Flame Inclination Research Articles

Quantification of the hetero-contact formation process for a CuO/CeO2 hetero-aggregate model system prepared by double flame spray pyrolysis

In hetero-aggregates, different materials form sintered hetero-contacts, which lead to new material properties. In this study, the influence of process parameters on the formation of hetero-contacts in Double Flame Spray Pyrolysis (DFSP) was quantified. The mixing of jets was monitored by Particle Image Velocimetry (PIV) measurements as well as by thermocouples and compared to the single flame setting. Overlap of the jets was evaluated using tracers to visualize the mixing zone. Ten CuO/CeO2 model material samples were prepared with different flame inclination angles, nozzle distances and different particle volume fractions. Mixing on hetero-aggregate level was quantified using Convolutional Neural Network (CNN) evaluations of STEM images, Temperature-Programmed Reduction (TPR) and Differential Centrifugal Sedimentation (DCS) disk centrifugation to determine cluster sizes and hetero-coordination numbers as mixing quantifiers. Here, good correlations between the differently measured quantifiers were observed.

Effect of ambient wind on horizontal flame spread over discrete multi-column fuel arrays

The flame spread behaviors of discrete charring fuels are significantly influenced by ambient wind. This paper studied the horizontal flame spread characteristics of discrete birch rod arrays under ambient wind experimentally and theoretically. Here, seven kinds of array spacings (denoted by S, 7–19 mm) and four kinds of wind speeds (denoted by U, 0.5–2.0 m/s) were designed to develop 28 experiments. The experimental results show that the flame inclination angle decreases as wind speed increases. The non-dimensional flame length and the non-dimensional heat release rate are also found to be correlated, and two ignition modes under the action of ambient wind were differentiated. The flame spread rate and wind speed have a linear relationship based on experimental data. The ratio of wind speed to fuel loading is introduced to further examine the variation of flame spread rate. In this article, a heat transfer model is established by simplifying discrete flame spread process and incorporating both radiative and convective heat transfer. A prediction model for flame spread rate is presented, which aligns well with the experimental results. Finally, the mass loss rate under the ambient wind is discussed.

Effects of wind speed, spacing distance and heat release rate on the combustion and flame merging characteristics of two extra-thin line fires

This paper investigated the mutual interaction between two extra-thin line fires under different wind speeds of 0.4, 0.6, 0.8, 1.0 and 1.2 m/s by using a small-scale wind tunnel. The experiments involved the spacing distances of 5, 10, 15, 20, 25, 30, 35 and 40 cm, and the heat release rates of 19.4, 25.7 and 32.7 kW, respectively. The results show that the flame merging probability increase, as the wind speed or the heat release rate increases. Compared with the two rectangular or square fires, the flame height and flame length will be smaller at the same heat release rate for the extra-thin line fires. Meanwhile, the line fires will decrease the flame merging, making the downstream flame temperature smaller than that of the upstream at the relatively larger wind speed or heat release rate. The interesting finding is that, with the increase of the heat release rate, the flame inclination angle will increase in the fully merging stage, which is opposite to that of square fires. Correspondingly, the flame merging model is built on the influences of the buoyancy force and inertial force of the horizontal wind, which can give the good explanation on this behavior.

Full-scale experimental study on combustion characteristics and smoke temperature of double-source fires in different tunnels

Through a series of full-scale fire tests conducted in three different tunnels, the common characteristics of combustion and smoke temperature of double pool fires in actual operation tunnel environments are investigated. The evolution process of the coupling effects of shielding entrainment and thermal feedback enhancement is revealed. It is found that the ventilation state and the fire source spacing can alter the dominant relationship between the shielding entrainment effect and the thermal feedback enhancement effect, resulting in different evolution patterns of combustion characteristics and smoke flow patterns of double pool fires in tunnels. The heat release rate increases by 4 times when the double pool fire flames merge under the longitudinal ventilation compared with the double pool fire flames without fusion under the natural ventilation. The flame tilt angles of double pool fires were determined through the image processing method, and the prediction model of the flame inclination angle of downstream fire sources was established, considering fire source spacing. At the same time, the characteristic of temperature measured by Fiber Bragg Grating in double-source fire scenarios was investigated, developing a model to predict the longitudinal temperature rise distribution. It is found that the maximum temperature rise prediction model based on steady-state fire has poor applicability in the weak-plume fire scenario of full-scale tunnels. The analysis of the smoke flow patterns shows that the two-stage ventilation is more suitable for smoke control compared to full longitudinal ventilation in tunnel double-source fire accidents, especially for ensuring the safety of individuals trapped in the area between the two fire sources.

