Visible Flame Height Research Articles

Thermal hazard analysis and fire risk assessment of rocket kerosene in oxygen-enriched environment

Fire hazard of liquid fuel exposed in oxygen-rich environment is significantly greater than that in air, which should be considered in the safety risk assessment of scenarios where oxygen and fuel coexist. To reveal the effect of oxygen concentration on fuel properties and combustion characteristics of liquid fuel, a series of experiments were conducted to measure the liquid-phase component, flash point, lower flammability limit, heat release rate and flame height of rocket kerosene at different oxygen concentrations. The results show that the flash point of rocket kerosene (with an average chemical formula of C11.98H22.64) decreases nonlinearly with the increased oxygen concentrations, while the oxygen concentration has a great enhancement effect on the heat release rate and visible flame height of rocket kerosene pool fire. Prediction models of the flash point and lower flammability limit based on the Clausius-Clapeyron equation, Le Chatelier rule and decreasing temperature assumption, as well as empirical equations of the heat release rate and visible flame height, were derived for different oxygen concentrations in this work, providing a new comprehensive understanding of the effect of oxygen concentration on the rocket kerosene, and could be further applied to fire risk assessment in liquid fuel and oxygen coexisting scenarios.

Effect of preheating air temperature on sooting tendency in laminar co-flow diffusion flame of n-heptane

This work investigates the effect of preheating air temperature on the sooting tendency in the laminar co-flow diffusion flames of n-heptane. A modified co-flow burner was employed to produce steady n-heptane laminar diffusion flames with the preheating temperatures of co-flow air varying from 344 K to 588 K. The planar laser-induced incandescence (LII) calibrated by the line-of-sight attenuation (LOSA) was performed to quantitatively measure the soot volume fraction and the soot yield in flames and an ICCD camera was used to capture the flame luminosity images. The results reveal that the visible flame height is decreased with the preheating co-flow air temperature, and it is hardly affected by the air velocity with a constant air temperature. As the co-flow air temperature increases, the soot inception and oxidation and the peak soot concentration initiate at the lower positions in flames, and the soot loading in flames has a remarkable increasing trend by assessing the evolution of the soot volume fraction and the soot yield. However, the enhancement rate of total soot loading in flames with the co-flow air temperature below the initial fuel temperature is lower than that for the co-flow air temperature above the initial fuel temperature. In addition, the temperature sensitivity of soot loading is assessed by the maximum soot volume fraction, which is in accordance with those of the alkane in previous research. According to the response of the maximum soot yield to the co-flow air temperature and adiabatic flame temperature, the temperature sensitivity of sooting tendency in n-heptane flames is further confirmed.

Experimental investigation of hydrogen enriched natural gas diffusion reactions using preheated air in a hot coflow burner

The present paper analyzes experimentally the morphology of a set of non-premixed diffusion reactions of hydrogen enriched natural gas (NG). For the analysis the H2 content was varied from 0 to 100 vol.-% and the mixture issues in a co-flow at variable preheating temperatures, from ambient conditions of 25 °C and up to 400 °C. For the various NG-H2 blends the thermal power input was held constant at 0.8 kW. For processing the images, a bitmap filter was used to isolate visible flame height, visible width variations, and soot free length fraction (SFLF). The results show that visible flame height always decreases when increasing H2 content in NG at any preheating temperature. The effects of air preheating summarize as follows: for NG enriched up to 75 vol.-% H2, the visible flame height reduces when increasing the air preheating temperature from 25 °C to 200 °C, then at 300 °C the visible flame height increases when rising the air temperature up to 400 °C. For the 100% H2 non-premixed flame the visible height presents a linear trend to increase as air temperature rises. Roper's theory for non-premixed flames in circular ports correlates reaction length to air preheating temperature and fuel composition variations, however those trends neglect buoyancy and diffusion phenomena, which results in significant error on predicting the effects of hydrogen addition to NG on the reaction length. A modified correlation is proposed to predict accurately the effects of air preheating and H2 fraction on visible flame height. Finally, a multidimensional scaling analysis shows that hydrogen addition up to 50 vol.-% does not modifies the visible flame morphology significantly when compared to pure NG.

