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This study developed an objective approach for determining fire source location based on an artificial neural network (ANN) model. The samples for the ANN model were obtained from computational fluid dynamics simulations. A data preprocessor was devised to transform numerical simulation results into a format that could be used by the ANN model prior to network training, and bootstrap aggregation was used to improve the model's predictive performance, which was evaluated by the leave-one-out approach. The results show that the 95% left-tailed confidence limit was 0.7921 m for planar dimensions of 5 m × 5 m, which is sufficiently accurate for practical application. Additionally, comprehensive experiments were conducted in the confined space of a fire compartment that was geometrically similar to various fire source locations to explore soot patterns and verify the ANN model. The experimental results reveal that the differences between the locations determined in scaling experiments and the locations predicted by the ANN were invariably less than 1 m. In particular, the difference was only 0.17 m when the fire source was located in the centre of the fire compartment. These results demonstrate the feasibility of the devised ANN model for reconstructing fire source location in engineering applications. [ABSTRACT FROM AUTHOR]

A three-dimensional-printed solid fuel grain with a star-fractal swirl port was developed to improve the fuel regression rate of hybrid rockets. The printing material used for the grains was an acrylonitrile-butadiene-styrene resin. Nitrous oxide was employed as the oxidizer. Combustion experiments on the hybrid rocket engine with the developed grain showed that the star-fractal swirl port appeared to improve the thrust and specific impulse compared to the classical circular and starfractal ports when tested using the same oxidizer mass flow rate that is a controllable parameter of hybrid rocket engines. After the experiments, the burned grains were cut and the grain web thicknesses were measured to evaluate the local regression rate. It was found that the fuel surface regressed more rapidly near the concave parts of the star fractal rather than the convex parts. Next, the measured local regression rates were axially averaged. The axially-averaged local regression rates of the star-fractal swirl port were much higher than those of the star-fractal and circular ports. Finally, a numerical approach using the level set method for evaluating time- and space-averaged regression rate was developed. This approach was validated by comparing the space-averaged regression rates with the axially-averaged local rates. [ABSTRACT FROM AUTHOR]

Wildfire is a threat for many boreal ecosystems and induces deep modifications in organic horizons. In this paper, we have considered fire-induced changes to the organic horizon properties. The effect of fire was studied by using a forest litter burning experiment. Sample heating was performed in the lab at fixed temperatures (200, 300 and 500 °C), on a set of O horizons developed under pine (Flavocetraria-Pinetum association) and spruce (Piceetum hylocomium splendens association) forest litters. Litters were analyzed in terms of pH, specific electrical conductivity, specific surface area, total carbon (Ctot) and nitrogen (Ntot) content, water-soluble carbon and nitrogen, δ13C and δ15N stable isotope analysis and 13C NMR spectroscopy. The mean pH values increased from ~5 to ~8.2 with an increase in the influence of temperature. The specific electrical conductivity and specific surface area properties increased as well from ~255 to ~432 and from 0.42 to 1.84, respectively. Ctot and Ntot decreased, but at the same time the inorganic carbon content increased. The aromaticity of organic matter after the fire increased. The results of the present study show that organic horizons are changed by wildfire and this discussion made it clear to help with the understanding how fire affects organic matter. [ABSTRACT FROM AUTHOR]

This study developed an objective approach for determining fire source location based on an artificial neural network (ANN) model. The samples for the ANN model were obtained from computational fluid dynamics simulations. A data preprocessor was devised to transform numerical simulation results into a format that could be used by the ANN model prior to network training, and bootstrap aggregation was used to improve the model’s predictive performance, which was evaluated by the leave-one-out approach. The results show that the 95% left-tailed confidence limit was 0.7921 m for planar dimensions of 5 m × 5 m, which is sufficiently accurate for practical application. Additionally, comprehensive experiments were conducted in the confined space of a fire compartment that was geometrically similar to various fire source locations to explore soot patterns and verify the ANN model. The experimental results reveal that the differences between the locations determined in scaling experiments and the locations predicted by the ANN were invariably less than 1 m. In particular, the difference was only 0.17 m when the fire source was located in the centre of the fire compartment. These results demonstrate the feasibility of the devised ANN model for reconstructing fire source location in engineering applications.