Experimental study on upward fire spread of polyurethane foam under double fire source conditions with different restricted facade Structures

This paper examines the impact of insulation material (PU) fire spread characteristics under dual fire source conditions considering various restricted facade Structures. It is found that the merging tendency is affected by the flame inclination angle θ1 and mapping length L. Additionally, the flame merging behavior is determined by the combined effects of the chimney effect, inter-flame air entrainment, and heat transfer changes caused by the restricted angle. The Inter-flame air entrainment λ was introduced to confirm that there is a positive correlation between flame height and Inter-flame air entrainment in the large-angle restricted facade Structures (θ=120°,150°，180°). By introducing the hydraulic diameter Deff* to compare the experimental data with the previous flame pulsation frequency model, the proposed f=0.5g/Deff* model can further improve the accuracy of the prediction results. During the flame merging stage, the axial temperature field distribution on the PU board surface was compared. The study found that the restricted facade Structures resulting in a cooling effect due to fresh air entrainment at the bottom with the chimney effect. As a result, the small-angle restricted facade Structures (θ=30°，60°，90°) led to an upper-high and lower-low distribution of axial temperature.

Влияние скорости воздушного потока на тепловое излучение от углеводородного пожара в резервуаре для хранения нефти

Purpose. The article assesses the effect of air flow velocity on the intensity of thermal radiation from a fire in a vertical steel tank with a floating roof of 65 000 m3 capacity (VSTWFR-65000) with crude oil. The indicators of hazardous fire factors - open flame, smoke and temperature at different wind speeds – have been studied. Methods. The method of numerical modeling in the Fire Dynamics Simulator software package, as well as the method of processing the obtained research results have been used in the study. Findings. The dependence of the flame inclination angle at different air flow speeds has been obtained. The simulation results have been shown: smoke distribution at different wind speeds, as well as temperature change at a distance from the fire source depending on the air flow velocity. Research application field. The results of the study can be used in the development of design documentation for measures to ensure fire safety of a tank farm with floating roof tanks, as well as in adjusting fire extinguishing plans. Conclusions. Based on the simulation results it has been found that with an increase in the air flow velocity the intensity of thermal radiation initially increases and then decreases. It has been found that at an air flow velocity of 9 m/s the maximum thermal radiation reaches 23.43 kW/m2 at the nearest point of the adjacent tank in the projection from the central axis of the burning tank. At an air flow velocity of 6.5 m/s the temperature at the top of the adjacent tank reaches 176 °C, and at 9 m/s – 426 °C, which is higher than the autoignition temperature of oil, which is within 222–256 °C, there by creating a threat of fire spread. The study has defined the maximum distances from the burning VSTWFR-65000 for the safe presence of people, amounting to 47.3; 48.9; 50.2; 53.4; 55.7; 56.8; 59.4 m for wind speed of classes 0, 1, 2, 3, 4, 5 and 6 respectively.

Study on combustion and flame merging characteristics of two n-heptane line fires under wind speed, spacing, and groove width

This paper studied the effects of wind speed, spacing and groove width on the combustion and flame merging characteristics of two n-heptane line fires. The experimental results show that the range of intermittent merging stage will increase with groove width; the greater the wind speed, the greater the probability of merging. At the non-merging stage, the influence of wind speed on the flame merging probability can be ignored. Under the influence of wind speed, mass loss rate per unit area, ??, of the downstream pool fire is greater than that of the upstream pool fire, at the stages of fully merging and intermittent merging. While when the flame spacing increases to the non-merging stage, ?? of the upstream pool fire begins to be gradually greater than that of the downstream pool fire. On the other hand, the downstream flame ?? increases firstly and then decreases, while the upstream flame ?? shows an increasing trend, with spacing distance. The smaller the groove width, the greater the value of ?". When the spacing is 0, ?? is the smallest. It is found that with the increase of spacing, the flame length under all tested conditions increases firstly and then decreases, and the flame inclination angle decreases firstly and then increases.