Experimental investigation of soot formation in inverse diffusion flames of CO2 and N2 addition: Isolation of dilution and thermal effects

ABSTRACT This experimental study compares the flame structure, temperature, and soot formation characteristics of normal (NDFs) and inverse diffusion flames (IDFs), evaluates the effect of CO2 addition, and isolates the thermal and dilution effects of CO2 and N2 addition on soot formation in IDFs. A hyperspectral imager using the TR-GSVD algorithm measures IDFs with different CO2 addition (XD) in the oxidant, with N2 addition as the comparison. In contrast to NDFs, IDFs have an opened tip, and the visible flame height and flame width decrease as XD grows. IDFs have a higher peak temperature than NDFs, but their peak soot volume fraction is substantially lower. Compared with N2 addition at the same XD, CO2 addition narrows IDFs and makes the reaction zone visible, and the peak temperature of CO2 addition is 350 K lower than that of N2 addition. The suppression effect of CO2 on soot formation is more potent than N2, with a soot formation rate of 30% that of N2 addition and a soot loading of 20–60%. The activation energy of soot formation reaction with CO2 addition is higher than N2 addition. The isolating results reveal that the thermal effect contributes to the main suppression effect of CO2 addition on soot formation, while the dilution effect of N2 addition is stronger than its thermal effect.

Jet fires involving releases of gas and solid particle

The high-pressure leakage of underground pipeline could entrain the nearby sands and soils, and thus cause the jet fire of gas-solid mixtures. In addition, the thermal runaway of Lithium ion batteries could also cause a typical gas-solid jet diffusion flame. In comparison with the gaseous jet diffusion flame and the gas-solid-air jet premixed flame, the gas-solid jet diffusion flame lacks of exploration. Thus, a new facility consisting of a jet fire apparatus and a sand feeder, was designed to explore the gas-solid jet fire. The test repeatability was justified for the proposed facility. The dynamical differences of gas-solid and gaseous jet fires are clarified. It is found that the gas-solid jet fire holds a larger lift-off height, a less visible flame height and a less radiative fraction than the purely gaseous jet fire. In particular, for gas-solid jet fires at high exit velocities, the lift-off height increases, but the visible flame height and radiative fraction seem to decrease, as the particle size of sand decreases to increase the jet height of sand. (1) Inside the flame volume, the sand plays a role of heat sink to decrease the flame temperature and thus the flame burning velocity. Moreover, in the lift-off region, the sand dilutes the gas fuel and isolates the surrounding oxygen to inhibit the combustion. Both effects of sand cause a large lift-off height, especially for the sand of little particle size. (2) A large lift-off height means the increase of the air mass entrained from flame base or the portion of the premixed flame to the whole flame. In addition, the sand particle-laden flow would significantly increase the ambient air entrainment rate of fire plume. Both effects result in a less visible flame height. (3) The portion of the premixed flame increases in the bottom, which reduces the total soot amount inside the whole flame volume. The decrease of the flame temperature and the total soot amount reduces the radiative fraction. (4) The sand significantly affects the flame geometry and radiative fraction, which alters the radiant heat flux distribution and challenges the development of thermal radiation model for gas-solid jet fires. The gas-solid jet fire holds a less peak radiant heat flux but a higher positon of peak radiant heat flux than the gaseous jet fire. In addition, the line source radiation model available in literature is revised to well predict the radiant heat flux distribution of the gas-solid jet fires.