By establishing a mathematical model to simulate a mixed jet of oxygen and superheated steam from a coherent supersonic jet oxygen lance, we studied the effect of superheated steam on the fluid characteristics of the mixed jet. The model was initially verified through laboratory experiments prior to analyzing the fluid characteristics of the mixed jet in detail. These characteristics included the jet velocity, the temperature, the turbulent kinetic energy (TKE), and the mass distribution. The results showed that, at an ambient temperature of 1700 K, the jet velocity measured in the laboratory experiment was consistent with the fluid velocity obtained by numerical simulations, with an error of only 2.7%. In a high-temperature environment, the jet velocity of the mixed oxygen and superheated steam jet was increased, the TKE around the center jet was enhanced, the superheated steam exhibited an inhibitory effect on the combustion reaction of annular methane, and the potential core length of the coherent supersonic jet was reduced, which was conducive to methane combustion and delayed the reduction in the central jet velocity. [ABSTRACT FROM AUTHOR]

In the study, crop residue burning (CRB) emissions were estimated based on field surveys and combustion experiments to assess the impact of the CRB on particulate matter over South Korea. The estimates of CRB emissions over South Korea are 9514, 8089, 4002, 2010, 172,407, 7675, 33, and 5053 Mg year−1 for PM10, PM2.5, OC, EC, CO, NOx, SO2, and NH3, respectively. Compared with another study, our estimates in the magnitudes of CRB emissions were not significantly different. When the CRB emissions are additionally considered in the simulation, the monthly mean differences in PM2.5 (i.e., △PM2.5) were marginal between 0.07 and 0.55 μg m−3 over South Korea. Those corresponded to 0.6–4.3% in relative differences. Additionally, the △PM10 was 0.07–0.60 μg m−3 over South Korea. In the spatial and temporal aspects, the increases in PM10 and PM2.5 were high in Gyeongbuk (GB) and Gyeongnam (GN) provinces in June, October, November, and December. [ABSTRACT FROM AUTHOR]

Coherent lances have been playing an extremely important role in the process of supplying oxygen to an electrical arc furnace, which has been widely used in metallurgy, and its metallurgical and operational benefits have been well reported. When compared with the conventional supersonic oxygen lance, the coherent lance could increase the oxygen utilization rate, strengthen penetration ability, and achieve a good stirring effect. However, there was limited research about the flow field characteristics of a coherent jet using different restriction structures for a coherent lance tip. This paper analyzed velocity and temperature profiles at various parameters and conditions. Both numerical simulation and combustion experiment have been carried out to investigate the velocity and temperature profiles using three kinds of restriction structures at room and high ambient temperature conditions. Further, the impact diameter and depth of the molten bath have also been analyzed at a certain lance height. The result shows that the restriction structure could delay energy transmission in a radial direction, which enlarges a high-temperature zone in an axial direction, resulting in the increase of the velocity potential core length and the improvement of the mixing ability of the main oxygen jet.

The coherent lance technology is widely used in the electric arc furnace (EAF) steelmaking process.It achieves a better metallurgical effect compared with the conventional supersonic lance technology.Herein, to further improve the stirring ability of the coherent lance, the effects of shrouding nozzle arrangement on the flow field and stirring ability of coherent jet were analyzed under two environment temperatures.Based on the results of the numerical simulation and combustion experiment, the characteristics of axial velocity and total temperature distributions has been introduced for researching the impaction ability of coherent jet using various shrouding nozzle arrangements.The appropriate simulation model was built by testing three types of mesh levels.The eddy dissipation concept (EDC) model and chemical kinetic mechanism were adopted to represent the combustion reactions of the O2-CH4jet flame in the numerical simulation process.Resultsreveals that the numerical simulation data shows good agreement with combustion experiment.The initial velocity at the exit of main oxygen Laval nozzle does not change with different shrouding nozzle arrangements.With increase in the distance between the main oxygen and shrouding nozzles, the length of the velocity potential core first increases and then reduces.Moreover, all shrouding nozzle arrangements increase the length of velocity potential core.