Characteristics of fires in coal mine roadways and comparative analysis of control effectiveness between longitudinal ventilation and cross-section sealing

Enhancing ventilation velocity and constructing sealing walls are prevalent strategies aimed at managing fires in coal mine roadways. To assess the efficacy of these control tactics, this study investigates the fire characteristics with varying heat release rates (HRR) using a 1:10 experiment and numerical simulations. Results reveal that an increase in the HRR corresponds to a decrease in ceiling temperature, alongside an increase in both smoke back-layering length and critical velocity. Longitudinal ventilation proves effective in lowering ceiling temperature and inhibiting upstream smoke propagation from fire source, but it does not extinguish the fire, instead reducing downstream visibility and escalating risk downstream of fire. When the actual velocity exceeds 3.1 m/s, it effectively prevents smoke backflow in a fire of 10 MW. Cross-section sealing works by reducing oxygen levels within roadway to suffocate the fire. As the sealing ratio increases, flame inclination angle and burning time decline, whereas ceiling temperature rises. When it exceeds 75%, CO concentration sharply rises and fire enters the extinguishment phase, if ratio is 100%, fire with higher HRR are extinguished more quickly. This study provides valuable insights into roadway fire control: longitudinal ventilation aids personnel evacuation, while cross-sectional sealing effectively extinguishes fires in unpopulated spaces.

Numerical study of flame inclination instability in a packed bed with extra lean methane/air intake by an adaptive multi-scale model

The common numerical method to simulate the evolution of flame instability during filtration combustion mainly includes volume average method and pore scale simulation. However, they are not satisfying in computation accuracy and cost respectively. In this paper, a self-developed adaptive multi-scale model is built to study the inclination instability of the flame front in a packed bed with honeycomb ceramics. The perturbations on the distribution of the intake parameters and physical properties of fillings in the packed bed lead to the flame inclination. The influences of the amplitude and range of the perturbations on the flame inclination development are investigated. The development mechanism of flame inclination is analyzed by method of flow competition (MFC) theory. The results show that the increase of the flame inclination angle will enhance the transversal heat transfer. Subsequently, the radiation and conduction fluxes restrain the increase of the flame inclination. Under the same level of perturbation amplitude, the result shows that the influence sequences of the four factors for the flame inclination are as follows: fillings porosity, feed flow rate, fillings heat capacity, and feed concentration. In addition, larger amplitude of perturbation leads to higher maximum flame inclination angle. However, the perturbation range has little influence on the development of flame inclination angle. Finally, the flame inclination is restrained successfully through adding new perturbation of intake parameters or elimination of initial perturbation. The above.studies are quite meaningful to the stable operation and wide application of porous media combustion technology in the utilization of low calorific value gas energy.

Effects of groove width, spacing distance and ullage height on combustion and flame merging characteristics of two-line n-heptane pool fires

This paper studied the combustion and flame merging characteristics of two n-heptane line pool fires. The effects of groove width (0.5, 1 and 1.5 cm), spacing (0, 5, 10, 15, 17.5, 20, 22.5, 25 and 30 cm) and ullage height (the dimensionless liquid fuel height H*=1/4,1/2,3/4 and 1) were revealed. It was found that, at the same spacing, the flame merging increases with the increase of dimensionless liquid fuel height H*.With the increase of groove width, the probability of flame merging also increases, and the values of S/hf,S=0 for the critical merging position will decrease, which is larger than that of gas fuel flame merging. With the spacing increase, the flame height will decrease and then increase, making the flame inclination angle increase and decrease. It is interestingly found that, at the intermittent merging and non-merging stages, ṁ″ is almost smaller than single case ṁs″. And the smallest of ṁ″ appears at the position of the largest inclination angle. Moreover, under the same spacing and H*, the smaller of the groove width is, the greater the mass loss rate per unit area ṁ″ is, which demonstrates that the smaller width of groove will promote the flame merging and burning. In addition, a heat transfer model is built, which can well address the burning behaviors with different W.