Effects of oxygen on soot formation in laminar co-flow flames of binary mixtures of ethane, DME, and oxygen

Soot volume fractions of binary mixtures of ethane, DME and oxygen were evaluated experimentally in a co-flow burner. Soot volume fractions were measured by diffuse-light line-of-sight attenuation technique. The carbon mass flow rate and the C/H ratio were kept constant for all mixtures, while oxygen was introduced into the fuel stream either as an additive or as intramolecular oxygen in DME or both. Visible flame heights were decreased with increasing oxygen in the fuel stream. Binary mixtures of ethane and DME did not show any synergistic effects on soot formation. The maximum soot volume fraction was decreased from 1.41 ppm in the neat ethane flame to 0.08 ppm in the neat DME flame. On the other hand, oxygen addition to either ethane or DME resulted in an increase in soot concentrations. The maximum soot volume fraction reached to 2.1 ppm and 0.29 ppm in ethane/oxygen and DME/oxygen mixtures, respectively. The peak soot yield initially decreased for all mixtures studied as oxygen was introduced into the fuel tube. A unique transition was observed in DME/oxygen mixtures at an equivalence ratio of 6.8. When more oxygen was added beyond this ratio, the effect of oxygen on soot formation was suddenly reversed, and the peak soot volume fraction and yield were significantly decreased. This sudden reversal was explained as a result of a transition into a more premixed mode of combustion, supported by the flame images as well as chemiluminescence measurements. A distinct two-zone flame structure, that is, an inner rich zone and an outer stoichiometric zone separated by a dark region, was observed for the neat DME flame and DME/oxygen mixture flames. It is argued that as oxygen becomes available from DME decomposition, it produces a premixed region, and the flame chemistry is significantly altered beyond a critical oxygen concentration. Current radially resolved soot volume fraction measurements suggest that the effects of oxygen on soot formation can be quite complex with nonmonotonic behaviour, sudden effect reversals and shifts in soot formation and oxidation zones.

Experimental study on flame height of two oil tank fires under different lip heights and distances

The combustion behavior of two oil tank fires will be influenced by the interaction of their respective flames. This paper presents the experiments to investigate the evolution of the visible flame height of two oil tank fires under different diameters, lip heights and distances. The results show that when the tank spacing is small, the vortex structure plays an important role in the flame behavior showing an enhancement of the flame height. The flame height increases with the increase in lip height and reaches a local maximum value. The flame merging characteristic is influenced by the burner size and shape. A dimensionless model of the visible flame height of two oil tanks fire has been proposed, taking the tank diameter, lip height, and tank spacing into consideration. The correlation is validated using the experimental data.

A new burner to characterize laminar diffusion flames generated from wildland fuels

A new burner is presented, designed to generate laminar and axisymmetric diffusion flames from wildland fuels. This burner consists of a porous sample holder where wildland fuel elements are deposited. The sample holder is mounted on a cylindrical structure which allows an oxidizer coflow injection around the fuel samples. When the sample is ignited, a well-controlled flame is generated because the coflow surrounds the flame and prevents the formation of instabilities. This was proved with flame stability measurements in several scenarios where sample holder diameter, size distribution of the fuel and porosity of the sample were varied. Ignition of the fuel was achieved with ethanol. Two fuels were tested: Pinus radiata pine needles and Eucalyptus globulus leaves. Both fuels were cut and sieved into three size distributions. The CH∗ spontaneous and visible emission from the flame were detected in order to analyze the flame structure after the ethanol is consumed. The visible flame height decreased linearly with time after the ignition period, and as the oxidizer flow rate increased. Finally, deconvoluted soot pyrometry measurements at two wavelengths were performed in order to demonstrate the ability of the burner to generate stable and axisymmetric flames apt for non-intrusive diagnostics.

Influence of Eddy-Generation Mechanism on the Characteristic of On-Source Fire Whirl

This paper numerically examines the characterisation of fire whirl formulated under various entrainment conditions in an enclosed configuration. The numerical framework, integrating large eddy simulation and detailed chemistry, is constructed to assess the whirling flame behaviours. The proposed model constraints the convoluted coupling effects, e.g., the interrelation between combustion, flow dynamics and radiative feedback, thus focuses on assessing the impact on flame structure and flow behaviour solely attribute to the eddy-generation mechanisms. The baseline model is validated well against the experimental data. The data of the comparison case, with the introduction of additional flow channelling slit, is subsequently generated for comparison. The result suggests that, with the intensified circulation, the generated fire whirl increased by 9.42 % in peak flame temperature, 84.38 % in visible flame height, 6.81 % in axial velocity, and 46.14 % in velocity dominant region. The fire whirl core radius of the comparison case was well constrained within all monitored heights, whereas that of the baseline tended to disperse at 0.5 m height-above-burner. This study demonstrates that amplified eddy generation via the additional flow channelling slit enhances the mixing of all reactant species and intensifies the combustion process, resulting in an elongated and converging whirling core of the reacting flow.

