Flame Temperature Profiles Research Articles

Flame height and temperature profile of window ejected thermal plume from compartment fire without facade wall

This paper investigates experimentally the flame height and temperature profile of window ejected thermal plume from compartment fire without facade wall. The previous works and correlations on these characteristics of such thermal plume mainly concern the condition with a facade wall, where the air entrainment of the thermal plume from the side of the facade wall is restricted. However, such entrainment constraint effect does not exist when the fire occurs at the top floor of the building noting that there is no facade above the top floor, for which scenario the flame height and temperature profile of the thermal plume characteristics have not been quantified in the literature. In this work, comprehensive experiments were carried out by employing a reduced-scale model (1:8), consisting of a 0.4 m cubic fire compartment with six different window openings corresponding to various ventilation factors (AH). A propane square porous burner was set as fire source with various fuel mass flow meters and hence heat release rate. All the tests were designed as un-ventilated condition that stable flame was observed outside the window. The flame height outside the window was recorded through a CCD camera from the side view. The temperature profiles of the ejected fire plume outside the window were measured by the thermocouple arrays (7 rows, 7 columns) located above the top of the compartment. These measured quantities without the facade wall were compared from those with a facade wall. Results showed that the flame height can be still well correlated non-dimensionally by the excess fuel heat release rate and the characteristic length scale (ℓ1=(AH)2/5) of the window. However, the flame height with a facade wall was higher, being 1.31 times of those without a facade wall. This difference was physically quantified by the air entrainment change due to constraint effect from the facade wall. The radial temperature profile in the ejected thermal fire plume at various height can be globally represented by the Gaussian function (Tz,x−T∞Tz,max−T∞=e[−β(x−xmFWHM)2]) with and without facade wall, where the value of β was found to be 2ln2. These quantifications and correlations on window-ejected thermal plume characteristics without a facade wall, providing a significant supplementary over previous works focusing on condition with the facade wall, will be an important addition for the estimation of such thermal plume characteristics and its thermal impacts. This work, providing experimental data and correlations on window ejected thermal plume characteristics from compartment fire at the top level of the building without the effect of facade wall, will be an important supplementary over previous knowledge focusing on the scenario with the effect of facade wall.

Effects of Electrostatic Voltage and Polarity on Diffusion-Controlled Propane Flame for Enhanced Efficiency

AbstractIn this study, the direct current (DC) electric field effect on the diffusion-swirling flame dynamics and flame temperature profiles was investigated experimentally with the aim of establis...

Comparison of hydrogen and hydrogen-rich reformate enrichment of JP-8 in an open flame

Hydrogen enhanced combustion of JP-8 provides an additional control parameter for external combustion based power sources. When supplied as part of a “reformer gas” mixture, hydrogen provides similar benefits as pure hydrogen, given sufficient oxygen mixing. Previous work showed benefits of hydrogen enhanced combustion for external combustion based power sources. As a step closer to practical applications, the present work examines the use of hydrogen rich reformate. This mixture of hydrogen, carbon monoxide, carbon dioxide, and nitrogen is produced by fuel reforming of JP-8 and other logistics fuels.Tests evaluated the temperature profiles of dual fueled flames using JP-8 and either hydrogen or a bottled mixture representing fuel reformate. Both supplemental fuels move combustion earlier, allowing more stable combustion and potential for reduced size. JP-8 flow rate was reduced to maintain fuel energy input at a constant 5.5kWth. In comparing two cases, the important factor was the total energy contribution. The ratio of hydrogen and carbon monoxide had little effect on the flame structure.This research also compared methods of hydrogen addition. It was added with either the atomizing air or the secondary air which reiterated the importance of oxygen availability. For example, hydrogen through the nozzle produces additional changes to the flame structure due to the combustible mixture of hydrogen and air in the nozzle. The equivalent flow rate of reformate in the nozzle does not produce the same effect because the air in the nozzle is replaced by the other gases in the reformate (CO, CO2, and N2).Hydrogen enrichment tests establish the benefit of dual firing hydrogen and JP-8. These reformate tests show the variables that must be considered in implementing this technique in a practical system.

Thermal Imaging of Flame in Air-assisted Atomizer for Burner System

Infrared thermography was used as a part of non-intrusion technique on the flame temperature analysis. This paper demonstrates the technique to generate the thermal images of flame from the air-assisted atomizer. The multi-circular jet plate acts as a turbulence generator to improve the fuel and air mixing in the atomizer. Three types of multi-circular jet plate geometry were analysed at different equivalence ratio. Thermal infrared imaging using FLIR thermal camera were used to obtain the flame temperature. Multi-circular jet 1 shows the highest flame temperature obtained compared to other plates. It can be concluded that the geometry of the plate influences the combustion, hence affects the flame temperature profile from the air-assisted atomizer.

