Horizontal Flames Research Articles

Effects of impinging object on geometrical flame features of horizontal jet flames

Accidental release of hydrocarbons can result in jet fires which have the potential to escalate accidental events to catastrophes. Jet fire can impinge on nearby equipment surface or a pasive firewall to make the fire plume temperature and the radiant heat flux complex. The present work experimentally investigated the flame characteristic of free horizontal jet fires and the impingement effect using propane as fuel, with different nozzle diameter, and exit velocity. To analyse the effect of flowrate to jet flame condition, the flow rates range between 30 and 600 g/min were employed with horizontal separation distance from the main source to target was at 0.8-m and 1.2-m. The results show that, the incremenet of flame features are faster for free release than impinging release. The presence of object downstream affect the flame profiles at some point. Thus, new correlations were proposed for the prediction of projected flame length and trajcetory length.

Numerical study on the effect of complex structural barrier walls on high-pressure hydrogen horizontal jet flames

Hydrogen has the potential to produce energy with no emissions, and therefore offers a strategic opportunity for rapid development of renewable energy storage. However, jet flames caused by the leakage of high-pressure hydrogen may cause casualties and damage equipment, so the safety issues associated with hydrogen incidents are a key issue restricting its development. Barrier walls can be an important mitigative action to reduce the hazard of hydrogen jet flames. Previous studies have evaluated the protective effect of different vertical or inclined arrangements of a single barrier wall in the vertical direction. However, in the vertical direction, a single barrier wall is not sufficient to reduce the hazards associated with high-pressure hydrogen jet flames. In this paper, a two-dimensional CFD model of high-pressure hydrogen jet flames are established. A simplified form of the hydrogen real gas equation of state is used to describe the complex behavior of high-pressure hydrogen. This CFD study employs the standard k-ε turbulence model, the eddy dissipation concept (EDC) model, and the discrete ordinate (DO) radiation model. The results display good agreement with the experimentally obtained flame shape and thermal radiation values, which confirms the applicability of the model. Based on this model, the characteristics of high-pressure jet flames are systematically studied under different forms of barrier walls and different pressures of hydrogen storage. Compared with the vertical barrier wall, barrier walls with complex structures can block the flames in front of the wall more effectively. This is proven through a remarkable decline in the vertical flame length and a reduction in the high temperature area. Comparing the five barrier wall patterns for their combined flame shape and flame temperature, it is more preferred to choose 60° Plate. The results of this study will help to better analyze the consequences of hydrogen jet flames and provide guidance for better design of barrier walls for mitigation.

Investigation of the mechanism of global and terminal flame uplifted in subsonic horizontal spray jet flame under sub-atmospheric pressure: From macroscopic to microscopic perspective

This work explored how subsonic horizontal spray flames behave under sub-atmospheric pressure and the mechanisms behind their combustion. For examine a horizontal spray flame with rated air volume flow and equivalence ratio, large eddy simulation (LES) and probability density function (PDF) were employed, based on the discrete phase (DPM) random trajectory model. The simulation results are in good agreement with the previous experiments. Through the micro-analysis of the burning time, burning path, and rate of the burn path of droplets under different atmospheric pressures, the combustion characteristics of the flame have been revealed; as well, a component change analysis was conducted to investigate the combustion mechanisms of the flame. Density distributions in buoyancy plumes can reveal the morphologic mechanisms in the corresponding flame regions. A detailed explanation of the varied mechanisms in horizontal spray flames in low-pressure environments is provided, in conjunction with the results of previous experiments on macroscopic flame morphology. There is also a proposed chain of influence across certain characteristics of horizontal spray flames under low pressure. This improves our understanding of mechanisms governing flame behavior in sub-atmospheric pressure environments by allowing us to theoretically design and regulate flames.

Experimental study on the effect of fan-shaped water mist on horizontal under-expanded hydrogen jet flames

A series of experiments were performed on the fan-shaped water mist interaction with the horizontal under-expanded hydrogen jet flames. The effects of various water mist pressures and horizontal release positions were focused on flame length, temperature, and radiant heat flux. The results show that, water mist causes the flame to be tilted and the tilt angle of the flame increases with the water mist pressure, and the horizontal length of the flame is shortened. It is also found that water mist may lead to the radiation and temperature enhancement on the axis and downstream of the action position of water mist and flame, which is closely related to the configuration of water mist. However, this situation disappears and the temperature and radiation decrease with the increase of water mist pressure.

