Flame Temperature Field Research Articles

A numerical study of quasi-steady burning characteristics of a condensed fuel: effect of angular orientation of fuel surface

A numerical study of laminar diffusion flames established over a condensed fuel surface, inclined at several angular orientations in the range of –90°⩽θ⩽+90° with respect to the vertical axis, under atmospheric pressure and normal gravity environment, is presented. Methanol is employed as the fuel. A numerical model, which solves transient gas-phase, two-dimensional governing conservation equations, with a single-step global reaction for methanol–air oxidation and an optically thin radiation sub-model, has been employed in the present investigation. Numerical results have been validated against the experimental data from the present study. Thereafter, the model is used to investigate the influence of angular orientation of fuel surface on its quasi-steady burning characteristics. Results in terms of fuel mass burning rate, flame stand-off distances, temperature field, velocity profiles and oxygen contours have been presented and discussed in detail. It is observed that orientation angles in the range of –45°⩽θ⩽ –30° (fuel surface facing upwards), yield the maximum mass burning rates. The flame anchoring location near the leading edge of the fuel surface, normal gradient of fuel vapor mass fraction at the surface and oxygen contours have been used to explore this unique behavior. Based on the numerical results, a theoretical correlation to predict the mass burning rate as a function of fuel surface orientation is also proposed. Furthermore, a discussion on the differences in the structure of laminar diffusion flame established over fuel surface as a function of its angular orientation is included.

A study of steady laminar diffusion flame over methanol pool surface

A numerical study of laminar, boundary layer type diffusion flames established over a liquid fuel pool, under the influence of forced air flow parallel to the pool surface, has been carried out. Burning of a confined methanol pool at atmospheric pressure and under normal gravity conditions is investigated. A numerical model, which solves transient, two-dimensional, mass, momentum, species and energy conservation equations, has been employed to predict the flame characteristics. The gas-phase alone is solved in a decoupled manner using appropriate interface boundary conditions, without considering the effects of liquid-phase transport on the combustion process. A single-step global reaction for methanol–air oxidation, considering carbon-dioxide dissociation, is employed to model the chemical kinetics. An optically thin radiation model has also been incorporated to account for thermal radiation losses by absorbing species in a non-luminous flame. At the outset, the model is validated against the experimental results available in literature. Thereafter, it has been used to investigate the influence of free stream air velocity on fuel mass burning rate, flame stand-off distance, temperature and flow fields. The study brings out the variation in the structure of confined laminar boundary layer type diffusion flames over methanol pool for several air velocities under normal gravity environment.

Study on the measurement of temperature field using laser holographic interferometry

The temperature field of an axisymmetric ethylene diffusion flame is measured using laser holographic interferometry. Temperature field inversion is completed with the aid of components distribution divided from numerical simulation of combustion and air components assumption. Error analysis of key steps is conducted using the theoretical formula of interference temperature measurement and characteristic structure of fringes obtained from optical simulation. Based on the calculation and analysis, air components assumption will not cause significant error in the low temperature region but will result in high error in the high temperature region. Moreover, the small error in environmental temperature measurement transfer to a high temperature range will expand more than tenfold. Results of temperature measurement using air components assumption relative to combustion simulation require the greatest amendment amounting to seven percent.

Turbulent Spray Flames of Acetone and Ethanol Approaching Extinction

This paper presents measurements of mean temperature, axial velocity, turbulence, and droplets fields in pilot-stabilized jet flames of dilute sprays where acetone or ethanol is used as liquid fuel. Laser-induced fluorescence (LIF) is employed to image hydroxyl radical OH which marks the existence of hot regions or reaction zones. Depending on the fuel used, droplets within the flow are delineated by imaging LIF from acetone or Mie scattering. As the jet velocity is increased, the flames gradually approach blow-off in a region further downstream from the stabilizing pilot. It is found that the mean velocity, turbulence, and droplet fields are somewhat similar for both ethanol and acetone flames, and these do not change much with increasing jet velocity, particularly when normalized with the relevant parameters. However, the temperature and reactive fields are varying and undergo departure indicative of nonpremixed to premixed flame behavior depending on the vapor pressure of the fuel and proximity to blow-off. Broad regions of OH as well as breaks in the OH profile marking possible local extinction are observed in the ethanol flames.