Entropy generation analysis of unsteady premixed methane/air flames in a narrow channel

The unsteady combustion process which is incurred by increased heat loss and thermal/radical quenching is easy to occur in micro channel. In order to control the unsteady flames in microscale, it is essential to figure out the formation mechanism of the instability process. In this work, transient numerical simulation of premixed methane/air combustion in a narrow channel is conducted using the DRM-19 reaction mechanism. Depending on the wall temperature profile, two types of flames were observed: the oscillating flame and flame repetitive extinction and ignition (FREI). High wall temperature profile results in oscillating flame and low wall temperature profile results in FREI. Entropy generation analysis method was used to identify the relative contributions of different factors to instability process. The major reactions during different phases in the both types of flames are confirmed. The main difference of major reactions between the two types of flames is related to the high hydrocarbons which are mainly formed at low temperature. The entropy generation by chemical reactions is dominant during the flame propagation phase, while in flame extinction phase, the thermal conductivity plays an important role in unsteady flame dynamics. As the flame gets weakened, the entropy generation by thermal conductivity is caused by heat loss through the wall and to the fresh mixture. The frequency of oscillating flame is much higher than that of FREI, but the maximum gas temperature of FREI is higher than that of oscillating flame. This work can provide the guideline for utilizing the unsteady flames or keeping the micro combustion stable in the micro power system.

Comparison of Soot Formation, Evolution, and Oxidation Reactivity of Two Biodiesel Surrogates

Experimental and chemical kinetics studies were carried out to compare soot particle morphology evolution in atmospheric pressure laminar co-flow diffusion flames of methyl butanoate (MB) and ethyl butanoate (EB), in order to investigate the effects of alcohol chain in biodiesel molecular on soot formation. The thermophoretic sampling technique was used to capture soot particles directly at different heights along flame centerlines. Transmission electron microscopy (TEM) was applied to obtain particle morphology information. Moreover, total sampling followed by thermogravimetric analysis and Raman spectroscopy analysis was performed to study soot oxidation reactivity and degree of disorder in soot structure. The results show that the flame structures and temperature profiles along flame centerlines of two test esters are similar. The primary particle diameters of EB are larger at almost all the sampling positions, and soot inception and aggregation process occur earlier in EB flame. The phenomenon can be illustrated through simulation work which indicated that EB could be decomposed quickly at lower temperature because of the six-centered unimolecular elimination reaction, leading to earlier and stronger formation of C2H4, and then promoting the formation of C2H2. It is also found that the oxidation reactivity of soot from MB flame becomes higher compared with that of EB.

Improved Kinetic Mechanism for Diethyl Ether Oxidation with a Reduced Model

An improved diethyl ether (DEE) reaction mechanism consisting of 174 species and 973 reactions has been proposed. The present model is derived from an original model of Yasunaga et al. [Yasunaga, K.; Gillespie, F.; Simmie, J. M.; Curran, H. J.; Kuraguchi, Y.; Hoshikawa, H.; Yamane, M.; Hidaka, Y. A multiple shock tube and chemical kinetic modeling study of diethyl ether pyrolysis and oxidation. J. Phys. Chem. A 2010, 114 (34), 9098−9109, DOI: 10.1021/jp104070a]. On the basis of shock tube results in the temperature range of 900–1900 K, pressure range of 1–40 bar, and equivalence ratios of 0.5–2 as well as rapid compression machine (RCM) measurements of a stoichiometric DEE/O2/inert gas mixture at temperatures of 500–900 K and pressures of 3–4 bar, the ignition delay times (IDTs) were validated. Two-stage ignition at temperatures below 650 K and negative temperature coefficient (NTC) behavior at temperatures between 621 and 746 K are observed. In addition, the freely propagating flame velocities of a stoichiometric DEE/air mixture were validated at various temperatures as well. Using directed relation graph (DRG)-based methods for the improved mechanism reduction, a reduced mechanism composed of 80 species and 329 reactions has been achieved. Calculations for IDTs, laminar flame velocities, and temperature and species profiles using the reduced mechanism show very close agreement with those obtained using the improved mechanism. Meanwhile, sensitivity analyses of the burning velocity and IDT for the improved and reduced mechanisms were performed. Competing reactions related to DEE + OH and consumption of C2H5OC2H4s and HO2 were identified as being important for IDTs at various temperatures.