Measurement of soot volume fraction and primary particle diameter in oxygen enriched ethylene diffusion flames using the laser-induced incandescence technique

The paper presents an experimental investigation of the effect of oxygen concentration in the oxidizer (O2+N2) on distributions of soot volume fraction (SVF) and flame centerline primary particle size in laminar coflow ethylene diffusion flames. The base flame has an oxygen index (OI, oxygen mole fraction in the oxidizer stream) of 21%. Three additional flames, with OI of 30%, 40% and 50%, are also examined. The fuel flow rate was maintained constant in all the experiments. The two-dimensional laser-induced incandescence (2D-LII) and two-color spectral band measurement based on the response spectrum of R, and G bands of a color 3-CCD camera are applied to measure distributions of SVF. The time resolved laser-induced incandescence (TIRE-LII) is used to measure SVF and primary particle size along the flame centerline at different heights above burner (HAB). The results of SVF are compared among the two-color method, 2D-LII, and light-of-sight attenuation (LOSA) from the literature in the base flame and compared between TIRE-LII and two-color spectral band method in oxygen enriched flames. Good agreements are observed in the measured SVF from different methods. Soot primary particle sizes, measured by TIRE-LII, are compared with those based on transmission electron microscopy (TEM) image analysis from the literature and a fairly good agreement is observed. The results indicate that soot yields increase and the flame becomes shorter and brighter with increasing OI. The primary particle diameter increases firstly and then decreases with the normalized HAB by the visible flame height (hf). At the same HAB/hf, the primary particle diameter generally increases with increasing OI from 21% up to 50%.

Investigation on building eave effect of fire-induced ejected plume from a room window and its heat flux imposing upon the facade wall

This paper investigates building eave effect of fire-induced ejected plume from a room window and its heat flux imposing upon the facade wall. Based on a 1:8 cubic model and Froude modeling, a series of reduced scale experiments are set up. The window dimensions and total heat release rate due to a room fire are changed during experiments. The eave upon the facade wall, made of noncombustible fiber board is installed horizontally above the window top, varying with different vertical heights (distance of the eave to the window top) and lengths (direction normal to the facade wall). The facade flame height is recorded by a CCD camera, while the heat fluxes imposing upon the facade wall are collected by five water-cooled heat flux gauges. Results show that the ejected flame with horizontal eave can be distinguished into the “free flame stage”, the “flame horizontal spread stage” and the “flame overflow stage”. The visible flame height and heat flux within the “flame overflow stage” are detailed discussed, revealing the physical mechanism of the vertical height and length of the horizontal eave effects. Finally, an implicit correlation in regarding with the visible flame height, the updated flame extension area beneath the horizontal eave as well as the vertical height of the horizontal eave to the window top is established. Taking the horizontal eave conditions into consideration, the heat flux correlation is well corrected and proposed. The results would provide theoretical basis for the fire-induced thermal protection in high buildings.

Effect of air jet momentum on the topological features of turbulent CNG inverse jet flame

Inverse jet flame (IJF) configuration is a variant of coaxial nonpremixed jet flame which can produce a nonluminous compact blue flame with independent control of air and fuel jet momentum. In the present work, the effect of central air jet velocity on visible topological features such as, visible flame height and base flame height is investigated experimentally. Also the fluid dynamics behind the evolution of base flame in IJF configuration is unraveled in this study. Notably, buoyancy induced oscillations of IJF, which is relatively unexplored in open literature is studied in this work. Moreover, a systematic classification of IJF based on the evolution of its visible flame features with variation in the central air jet and annular fuel jet velocities is reported. In addition, a semi-empirical correlation for visible flame height of IJF with air-fuel momentum ratio is arrived in the present work which can be useful in the design of IJF based burners utilized for impingement heat transfer applications.

