Flame Deflection Research Articles

Investigation on the morphology and temperature distribution of hydrogen jet flames impinging on barrier walls

Hydrogen is often stored and transported in a high-pressure state, posing a risk of jet flames in the event of accidental leakage. Firewalls are commonly installed around high-pressure hydrogen storage and transportation equipment to protect surrounding facilities and personnel from the fire hazards caused by hydrogen leaks. By combining experimental and numerical simulation methods, this study investigated the effects of varying hydrogen release pressure, nozzle shape, nozzle-wall distance, and barrier height on the behavior of high-pressure hydrogen jet flames. A predictive model for the flame extension length after contact with the wall was proposed. The study found that when the wall height is sufficient to cause complete flame deflection, the temperature distribution near the wall exhibits a strong regularity. The temperature of the barrier wall below the nozzle height is higher than that above the nozzle height, indicating that enhanced thermal protection is needed in this region for practical applications.

Effect of water injection on the cooling performance of flame deflector in rocket engine testing platform

Ground test is an essential step to ensure the reliability of the design and assess the quantity and performance of rocket engine. However, supersonic and high-temperature rocket exhaust gas directly impinging on the flame deflector of test platform cause severe heat damage which brings about a low repeated utilization and construction cost of the deflector. Generally, the water is employed as the coolant for the spray cooling system to protect the flame defector of test platform. In this paper, Euler-Euler approach is adopted to investigate the multi-phase flow in a flame deflection of rocket engine test platform. An evaporation model based on concentration difference is chosen to simulate the mass and heat transfer between water injection and exhaust plume. Model validation shows that the predicted results are in good agreement with the experimental data. The effect of water injection, including spray location and angle, and mass flow rate, on the afterburning and cooling performance of flame deflector is numerically investigated. The results show that the afterburning of exhaust plume could be inhibited by the water injection. In terms of maximum and area-averaged temperature on the bottom and inclined surfaces of flame deflector, the configuration with spray nozzle angle of 60° has the lowest area-averaged temperature. For the simulated cases with different spray nozzle diameters, the difference of maximum and area-averaged temperatures is below 11.0 K and 6.1 K, respectively. In addition, the maximum and area-averaged temperatures increase first and then decrease with the increase of spray nozzle diameter.

Effects of ventilation system design on flame behavior and smoke characteristics for mitigating marine engine room fire hazards

Engine room fires are one of the most harmful types of ship fires, the development of which is closely related to the design of marine ventilation system. In this paper, a full-scale numerical study of ship's engine room fire is carried out using a fire dynamics simulator, and the effects of vent layout and air velocity on the flame behavior, smoke stratification and diffusion are investigated. The three-dimensional model of the engine room is built based on the ocean-going training ship Yukun of Dalian Maritime University. First, the variations of flame behavior under different air vent layouts and wind speeds are explored, and a mathematical model is derived to quantify the flame deflection angle. Then, the effects of ventilation conditions on the smoke stratification in the cabin are analyzed, and the characteristics of hot smoke diffusion are revealed. The results show that a higher ventilation velocity is beneficial to the rapid cooling of the ship's engine room, and the symmetric ventilation layout of Method 3 with a central intake on the upper side and a bottom exhaust on both sides is more conducive to the safety of the engine and other heat source equipment in a fire. This study provides references to the design and optimization of ventilation systems on ships, which can improve the safety of the important equipment in the engine room and prevent further expansion of fire.

Full-scale experimental study on fire characteristics induced by double fire sources in a two-lane road tunnel