Numerical Simulation of Transient Development of Flame, Temperature and Velocity under Reduced Gravity in a Methane Air Diffusion Flame

A methane air co flow diffusion flame has been numerically simulated with the help of an in-house developed code at normal gravity, 0.5 G, and 0.0001 G (microgravity) for the study of transient behavior of the flame in terms of flame shape, temperature profile and velocity (streamlines). The study indicates that lower is the gravity level, the higher is the time of early transience. The flame developments during transience are marked by the formation of a secondary flamelet at different heights above the primary flame at all gravity levels. The development of temperature profile at microgravity takes a much longer time to stabilize than the flame development. At normal gravity and 0.5 G gravity level, streamlines, during transience, show intermediate vortices which are finally replaced by recirculation of ambient air from the exit plane. At microgravity, neither any vortex nor any recirculation at any stage is observed. Centerline temperature plots, at all gravity levels during transience, demonstrate a secondary peak at some instants as a consequence of the secondary flamelet formation. The centerline velocity at microgravity decreases gradually during transience, unlike at other two gravity levels where the fall is very sharp and is indicative of negligible buoyancy at microgravity.

Experimental and numerical study of MILD combustion in a bench-scale natural gas partial oxidation gasifier

Moderate and intense low-oxygen dilution (MILD) is a promising combustion technology for the non-catalytic partial oxidation (POX) process of natural gas. This study investigates the establishment of MILD combustion in a bench-scale non-catalytic partial oxidation gasifier. Experiments under both inverse diffusion configuration (IDC) and normal diffusion configuration (NDC) are carried out using methane and pure oxygen as reactants. The flame appearances and temperature profiles are recorded using an imaging system and thermocouples, respectively. Results show that no visible flame can be observed in IDC case while a flame can be observed near the burner exit in NDC case. The effects of jet velocity and O2/CH4 ratio on the IDC flame are further studied. Numerical simulations of the experimental cases are also performed and the results agree well with the experimental results. It is found that the recirculation rate inside the furnace is sufficiently high to fully dilute the reactants. Combustion regime classification on grid scale shows that MILD combustion is established in the gasifier in IDC case. Analysis on the flame structure in IDC case shows that dilution of oxygen before ignition is the reason for the establishment of MILD combustion and the barrier effect of fuel between oxygen and hot syngas in the necessary condition for this process.

Thermal environment induced by jatropha oil pool fire in a compartment

This article evaluates the burning characteristics of jatropha oil pool fire. Experiments have been carried out in a compartment of size 4 m × 4 m × 4 m, with a door opening of 1 m × 2 m for ventilation purpose. Crude jatropha oil is burned in a pool diameters of 0.3, 0.4, 0.5 and 0.6 m and having an initial fuel depth of 0.045 m. Heat release rate, mass loss rate, exhaust gases concentration (CO2 and O2), profiles of flame temperature, flame height, room corner temperature, door temperature and heat flux at different locations have been recorded. The smoke layer interface is also estimated by means of a thermocouple tree with 19 thermocouples using the integral ratio method. Experimental results showed that the flame temperature profile is similar for all four experiments. Maximum heat release rate achieved is 312.5 kW for the pool size of 0.6 m, and corresponding average mass loss rate is 8.62 g s−1. Also the interface height determined by visual method and integral ratio method matched well during the steady profile phase.

Experimental investigation on flame spread over diesel fuel near sea level and at high altitude

Flame spread over a petroleum-based diesel fuel was experimentally examined at two different altitude conditions (Lhasa plateau 3658m, and Hefei Plain, 50m). Based on the test results, the flame appearance, velocity of flame spread and temperature profile near oil surface were comprehensively characterized. Two types of flame are observed during the flame spread: a blue precursor flame and a yellow main flame. The main flame possesses a flame shape under diffusion combustion, whereas the precursor flame belongs to premixed combustion. The liquid temperature initiating flame propagation over diesel fuel is lower in Lhasa, indicating that oils can more easily catch fire at a higher altitude. For a wide range of fuel temperatures, the velocity of flame spread at low-pressure region is considerably larger than that near sea level. The intrinsic reasons are predicted by variations in flashpoint and surface tension of liquid fuel with altitude. Theoretical analyses confirm that the flashpoint of liquid fuel decreases with altitude while the surface tension increases. Moreover, the measured temperature distributions normal to the oil surface reveal that the oil surface temperature as well as the liquid temperature inside the subsurface convection flow is larger at high altitude, while the time interval between the flame leading edge and the subsurface convection flow front is smaller.