Simultaneous Measurement of Three-Dimensional Soot Temperature and Volume Fraction Fields in Axisymmetric or Asymmetric Small Unconfined Flames With CCD Cameras

Abstract A nonintrusive measurement technique is presented numerically for simultaneous measurement of three-dimensional (3D) soot temperature and volume fraction fields in the axisymmetric or asymmetric flames with charge-coupled device (CCD) cameras. CCD cameras were introduced to capture the flame images for obtaining the line-of-sight radiation intensities. The distributions of local emission source under two wavelengths can be deduced through solving the reconstruction matrix equation by the least-square QR decomposition method from the knowledge of the line-of-sight radiation intensities of the flames. The two-color distributions of the local emission source were used to retrieve the soot temperature and volume fraction distributions. The effects of the discrete ray number of CCD cameras, the number of CCD cameras, and the system signal-to-noise ratio (SNR) on the measurement were investigated. The results show that for accurate measurement of soot volume fraction field, the CCD cameras number should not be less than four and the system SNR can be as low as 54 dB. The proposed technique can be capable for reconstructing the 3D soot temperature and volume fraction fields in both axisymmetric and asymmetric flames well.

Analysis of a spray diffusion flame and its extinction in a shear layer

A new semi-analytical solution for a laminar spray diffusion flame in the shear layer between fuel and oxidant streams is developed. The Stokes number is identified as a small spray droplet-related parameter to be used in a perturbation analysis of the liquid phase governing equations. Appropriate specification of an additional parameter ensures that similarity is achieved so that the concentration field of the liquid in the spray can be readily found. The coupled gas-phase equations are treated using the usual inverse of the large Zeldovitch number for the asymptotic analysis. Numerical results demonstrate how the distribution of the liquid phase in the developing shear layer between two unidirectional gas streams flowing over one another with (the possibility of) dissimilar velocities in their respective free-streams influences the flame shape, location, fuel vapour and temperature fields. An extinction analysis enables a parametric mapping of conditions for extinguishment of the spray diffusion flames to be drawn.

Experimental Study of the Combustion Dynamics of Renewable & Fossil Fuel Co-Fire in Swirling Flame

Experimental Study of the Combustion Dynamics of Renewable & Fossil Fuel Co-Fire in Swirling FlameThe complex experimental research into the combustion dynamics of rene-wable (wood biomass) and fossil (propane) fuel co-fire in a swirling flame flow has been carried out with the aim to achieve clean and effective heat production with reduced carbon emissions. The effect of propane co-fire on the formation of the swirling flame velocity, temperature and composition fields as well as on the combustion efficiency and heat output has been analysed. The results of experimental study show that the propane supply into the wood biomass gasifier provides faster wood fuel gasification with active release of volatiles at the primary stage of swirling flame flow formation, while the swirl-induced recirculation with enhanced mixing of the flame components results in a more complete burnout of wood volatiles downstream of the combustor with reduced mass fraction of polluting impurities in the emissions.

Temperature measurement of an axisymmetric flame by using a schlieren system

We present an expanded article based on the research presented at the RIAO/OPTILAS07 conference. The application presented at the conference has been extended to the measurement of temperature by using a schlieren system of an axisymmetric flame issuing from a circular nozzle of a butane head torch. As the temperature of the flame varies with the air/fuel mixture, two different flow conditions, with full and partial air/fuel mixtures, have been analyzed. In order to find out any differences in the structure of the flame for the two cases, the proper orthogonal decomposition (POD) method is applied. From the flame temperature measurements, we compute the eigenfunctions and the eigenvalues by the POD analysis. Two and one dominant POD modes for the partial and full air/fuel mixture were found, respectively. Also, the essential features of the flame temperature fields can be described by considering only the first ten POD modes.

Numerical simulation of nanoparticle synthesis in diffusion flame reactor

A computational model combining the fluid dynamics with the particle kinetics was employed to study TiO 2 nanoparticle synthesis in a diffusion flame reactor. A one-step chemical kinetics approach was used to model titanium tetraisopropoxide (TTIP) decomposition that leads to homogeneous nucleation and particle formation. The momentum, heat, and mass transfer, Brownian coagulation and diffusion, surface growth, coalescence and thermophoresis have been taken into account. Based on the particle size distributions, an efficient quadrature method of moments was allowed to approximate the general dynamics equation of particle, and the eddy dissipation concept (EDC) combustion model was used to estimate the flame temperature field. Excellent agreements between the model predictions and experimental data, with respect to the flame temperature distribution and particle kinetics, are reached. By taking the particle size and surface area as independent variables, the full distributions of volume equivalent diameters, evolution of the agglomerate number, the geometric standard deviation based on volume and agglomerate fractal nature, mean primary particle size and the number of primary particles per agglomerate are revealed. The variation of oxygen flow rate has an important influence on the temperature distribution and hence on the particle kinetics accordingly.

