as a heterogeneous structure with high porosity and the thermophysical characteristics of this layer are described using additive mathematical models of thermal conductivity, heat capacity, and density. Experimental studies of the main thermophysical characteristics (thermal conductivity, heat capacity, and thermal diffusivity) of typical FFs were performed. Mathematical modeling of heat- and mass-transfer processes under the above conditions was performed, and the suppression characteristics of the destruction reaction of a typical FF were determined using the values of thermophysical characteristics established in the experiments. The ranges of the integral characteristics of FF flame suppression with varying thermophysical characteristics of FFs within permissible limits were identified. [ABSTRACT FROM AUTHOR]

Results of an experimental study of heat and mass transfer and phase transitions during suppression of flaming combustion and thermal decomposition of condensed matter (CM) by an example of typical combustible materials in the forest (mixtures of leaves, conifer needles, and twigs) by means of the action of a non-atomized water array at different stages of its transformations are reported. The liquid volume and the height of its discharging with respect to the CM surface are varied with allowance for the known stages of water array transformations to illustrate possible differences in the cross-sectional areas of these arrays, which determine the water–CM contact area. The characteristics of CM burning termination are obtained as functions of the height of the beginning of water array motion. [ABSTRACT FROM AUTHOR]

On the flaming combustion of highly densified cypress cylindrical briquette of which diameter/length ratio is 1/2 in the high temperature air, it was reported that the flaming combustion duration is proportional to the product of the inverse square of the specific surface area and the briquette density. However, the influence of biomass raw material on the combustion behavior is not clarified yet. To utilize various biomass as raw material of briquette fuel, the knowledge on this should be obtained. The objective of the present study is to confirm the influence of biomass raw material on the flaming combustion behavior, especially, the flaming combustion duration. Cypress, bamboo, rice husk and paper are used as raw material of the briquette. From the results of the thermogravimetric analysis and the estimation of lignin content in the biomass samples, it was observed that the activation energy decreases with increasing the lignin content. From the results of combustion experiments, it was found that the flaming combustion durations for each biomass raw material are proportional to the product of the inverse square of the specific surface area and the briquette density. It is suggested that these proportional constants have the correlation with the mass percentage of the cellulose in the biomass.

This paper presents the results of an experimental study of the initiation and containment of the flaming combustion and thermal decomposition of typical forest fuels by creating a fire break in the form of a wet layer of fixed width, length, and depth with a known volume of contained liquid. The ranges of parameter values that ensure stable suppression of the flaming combustion and thermal decomposition of forest fuel material were determined Experiments were performed for all major types of forest fuels: leaves, needles, branches, and mixtures thereof. The minimum water volumes and fire-break sizes required for guaranteed containment of combustion of the investigated forest fuels are predicted. [ABSTRACT FROM AUTHOR]

Understanding the combustion dynamics of fuels, and the generation and propagation of smoke in a wildland fire, can inform short-range and long-range pollutant transport models, and help address and mitigate air quality concerns in communities. Smoldering smoke can cause health issues in nearby valley bottoms, and can create hazardous road conditions due to low-visibility. We studied near-field smoke dynamics in a prescribed fire of 3.4 hectares of land in a boreal black spruce forest in central Alberta. Smoke generated from the fire was monitored through a network of five field-deployable micro sensor systems. Sensors were placed within 500–1000 m of the fire area at various angles in downwind. Smoke generated from flaming and smoldering combustions showed distinct characteristics. The propagation rates of flaming and smoldering smoke, based on the fine particulate (PM2.5) component, were 0.8 and 0.2 m/s, respectively. The flaming smoke was characterized by sharp rise of PM2.5 in air with concentrations of up to 940 µg/m3, followed by an exponential decay with a half-life of ~10 min. Smoldering combustion related smoke contributed to PM2.5 concentrations above 1000 µg/m3 with slower decay half-life of ~18 min. PM2.5 emissions from the burn area during flaming and smoldering phases, integrated over the combustion duration of 2.5 h, were ~15 and ~16 kilograms, respectively, as estimated by our mass balance model.

Experimental studies of the dynamics of temperature, transmittance coefficient and forward scatter of radiation in the smoke under the ceiling space when burning paper where conducted. Behavior of main signs of fire at an early stage, common for the mentioned type of inflammables, was studied.

