В докладе представлены результаты экспериментальных исследований модельных очагов пожаров на локальные характеристики атмосферы. Эксперименты проводились в полунатурных условиях на Базовом экспериментальном комплексе ИОА СО РАН. Зарегистрировано, что вследствие распространения модельного пожара происходит формирование индуцированной атмосферной турбулентности, проявляющееся в изменении структурной характеристики флуктуаций показателя преломления, изменении локальных метеопараметров, выброс в атмосферу газообразных и конденсированных продуктов горения. Показано, что на расстоянии до 500 м от очага горения наибольшая концентрация конденсированных продуктов горения регистрируется на высоте 10-20 м. Установлено, что в результате горения в окрестности эксперимента преобладают фракции аэрозолей с диаметром частиц менее 0.65 мкм. The report presents the results of experimental studies of model fires on the local characteristics of the atmosphere. The experiments were carried out in semi-natural conditions at the Basic Experimental Complex of the IOA SB RAS. It has been recorded that due to the spread of a model fire, induced atmospheric turbulence is formed, manifested in a change in the structural characteristics of fluctuations in the refractive index, changes in local meteorological parameters, and the release of gaseous and condensed combustion products into the atmosphere. Gorenje It has been shown that at a distance of up to 500 m from the gorenje gorenje, the highest concentration of condensed combustion products is recorded at an altitude of 10-20 m. It was found that as a result of gorenje, aerosol fractions with a particle diameter of less than 0.65 microns predominate in the vicinity of the experiment.

Results of mathematical simulation of the influence of the swirling of a flow of an equilibrially dissociating heattransfer agent (nitrogen tetroxide) in a tube on the heat transfer and the chemical reaction in it are presented. It is shown that an increase in the intensity of swirling of such a flow in a tube increases the rate of heat exchange in it, with the result that the Nusselt number of the flow increases. In this case, the heat transfer in the flow depends not only on the integral intensity of its swirling but also on the method of organization of the flow swirling. It was established that, in the case of active action of the centrifugal forces on this flow, the turbulent disturbances arising in it cause its heat-transfer coefficient to increase, and, in the case of conservative action of the centrifugal forces on the flow, its heat transfer coefficient decreases. It is shown that the rate of heat exchange in the indicated flow can be controlled by changing the tangential component of the velocity of the flow along the radius of the tube.

The study investigates the transition process from a ground fire to a crown fire. The studies were carried out in seminatural conditions on the territory of the Base Experimental Complex (BEC) of the IAO SB RAS. Previously, reconstruction of the forest canopy was carried out. The emergence of a crown fire occurred due to the transition of a ground fire to the bottom layers and further to the crowns of trees. Non-contact diagnostic methods (IR thermography) were predominantly used to measure combustion front parameters.

Results of investigations of the heat exchange in the turbulent flow of nitrogen tetroxide in a cylindrical channel are presented. The equilibrium stage of the dissociation reaction N 2 O 4 ⇄ 2NO 2 was considered. It was established that an increase in the temperature of the wall of the channel leads to an intensification of the chemical reaction proceeding in the N 2 O 4 flow and causes the absorption of the heat, transferred from the channel wall, in this flow to increase, with the result that the temperature of the near-wall layers and the thickness of the thermal boundary layer in the chemically reactive gas flow decrease to a level lower than those of a chemically inert heat-transfer agent. It is shown that the use of a dissociating heat-transfer agent in a short channel is advantageous in the case where the rate of its flow is small, and, to increase the efficiency of heat exchange in a high-velocity flow of such an agent, it is necessary to increase the length of a heat exchanger. Approximation formulas for determining the criteria of heat exchange in flows of chemically inert and reactive gases have been obtained.

The article is concerned with the experimental study of the crown fire effect on atmospheric transport processes: the formation of induced turbulence in the vicinity of the fire source and the transport of aerosol combustion products in the atmosphere surface layer at low altitudes. The studies were carried out in seminatural conditions on the reconstructed forest canopy. It was established that the structural characteristics of fluctuations of some atmosphere physical parameters in the case of a crown fire practically coincide with the obtained earlier values for a steppe fire. The highest concentration of aerosol combustion products was recorded at a height of 10–20 m from the ground surface. It was found that the largest number of aerosol particles formed during a crown fire had a particle diameter of 0.3 to 0.5 µm. As a result of experimental data extrapolation, it is concluded that an excess of aerosol concentration over the background value will be recorded at a distance of up to 2000 m for a given volume of burnt vegetation. It is of interest to further study these factors of the impact of wildfires on atmosphere under the conditions of a real large natural wildfire and determine the limiting distance of aerosol concentration excesses over background values.

В докладе представлены некоторые результаты многолетних экспериментальных исследований влияния модельных степных пожаров на характеристики атмосферы. Установлено локальное изменение метеопараметров и параметры наведенной атмосферной турбулентности, определены характерные газообразные продукты пиролиза и горения, которые попадают в атмосферу в результате природных пожаров. Полученные результаты позволят осуществлять оценку влияния массовых пожаров на экологию регионов, глобальные атмосферные и климатические процессы.