Flame extension length of inclined hydrogen jet fire impinging on a water curtain

The use of a water curtain system to prevent fire spread has been extensively investigated, but the case of an inclined jet fire inhibited with a water curtain is not involved. A series of experiments were conducted on inclined hydrogen jet fires with various fuel flow rates, nozzle diameters and inclination angles under the influence of a vertical water curtain. This study aims to explore the burning behaviors of inclined jet flames at the impingement area, specifically the flame extension lengths. The experimental results show that an increase in fuel flow rates or nozzle diameter leads to a larger flame extension length. With the increase of flame inclination angle, the flame extension length decreases and the influence of nozzle diameter on the flame extension length is attenuated. A new dimensionless heat release rate is proposed to correlate with the dimensionless flame extension length by incorporating an air entrainment coefficient. The model built in this study can be used to predict the flame extension length of jet flames with different diameters, fuel flows and inclinations under the influence of a water curtain, and is validated by data in the previous study.

Experimental study on flame spread and extinction over horizontal power cables under longitudinal ventilation in a utility tunnel

Flame spread and extinction over horizontal power cables (polyethylene (PE) sheathed and cross-linked polyethylene (XLPE) insulated power cable) under longitudinal ventilation in a utility tunnel was experimentally studied. Power cables (1.35 mm/8.5 mm in core diameter/cable diameter) of five components (sheath: PE, wrapping: Non-woven fabric, filling: PP, insulation: XLPE, copper: Cu) are used as samples. Flame geometrical characteristics (average flame height Hf, U∞, average flame width Wf, average pyrolysis length Lp) are analyzed. A prediction model of Hf, U∞ based on three main characteristic length scales (the length scale lD, the flow momentum-buoyancy length scale lM and the characteristic length scale of a purely buoyant plume lQ) that control flame dynamics, there is a good agreement between experimental and prediction results. The increasing wind speed and number of cables lead to the increasing mass loss and mass loss rate (MLR), and the reason for the delay in cable mass loss is revealed. The flame spread rate (FSR) prediction model considering the exposed copper wire length in the combustion zone based on Hf, U∞, Wf, flame inclination angle (β) and Lp was optimized. FSR increases with wind speed and the number of cables increase. The study contributes to a better knowledge of the cable's fire risk in utility tunnels.

Can heavy rainfall affect the burning and smoke spreading characteristics of fire in tunnels?

Extreme rainfall events are increasingly common under the current trend of global warming. This work investigates how a heavy rainfall on one exit affects the fire burning and the smoke spread in tunnels. Several reduced-scale tests are designed with various rainfall intensities (up to 60 mm/h, equivalent to 232 mm/h in nature), raindrop sizes (1.0-1.5 mm, equivalent to 4-6 mm in nature), and tunnel fire heat release rates (2.1-6.7 kW, equivalent to 2-6 MW in real scale). Experiments show that heavy rainfall on one exit can induce a longitudinal airflow inside the tunnel, and the induced airflow is caused by the increased pressure at the rainfall exit. The airflow pushes the flame tilting towards the no-rainfall portal, and the correlation models of the flame length and flame inclination are characterized by considering the induced airflow and rainfall. The rainfall-induced airflow has a limited effect on the burning rate of pool fires, but it can change the ceiling temperature and limit the smoke back-layering toward the rainfall portal. In contrast, the ceiling temperature distribution towards the no-rainfall portal is found not sensitive to rainfall, which can be well described by an empirical model.

Flame spread over cables in a utility tunnel: Effect of longitudinal wind and inclination angle

Tables in utility tunnels pose a major fire hazard. This work aims to provide a comprehensive understanding of the effects of cable inclination angle and longitudinal wind (U∞) on the flame spread behaviors of cables in a utility tunnel. Flame inclination angle (β) increases with the increase of cable inclination angle and longitudinal wind speed, while the amplification decreases as the longitudinal wind speed increases. Both flame length (xf) and pyrolysis length (xp) increase linearly with sinθ when U∞ is smaller than 0.65 m/s and they also increase with the increase of longitudinal wind speed. The increasing inclination angle and longitudinal wind speed contribute to the increasing flame spread rates. The flame spread rate accelerates significantly when the longitudinal wind speed and inclination angle are 0.65 m/s and 12° respectively. In addition, a model based on heat transfer analysis was established to predict the flame propagation rate under different cable inclination angles, and the experimental results were in good agreement with the predicted results. The results of the study contribute to cable fire risk assessment, which is beneficial for cable fire prevention and control in utility tunnels.