05/02675 Influence of oblique angle and heating height on flame structure, temperature field and efficiency of an impinging laminar jet flame

05/02675 Influence of oblique angle and heating height on flame structure, temperature field and efficiency of an impinging laminar jet flame

Laminate Propellant Combustion (Review) 1. Experimental Investigations

A review of experimental research of the combustion of laminate propellants of solid oxidizer (primarily ammonium perchlorate) and hydrocarbon binder is given. The purpose and description of the simplification of heterogeneous propellants through the use of constituent layers is detailed. This first of a two-part review describes the development of knowledge of the deflagration of laminates through a number of experimental methods used to quantitatively and qualitatively observe the condensed phase, surface structure, gas phase flame structure, burning rate, species concentrations, and temperature fields. These observations have generated a wealth of two-dimensional experimental data that can be used for validating computational and theoretical models.

STUDY OF GAS COMBUSTION IN A VENTED CYLINDRICAL VESSEL

Complicated interaction of a flame front with a turbulent flow induced by venting is studied during combustion of the stoichiometric propane/air mixture in a relatively large vented cylindrical vessel. Flame position, its shape, and combustion pressure were measured as a function of time and vent parameters. The experimental data were used to verify numerical simulation of the combustion process. The proposed numerical model satisfactorily simulates the main features of combustion in a closed and vented vessel such as flame configuration, flow and temperature fields, and pressure variation pattern. Simulated velocity and temperature distribution are very useful pieces of information because they are not available from experiments.

Burning velocity measurements of microgravity spherical sooting premixed flames using rainbow Schlieren deflectometry

The determination of the sooting flame speed of an ethylene/air mixture was explored using two quasi-one-dimensional flame configurations: a counterflow configuration in normal gravity and a spherical flame in microgravity. The widely used counterflow configuration was demonstrated to be unsuitable for burning velocity measurements of sooting flames. In the second configuration, a burner-supported, spherical flame was generated by discharging a reactant mixture from a porous spherical burner into a quiescent ambience in microgravity. The purely curved spherical flame allows the measurement of sooting flame speeds without the complications of hydrodynamic straining and heat loss to the burner. A compact rainbow Schlieren deflectometry (RSD) system was developed and utilized to characterize the flame radius and temperature field. This optical technique was able to provide data even under heavily sooting conditions and allowed us to measure the sooting flame speed with reasonable accuracy. The flame speed of an ethylene/air mixture with an equivalence ratio equal to 3.5 was determined. The adiabatic flame speed value predicted by gas-phase reactions, without soot chemistry, was twice the experimental value. Clearly this difference points to the strong influence of soot chemistry and radiation on sooting flame propagation.

04/02962 Effects of heating height on flame appearance,temperature field and efficiency of an impinging laminar jet flame used in domestic gas stoves: Hou, S.-S. and Ko, Y.-C. Energy Conversion and Management, 2004, 45, (9–10), 1583–1595

04/02962 Effects of heating height on flame appearance,temperature field and efficiency of an impinging laminar jet flame used in domestic gas stoves: Hou, S.-S. and Ko, Y.-C. Energy Conversion and Management, 2004, 45, (9–10), 1583–1595

Influence of oblique angle and heating height on flame structure, temperature field and efficiency of an impinging laminar jet flame

An experimental study is performed to determine the combined effects of oblique angle (θ) and heating height (H) on the flame structure, temperature field and thermal efficiency of a laminar premixed methane–air flame impinging on a plane surface. A double-flame burning of a Bunsen flame under a fuel-rich condition is used. It is found that the flame structure, temperature distribution and thermal efficiency depend strongly on the oblique angle and heating height. The influence of the oblique angle on flame structure is stronger for lower heating heights but is relatively weak for higher heating heights. For normal impingement, axisymmetric temperature distributions are found, which is attributed to the axisymmetric flame structure. However, a jet flame impinging at an angle onto the horizontal plate creates an asymmetric flame structure and, thus, results in asymmetric temperature distributions. The results show that as the oblique angle is reduced from 90° to 60°, the high-temperature zone shifts toward the major flow region. An optimum operating condition of the burner, identified by the widest high-temperature zone and the highest thermal efficiency, is achieved under the condition of θ = 60° and H = 12 mm. In general, a decrease of the oblique angle leads to a decrease in thermal efficiency. However, for the cases of lower heating heights (i.e. H ⩽ 12 mm), the trend may be reversed. Furthermore, for a fixed oblique angle, as the heating height is increased, the thermal efficiency first increases to a maximum value and then decreases.