Projected flame length and flame extension length of horizontal buoyant jet flames

Abstract Jet fires are a type of dangerous fire caused by the sudden release of flammable materials. In this work, propane was used as fuel and released through a 7.15mm and 9.8 mm circular nozzle with the exit velocities were set ranging between 27 and 65 m/s. The data of this study are compared against theoretical measurement and prediction using previously suggested correlation for projected flame length and flame extension length. It was determined, the projected flame length gives a good prediction by using theoretical measurement while for the prediction of flame extension length, an elliptical shape assumption was suitable to be used after impinging point for a horizontal buoyant jet fire.

The effects of geometrical flame feature on radiant heat flux prediction of horizontal jet flames using line source model

AbstractRadiant heat flux and impingement are the most common contributors to accident escalation involving jet fire. Thus, it is important to account for the radiant heat flux by using a semi‐empirical model as it is easy, cheaper, and could provide a reliable prediction. In this study, experimental observations were carried out for both free and impinging jet release. Propane was used as fuel and released from a circular nozzle with a diameter of 7.15 and 9.8 mm. The release velocity was fixed between 27 to 65 m/s, which is considered a subsonic release. In this work, two bases for radiant heat prediction using LSM were used: (i) horizontal kite shape approach and (ii) flame trajectory approach. It was observed that the prediction of radiant heat flux based on the flame trajectory for the free jet fire scenario gave the R2 value of 0.99, suggesting that the flame trajectory could give a better prediction as compared to the horizontal kite shape approach with R2 = 0.94. By using a similar assumption for impinging jet flames, it was observed that LSM based on flame trajectory could be used to predict the radiant heat flux with R2 = 0.99 for each case scenario.

Flame shapes and thermal fluxes for an extensive range of horizontal jet flames

The prediction of the flame-geometry descriptors and thermal fluxes of jet flames may contributes to the provision of effective fire protection measures in industry plants. Previous works were mainly devoted to assess the related-hazardous effects of vertical jet fires, while horizontal ones were barely investigated. This paper collects a vast database of horizontal sonic and subsonic jet fire experiments involving multiple gas fuels and release conditions. Based on the experimental results, state-of-the-art correlations are developed to describe the flame shapes and thermal fluxes for extensive ranges of jet flames horizontally released.

Effect of crossflow on the air entrainment of propane jet diffusion flames and a modified Froude number

Gas leakage fire is increasingly common with urbanization and industrialization. Understanding of the entrainment behavior of the jet flame is significant to improve the fuel security management and fire prevention strategy. Many studies have been done in still air and limited studies have focused on the air entrainment of the jet flame under crossflow. This work firstly deduced an expression of the air entrainment ratio (n) incorporating with the flame length and tilt angle based on the momentum balance and, defined a modified Froude number (Fr∗) to explore effects of the inertia force (owing to the fuel jet and crossflow) and the combustion-induced buoyancy. Secondly, experiments of propane jet diffusion flames under crossflow were performed. Fuel jet Reynolds number (Re) and jet-to-crossflow momentum flux ratio (RM) were 310–3305 and 0.004–124, respectively. The flame length divided by Re first increased and then decreased with RM, and its curves were more like parabolas other than polylines. The flame tilt angle decreased with RM. Moreover, Fr∗ had a negative relationship with RM, indicating the jet and crossflow momenta, instead of combustion-induced buoyancy, gradually dominated the air entrainment with increasing wind velocity. The calculated n was dominated by the flame length but effected by the tilt angle, because the local entrainment velocity was proportional to the magnitudes of the crossflow velocity and flame axial velocity differences that were relevant to the flame tilt angle. Finally, there were three trends of n with Fr∗ according to Re. For Re < 900, the crossflow was always dominant and n varied slowly. For 900 < Re < 2300, n first grew quickly with stretched and slightly inclined flames and then decreased to some almost constants with nearly horizontal flames. For Re > 2300, n increased rapidly owing to the dominated-effect of the momentum and then decreased until the flame began to shorten.

