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.
The paper presents the results of studies of diffusion combustion of gaseous methane in the presence of external pressure pulsations with low amplitude on the flame plume. The analysis of the temperature field and the stabilization time of the combustion mode has been carried out. It is established that the presence of pressure pulsations leads to characteristic changes in the temperature field, which are expressed by a growth of the temperature pulsation amplitude, corresponding to the frequency of external influences. A characteristic time for stabilizing the combustion regime from the moment when there is no external influence to their appearance is determined.
The paper presents experimental data on determining a level of turbulence over a heated metal surface in the saturated turbulence regime, which cannot be explained by the classical Kolmogovov-Obukhov theory. A spectral behavior of temperature fluctuations is studied. Based on the calculated data of the structural function and the spectrum of temperature fluctuations, the level of turbulence over the heated surface is determined along the height. Estimation of the outer scale of turbulence showed that in the center of the metal surface the outer scale increases with height. At the surface boundary, cascade generation-dissipation of vortices is observed.
The processes of combustion and flame propagation in various technological devices and during wildfires are carried out, specifically, under turbulence conditions. Turbulent combustion is a non-stationary process of turbulent mixing of combustion products with a fresh mixture and its ignition due to the temperature increase. This article compares estimates of the turbulence scale in a flame during the combustion of forest fuels in laboratory conditions and in a test site.
The paper examines the effect of low-amplitude pressure pulsations on the temperature field in the flame formed during methane combustion. Using the Ansys Fluent solver, the fields of temperature, velocity, and other flow characteristics in the presence of internal pressure pulsations were analyzed. As a result of the analysis of the obtained data, qualitative estimates of the effect of pressure pulsations on the flame plume were obtained. It is shown that the effect of acoustic oscillations on the flame plume leads to a change in the rate of combustion of fuel.
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 paper presents the results of a study of diffusion combustion of gasoline in the presence of external pressure pulsations with small amplitude. It is found that external pressure pulsations lead to characteristic changes in the temperature field, which are expressed by an increase in the amplitude of the temperature pulsation for certain modes of pressure pulsations. Analysis of the spectra of temperature changes in the entire recorded area showed an uneven distribution of frequency maxima.
The paper presents the effect of low amplitude acoustic pulsations on the temperature field in a flame formed during gasoline combustion. The analysis of the high-temperature inhomogeneities distribution in the flame plume is carried out. It is shown that the effect of acoustic vibrations on the flame plume causes a change in the height of the flame and a change in the rate combustion of the fuel. After analyzing the spectra of temperature changes, the characteristic pulsations are noticed. They differ, depending on the flame zone.
The paper presents an analysis of the turbulent structure of a diffusion flame obtained using IR thermography data. The flame separation into several specific regions is proposed, where various combustion mechanisms are realized for diverse ranges of values of the turbulent Reynolds number. The results of applying an original technique for visualizing the distribution of temperature inhomogeneities in a flame are also presented.
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.
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 paper presents the experimental study results on the effect of external pressure fluctuations on the temperature field in a flame during the combustion of certain liquid hydrocarbon fuels. It is determined that the height of the flame is changed with an external effect occurrence in the form of small amplitude pressure pulsations. Identified oscillations correspond to the frequency of external sound exposure in the spectrum of flame temperature change.
This paper represents physical and mathematical modeling of the flame flow generated during the combustion of diesel fuel. The scale of vortex structures and the change in the Reynolds number in flame were estimated using the methods of IR thermography. The main thermodynamic parameters of flame are in good agreement with the scale of turbulent vortices in flame.
The paper presents experimental investigation results of turbulent vortices scales in diffusion flames. Comparison of obtained data on the basis of digital tracer visualization and thermography was carried out. A good correlation is obtained between the sizes of large vortex structures in the velocity field, recorded using the PIV method, and the size of temperature inhomogeneities, recorded by flame thermography.
This paper represents an experimental study of the effect of low-amplitude external-pressure fluctuations on the field of temperatures in flame during the combustion of some liquid hydrocarbon fuels.