Assessing the influence of fuel geometrical shape on fire dynamics simulator (FDS) predictions for a large-scale heavy goods vehicle tunnel fire experiment

This paper uses four different simple geometrical shapes to simulate a large-scale heavy goods vehicle (HGV) tunnel fire experiment using Fire Dynamics Simulator, version 6 (FDS6) in order to investigate the influence of using different fuel package shapes. Simulations also investigate the influence on temperature profiles when a large target is placed downstream of the fuel package. Predictions of flame extension, temperature profiles and gas species concentrations are compared with the experimental data. The use of the geometrical shapes causes significant differences in flame extension lengths during the fully developed fire phase. The variation in temperature predictions caused by using the different fuel shapes are insignificant when a large target is present behind the fire, however this is not the case if the target is omitted especially during the fully developed phase.

Power-to-Gas: Safety Characteristics of Hydrogen/Natural- Gas Mixtures

Safety characteristics for explosion protection of natural gas/hydrogen mixtures relevant in connection with the Power2Gas technology were studied in this work. Lower explosion limits (LEL) and upper explosion limits (UEL), limiting oxygen concentrations (LOC), maximum experimental safety gaps (MESG), maximum explosion pressures (pmax) and maximum rates of pressure rise (dp/dt)max were determined experimentally in dependence of the hydrogen fraction. Adding hydrogen did mainly effect the UEL, LOC, MESG and (dp/dt)max. The mixtures become more critical concerning the explosion hazards with increasing hydrogen fraction. However, the dependency of the safety characteristics from the hydrogen fraction is mainly not linear. Adding up to 10% hydrogen to natural gas had nearly no effect on the safety characteristics. More significant effects on the safety characteristics were observed at hydrogen fractions of more than 25%. For example the explosion group changes from IIA to IIB. Considering the huge explosion region and very high (dp/dt)max of hydrogen compared to natural gas, even adding 50% hydrogen to natural gas has a rather small effect on these characteristics. Furthermore pmax of hydrogen/natural-gas mixtures can be calculated with good accuracy assuming ideal adiabatic conditions. EL and LOC of natural gas/hydrogen mixtures in ternary systems with inert gas and air were calculated in dependence of the type of inert gas with the so called “model of constant adiabatic flame temperature profiles” (Askar et al./2010).

Comparative study on the effects of nitrogen and carbon dioxide on methane/air flames

The measurement of flame temperature profile and flame computation were conducted to analyze the effects of carbon dioxide and nitrogen dilution on methane/air flames. Results indicated that carbon dioxide addition shows more significant effects on the thermal properties of flame, except for flame thickness. Flame kinetic analyses were implemented for the heat release of individual reaction. It is suggested that the heat release contribution of dominant reaction is primarily affected by flame stoichiometry, while the dilution shows weak effect. The concentrations of reactive species play important influences on the progress rate of reaction. The peak product of reactive species concentrations of the dominant reactions could be approximated by an exponent expression of the concentration of initial reactants and dilution rate, and a greater exponential index was obtained for the flames with carbon dioxide addition. The emission indices and combustion efficiency were evaluated to assess the profit in NO suppression and the loss in combustion deterioration. Results indicated that the profit-loss ratio is influenced by both flame equivalence ratio and the component of diluent gas. For rich methane/air flame, nitrogen dilution shows a greater value, while a larger benefit is obtained for stoichiometric flame diluted by carbon dioxide.

On dynamic behavior of premixed counterflow flame propagation

We have provided a detailed numerical model for simulating flame propagation in a premixed counterflow configuration. It is an unsteady state, one-dimensional model based on the heat and mass balance equations. Attention is focused on the impact of the non-dimensional numbers namely Lewis number, Damkohler number, and Zeldovich number on the flame temperature profile. Also, we have explored what happens when we continue the solutions for higher heat losses. It was found that with increasing the Lewis number the flame temperature decreases, while a further increase in Lewis number results in constant value of the flame temperature. Model predictions have been compared with available data from the literature, which have showed fully good agreement.

A numerical study of laminar flames propagating in stratified mixtures

Numerical simulations are carried out to study flame propagation in laminar stratified fuel–air mixtures. Studies are carried out in hydrogen–air and methane–air mixtures. A 30-species 184-step skeletal mechanism is employed for methane oxidation and a 9-species 21-step mechanism for hydrogen oxidation. The study seeks to provide an improved understanding of possible differences in the local flame speed at an equivalence ratio in the compositionally stratified mixture from the speed in a homogeneous mixture at the same equivalence ratio. Flame speed and temperature profiles are evaluated and compared with corresponding values for homogeneous mixtures. As shown in prior experimental work, the numerical results suggest that when the flame propagates from a richer mixture to a leaner mixture, the flame speed is faster than the corresponding speed of the homogeneous mixture. The flame zone thickness is observed to be thinner in the stratified mixture resulting in sharper gradients. As a result, the rate of diffusion of heat and species increases resulting in increased flame speed. The effects become more pronounced in leaner mixtures. The stratification gradient influences the results with shallower gradients showing less difference in flame speeds between stratified and homogeneous mixtures. The comparative effect of thermal diffusion and species diffusion on the differences in flame speed is studied. It is shown that the species diffusion effect is more important.