The vehicle collisions, intense heat radiation and convection from flame and high-temperature smoke can easily cause double-source fire disasters in tunnels. In this paper, four full-scale fire experiments were performed in Jiangpu road tunnel to investigate the characteristics of double fire sources. The whole process of the ventilation velocity, heat release rate, longitudinal ceiling temperature, vertical temperature, carbon monoxide and flame deflection angle are analyzed. The results indicate that the interaction between the double fire sources affects the heat release rate and flame deflection angle and other parameters of each fire source. The ventilation and the fire source spacing can change the coupling state of thermal feedback mechanism and the shielding and entrainment effect of double fire sources. The fire source spacing affects the interaction mechanism and the smoke flow state between the ceiling jets of the double fire sources, which leads to the difference in the longitudinal ceiling temperature distribution between the double fire sources. According to the characteristics of smoke movement between double fire sources, the schematic diagrams of ceiling jets between double fire sources are established. The longitudinal ceiling temperature rise of double fire sources is analyzed from the perspective of steady state and unsteady state. The longitudinal ceiling temperature data of full-scale fire tests is compared with the prediction models proposed by other researchers. The “barrier effect” phenomenon was also observed in the double-source fire tests, especially in the vertical smoke temperature. The findings contribute to deepening the understanding of the fire characteristics of the double-source fire disasters.

Study of the evolution mechanism of multi-window carriage fire under longitudinal ventilation in a metro tunnel

The fire evolution and ejected flame characteristics of a metro train under longitudinal wind were investigated by numerical simulation and scale-model experiment. The combustion heat release rate (HRR), geometric characteristics of the external flame, and temperature distribution beneath the tunnel ceiling were studied under a total of 159 working conditions. The results show the influence of longitudinal ventilation in the metro tunnel on the airflow of upstream and downstream windows. The airflow enters the carriage from downstream windows and exits through upstream windows. The flow rate of windows is positively correlated with ventilation velocity. Parameters such as fire load, ventilation factor and longitudinal ventilation determine the heat release rate of fire combustion in the enclosed space. When the fire load is less than 1500 times the ventilation factor, longitudinal ventilation will reduce the combustion heat release rate; otherwise, the longitudinal ventilation will promote combustion reaction. Longitudinal ventilation affects the external flame size by changing the window airflow and air entrainment. In addition, the longitudinal inertial force increases the flame deflection angle and horizontal length. The temperature beneath the tunnel ceiling decreases significantly under longitudinal ventilation. Therefore, in a metro tunnel with longitudinal ventilation, passengers should be protected from high temperature when passing by the fire carriage during evacuation.

Comprehensive optical diagnostics for flame behavior and soot emission response to a non-equilibrium plasma

This study reported comprehensive optical diagnostics for flame behavior and soot emission under directly coupling of the plasma with the flame at specific heights. The morphometric parameters of unstable flames under the direct plasma coupling were quantified. We also proposed an optical method to eliminate plasma luminescence from the field of view to extract flame intensity. At the same discharge height, with the increase of discharge frequency, the flame height decreased, while the flame horizontal extension distance and deflection angle increased. The relationships between flame morphologic and electrical parameters were obtained. The experimental results suggested a one-to-one correspondence between plasma action and flame deflection or shortening. When the plasma interacted with the flame, the overall temperature and soot emission of the flame decreased compared with that without plasma. At the same discharge height, the flame temperature and soot decreased further with the increase of discharge frequency. The soot emission changed more remarkably with the discharge frequency for higher discharge heights. With the increase of voltage, the flame temperature and soot increased at the lower discharge heights. The analysis of the experiment data demonstrated that the variation of soot emission was caused by the cooperation of multiple factors.

Influence of air ratio on combustion and NO x emission characteristics of pulverized coal industrial boiler

ABSTRACT A 46 MW pulverized coal industrial boiler with swirl burner had severe slagging and high NO x emission during actual operation. To solve these problems, a full-scale industrial test was carried out. The flue gas temperature and the composition of exhaust gas were obtained under different ratios of secondary and separated secondary air. The results shown that reducing the ratio of secondary and separated secondary air could delay the ignition of pulverized coal and weaken the flame deflection, which was conducive to slowing down the burner slagging problem. However, it will aggravate the erosion of high temperature flue gas on the back wall, and further aggravated the furnace slagging problem. Changing the air ratio couldn’t substantially improve the problem of high exhaust temperature. Properly reducing the ratio of secondary and separated secondary air could effectively control NO x emission. When the ratio of secondary and separated secondary air was reduced from 73:27 to 52:48, the NO x emission was reduced by 44.8%. Reducing the ratio of secondary and separated secondary air leaded to the increase of carbon content in fly ash and slag, but the heat loss of exhaust gas was reduced and the thermal efficiency of boiler was increased.