Проведено численное моделирование формирования подъема и распространения загрязняющих веществ. Расчеты показывают, что для спокойной атмосферы взаимодействие облака примеси с окружающим воздухом незначительно, и разбавление происходит на больших высотах. С увеличением интенсивности атмосферной турбулентности происходит интенсификация смешения, при этом наблюдается увеличение размеров облака и большее разбавление примеси. Проведенные расчеты позволили определить уровень загрязненности для различных метеорологических условий и источников загрязнения.

The article presents the results of a series of mesoscale experiments to study wildfires and their impact on the atmosphere. A change in meteorological parameters, a significant increase in fluctuations of the refractive index, speed of sound and temperature in the vicinity of the experiment, which are a reflection of the occurrence of turbulent processes in the atmosphere, were established, experimental data were obtained on changes in the concentration of methane and carbon dioxide as a result of a fire, and data were obtained on the mechanism of occurrence of crown fire.

The results of seminatural experiments on the study of steppe and field wildfires characteristic of the steppe and forest-steppe zones of Western Siberia are presented. Using infrared (IR) thermography methods, the main thermal characteristics of the fire front are derived, the flame turbulence scale is estimated, and changes in the structure function of the air refractive index are analyzed in the vicinity of a fire. The effect of a model fire on the change of meteorological parameters (wind velocity components, relative air humidity, and temperature) is ascertained. Large-scale turbulence is observed in the front of a seminatural fire, which is absent in laboratory conditions. The predominance of large-scale turbulence in a flame results in turbulization of the atmosphere in the vicinity of a combustion center. Strong heat release in the combustion zone and flame turbulence increase the vertical component of the wind velocity and produce fluctuations in the air refractive index, which is an indicator of atmospheric turbulization. This creates prerequisites for the formation of a proper wind during large fires. Variations in the gas and aerosol compositions of the atmosphere are measured in the vicinity of the experimental site.

As the set of experiments result, statistically substantiated data were obtained on the laws of ignition of a model angular structure under conditions of a point source of heat exposure. The use of IR diagnostics made it possible to control the thermal picture in the experimental area, as well as to capture areas of the highest and lowest heating. In the Large Aerosol Chamber of IAO SB RAS, preliminary experiments were carried out on a “firebrand shower” model exposure, which is naturally occurring firebrands (flaming or glowing embers) with some types of construction materials (chipboards). The exposure of the samples to firebrands stream was provided using a firebrand generator of own original design. It was experimentally confirmed that particle size plays a significant role in the ignition of a building structure. If the characteristic particle size, which can be defined as the ratio of its volume to the surface area in contact with the wood, is less than a certain characteristic value, then the ignition mode with a sharp temperature maximum near the phase interface is not fulfilled. This can be explained by the prevailing heat removal into the external environment in comparison with the amount of heat coming from a heat gun and resulting from chemical reactions.

The paper represents the experimental study of combustion over the surface of a vertically-mounted oriented wood-based panels (plywood, chipboard and oriented strand board) under different environmental conditions. The IR thermography was used as a diagnostic method. An infrared camera JADE J530SB was used to obtain the sequences of thermograms characterizing the heat flow pattern on the surface of the sample during vertical combustion and determine the velocity of the combustion wave under laboratory and field conditions. In addition, during the field tests the change in the angle of the combustion front was estimated depending on time.

The paper presents results of an experimental study of the propagation characteristics of grassland fire front, its effect on meteorological parameters and the emission of gaseous combustion products. As a result of the study, it was found that the seat of fire of a small-scale combustion lead to an increase in air temperature by 2-3 degrees and a decrease in relative humidity by 5%. The highest pulsations amplitude of the wind velocity vertical component of 12 m/s was recorded using a weather station installed at a relatively low height. These pulsations are due to the strong inhomogeneous of the upward flow of combustion products.

This paper presents the experimental study results on the effect of heat flux emitted by a standard source on the charring and ignition characteristics of wood construction materials (plywood, chipboard, and oriented strand board) using infrared thermography (IRT) in the narrow spectral ranges of infrared wavelength. The time to ignition (TTI), charring rate and depth were obtained for the samples. In addition, the effect of several fire retardants on the charring rate and depth of the samples and TTI was analyzed. All fire retardants contribute to an increase in TTI, which confirms their main function—fire protection. However, the effect of fire retardants differs noticeably depending on the material. A new experimental technique is suggested, with the infrared imaging of the temperature distribution along the end of a sample under the heat flux effect on its frontal surface. The uniqueness of this approach consists in the registration of the entire process of ignition and combustion of the presented materials, which occurs in real time without contact with high spatial and temporal resolution. Using the infrared camera of the research class, it becomes possible to record the entire process from the occurrence of the temperature exposure region to the deep carbonized crater in the body of the material. The results can serve as additional recommendations in the development of fire hazard testing methods for construction materials and fire retardants.