Hybrid rockets have the technical problem of a low fuel regression rate, which thereby causes a low fuel mass flow rate. Owing to recent developments in additive manufacturing technologies, using a solid fuel grain with a complicated geometrical port is one method for improving the flow rate. Star fractal geometry was employed as a complicated geometry. Combustion experiments using the grain with a star fractal port were performed. A conventional circular port was also tested for comparison. Local fuel regression rate, axial-direction-averaged local fuel regression rate, thrust, specific impulse and c* efficiency were evaluated. The local regression rate was high near the injector as a result of the impingement of injected oxidizer flow on the surface. While the axial-direction-averaged local regression rate of the star fractal port was slightly less than or almost comparable to that of the circular port, the thrust of the star fractal port was higher than that of the circular port because of the higher fuel mass flow rate. In addition, there was little difference in the specific impulse and c* efficiency when comparing the star fractal and circular ports. Therefore, star fractal geometry is superior to the circular port as the port geometry for hybrid rocket fuel grain. [ABSTRACT FROM AUTHOR]

By establishing a mathematical model to simulate a mixed jet of oxygen and superheated steam from a coherent supersonic jet oxygen lance, we studied the effect of superheated steam on the fluid characteristics of the mixed jet. The model was initially verified through laboratory experiments prior to analyzing the fluid characteristics of the mixed jet in detail. These characteristics included the jet velocity, the temperature, the turbulent kinetic energy (TKE), and the mass distribution. The results showed that, at an ambient temperature of 1700 K, the jet velocity measured in the laboratory experiment was consistent with the fluid velocity obtained by numerical simulations, with an error of only 2.7%. In a high-temperature environment, the jet velocity of the mixed oxygen and superheated steam jet was increased, the TKE around the center jet was enhanced, the superheated steam exhibited an inhibitory effect on the combustion reaction of annular methane, and the potential core length of the coherent supersonic jet was reduced, which was conducive to methane combustion and delayed the reduction in the central jet velocity.

Metal iron powder is a promising new energy source that is of significant practical and research interest for future automotive power systems. However, the shapes of the particles are typically assumed to be spherical or an equivalent sphere when estimating the specific impulse of motors. Such an assumption lacks objectivity and can result in unreasonable estimations of two-phase flow losses. In order to better optimize the design of an engine, this study focuses on the influence of non-spherical particles (such as ellipsoidal and cuboid particles) on the characteristics of nozzle two-phase flow. Models for the governing equations of nozzle two-phase flow are developed to conduct a theoretical study to analyze the combustion properties of iron oxide particles and flow in the nozzle. In addition, experimental studies involving nanometer iron-powder particle combustion and engine thrust measurements are conducted to validate the results obtained from numerical calculations that are conducted using a fourth order Runge–Kutta–Gill method. The results indicate that particle morphology, size, and coagulation content play a significant role in the motor performance and the two-phase flow losses. Specifically, the hypothesis of the ellipsoidal model is in better agreement with the experimental findings compared to the other particle models. [ABSTRACT FROM AUTHOR]

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During the converter steelmaking process, the presence of supersonic oxygen jets can provide oxygen to high-temperature metal baths that promotes chemical reactions in the bath, accelerates the smelting rhythm, and facilitates a uniform distribution of the ingredients in the bath. In this paper, a computational fluid dynamics (CFD) model with combustion reactions is established and compared to the results of combustion experiment. This paper studies the behavior and fluid flow characteristics of supersonic oxygen jets under different environmental compositions under a steelmaking temperature of 1873 K. This validated CFD model can be used to investigate the effect of furnace gas on supersonic oxygen jet characteristics during the converter steelmaking process. The results indicate that the composition of furnace gas has an impact on the characteristics of the oxygen jet. Specifically, as the carbon monoxide (CO) volume fraction increases, the high velocity region of supersonic oxygen jet increases, and the high temperature and the high turbulent kinetic energy regions expand.

During the electric arc furnace steelmaking process, the coherent jet technology was widely used to protect the kinetic energy of the supersonic oxygen jet and achieve better mixing effects. Comparing with the conventional oxygen lance, the coherent lance could increase the surface area of impaction cavity, resulting in a better stirring effect and higher reaction rate. However, there was limited research about the effect of restriction structure for the coherent lance tip on the flow field characteristic of the main oxygen jet. In this research, three kinds of restriction structures have been investigated by numerical simulation and combustion experiment at room and high ambient temperature conditions. Then an optimum restriction structure would be tested in a 75 t electrical arc furnace steelmaking process to verify its metallurgical property.