An experimental study has been performed to investigate the integral characteristics of the processes of heat and mass transfer and phase transformations during interaction of a droplet flow with the combustion front of a highly porous condensed material. The macroscopic regularities of the suppression of flaming combustion and thermal decomposition of typical forest fuel material due to the removal of heat as a result of its absorption during vaporization and convective cooling were studied. Three modes of interaction of a droplet aerosol with the burning forest fuel materials were considered. The time of combustion termination and the time of thermal decomposition of forest fuel materials were determined. The mechanisms of the main physicochemical processes occurring during interaction of droplet flow with the combustion front of typical forest fuel materials were established. [ABSTRACT FROM AUTHOR]

Coal slime, a low-calorific-value fuel, is a by-product during coal washing, which can be disposed in quantity and fully utilized in circulating fluidized bed (CFB) boiler. This research paid attention to the ignition and combustion behaviors of single coal slime particles, which affect the normal combustion, operation stability and burning efficiency in circulating fluidized bed boiler. The ignition and combustion behaviors including ignition mechanism, ignition delay, ignition temperature and combustion process of single coal slime particles in a vertical heating tube furnace in CO 2 /O 2 atmosphere were researched under different operation condition parameters, for different gas temperatures ( T g  = 923, 1073, and 1173 K), gas flow rates ( V  = 0–20 L/min), and oxygen mole concentrations (O 2 % = 5–80%). Coal slime particle had three ignition mechanisms in CO 2 /O 2 atmosphere, namely, homogeneous ignition of volatiles at the windward and leeside of particle, heterogeneous ignition of char and heterogeneous ignition of coal. Only heterogeneous ignition of char and homogeneous ignition of volatiles at the windward of particle occurred in quiescent atmosphere. However, homogeneous ignition region decreased while heterogeneous ignition region increased gradually with the increasing flow rates in the oxygen concentration-gas temperature plane. Different ignition mechanisms were accompanied with various combustion processes. The combustion processes corresponding to heterogeneous ignition of char changed from flameless combustion to flaming combustion as oxygen concentration increased. Moreover, the critical oxygen concentration elevated from 30% to 50% with the increasing flow rate. The ignition temperatures and ignition delays decreased with the increasing gas temperature and oxygen concentration. As the flow rate increased, the trends became more obvious in medium-to-low oxygen concentrations. Compared with the ignition characteristics and combustion processes of coal slime particles in N 2 /O 2 atmosphere, those in CO 2 /O 2 atmosphere were suppressed due to the higher mole heat capacity and lower diffusion rate of oxygen molecule in CO 2 . [ABSTRACT FROM AUTHOR]

To investigate the influence of briquette size and density on the combustion behavior in both flaming and char combustion stage, the combustion experiments with the highly densified columnar briquette made from cypress sawdust were carried out. Three sizes of the briquette, φ30 mm×60 mm, φ35 mm×70 mm and φ40 mm×80 mm, of which diameter/length ratio is kept constant at 1/2 and three types of the briquette density, 900, 1100 and 1300 kg/m3 were employed. The water content of the briquette was kept around 10 wt%. The mass loss rate and the duration in both combustion stages were measured. In the flaming combustion stage, it is observed that the average mass loss rate per unit specific surface area is proportional to the briquette surface area, while it doesn't depend on the briquette density. It is expected by considering Fourier number that the flaming combustion duration is proportional to the product of the inverse square of the specific surface area and the briquette density and it is shown that the experimental results correspond to the expectation. It is found that the relationship between normalized mass loss rate and normalized time is nearly the same regardless of the briquette size and density. In the char combustion stage, normalized mass loss can be approximately expressed with the shrinking core model by assuming the effective oxygen diffusion coefficient in the ash layer for each briquette density used in this study. And it is found that the effective oxygen diffusion coefficient in the ash layer obtained by the shrinking core model decreases with increasing the briquette density.

This paper presents an experimental study of heat and mass transfer and phase transformations in the suppression of flaming combustion and thermal decomposition of model ground, crown, and mixed forest fires due to local exposure to water. The experiments were carried out with typical combustible forest materials (mixture of leaves, needles, and twigs) and models of trunks and branches of trees. The conditions and characteristics of suppression of the flaming combustion and thermal decomposition of combustible forest materials were determined. It is shown that in the case of crown and mixed fires, local short-term (a few seconds) action of a liquid projectile does not suppress the thermal decomposition of the material (but can only lead to localization of flaming combustion). In the case of ground forest fires, this approach can be efficient with an appropriate choice of the water-irrigated area of the combustion zone and the rate and time of water spraying. [ABSTRACT FROM AUTHOR]

Diverse sensing techniques have been developed and combined with machine learning method for forest fire detection, but none of them referred to identifying smoldering and flaming combustion phases. This study attempts to real-time identify different combustion phases using a developed wireless sensor network (WSN)-based multi-sensor system and artificial neural network (ANN). Sensors (CO, CO2, smoke, air temperature and relative humidity) were integrated into one node of WSN. An experiment was conducted using burning materials from residual of forest to test responses of each node under no, smoldering-dominated and flaming-dominated combustion conditions. The results showed that the five sensors have reasonable responses to artificial forest fire. To reduce cost of the nodes, smoke, CO2 and temperature sensors were chiefly selected through correlation analysis. For achieving higher identification rate, an ANN model was built and trained with inputs of four sensor groups: smoke; smoke and CO2; smoke and temperature; smoke, CO2 and temperature. The model test results showed that multi-sensor input yielded higher predicting accuracy (¥82.5%) than single-sensor input (50.9%-92.5%). Based on these, it is possible to reduce the cost with a relatively high fire identification rate and potential application of the system can be tested in future under real forest condition. [ABSTRACT FROM AUTHOR]