The onset of extreme fire behaviour in a mine drift

The onset of extreme fire behaviour in a mine drift with longitudinal ventilation was analysed. A fire in a mine drift with continuous fuel load, involving several separate fires may lead to flames tilted horizontally and filling up the entire cross section. This will lead to earlier ignition, higher fire growth rate, higher fire spread rate and a severe fire behaviour. The focus has been on what changes take place at the onset and signs of the impending phenomenon. It was found that the fire gas temperature at the ceiling level provided a poor indicator. At the downstream far-field region of the fire, the sudden temperature increase at the lowest levels of the cross section and the sudden increase in flow velocities would provide signs of extreme fire behaviour. The corresponding full-scale heat release rates of the experiments at the onset of extreme fire behaviour were found to be very high for mining applications but not necessarily for tunnel fires. The heat release rate threshold for a mine drift with smaller cross-sectional dimensions would decrease considerably, increasing the likelihood of occurrence. The distance between the fuel items will play an important role during the initiation of horizontal flames.

Heat transfer blockage effect of small-scale PMMA flame under exterior heat radiation

In this work, experiments of small-scale vertical and horizontal PMMA flames were performed under exterior heat radiation, in order to investigate the heat transfer blockage effect based on energy balance of steady state. It is found that for both sample orientations, the mass loss rate of PMMA increased linearly with increasing exterior heat radiation, and the flame height depends linearly on mass loss rate to the power 2/3. Calculated and measured mass loss data indicate that the heat transfer blockage fraction is independent of the exterior heat radiation for both sample orientations. For vertical PMMA flame, the radiation blockage fraction increases with vertical height. For horizontal PMMA flame, the radiation blockage fraction is the highest at the sample center. For both horizontal and vertical samples, the mean radiation blockage fraction increases with exterior heat radiation and gradually reaches an equilibrium value. The convective heating to the sample surface is enhanced by hot gas flow for vertical PMMA flame, while it is weakened for horizontal PMMA flame.

Experimental study on propane jet fire hazards: Assessment of the main geometrical features of horizontal jet flames

Jet fires are among the least severe fires in terms of direct effects, but are very important in terms of risk assessment due to the potential escalation of the incident by impingement or engulfment of the jet fire on the surrounding vessel, pipework or other components. This paper focuses on the determination of the main geometrical features (flame shape, length, and width) of medium-scale horizontal jet fires in air. The study is based on the experimental results of LPG jet fire released from a horizontal pipe of 1.9 cm diameter at different flow rates, with vapor flows, reaching a flame size of 1–10 m long. For each test, visible and infrared visualizations were recorded. First, the two visualization techniques are compared with each other, and with the different methods of flame shape determination available in the literature. The flame detected with each technique, both instantaneous and averaged, is then compared with basic flame shapes.

Cold Climate Fire Risk; A Case Study of the Lærdalsøyri Fire, January 2014

Parameters leading to the severity of the fire in Lærdalsøyri, Norway, January 18th to 19th 2014, have been analyzed. The fire in the first villa developed significantly faster than the fire fighters could handle and the fire quickly spread to other structures. In addition to 36 modern buildings, 4 historic buildings in Gamle Lærdalsøyri cultural heritage area were lost. Heroic effort of local and neighbor community fire brigades, police, military forces and volunteers prevented the fire from destroying the whole village, including the remaining 157 historic buildings. Adiabatically heated (low humidity) air from surrounding high mountains gave outdoor wood fuel moisture content (FMC) of about 7.6%. Inside inhabited buildings, it is shown that the wooden products reached about 4.5% FMC prior to the blaze. When ignited, this resulted in rapid fire development. Two story villas burned down in less than 1 h while producing much embers and firebrands. Strong shifting winds subsequently spread the fire to neighbor houses by flame contact (periodically 20 m long horizontal flames) and over long distances (200 m) by embers and firebrands. Based on the present work, an increased fire risk associated with low FMC in inhabited wooden houses during winter time can be predicted. This is of value when considering measures to reduce the probability of a fire outbreak as well as measures mitigating the escalation of a potential fire.