Numerical simulation on the effect of inclination on rectangular buoyancy-driven, turbulent diffusion flame

The presence of an inclined wall can significantly alter the flow dynamics of a buoyancy-driven turbulent flame. Although flame structure on an inclined wall has been widely investigated, fluid flow has not been widely investigated. A large eddy simulation is performed to study the effect of inclination on the flow dynamics of a flame. The results show that at the initial stage of combustion, a vortex forms at the left side of the flame due to its expansion and the adverse pressure gradient downward. The vortex expands and lifts with the combustion flow, splitting the flame by stretching its left edge. During the continuous combustion stage, the flame is inclined on the inclined wall. Air entrainment on the left side of the flame flows parallel to the inclined wall, while air entrainment on the right side is significantly reduced due to the upward movement of the combustion flow. The flame inclination angle increases with increasing inclination angle and attaches the inclined wall when the inclination angle is 30°, leading to a higher mean temperature and velocity near the inclined wall.

Effects of Key Influencing Factors on the Flame Inclination of Low Concentration Methane (LCM) Combustion in Porous Burner

ABSTRACT In present work, a local thermal non-equilibrium numerical model of low concentration methane combustion in porous media is established. The modified thermal effective thermal conductivity of foam ceramics was introduced. The heat and mass dispersion effect as well as the influence of porous media structure on the heat transfer were fully considered. Studies found that the combustion flame front of low concentration methane in porous media always show a S-shaped state under special conditions. The influencing factors of inlet velocity, methane concentration, wall heat loss, and the porous burner size were analyzed. Results show that without initial thermal perturbation and the absence of defects in the porous media, the flame front in porous burner still has the possibility of inclination. As the inclination of the flame front continues to increase, the flame keeps approaching the burner outlet until blow off. Among the considered four influencing factors, the size of porous burner has the greatest influence on the inclination of flame front. As the burner diameter increases from 0.04 m to 0.12 m, the inclination angle of the flame front increases continuously, and the maximum inclination angle is 36°. The flame inclination will cause uneven temperature distribution downstream of the burner and local heat concentration. With the increase of wall heat loss, the high-temperature zone downstream of the burner will evolve into a local high-temperature zone near the flame front. With the reducing of porous burner diameter, the inclinational instability could be suppressed to some extent.

Experimental study on control of flame inclination in a thermal flow reversal reactor with extra lean premixed methane/air intake

Combustion instability is a basic obstacle to the wide application of porous media combustion devices in industry. However, the investigation about it with extremely dilute gas fuel issorelylacking due to the limitation of laboratory test conditions. In this study, inclinational instability of extra lean-premixed flame (with volume fraction below 1%) in a thermal flow-reversal reactor with honeycomb ceramic packings is investigated experimentally. The effects of inlet methane concentration on the flame inclination are studied. Then the flame inclination is restrained through electronically controlled adjustment on the valve opening and switch time. The experimental results show that the intake methane concentration has a remarkable effect on the flame inclination angle variation in each semi cycle. When the intake concentration decreases from 0.6 vol% to 0.2 vol% and the flow direction is downward, the growth of the flame inclination angle in each semi cycle gets lower. The adjustment on the scale of the high temperature zones in two half parts of the packed bed through the valve opening has a great influence on the flame front position and flame inclination angle. The setting of asymmetric switch time for the reverse flow also has obvious effect on the evolution of the flame inclination. Finally, the flame inclination angle drops firmly for approach of the two high temperature zones in size and height. The synchronous adjustment of valve opening and switch time fastens the convergence of the two high temperature zones in two half parts of the packed bed. This work is beneficial to the development of thermal flow-reversal reactor technique for better dealing with ventilation air methane and other lean gaseous fuel streams.