Graphical abstract Highlights • Combustion modeling of particle and governing equation was performed. • Impact of grain size and condensed content on specific impulse were studied. • Mean specific impulse of the engine reaches up to 3100 N·s/kg. • Computational results show good agreement with the experimental data. Abstract Metal iron powder is a promising new type of energy source that is of enormous practical and research interest for future automotive power systems. To better optimize engine design, this study was devoted to the characteristic investigation of a two-phase flow. Experimental studies involving nanometer iron powder particle combustion and engine thrust measurement were conducted to confirm the results obtained from numerical calculations that were performed using a fourth-order Runge–Kutta–Gill method. Governing equations for nozzle two-phase flow were established to perform a theoretical study to analyze the combustion properties of iron oxide particles and flow in the nozzle. The results indicate that variations in the size and coagulation content of particles play a significant role in the loss of two-phase flow. Significant emphasis was placed on the effect of particle size (0.4–1.0 μm) and condensate content (10–40%) of ultrafine particles on the specific impulse. To further validate the theoretical results, the burning rates of particles of three different sizes were experimentally measured. In addition, the motor thrust and the specific impulse with the particle size of 50 nm were tested through combustion experiment, and the results show excellent agreement. [ABSTRACT FROM AUTHOR]

Characteristics of flow field and stirring ability of coherent jet with various shrouding CH flow rates on the molten bath were studied by combustion experiment and numerical simulation. The axial velocity and total temperature distributions of coherent jet under hot (1700 K) and cold (298 K) ambient condition were analyzed. The Eddy Dissipation Concept model was used in simulation with detail chemical kinetic mechanisms, and the numerical simulation results were agreed well with the combustion experiment in this research. Based on the simulation and experiment results, when the CH rate was 230, 207 and 184 Nm/h, their disparity rate of average velocity and total temperature was small than 5 and 6 %, respectively, at high ambient temperature. Hence, the same stirring effect might be achieved by those three kinds of CH flow rates in EAF steelmaking process. According to the industrial application research, the best CH flow rate is 184 Nm/h, which could stir molten bath well and reduce energy consumption in steelmaking process. [ABSTRACT FROM AUTHOR]

Hybrid rocket combustion frequently displays a sudden amplification of combustion pressures leading into low frequency instability (LFI) with peak frequency of 10 – 20 Hz . A series of experimental tests was designed to examine the triggering mechanism of LFI, which occurred at a certain combustion condition. To this end, a couple of parameters was selected and the sensitivity of each parameter to instability was evaluated including volume ratios between main and post chambers, oxidizer mass flow rates, and solid fuel types. The results showed that the initiation of LFI was related to the flow modifications caused by vortex shedding and volume ratios between main and post chambers. Once LFI was initiated at a certain chamber configuration, the variation of oxidizer mass flow rates and the use of different solid fuel did not alter the triggering mechanism of LFI. Additional attention was focused to understand the critical role of vortex shedding on the initiation of LFI in the post chamber. The results confirmed that pressure oscillations by the thermal lag of solid fuel could be suddenly amplified, which leads to LFI in the case of resonating with unknown sources of pressure oscillations associated with vortex shedding in the post chamber. However, the details of triggering mechanism and the coupling of vortex shedding with additional pressure perturbations still remain unresolved. [ABSTRACT FROM AUTHOR]