The paper represents the experimental study of the dimensions of turbulent vortices in diffusion flames. The data obtained by the particle image velocimetry method are compared to the data obtained by the thermography method.
Data are presented about the variations in the average power of lidar echo signals with coherent and incoherent receiving over wide range of variations of the refractive turbulence strength in the atmosphere. It is established that in the case of incoherent receiving the backscatter amplification coefficient first increases with increase of the turbulence strength, then saturates at a certain level in the regime of strong turbulence on the probing path and decreases with further refractive turbulence strength increase. The maximum value of the amplification coefficient achievable at a given distance depends on the refractive turbulence strength at the moment of measurement. The time course of the backscattering amplification coefficient is in a good agreement with the temporal changes of the structural constant of turbulent fluctuations of the air refractive index, determined from independent measurements.
The paper represents experimental studying the scales of turbulent vortices in diffusion flames by using the measurements of thermodynamic characteristics obtained by thermography and the aerodynamic characteristics obtained by the PIV method.
The paper represents experimental studying the pulsations of temperature fields and the structure of a flow in the flame formed during the combustion of certain fuels. Also, the paper provides the mathematical modeling of a flow in the flame formed during the combustion of diesel fuels, as well as the comparison with experimental data and the estimation of the scale for turbulent vortices in flame. The experimental results are in satisfactory agreement with numerical modeling, which confirms the hypothesis of similarity for the pulsations of hydrodynamic and thermodynamic parameters.
This paper presents the results of mathematical modeling of the flow in the flame produced during the combustion of diesel fuel and the experimental estimation of the turbulent eddy scale in the flame using thermography methods. Comparison of the numerical results and the experimental data shows that the basic thermodynamic parameters of the flame are in good agreement with the scale of turbulent eddies in the flame.
This paper provides the method for the calibration of the thermal imager to be used in the experimental studies of the temperature field in the plasma jet, using carbon dioxide as a working medium.
This paper presents the experimental study concerning the infrasound effect on the spectrum of the temperature change in flame during the combustion of ethanol.
The paper presents the emission spectra of flame formed during combustion of different fuels and gives the grounds for application of various narrow spectral ranges in the mid-infrared region to record the temperature fields in flame and flame screened objects.
The paper presents the experimental measurements of temperature fields in a narrow mid-infrared spectral range during combustion of different fuels (plant fuels, alcohol, petroleum, kerosene, and diesel fuel). The spectra of temperature changes are obtained in flame. The scale of turbulence in flame is estimated on the basis of temperature nonuniformity measurements and the analysis of temperature spectra in flame.
Mathematical model of heat and mass transfer of crown forest fire is used in this paper, which is developed on the base of experimental research data and laws and methods of mechanics of reacting media. The numerical calculation carried out using software PHOENICS for non stationary three dimensional case. K-Ɛ model of turbulence is taken into account. It is studied the influence of temperature and wind velocity in boundary layer of atmosphere on the turbulent kinematic viscosity coefficient value and distribution of temperature above the crown forest fire front.
Ignition of softwood is experimentally studied during combustion of the peat layer. The characteristic stages of ignition and temperatures are revealed. Wood is found to ignite in a localized center of fire, where the surface temperature of wood reaches the known experimental values.
The paper presents the results of experimental studies required to determine the depth of the combustion front of the peat layer. The studied samples represented four types of peat with a different botanical composition, density, humidity content and degree of decomposition. The depth of the combustion front of peat and the temperature profiles were determined.
This paper presents the results of experimental studies of the properties of the flame in the mid-IR range. Transmittances defined flame for different spectral intervals research shows relationship between the recorded radiance of the flame shielded object and its true characteristics.
This paper presents the emission spectra of the flame produced by combustion of various fuels, provides the rationale for the applicability of various narrow spectral intervals in the range of 2-5 μm for registration problems of temperature fields in the flame and flame shielded registering objects.
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