Microgravity opposed-flow flame spread in polyvinyl chloride tubes

The effects of gravity on opposed-flow flame spread in a confined geometry were investigated experimentally in the 2.2-s drop tower at the NASA Glenn Research Center. Pure oxygen flowed through samples of 0.64-cm-inner-diameter polyvinyl chloride (PVC) tubing held either horizontally or vertically in a combustion chamber filled with nitrogen. The sample was ignited in normal gravity with a hot wire, and once a flame was established, the apparatus was dropped to observe microgravity effects. Flame spread rate was measured in normal and microgravity at pressures of 1.0 and 0.5 atm. A low-flow ignition limit was observed at an opposed-flow velocity of 1.36 cm/s, at which point the horizontal, vertical, and microgravity flame spread rates were 0.40, 0.30, and 0.16 cm/s, respectively. For flow velocities above approximately 5.2 cm/s, there was no difference in the flame spread rates for normal and microgravity and the flame spread rate increased with a nearly square root dependence with respect to opposed-flow velocity. Buoyant flow velocities of 2.5 and 1.5 cm/s were estimated for horizontal and vertical flames, respectively. Vertical tests conducted at 0.5 atm pressure demonstrated no difference in flame spread rate between normal and microgravity. These results suggest that the fire risk associated with the use of PVC tubes during general anesthesia in either space or ground applications may be reduced if the application of a high-energy surgical tool is prevented during an active phase of the breathing cycle (inhale or exhale).

Trajectory and Characteristics of Buoyancy and Momentum Dominated Horizontal Jet Flames From Circular and Elliptic Burners

Relative effects of buoyancy and momentum on the characteristics of horizontally oriented circular (Circ) and elliptic (E) burner flames in a quiescent environment over a wide range of jet exit velocities are presented. The major axis of the elliptic burner was oriented horizontally and vertically (referred to as Emaj and Emin flames, respectively). Propane was used as fuel and a small amount of hydrogen was piloted to attach flames to the burner. Global flame characteristics such as flame dimensions, centerline trajectory, emission indices (EI) and radiative fraction, and in-flame transverse concentration and temperature profiles were measured. At a jet exit Reynolds number (Rej) of 2000, based on the area-equivalent diameter of the burner, the flame characteristics were affected by the burner geometry and its orientation. Also, the vertical dimension of the burner exit dictated buoyancy effects. At Rej=12,500, the influence of burner geometry or its orientation was negligible. Elliptic burner flames exhibited lower liftoff and blowout velocities than circular burner flames. Furthermore, the flame stability and nitric oxide emissions were not much affected by the orientation of elliptic burner. Although the elliptic burners produced higher EINO at lower jet exit velocities, the variation in EINO among three burners (Circ, Emaj, and Emin) was insignificant at higher velocities. Some effects of buoyancy on EICO were observed at lower jet exit velocities and the EICO was the lowest for the burners with largest buoyancy flux. Elliptic burner flames produced greater peak flame temperature than the corresponding circular burner flames under most conditions.

Aerodynamic Characterization Of A Compartment Fire As A Function Of Its Behavior

An experimental setup is realized to study the behavior of a confined fire when the fire source is placed in combustion products trapped by a soffit, or located at the lower part of the rear wall of an enclosure. As a function of the source position, the flame, the heat release rate and the ventilation factor are drastically modified. In the first configuration, different flame behaviors are identified corresponding to jet flames, horizontal flames on the whole room surface at the level of the soffit, or extinction. In the second one, the wall fire interacts with the burnt gases close to the ceiling. The outwards hot smoke layer at the aperture always occupies one third of the open height. Based on the analysis of Babrauskas et al [1], a two zones hydrostatic model is developed, and a relation between the input air mass flow rate entering the room, the ventilation factor Fv and the heat release rate Q is obtained : mair = f(F 2 / 3Q1/ 3 ). For a fixed heat release rate, mair only depends on the ventilation factor but stays independent of the flame structure in the room. This relation corroborates the experimental data and the theoretical analysis to results available in the literature and can be used to model for the structure of such flames.

On the alignment of strain, vorticity and scalar gradient in turbulent, buoyant, nonpremixed flames

The alignment of vorticity and scalar gradient with the eigendirections of the rate of strain tensor is investigated in turbulent buoyant nonpremixed horizontal and vertical flames. The uniqueness of a buoyant nonpremixed flame is that it contains regions with distinct alignment characteristics. The strain-enstrophy angle Ψ is used to identify these regions. Examination of the vorticity field and the vorticity production in these different regions indicates that Ψ and consequently the alignment properties near the flame surface identified by the mixture fraction band F≈Fst differ from those in the fuel region, F&amp;gt;Fst and the oxidizer region, F&amp;lt;Fst. The F≈Fst band shows strain-dominance resulting in vorticity/α alignment while F&amp;gt;Fst (and F&amp;lt;Fst for the vertical flame) band(s) show(s) vorticity/β alignment. The implication of this result is that the scalar dissipation, εF, attains its maximum value always near F≈Fst. These results are also discussed within the framework of recent dynamical results [Galanti et al., Nonlinearity 10, 1675 (1997)] suggesting that the Navier-Stokes equations evolve towards an attracting solution. It is shown that the properties of such an attracting solution are also consistent with our results of buoyant turbulent nonpremixed flames.