The Tibet Autonomous Region in China is a unique place with high altitude and special Tibetan culture. The residents have different living habits and domestic fuels from those in other parts of China, however, knowledge on the emission characteristics of local residential fuels remain poorly understood until now. In this study, nine popular residential fuels in the Tibet are burned in situ to study the aerosol chemical compositions, mass spectral signatures, and emission characteristics from their burning emissions. Overall, emissions of particulate and gaseous pollutants depend strongly on the burning conditions, in addition to the fuel constituents themselves. Burning the biofuels of yak dung, WeiSang mixture fuels, and two powdery Tibetan incenses with relatively low combustion efficiencies can emit large amounts of CO and aerosols, especially organic aerosols (>90%) with large diameters. In contrast, burning of wood, coal, ghee lamp, stick-like Tibetan incense, and diesel can release abundant CO 2 but fewer aerosols from their flaming combustion. A comprehensive database consisting of the high-resolution mass spectra of organics and emission factors of multiple chemical components are established. Distinctly different mass spectral signatures are found among the different fuels, in particularly those unique Tibetan biofuels. All these findings have significant implications for the identification of aerosol sources, compilation of pollutant emission inventories, and assessment of potential environment effects in this remote region.

We investigate experimentally and analytically the combustion behavior of a high-metal magnesium-based hydroreactive fuel under high temperature gaseous atmosphere. The fuel studied in this paper contains 73% magnesium powders. An experimental system is designed and experiments are carried out in both argon and water vapor atmospheres. It is found that the burning surface temperature of the fuel is higher in water vapor than that in argon and both of them are higher than the melting point of magnesium, which indicates the molten state of magnesium particles in the burning surface of the fuel. Based on physical considerations and experimental results, a mathematical one-dimensional model is formulated to describe the combustion behavior of the high-metal magnesium-based hydro-reactive fuel. The model enables the evaluation of the burning surface temperature, the burning rate and the flame standoff distance each as a function of chamber pressure and water vapor concentration. The results predicted by the model show that the burning rate and the surface temperature increase when the chamber pressure and the water vapor concentration increase, which are in agreement with the observed experimental trends. [ABSTRACT FROM AUTHOR]

Abstract: Typical burnt smell often results from fire accidents or in general from incomplete combustion. Recently, eleven compounds were identified, which are basically responsible for this odour. When analyzing residual materials from different fire accidents, the pattern that means the relative ratios of these compounds among each other varies strongly, although always causing a burnt smelling. Consequently, lab-scale combustion experiments were performed in order to investigate the influence of defined materials from domestic environment on the burnt-smell fingerprints. Furthermore, the occurrence of other polar and higher molecular combustion products was studied. It was found that under good combustion conditions, the burnt smell patterns resulting from the single materials were astonishingly consistent, mostly dominated by methylphenols or naphthalene. No correlation could be found between these ‘fingerprints’ and combustion product groups identified by GC/MS-screenings. LC/MS/MS-measurements especially pointed at the existence of higher molecular weight phenolic and acidic functionalized compounds in the combustion residues. [Copyright &y& Elsevier]

The multilevel stepped-wall chamber is designed to study the combustion stability control mechanism of the bulk-loaded liquid propellant gun (BLPG). The cold state experiment of the interaction of the high speed gas jet with liquid medium is conducted by means of high speed digital camera system. The simulated small caliber bulk-loaded liquid propellant combustion propulsion device is designed to study the effect of the stepped-wall chamber size on the combustion stability. The experimental results indicate that, the stepped-wall structure can restrain the expansion randomness of the Taylor cavity and leads smooth expansion at each step. In 4 stepped-wall chamber with ΔD/L = 3/40, the interior ballistic performance of BLPG is stable and the consistency of the p-t curves is good. Two-dimensional unsteady model is developed based on the BLPG combustion propulsion experiment. The numerical simulation results coincide well with the experiment [ABSTRACT FROM AUTHOR]

In order to provide experimental guide to commercial use of fluorine pollution control during coal combustion, with fluorine pollution control during coal combustion in mind, this paper proposed the theory of combustion fluorine retention technology. Feasibility of fluorine retention reaction with calcium-based fluorine retention agent was analyzed through thermo-dynamic calculation during coal combustion. By simulating the restraining and retention effects and influential factors of calcium-based sorbets on vaporized fluoride during experimental combustion using fixed bed tube furnace, the paper systematically explored the influential law of such factors as combustion temperature, retention time, and added quantities of calcium-based sorbets on effects of fluorine retention. The research result shows that adding calcium-based fluorine retention agent in coal combustion has double effects of fluorine retention and sulfur retention, it lays an experimental foundation for commercial test of combustion fluorine retention. [ABSTRACT FROM AUTHOR]