Smouldering is slow, low-temperature and flameless, and has been potentially regarded as an alternative for organic waste removal technology. However, as an incomplete combustion process, toxic smoke and pollution from the smouldering are significant concerns that limit its popularization. This work applies a newly developed smouldering-based waste removal technology to investigate the removal of coffee waste, wood waste, and organic soil (simulated sludge) via using a flame to clean smouldering emissions at different airflow velocities (3–24 mm/s). Once ignited from the top, the smouldering front first propagates downwards where a stable flame situated above could be piloted and sustained to purify the smouldering emissions until the smouldering front reached the bottom of the fuel bed. The efficiency of pollution mitigation was demonstrated by significantly lower CO and VOCs emission after purification by self-sustained flame. The equivalent critical mass flux of flammable gases required for igniting the smouldering emissions is 0.5 g/m2∙s, regardless of the fuel type. The smouldering temperature, propagation rate and burning flux all increase with the airflow velocity but are also slightly sensitive to the type of waste. This work enriches strategies for the clean treatment of smouldering emissions and promotes an energy efficient and environmentally friendly method for organic waste removal. [ABSTRACT FROM AUTHOR]

A heat transfer model based on the well-known Henderson equation has been modified to allow for self-sustained ignition and the flaming combustion phenomena of E-glass fibre-reinforced epoxy composites to be predicted from first principles using known thermal-physical and thermodynamic data for their constituents. The modifications consider: (1) the assignment of thermodynamic conditions (e.g. ignition temperature and mass flux of volatiles) necessary and sufficient to trigger self-sustained ignition, and (2) the inclusion of an integrated loop allowing the heat energy generated from the flaming combustion process to be fed back into the burning laminate. The model compares moderately well with experimental results obtained from cone calorimetric measurements. The additional modelling capabilities considered in this study provide the basis for an analytical model that can more accurately predict the thermal response and flaming combustion of glass fibre-reinforced polymer composites exposed to a one-sided radiant heating environment in the presence of an ignition source. [ABSTRACT FROM AUTHOR]

Single particle combustion behaviours of coal-biomass fuel mixtures are studied. Different biomass i.e. sawdust, wood and rice husk is blended with locally available low grade coal to carry out the experimental investigation. The combustion of solid fuel consists of flaming combustion and char combustion. Rice husk showed higher flaming time and char glowing time because of higher ash and particle density. The burning time of coal-rice husk mixture fuel sample is higher compared to other samples due to the combine effect of particle density and ash content of the fuel samples. Ignition mass flux of saw dust is higher compared to rice husk and wood fuel particles because of the presence of higher volatiles in sawdust. The diameter index for flaming combustion, char combustion are 1.13 to 0.47 and 0.63 to 1.23 respectively for 0%–40% coal in coal/wood fuel mixtures. It is observed that with the increases in surface area/volume ratio, flaming and char combustion decreases due to reduction in effective surface area of the particle for combustion. This study concludes that particle size or surface area/volume together with particle density are the primary controlling parameter for better conversion of fuel mixtures in any co-combustion system. • Single particle combustion studies of coal/biomass fuel mixtures. • Ignition mass flux of saw dust is higher compared to rice husk and wood. • Diameter index for flaming and char combustion are 1.13 to 0.47 and 0.63 to 1.23 • Increases in surface area/volume ratio decrease the flaming and char combustio n. [ABSTRACT FROM AUTHOR]

Diverse sensing techniques have been developed and combined with machine learning method for forest fire detection, but none of them referred to identifying smoldering and flaming combustion phases. This study attempts to real-time identify different combustion phases using a developed wireless sensor network (WSN)-based multi-sensor system and artificial neural network (ANN). Sensors (CO, CO₂, smoke, air temperature and relative humidity) were integrated into one node of WSN. An experiment was conducted using burning materials from residual of forest to test responses of each node under no, smoldering-dominated and flaming-dominated combustion conditions. The results showed that the five sensors have reasonable responses to artificial forest fire. To reduce cost of the nodes, smoke, CO₂ and temperature sensors were chiefly selected through correlation analysis. For achieving higher identification rate, an ANN model was built and trained with inputs of four sensor groups: smoke; smoke and CO₂; smoke and temperature; smoke, CO₂ and temperature. The model test results showed that multi-sensor input yielded higher predicting accuracy (≥82.5%) than single-sensor input (50.9%-92.5%). Based on these, it is possible to reduce the cost with a relatively high fire identification rate and potential application of the system can be tested in future under real forest condition.