Study on the flame morphological characteristics of dual fire sources in tunnel under longitudinal ventilation

SummaryIn this article, a small‐scale experiment (1:10) is used to study the flame morphology of the dual fire sources in the tunnel under longitudinal ventilation. The experimental results show that: (1) The flame height increases with the heat release rate of the fire source. When there is no wind, the flame height will increase as the fire source spacing increases. Under the effect of longitudinal ventilation, the flame height decreases first and then increases as the fire source spacing increases. (2) The flame inclination angle increases as the heat release rate of the fire source increases. When there is no wind, the flame inclination angle decreases with the increase of the fire source spacing. Under the effect of longitudinal ventilation, as the fire source spacing increases, the flame inclination angle decreases first and then increases, which is consistent with the variation law of the flame height with the fire source spacing. For the experimental conditions of smaller heat release rate of fire source and larger fire source spacing, the flame merged phenomenon gradually decreases.

Surface Chemistry Studies of Emission and Thermal Behaviour of Developed Composites for Building Ceiling Materials

The emission of harmful elements from burning building ceiling materials and their attendant health effects on inhabitants within the vicinity of the emitted harmful elements is increasingly becoming a source of concern globally. Hence, the need to develop eco-friendly flame-retardant composite materials suitable for house ceiling purposes to forestall unwanted toxic emissions. This work identified the chemical structure of developed composite products and their emission performance during combustion. X-ray Diffraction (XRD) analysis was used for phase quantification and E550 combustion gas analyzer for emission characterization of the developed composites. Thermolyne 950 °C oven was employed for the combustion analysis of the prepared composite at 500 °C. Quasi negligible SO2 and CO2 levels existed, while A4, 0.3Aldr0.23Cmt0.3Si0.05G0.12CS recorded maximum CO level, indicating toxic affluence. The low mass losses of all composite materials, especially for A2, 0.6Aldr0.34Cmt0.05G0.01OBSretard significantly due to its activities by the retardant constituent. The flame retardant nature of all produced composites was evidenced in their elemental composition. There was an absence of a flammable element and stable insulating compounds providing retardance to flame occurrences. These suppressions in flame inclination of the reinforced materials were noticed within the boundaries of the ceiling crystals from the structural examination. The intermetallic phase from the diffraction intensities showed the presence of a significant second bond interstitial solid-phase across the matrix, especially for 0.6Aldr0.34Cmt0.05G0.01OBS ceiling material. This study has established the eco-friendliness of developed building ceiling composite and the potential to reduce the importation of building ceilings. The developed ceiling composite evidently demonstrated high potential to compete favourably with imported ceiling materials in terms of fire resistance performance, low cost of production, and abundant availability of raw materials in the environment. Oil beanstalk is a novel material introduced as a reinforcement to developed building ceiling composite. This research provides a blueprint for manufacturers, construction and allied industry, and stakeholders in developing eco-friendly flame retardant composite ceilings whose materials can be readily sourced locally available in the environment.

Experimental study on the diffusion burning and radiative heat delivery of two adjacent heptane pool fires

This paper investigated the effect of separation distance on the flame appearance and radiation heat flux of medium-scale pool fires dominated by radiation. A series of experiments were conducted on two adjacent heptane pool fires with diameters of 20 cm, 40 cm and 60 cm at separation distances ranging from 0 to 60 cm. According to experimental results, flame height and flame inclination angle increase monotonously with the increase of pool diameter. As separation distance increases, flame height increases first and decreases gradually for 3 different sized pool fires. However, the variation law of flame inclination angle with separation distance varies with pool diameter. The normalized flame height (Hf/D) is found to increase exponentially with the dimensionless heat release rate (Q*) with an exponent of 0.71. The radiative heat flux at the center of the pool surface peaks at the critical separation distance of flame merging, which results from increased flame emissivity and view factor. Based on thermal analysis, a model to predict the radiative heat flux on the fuel surface is developed. The predicted radiative heat fluxes quantitatively match the experimental results but with 20% overvalued, due to the neglection of radiation blockage effect of cool fuel vapors zone and soot. The blockage effect is more pronounced for the merging pool fires with a diameter of 60 cm.