Comprehensive Modeling of Turbulent Flames With the Coherent Flame-Sheet Model—Part II: High-Momentum Reactive Jets

This paper describes the application of computational fluid dynamics (CFD) to the prediction of the characteristics of high-momentum vertical and horizontal flames in ambient air flows. The KIVA-II code has been modified by extending the range of boundary conditions and by the addition of the following: a version of the coherent flame-sheet model, Tesner’s soot generation and Magnussen’s soot oxidation model, and an implementation of the discrete transfer radiation model. To assess the accuracy of the complete model for prediction purposes, results are compared with experimental data. Predictions of temperature and flame profiles are in good agreement with data while predictions of radiative heat transfer are not entirely satisfactory.

Numerical modeling of turbulent jet diffusion flames in the atmospheric surface layer

The evolution of turbulent jet diffusion flames of natural gas in air is predicted using a finite-volume procedure for solving the flow equations. The model is three dimensional, elliptic and based on the conserved-scalar approach and the laminar flamelet concept. A laminar flamelet prescription for temperature, which is in agreement with measurements in methane/air flames and accounts for radiative heat losses, has been modified and adapted to natural-gas flames. The k- ϵ- g turbulence model has been used. Different probability-density functions for the conserved scalar and an alternative method which does not require the use of a pdf are employed. The model has been applied to flames in the buoyancy-momentum transition regime, in both cases where the fuel jet is immersed in a co-flowing or in a cross-flow air stream whose properties correspond to the atmospheric surface layer. Experiments have been carried out for a horizontal flame in a wind tunnel with simulated atmospheric boundary layer, and measurements of temperature distributions are compared with the numerical results; a good agreement is found. The influence of wind properties on flame shape has been investigated. For horizontal flames, a correlation is proposed for the stoichiometric flame length as a function of the Froude number and the wind to jet velocity ratio. Flame length predictions have been compared with available experimental data and correlations proposed in the literature.

Analytical solution to the flame trajectory based on the analysis of “Scaling of buoyant turbulent jet diffusion flames” by N. Peters and J. Göttgens

Horizontal jet flames are formed in oil and gas well diverter fires, some accidental leak fires, and furnaces that utilize horizontal fuel injectors. In spite of these applications, only a few studies of flames in the horizontal configuration have been reported in the literature [1–3].

The contribution of flames under ceilings to fire spread in compartments

An experimental investigation has been made of flames spreading beneath both combustible and non-combustible ceilings. Experiments were performed in a model representing the ceiling of a corridor with a fire at one end: a gas burner was used to represent the fire, this was replaced by wooden cribs in experiments to be described in later part of this report. The flames rising vertically from the fire in effect drew air up into the horizontal layer of flames and gases beneath the ceiling. Depending on the rate of flow of fuel gas (or rate of burning of the cribs) this air could be sufficient for complete combusion of the fuel gases and the flame length was then apparently determined by mixing processes within the layer. When this air was not sufficient, the remaining air for combustion was entrained vertically into the horizontal layer from the cool air beneath and the flames became much longer. Correlations of lengths of horizontal flames beneath non-combustible ceilings have been derived and related to the much shorter lengths of vertical flames. Relationships have been derived from the experimental data from which it is possible to estimate the radiation downwards from a hot non-combustible ceiling and the gases beneath it to the floor with a view to estimating the contribution to fire spread on the floor. A heat balance of the ceiling gases was satisfactory, so confirming the validity of the calculations. Horizontal flames radiate more of the heat produced at a level sufficient to assist fire spread than do vertical ones. A combustible ceiling lining results in longer flames, an increase in the distance over which heat radiated downwards at an intensity sufficient to promote fire spread and a faster rate of increase of radiation than a non-combustible one with similar thermal constants. The aspect of performance which best related to the results of BS 476 tests was the rate of increase of radiation downwards in the early part of the experiments. The radiation downwards was apparently partly determined by extraneous factors such as the detachment of the board from its holding nails and whether the decomposition products were emitted as jets. The rate of spread of fire along a narrow strip of wood on the floor beneath a burning ceiling lining has been calculated and the results related to the index of performance on the Fire Propagation Test.