During the converter steelmaking process, the presence of supersonic oxygen jets can provide oxygen to high-temperature metal baths that promotes chemical reactions in the bath, accelerates the smelting rhythm, and facilitates a uniform distribution of the ingredients in the bath. In this paper, a computational fluid dynamics (CFD) model with combustion reactions is established and compared to the results of combustion experiment. This paper studies the behavior and fluid flow characteristics of supersonic oxygen jets under different environmental compositions under a steelmaking temperature of 1873 K. This validated CFD model can be used to investigate the effect of furnace gas on supersonic oxygen jet characteristics during the converter steelmaking process. The results indicate that the composition of furnace gas has an impact on the characteristics of the oxygen jet. Specifically, as the carbon monoxide (CO) volume fraction increases, the high velocity region of supersonic oxygen jet increases, and the high temperature and the high turbulent kinetic energy regions expand. [ABSTRACT FROM AUTHOR]

During the electric arc furnace steelmaking process, the coherent jet technology was widely used to protect the kinetic energy of the supersonic oxygen jet and achieve better mixing effects. Comparing with the conventional oxygen lance, the coherent lance could increase the surface area of impaction cavity, resulting in a better stirring effect and higher reaction rate. However, there was limited research about the effect of restriction structure for the coherent lance tip on the flow field characteristic of the main oxygen jet. In this research, three kinds of restriction structures have been investigated by numerical simulation and combustion experiment at room and high ambient temperature conditions. Then an optimum restriction structure would be tested in a 75 t electrical arc furnace steelmaking process to verify its metallurgical property. [ABSTRACT FROM AUTHOR]

Exploring a green and safe primary explosive to replace very toxic and sensitive lead azide and lead styphnate takes great efforts. Here, a series of polynitro-functionalized triazolylfurazanate energetic materials have been reported. These new compounds were fully characterized by infrared, multinuclear NMR spectra, mass spectra, elemental analysis, and differential scanning calorimetry measurements. The structure of mono-diaminoguanidinium salt ( 17 ) was determined by single-crystal X-ray diffraction. Inspired by the high pressurization rate and fast energy release in triaminoguanidinium salts, some suitability evaluation for primary explosives has been applied. Di(triaminoguanidinium) 3-nitramino-4-(3-(dinitromethanidyl)-1,2,4-triazol-5-yl)furazanate exhibits an excellent gas-generating capability ( P max = 9.03 Mpa) and combustion performance (d P /d t max = 201.5 GPa s -1 ) close to fast thermite Al/CuO ( P max = 8.49 Mpa, d P /d t max = 252.2 GPa s -1 ). Moreover, the good initiation capacity (60 mg for 500 mg RDX) coupled with insensitivity in this compound (IS = 17.4 J, FS = 240 N, ESD > 0.225 J) make it a promising green and insensitive primary explosive.

We established a fire simulation experiment in the harvested site of Larix olgensis plantation and recorded the temperature of each test point at 500, 1000 and 1500 s during the fire by thermocouple temperature measurement. The data were displayed in the form of images to show soil temperature field at each layer during the fire. The results showed that when the wind speed was less than or equal to 2 m·s -1 or greater than or equal to 10 m·s -1 , combustibles could not be fully burned. In the case of full combustion of combustibles, soil temperature at each layer was the highe-st when the wind speed was 6 m·s -1 , with the affected soil depth being up to 12 cm or more. The maximum temperature at soil layer of 3 cm could reach 300 ℃. Compared with that at the non-cut stump, soil at the stump had a higher maximum temperature during the fire, with the soil temperature being higher near the stump. When the wind speed was 6 m·s -1 , the temperature range at soil layer of 3 cm from the farthest and the nearest to the stump was from 198 ℃ to 315 ℃. With the deepening of soil layer, soil temperature sharply decreased. The temperature at the soil layer of 15 cm was almost unchanged during the fire test. The temperature at the soil layer of 12 cm was increased only when the wind speed was 6 m·s -1 , and the temperature at the soil layer of 3 cm was the highest. When the wind speed was 6 m·s -1 , the influence of fire on the soil temperature was the greatest, and soil at stump had the severest damage.