The flame mitigation effect of vertical barrier wall in hydrogen refueling stations

Reliability and safety of hydrogen refueling stations directly affect the public acceptance of hydrogen energy. Due to high storage pressure (up to 90 MPa), the firefighting measures in hydrogen refueling stations are different from those in traditional gas stations. The mitigation effect of barrier walls against jet flame, the reduction ratio of flame length and flame deflection angle were studied by an in-house version of FireFOAM solver. The code employed a modified eddy-dissipation concept combustion model within the framework of large eddy simulation. A real-gas state equation of hydrogen in a simplified form was adopted to describe the complex behavior of high-pressure hydrogen. The notional nozzle approach was applied to replace the actual hydrogen jet exit based on mass and momentum conservation. The simulation results show that the visible flame length decreases with the growth of height difference between the barrier wall and hydrogen jet exit, which can be fit using the power function. The flame deflection angle is proportional to the height difference, which means the barrier wall can greatly reduce the dangerous area behind the wall. However, the increase of the wall height can also cause a significant increase in the flame radiation fraction, because the surface area of the flame grows after impinging on the barrier wall. When the height difference is larger than 1 m, further increase in the height of barrier wall cannot significantly promote the fire resistance effect.

Experimental investigation on the fire and thermal smoke spread in tunnels: Effects of fire elevation

Previously, studies related to tunnel fires predominately concentrated on the fire at ground level while the risk of elevated fires caused by different vehicle heights was mostly ignored. In the current research, pool fires elevated at seven levels were experimentally studied in two reduced-scale model tunnels with both natural and longitudinal ventilation. Fuel burning rate, temperature profile, and thermal smoke stratification affected by the fire elevation were successively explored. Experimental results declared the major findings as 1) Fuel burning rate of the 8 cm × 8 cm pool fire was indistinctly affected by the fire elevation while it increased rapidly with the elevated height as pool size increased; 2) In the natural-ventilated tunnel, the maximum temperature significantly increased with the fire elevation and was found to be well predicted by the modified models with a linear correlation versus Q2/5Hd¯ or QD∗2/5·DfHd¯ and a constant value equal to 2.9. When longitudinal ventilation was activated, flame deflection, shortened back-layering length, and decreased maximum temperature were respectively observed. 3) Interface of the smoke-air layer was lifted, and thermal smoke stratification was promoted by the fire elevation. Good agreement was achieved between the present measurements and temperature quotient proposed by Newman. Correlation by using modified Froude number denoted different characteristics of smoke stratification of ground fire and elevated fire.

Effects of nonlinear characteristics on flow and combustion in the core-fired boiler

The asymmetric phenomenon of flame deflection in the combustion process of coal-fired boiler for different flow pattern, deflection angle and primary temperature were presented in this work. Numerical simulation was used for this paper to analyze the flow and heat transfer of the boiler furnace combustion. Air flow and combustion condition for the furnace firstly was simulated. And the nonlinear characteristics were loaded to analysis the furnace combustion. Thermal deviation which is the critical parameter for boiler was studied for the range of deflection angle from 0° to 18°, and the inlet primary temperature added + 0 K(BMCR), + 5 K, + 10 K, + 15 K by carrying out the numerical calculation. So the improvement methods for the thermal deviation are studied in the paper.

Evaluation of Mechanical Properties of Banana and Glass-Epoxy Hybrid Composites with Addition of Copper Powder

More studies have been made in recent years on the fibre reinforced polymer. Natural fibres play an important role in modern FRPs. To obtain higher mechanical properties, glass fibres are incorporated to prepare hybrid FRP composites. Present study, focuses the effect of adding the copper metal powder in polymer matrix i.e. the metal powder is mixed in the resin with varying proportions along with the banana and glass fibres. Five laminates were fabricated by varying the copper content from 1% to 5% and keeping the banana and glass fibres weight as common. The study concentrates on mechanical properties of the obtained hybrid composites. Good flexural and ultimate tensile strengths were obtained. The flame deflection test shows the hybrid composite is not suitable for high temperature application as it breaks the bond between the resin and the reinforcements due to thermal conductivity of copper.