Effects of heating height on flame appearance, temperature field and efficiency of an impinging laminar jet flame used in domestic gas stoves

Laminar jet flames are used in most domestic gas burners. However, the literature on combustion characteristics and thermal efficiencies of a single laminar impinging jet flame is very limited. Heating height is a significant operating parameter of a domestic gas stove, but it has received little attention in the literature. In this study, our aim is to simulate and examine the effect of heating height on the flame characteristics of a domestic gas stove. We emphasize the importance of heating height on flame structure, temperature distribution and thermal efficiency for low-Reynolds-number fuel-rich methane–air flames impinging normal to a plane surface, which has not been documented yet. Results show that flame structure, temperature distribution and thermal efficiency are greatly influenced by the heating height. With increasing heating height, the thermal efficiency first increases to a maximum value and then decreases. An optimum heating height, identified by the widest high temperature zone and the highest thermal efficiency, is achieved under the condition of Type-C flame burning, in which both the inner premixed flame and outer diffusion flame are open and diverge. Furthermore, we find that the optimum heating height increases with increasing methane concentration or injection velocity. Note that the maximum thermal efficiency occurs when the heating height is slightly lower than the tip of the inner rich premixed flame. This important characteristic can be applied to the design of domestic gas stoves, and it was not found in the available published work.

Suppression limits of low strain rate non-premixed methane flames

The suppression of low strain rate non-premixed flames was investigated experimentally in a counterflow configuration for laminar flames with minimal conductive heat losses. This was accomplished by varying the velocity ratio of fuel to oxidizer to adjust the flame position such that conductive losses to the burner were reduced and was confirmed by temperature measurements using thermocouples near the reactant ducts. Thin filament pyrometry was used to measure the flame temperature field for a curved diluted methane-air flame near extinction at a global strain rate of 20 s −1. The maximum flame temperature did not change as a function of position along the curved flame surface, suggesting that the local agent concentration required for suppression will not differ significantly along the flame sheet. The concentration of N 2, CO 2, and CF 3Br added to the fuel and the oxidizer streams required to obtain extinction was measured as a function of the global strain rate. In agreement with previous measurements performed under microgravity conditions, limiting non-premixed flame extinction behavior in which the agent concentration obtained a value that insures suppression for all global strain rates was observed. A series of extinction measurements varying the air:fuel velocity ratio showed that the critical N 2 concentration was invariant with this ratio, unless conductive losses were present. In terms of fire safety, the measurements demonstrate the existence of a fundamental limit for suppressant requirements in normal gravity flames, analogous to agent flammability limits in premixed flames. The critical agent volume fraction in the methane fuel stream assuring suppression for all global strain rates was measured to be 0.841 ± 0.01 for N 2, 0.773 ± 0.009 for CO 2, and 0.437 ± 0.005 for CF 3Br. The critical agent volume fraction in the oxidizer stream assuring suppression for all global strain rates was measured as 0.299 ± 0.004 for N 2, 0.187 ± 0.002 for CO 2, and 0.043 ± 0.001 for CF 3Br.

Comparison and analysis of three different non-contacting flame temperature field measurements

Comparison and analysis of three different non-contacting flame temperature field measurements

층류 예혼합 화염의 예열공기 연소특성

Co-flow axisymmetric laminar premixed flame of methane was used to study the influence of air temperature and N₂ addition on the flame structure, temperature field and emission characteristics. OH 2-D images and temperatures along the centerline were measured experimentally by PUF and CARS techniques respectively to observe the influences of dilution and thermal effects of N₂ in the gas mixture. Also, the concentration of NOx was measured at each condition by gas analyser to see the suppression effect of N₂ addition on NOx emissions. It was found that OH concentrations distribute widely as air temperature goes higher. while the effect of N₂ addition is not significant. But N₂ addition highly contributes to the flame front and NOx emissions which was argued to be due to the reduction of flame temperature. In accordance with experimental study. numerical simulation using CHEMKIN code was carried out to compare the temperature results with those acquired by CARS measurement, and we could find that there is good agreement between those results.

Fast wavelength switching of narrow-band excimer lasers

A novel system was developed, which allows one to switch the wavelength of a narrow-band excimer laser between two successive light pulses at a repetition rate of at least 250 Hz. This is realized by a periodically driven piezo actuator, which is attached to the diffraction grating of the narrow-band KrF excimer laser. The achieved position accuracy of the grating leads to a wavelength reproducibility of ±0.2 pm, which allows one to apply this system to laser spectroscopic investigations like LIF or LIPF of OH in flames. Using the fast wavelength switching system background reduced concentration and temperature fields in flames can be measured within one sequence. Some possible realized and planned applications like the measurement of gas temperature, the diagnostic of turbulent combustion processes, and the investigation of combustion processes under microgravity are discussed.