Experimental and Numerical Comparison of Small-scale Gaseous Fire Whirls

Fire whirls can occur during urban fires, especially in intense fires in combustible building structures, and more often in forest or wildland fires. They are a special swirling diffusion flame characterized by significant enhancement in burning rates, flame heights and flame temperatures, along with a strong whirling motion of the flame. This whirling motion can pick up large firebrands and scatter them afar leading to spot fires. Many researchers have published experimental work on small- and medium-scale pool fire whirls and gaseous fuel fire whirls using split cylinders and various fixed-frame apparatus to investigate axial and tangential velocity profiles, axial and radial temperature distribution, burning rates, and flame heights. Likewise, several researchers have attempted to predict the experimental results of fire whirls using different modelling approaches and simulation software.In this paper, experiments were undertaken to study the dynamics of propane gas fire whirls in a small-scale, square-based, fixed-frame apparatus. Measurements of flame height and temperature profiles (both axial centerline and radial) were made for a low initial momentum burner of 76.2 mm internal diameter. The burner was operated at a volumetric flow rate of 6 dm3/min, which gave a heat release rate of 9.12 kW. Simulations using Fire Dynamics Simulator (FDS 6.6.0) and ANSYS Fluent 17.1 were performed to compare with the experimental measurements. Four separate mesh refinements were employed and four different sub-grid-scale (SGS) turbulence models were tested with FDS. The Deardorff, Wall-Adapting Local Eddy-viscosity (WALE), and dynamic Smagorinsky models, formed stable fire whirls for the two largest mesh refinements.The temperature profiles were overpredicted at the core of the flame with FDS and underpredicted with Fluent. The FDS simulation prematurely predicts the peak temperature for the axial centreline profile, whereas with Fluent the axial temperature profile matches the general trend of the experimental measurements.The visible flame height, determined through image processing, was approximately 0.88 ± 0.06 m, which corresponds to a measured temperature of ∼500°C. The 500°C temperature contour was used as a rough approximation of the flame height in the numerical simulations. It was found that with Fluent the 500°C contour grew until the fire whirl stabilized and reached the top of the hood at 1.6 m, clearly overpredicting the flame height. The height estimates based on the predicted 500°C contours show a strong dependence on the mesh resolution. This is primarily due to increased instability resulting in more mixing and spreading of the temperature for the coarser mesh size. However, the simulated flame heights show less dependence on the SGS turbulence models.

Soot aggregate morphology in coflow laminar ethylene diffusion flames at elevated pressures

The effect of combustion pressure on soot aggregate morphology and on primary soot particle diameter was investigated by thermophoretic sampling in nitrogen-diluted ethylene flames. Soot aggregate samples were collected using a high-pressure thermophoretic sampling system installed inside the high-pressure combustion chamber. Collected samples were imaged by transmission electron microscopy followed by an automated image analysis process to yield aggregate morphology information. The experiments covered pressures from 3 to 6 bar, and samples were collected at heights of 2 and 5 mm above the burner exit in nitrogen-diluted ethylene (ethylene to nitrogen mole ratio 2:1) flames with nominal visible flame heights of about 20 mm. It was observed that average primary soot particle diameter increased with increasing pressure within the pressure range considered, at both measurement locations within the flame. Fractal parameters of the soot aggregates were inferred directly from the experimental data (as opposed to the usual practice of assuming a priori values for fractal dimension and pre-factor). Near to the soot nucleation and growth regions of the co-flow laminar diffusion flames, at 2 mm above the burner exit, the fractal dimension of the aggregates was not as high as the accepted universal value of about 1.9, in spite of the fact that number of primary particles per aggregate is quite high and pressure is well above atmospheric. At 5 mm above the burner exit, however, the fractal dimension of the soot aggregates approached the accepted universal value of 1.9, at high pressures; at relatively lower pressures, the fractal dimension was about 1.6 at the same location within the flame. In view of the inferred fractal results, caution should be exercised when applying fractal analysis to low heights in flames at lower pressures where soot inception and growth are relatively dominant.