Numerical Simulation and Unsteady Combustion Model of AP/HTPB Propellant under Depressurization by Rotation

AbstractIn order to study micro‐scale combustion characteristics of base‐bleed propellant ammonium perchlorate/hydroxyl terminated polybutadiene (AP/HTPB) under rotation condition, a two‐dimensional unsteady rotating combustion model of periodic sandwich model of AP/HTPB was established. In the gas phase, a two‐step overall reaction was used to couple the gas‐solid boundary layer, the rotational momentum was fitted and the numerical simulation comparative analysis under the initial combustion pressure of 0.1 MPa–5 MPa and the rotation velocity of 0–10 800 r min−1 was experimented. The results show that under the conditions of an initial combustion pressure of 3.5 MPa, a depressurization rate of 1000 MPa s−1 and a rotation velocity of 10 200 r min−1, the formation of a narrow diffusion‐controlled chemical reaction zone appears in the initial stage of depressurization. When the combustion pressure drops to about 0.88 MPa, the flame shows dual characteristics: diffusion‐controlled and premixed combustion. When the pressure dropped to 0.1 MPa, the flame is premixed combustion. The steady combustion process at different combustion pressures and different rotational velocities was analyzed numerically. The results show that there is a linear positive correlation between the flame deflection angle and the pressure. When the rotation velocity is lower than 10 000 r min−1, the deflection angle of the gas flame increases linearly with the rotation velocity. However, when the rotation velocity is higher than 10 000 r min−1, the deflection angle and the rotation velocity of the gas flame increase exponentially. The trend of the average Reynolds number of the combustion surface is basically the same as that of the deflection angle of the gas flame. Therefore, the average Reynolds number of the combustion surface can be used to describe the influence of rotation and pressure on the deflection angle of the gas phase flame.

Fire‐induced reradiation underneath photovoltaic arrays on flat roofs

SummaryThe impact of the reflection of fire‐induced heat from a gas burner was studied experimentally to gain knowledge on the interaction between photovoltaic (PV) panels and a fire on flat roofs. The heat flux was measured in a total of eight points at the same level as the top of the gas burner. The gas burner was placed underneath the center of a PV panel, installed in a geometry similar to a commercial east‐west orientated mounting system, and the eight points were symmetrical pairs of two at four different distances from the burner. Measurements were compared with tests with no PV panel, and thereby without the reflection from the PV panel. A significant increase of the received heat flux was recorded, with ascending percentage‐wise difference for increased heat release rates. This indicates that PV panels can have a significant contribution in roof fires, primarily because they stimulate fire spread over the roof on which they have been mounted. The received heat flux is higher underneath the most elevated part of the PV panel, due to two important, flame‐related reasons: 1) the flame deflection toward the most elevated part of the panel and 2) a nonhomogeneous temperature distribution on the PV panel surface, due to the deflected flame, and thereby a nonhomogeneous emission from the heated PV panel. Finally, the results were very similar for a brand new PV panel and a PV panel tested for the fourth time, except during the period when the thin combustible film underneath the new PV panel is burning, supporting that it is the fire dynamics and not the fire load associated with the PV panels that is promoting fire spread associated with PV panels on flat roofs. With this in mind, the current results are relevant not only for PV panels but also for any inclined roof covering panel with limited combustibility.