KESAN SUDUT PUSARAN TERHADAP PEMBAKARAN MENGGUNAKAN PEMUSAR JEJARIAN DWI ALIRAN

Development of combustion systems which involves retrofitting or design of new burners, is made to reduce the formation of pollutant emissions. The reduction of this pollutant emission results from the complete mixing of fuel and air during the combustion process. Meanwhile, non-complete mixing of fuel and air during combustion process can cause ignition problem and create problems in terms of flame stability and combustion efficiency. This article describes a study on the effects of swirling flow generated by a double radial swirler on flame characteristics that is related to the emission of NO. The double radial swirlers used in this study have the angles of 30°/40°, 30°/50° and 30°/60°. Diesel is used as a fuel in this study. The results show that all double radial swirlers used have different effects on the flame characteristics and temperature profile. From all these double radial swirlers, the one with an angle of 30°/60° produces flame with high temperature, short flame length with blue colour and wide spread.

A Study on Reactive Spray Deposition Technology Processing Parameters in the Context of Pt Nanoparticle Formation

Catalytic materials are complex systems in which achieving the desired properties (i.e., activity, selectivity and stability) depends on exploiting the many degrees of freedom in surface and bulk composition, geometry, and defects. Flame aerosol synthesis is a process for producing nanoparticles with ample processing parameter space to tune the desired properties. Flame dynamics inside the reactor are determined by the input process variables such as solubility of precursor in the fuel; solvent boiling point; reactant flow rate and concentration; flow rates of air, fuel and the carrier gas; and the burner geometry. In this study, the processing parameters for reactive spray deposition technology, a flame-based synthesis method, are systematically evaluated to understand the residence times, reactant mixing, and temperature profiles of flames used in the synthesis of Pt nanoparticles. This provides a framework for further study and modeling. The flame temperature and length are also studied as a function of O2 and fuel flow rates.

Effects of Flue Gas Addition on the Premixed Oxy-methane Flames in Atmospheric Condition

This numerical study investigates the flame characteristics of premixed methane with various inert gas dilutions in order to simulate oxy-combustion of hydrocarbon fuels with flue gas recirculation system. In general, a flue gas consists of high concentration CO2/H2O and high gas temperature. The diluent gas in oxy-combustion has been changed compared with air-combustion, so that the flame behavior and combustion characteristics of oxy-fuel must be influenced. By observing the resultant flame temperature and species concentration profiles can identify that the flame location shifts, and the concentration profile of major chemical reaction radicals varies, indicating the change of flame structure and flame chemical reaction paths. The dominant initial consumption reaction step of methane shifts from R53 (H+CH4=CH3+H2) to R98 (OH+CH4=CH3+H2O) when nitrogen is replaced by the recirculated gases. It is because that the chemical effects of the recirculated gases changes the flame reaction pathway, and further affect reaction rate, species and radical concentrations.

Combustion of a single magnesium particle in water vapor**Project supported by the National Natural Science Foundation of China (Grant No. 51406231).

The combustion of magnesium particles in water vapor is of interest for underwater propulsion and hydrogen production. In this work, the combustion process of a single magnesium particle in water vapor is studied both experimentally and theoretically. Combustion experiments are conducted in a combustor filled with motionless water vapor. Condensation of gas-phase magnesia on the particle surface is confirmed and gas-phase combustion flame characteristics are observed. With the help of an optical filter and a neutral optical attenuator, flame structures are captured and determined. Flame temperature profiles are measured by an infrared thermometer. Combustion residue is a porous oxide shell of disordered magnesia crystal, which may impose a certain influence on the diffusivity of gas phases. A simplified one-dimensional, spherically symmetric, quasi-steady combustion model is then developed. In this model, the condensation of gas-phase magnesia on the particle surface and its influence on the combustion process are included, and the Stefan problem on the particle surface is also taken into consideration. With the combustion model, the parameters of flame temperature, flame diameter, and the burning time of the particle are solved analytically under the experimental conditions. A reasonable agreement between the experimental and modeling results is demonstrated, and several features to improve the model are identified.