Experimental and numerical study of variable oxygen index effects on soot yield and distribution in laminar co-flow diffusion flames

We study experimentally and numerically a series of methane-fueled laminar co-flow diffusion flames to investigate the effects of variable Oxygen Index (OI) on soot yield and distribution. OI is defined as the mole fraction of oxygen in the oxidizer. Sixteen flames are studied with OI ranging from 21% (air) to 76.3%, so that OI varies in small increments and its effects are precisely resolved. The soot volume fraction distribution is measured experimentally for all flames using color-ratio pyrometry. Simulations are carried out using an extensively validated chemical kinetic mechanism and an aggregate-based soot model that accounts for all major processes of soot inception, growth, and oxidation. The experimental measurements show that the visible flame height decreases with increasing OI, which is consistent with theoretical estimates and the numerical simulations. The measurements also indicate that increasing OI (from 21% to 36.8%) first results in an increase in the maximum soot concentration, but a further increase in OI leads to a decrease in the soot yield. Additionally, the maximum soot concentration occurs on the flame centerline for low OI flames (below 36.8%), but for higher OI, the peak soot yield occurs in the flame wings. All of these experimental observations are well reproduced by the simulations, with the maximum soot volume fraction magnitudes lying within the error bounds of the experimental measurements. The computational results are used to reveal the underlying physical mechanisms, by examining soot evolution along characteristic Lagrangian trajectories through flame regions. We find that increasing OI leads to higher flame temperature, which results in a stronger soot production rate, but also reduced soot residence time in flame regions, which allows less time for soot production. These competing effects cause the initial increase and subsequent decrease in the maximum soot yield and the shift in the maximum soot yield location with increasing OI.

Investigation on Soot Characteristics of Gasoline/Diesel Blends in a Laminar Coflow Diffusion Flame

Gasoline addition in diesel fuel could not only improve the overall energy efficiency, but also could reduce the soot emission on diesel engine. However, the influence of gasoline on the soot forming characteristics has not been revealed fundamentally. A liquid burner system, modified from a Gülder burner, was applied to create strict laminar diffusion flame to carry out the related study. Also, optical diagnostics technologies including digital camera imaging and high speed two-dimension line-of-sight attenuation (2D-LOSA) were used to record the natural luminosity flame structure, smoke point, and soot volume fraction. During the experiments, the diesel ratio was varied as 0%, 20%, and 40% by volume, while the fuel flow rate was varied from 6 to 9 g/h. The results show that diffusion flames of blends can be distributed into three typical parts, soot free region, soot growth region, and soot oxidation region. With the fuel flow rate increasing, more soot was generated and the flame height was lifted. With the diesel ratio increasing in gasoline/diesel blends, the visible flame height decreased, the flame luminosity intensity decreased, the smoke point increased, and the 2D soot volume fraction value reduced, which indicates that diesel is less likely to produce soot than is gasoline in the laminar diffusion flame. The soot reducing effect of diesel is regarded because diesel can enhance the cool flame combustion in the free soot region due to its more obvious NTC (negative temperature coefficient) effect. It is also reasonable to expound that the soot emission reduces with addition of gasoline in diesel on engines mostly because of its volatility rather than its chemical characteristics.

Radiation Emissions from Turbulent Diffusion Flames Burning Vaporized Jet and Jet-like Fuels