Louvered jet fire deflector – concept and concept validation for flame length reduction, flame deflection and explosion overpressure reduction

In hydrocarbon processing industries, the standard approach to prevent jet fire escalation to adjacent facilities is to provide a solid fire wall. However, a solid firewall impedes the air flow through the plant, decreasing ventilation and increasing the potential flammable gas cloud size resulting in the generation of higher explosion overpressures if the gas cloud finds an ignition source. The conflicting impact of solid fire walls in preventing jet fire escalates but conversely increasing the potential explosion overpressures is a perennial design issue faced by safety engineers. This paper presents an alternate louvered jet fire deflector design concept; along with the validation work undertaken to demonstrate the explosion overpressure reduction benefits of the louvered wall application. This louvered jet fire deflector concept was subsequently engineered, fabricated, tested and has been incorporated into the plant design. This paper is written to increase the knowledge and awareness of safety engineers of an alternate option to optimise and balance the fire and explosion risk management.

Experimental Investigation on the Mass Loss Rates of Thin-Layered n-Heptane Pool Fires in Longitudinally Ventilated Reduced Scale Tunnel

ABSTRACTThin-layered n-heptane pool fires are burned with varied pool depths under longitudinal ventilation velocities ranging between 0.5–2.5 m/s in a reduced scale tunnel model. The combined effects of ventilation, pool size, and depth are investigated on the heat release rate, temperature distribution, and mass loss rate of fire. The gas temperature distribution and heat release rate results indicate that the critical ventilation velocity is achieved around 1 m/s in the scaled model, corresponding to 3.6 m/s in the real scale tunnel. It is observed that the gas temperature downstream of the fire increases at 2.5 m/s ventilation due to an enhancing effect of oxygen supply to the fire and increased flame deflection towards the leeward side of the pan. Results show that maximum heat release rate and total heat release normalized by fuel amount tend to occur at critical ventilation velocity. The measured mass loss rates show a considerable increasing trend with pool depth.

Influence of Jet Angle on Diffusion Flames in Centrifugal Field

Diffusion combustion of propane and air in a rotational combustor was simulated by three-dimensional numerical model based on FLUENT. Influence of centrifugal field on the flame shapes and temperatures were discussed under various jet angles changing in the plane perpendicular to the rotational axis. The flame is compressed when the value of jet angle θ is less 90°, otherwise, the flame is stretched when |θ|>90°. When θ<90°, the deflection of flame becomes larger with an increase of θ. As contrasted to positive θ cases, the zones of high temperature in combustion chamber corresponding to negative are larger, and the maximal flame temperatures are likewise larger. The negative jet angle is useful to flame stability. External fluid is an important factor influence the distribution of temperature in combustion chamber.

Droplet combustion in the presence of acoustic excitation

This experimental study focused on droplet combustion characteristics for various liquid fuels during exposure to external acoustical perturbations generated within an acoustic waveguide. The alternative liquid fuels include alcohols, aviation fuel (JP-8), and liquid synthetic fuel derived via the Fischer–Tropsch process. The study examined combustion during excitation conditions in which the droplet was situated in the vicinity of a pressure node (PN). In response to such acoustic excitation, the flame surrounding the droplet was observed to be deflected, on average, with an orientation depending on the droplet’s relative position with respect to the PN. Flame orientation was always found to be consistent with the sign of a theoretical bulk acoustic acceleration, analogous to a gravitational acceleration, acting on the burning system. Yet experimentally measured acoustic accelerations based on mean flame deflection differed quantitatively from that predicted by the theory. Phase-locked OH∗ chemiluminescence imaging revealed temporal oscillations in flame standoff distance from the droplet as well as chemiluminescent intensity; these oscillations were especially pronounced when the droplets were situated close to the PN. Simultaneous imaging and pressure measurements enabled quantification of combustion-acoustic coupling via the Rayleigh index, and hence a more detailed understanding of dynamical phenomena associated with acoustically coupled condensed phase combustion processes.