The paper presents the results of studies of gasoline and diesel fuel diffusion combustion using IR thermography methods. Experimental results of the effect of small amplitude pressure pulsations with various frequencies on the spectra of temperature changes in the flame and other characteristics are obtained. It is shown that the effect of pressure pulsations with certain frequencies leads to a change in the flame height, fuel burning-up rate and the appearance of characteristic frequency maximum in the spectra of temperature changes in the flame.

The paper represents the experimental study of combustion over the surface of a vertically-mounted oriented strand board panel under different environmental conditions. An infrared camera was used to obtain the sequences of thermograms characterizing the heat flow pattern on the surface of the sample during vertical combustion and determine the velocity of the combustion wave under laboratory and field conditions. In addition, the change in the angle of the combustion front was estimated depending on time.

The behavior of wood building materials (plywood, oriented strand board, particle board) exposed to burning and smoldering firebrands is investigated in this work. To control the temperature on the surface of the samples, an infrared camera (JADE J530SB) with a 2.5–2.7 micron optical filter that can record the temperature in the range of 300–800 °C was used. The Canon HF R88 video camera was used to evaluate the ignition delay and the behavior of firebrands after falling onto the surface of wood building material samples. In the wind speed range of 0–1 m/s, the ignition of the samples was not observed. A small amount of additional oxidant influx in the landing zone of firebrands caused their slow smoldering on the surface until complete combustion. Thus, it can be concluded that smoldering natural firebrands does not affect the ignition of wood building material samples for the selected experimental parameters. The probability of ignition and the ignition delay of wood were determined depending on the size and number of firebrands, the presence of the air flow in the landing zone of particles, as well as on the initial temperature of wood. The experimental temperature distribution was obtained on the surface of wood exposed to the model ground fire using infrared thermography.

The paper presents the experimental study results on the effect of heat flux emitted by a standard source on the charring and ignition characteristics of pine wood. Using a new method of setting the experiment with the recording of IR image, the charring rate and depth of the wood as a result of heat exposure from a standard source. The influence of several fire retardants on the charring rate and depth of samples is analysed. The use of noncontact IR diagnostics allows one to analyse the charring rate of pine wood depending on the intensity of heat flux and to draw up the temperature field.

Much heat is released during the propagation of ground and crown fires, which can be a reason of wood construction firing in the settlements located near the forest border. There are a great number of experimental studies on the fire hazard of wooden materials. However, the available data require additional experimental results to study the fire-hazardous characteristics of various construction materials by using infrared diagnostics. The paper presents the results of experimental study of the impact of heat flux emitted by a standard source on the charring and ignition characteristics of wood construction materials using thermography. The effect of various fire retardants on the charring rate and depth of the samples as well as the ignition time are analyzed. The following widespread wood construction materials are used as studied samples: plywood, chipboard, and oriented strand board. As a result of experimental studies carried out using thermocouples and infrared camera, a good agreement in the maximum temperature on the surface exposed to the heat effect was obtained. The use of the fire retardant impregnation results in an increase in the ignition time of the sample. At the same time it does not eliminate a possibility of the flame occurrence on the sample surface. The experimental method proposed in this paper allows one to estimate the charring depth and rate of the material exposed to the heat flux effect, and to determine the ignition time.

This paper represents a study on the characterization of firebrand production which was carried out, using experimental fires conducted as prescribed fires in the New Jersey Pine Barrens, USA in March of 2013–2015. Several preliminary techniques were tested to characterize the firebrand production. Firebrands were collected from three plots for each year and analyzed for mass and size distribution. Thermal imagery was used to measure the velocity, size and number of firebrands in 2014 and 2015. The distribution of firebrands was evaluated in a monitored volume during the experiment. It was found that not less than 70% of collected particles were bark fragments and the rest were pine and shrub branches. The number of firebrands decreases with increasing the cross section area of firebrands. The mass of the particles varied from 5 to 50mg, and the maximum number of the particles was observed for the mass range of 10–20mg. About 80% of firebrands were particles with the cross section area of (5–20) × 10−5 m2. These results are consistent with the available observations of real fires [1], [2]. Processing of infrared video showed that starting from a distance of 13m from fire front, an increasing number of firebrands were observed in a controlled volume, increasing in number up to 180 per second. Relationships describing the time-variation of the number of particles that dropped on a 1.4m2 surface and the number of particles that flew through a 1m3 volume were obtained. Comparing the experimental and calculated data, we can conclude that these relationships allow us to describe the two numbers with an acceptable accuracy (adj. R2 0.74 and 0.86, respectively). In addition, the velocity of the particles, which depended on the wind velocity, was in the 0.1–10.5m/s range, with an average value of 2.5m/s.