This study measured and compared the size and radiation emissions from turbulent diffusion flames burning large hydrocarbon fuels, including jet fuels. This effort is motivated by the need to understand how burning conventional or alternative jet-like fuels changes radiation emissions. Radiative heat transfer is significant because it is can alter pollutant formation and the lifetime of combustion devices. Eleven fuels were evaluated, consisting of traditional and alternative aviation fuels (e.g., Jet-A) and 1–3 component fuels. The flames were burned on a reduced-scale piloted Sydney turbulent diffusion burner with Reynolds numbers (Re) ranging from 7500 to 45 000. The vaporized fuel exited the burner near 300 °C. The radiative heat flux and the radiation intensity were measured using a radiometer (Medtherm, Model 64-0.2-20) and a mid-infrared camera (FLIR, Model SC6700), respectively. The radiant fraction (χR) is reported for the different fuels. χR typically varied by <15% at similar Re for the different flames, despite the aromatic content ranging from 0% to 31%. The χR had a tendency to be relatively insensitive to aromatic content, but was sensitive to the weight percent of hydrogen in the fuel. Differences in the molecular structure of the fuels, even for fuels with similar hydrogen contents, can significantly affect χR. χR values initially increased as the Re was increased, but then decreased monotonically for Re > 20 000. This trend is attributed to competing effects of flame stretch, entrainment, and surface-to-volume ratio on radiation emissions. The peak radiation intensity occurs near the location of the peak heat flux, which corresponds to the visible flame height. Radiation emitted from soot and unburned hydrocarbons is predominantly observed from within the flame sheet; significant variations in radiation emissions was observed between the different fuels. In contrast, emissions from CO2 for all the fuels varied by <10% and were more broadly distributed across the flame. Fluctuations in radiation emissions have a tendency to be greatest near the flame sheet for CO2 and within the flame sheet for soot and unburned hydrocarbons. Total radiation emissions from these flames have a tendency to be dominated by emissions from gaseous combustion products instead of emissions from soot or unburned hydrocarbons.

Flame extension length beneath a horizontal eave in fire-induced thermal plume ejected from a compartment

This work focuses on the flame extension length beneath a horizontal eave in fire-induced thermal plume ejected from a compartment window. Series of small scale experiments are conducted in a cubic compartment of 0.4m with a facade wall and a variable window. A noncombustible board is installed horizontally attached to the facade wall to simulate the eave upon building facade. The window dimensions, the vertical distance of horizontal eave to the window top and the total heat release rate are altered in our experiments. Two CCD cameras are employed to record the ejected flame videos from both front and lateral directions. Results show that the flame extension behavior appears when the horizontal eave level is lower than the corresponding free facade flame tip. The flame extends almost symmetrically, becoming longer for a higher excess heat release rate, but turning shorter when the horizontal eave is moved up. A dimensionless model in relation to the free visible flame height, the excess heat release rate and the vertical height of horizontal eave is well developed based on experimental observations. The findings would provide an important basis in the practically applications of horizontal eaves for better building fire protections.

Influences of elevated pressures on soot formation in coaxial ethylene–air diffusion flames under different ventilation conditions

The effect of elevated pressures on the soot formation in coaxial ethylene-diffusion flame was investigated under different ventilation conditions, i.e. one with a chamber valve closed and the other with a chamber valve open. Experimental measurements include the soot volume fraction and macroscopic flame behaviors such as visible height and flame shape. The presence of ventilation-assisted flow around the flame was found to further increase the visible flame radius and height at elevated pressures. The maximum soot volume fraction measured within the flame was also increased with the ventilation-assisted flow as well as with the ambient pressure. Experimental results clearly indicate that changes in the physical appearance of the flames altered by ventilation-assisted flow are an important factor to affect the sooting behavior in coaxial diffusion flames.

Experimental characterization of the different nitrogen dilution effects on soot formation in ethylene diffusion flames

This paper addresses the discrimination of dilution and thermal effects on soot production when nitrogen is added to the fuel stream of a steady laminar ethylene diffusion flame. In this context, the mixture-strength flame height Hf and visible flame height Hv are unambiguously documented and exhibit opposite trends within experimental diluted range (N2 volume fraction from 0 to 0.56). Simultaneous soot volume fraction and temperature fields are mapped for different N2 volume fractions by the Modulated Absorption/Emission (MAE) technique. Two characteristic flame heights and the temperature at the peak soot volume fraction are shown to be crucial parameters to assess the extent of the dilution and thermal effects together with their impact on soot formation in the flame. As a result, the mixture-strength flame height is proposed to characterize the soot formation rate within soot growth region, while the visible flame height is more appropriate to describe the overall sooting propensity in the flame. The probed soot temperature is recommended as the characteristic temperature to assess N2 dilution and thermal effects since the thermal effect is overestimated when using the adiabatic temperature.