A study of barrier walls for mitigation of unintended releases of hydrogen

Hydrogen jet flames resulting from ignition of unintended releases can be extensive in length and pose significant radiation and impingement hazards. Depending on the leak diameter and source pressure, the resulting consequence distances can be unacceptably large. One possible mitigation strategy to reduce exposure to jet flames is to incorporate barriers around hydrogen storage and delivery equipment. An experimental and modeling program has been performed at Sandia National Laboratories to better characterize the effectiveness of barrier walls to reduce hazards. This paper describes the experimental and modeling program and presents results obtained for various barrier configurations. The experimental measurements include flame deflection using standard and infrared video and high-speed movies (500 fps) to study initial flame propagation from the ignition source. Measurements of the ignition overpressure, wall deflection, radiative heat flux, and wall and gas temperature were also made at strategic locations. The modeling effort includes three-dimensional calculations of jet flame deflection by the barriers, computations of the thermal radiation field around barriers, predicted overpressure from ignition, and the computation of the concentration field from deflected unignited hydrogen releases. The various barrier designs are evaluated in terms of their mitigation effectiveness for the associated hazards present. The results show that barrier walls are effective at deflecting jet flames in a desired direction and can help attenuate the effects of ignition overpressure and flame radiative heat flux.

Evaluation of barrier walls for mitigation of unintended releases of hydrogen

Hydrogen jet flames resulting from ignition of unintended releases can be extensive in length and pose significant radiation and impingement hazards. Depending on the leak diameter and source pressure, the resulting consequence distances can be unacceptably large. One possible mitigation strategy to reduce exposure to jet flames is to incorporate barriers around hydrogen storage and delivery equipment. While reducing the extent of unacceptable consequences, the walls may introduce other hazards if not properly configured. An experimental and modeling program has been performed at Sandia National Laboratories to better characterize the effectiveness of barrier walls to reduce hazards. This paper describes the experimental and modeling program and presents results obtained for various barrier configurations. The experimental measurements include flame deflection using standard and infrared video and high-speed movies (500 fps) to study initial flame propagation from the ignition source. Measurements of the ignition overpressure, wall deflection, radiative heat flux, and wall and gas temperature were also made at strategic locations. The modeling effort includes three-dimensional calculations of jet flame deflection by the barriers, computations of the thermal radiation field around barriers, predicted overpressure from ignition, and the computation of the concentration field from deflected unignited hydrogen releases. The various barrier designs are evaluated in terms of their mitigation effectiveness for the associated hazards present. The results show that barrier walls are effective at deflecting jet flames in a desired direction and can help attenuate the effects of ignition overpressure and flame radiative heat flux.

Analysis of jet flames and unignited jets from unintended releases of hydrogen

Abstract A combined experimental and modeling program is being carried out at Sandia National Laboratories to characterize and predict the behavior of unintended hydrogen releases. In the case where the hydrogen leak remains unignited, knowledge of the concentration field and flammability envelope is an issue of importance in determining consequence distances for the safe use of hydrogen. In the case where a high-pressure leak of hydrogen is ignited, a classic turbulent jet flame forms. Knowledge of the flame length and thermal radiation heat flux distribution is important to safety. Depending on the effective diameter of the leak and the tank source pressure, free jet flames can be extensive in length and pose significant radiation and impingement hazard, resulting in consequence distances that are unacceptably large. One possible mitigation strategy to potentially reduce the exposure to jet flames is to incorporate barriers around hydrogen storage equipment. The reasoning is that walls will reduce the extent of unacceptable consequences due to jet releases resulting from accidents involving high-pressure equipment. While reducing the jet extent, the walls may introduce other hazards if not configured properly. The goal of this work is to provide guidance on configuration and placement of these walls to minimize overall hazards using a quantitative risk assessment approach. The program includes detailed CFD calculations of jet flames and unignited jets to predict how hydrogen leaks and jet flames interact with barriers, complemented by an experimental validation program that considers the interaction of jet flames and unignited jets with barriers. As a first step in this work on barrier release interaction the Sandia CFD model has been validated by computing the concentration decay of unignited turbulent free jets and comparing the results with the classic concentration decay laws for turbulent free jets taken from experimental data. Computations for turbulent hydrogen free jet flames are also presented and compared with experimental data for the temperature profile in lab-scale turbulent free hydrogen jet flames. Finally, preliminary results of calculations of hydrogen jet flame impingement on barriers are presented and compared with images of large-scale hydrogen jet flame deflection from barrier wall experimental tests.