Stoichiometric Flame Research Articles

A Direct Numerical Simulation Investigation of Spherically Expanding Flames Propagating in Fuel Droplet-Mists for Different Droplet Diameters and Overall Equivalence Ratios

ABSTRACTLaminar and turbulent spherically expanding n-heptane flames in mono-sized fuel droplet-mists have been simulated for a range of different overall equivalence ratios and droplet diameters using three-dimensional Direct Numerical Simulations (DNS). Flame wrinkling and the evolutions of flame surface area and burned gas volume have been investigated for spherically expanding spray and gaseous premixed flames with the same initial burned gas radius and overall equivalence ratios. It has been found that droplet-induced wrinkling for laminar flame kernels strengthens with increasing overall equivalence ratio and droplet diameter. However, the effects of droplet-induced flame wrinkling are masked by wrinkling induced by fluid motion in turbulent spherically expanding spray flames. The gaseous phase mixture within the flame has been found to have smaller equivalence ratios (predominantly fuel-lean) in comparison to the overall equivalence ratio for globally stoichiometric and fuel-rich droplet cases and this tendency strengthens with increasing droplet diameter. By contrast, it is possible to obtain higher local equivalence ratio values than the overall equivalence ratio in globally fuel-lean spray flames. The presence of droplets in the globally fuel-lean cases enhances the growth of flame surface area under laminar and turbulent conditions. However, for the laminar globally stoichiometric spray flame, flame surface area for small droplets grows faster than the corresponding laminar premixed flame and this tendency is observed also for turbulent globally fuel-rich spray flames. It has been found that the burned gas mass increases for large (small) droplets for overall fuel-lean (fuel-rich) mixtures for flame propagation in droplet-laden mixtures, which is in qualitative agreement with previous experimental findings.

Experimental investigation of reattachment behavior of turbulent lifted diffusion jet flames induced by repetitive DC electric pulse discharges with conditional PIV

ABSTRACTAmong the recently prevailing flame stabilization enhancement by electric field and plasma, repetitive DC electric pulse discharge is applied to a turbulent lifted diffusion jet flame to improve the reattachment in this study. The main objectove of this study is to characterize experimentally the stability and the reattachment behaviors of lifted flames under the electric pulse effect with a proposed electrode configuration. The effects of pulse repetition frequency (PRF) and voltage polarity on flame are investigated. The reattachment velocity increases by increasing PRF. The time history of flame base trace and absolute flame speed with positive-voltage-pulse are illustrated. The electric corona discharge is observed during upstream propagation process, and its role in flame acceleration is discussed. In addition, 2D-PIV measurement conditioned by high speed sequence images is conducted. Finally, the conditionally instantaneous flame propagation speed is enhanced and exceeds 3 times that of stoichiometric laminar flame speed, which leads to lifted flame reattachment.

Simulating upstream flame propagation in a narrow channel after wall preheating: Flame analysis and chemistry reduction strategy

The response of a premixed laminar flame, stabilised in a narrow channel (ℓi=5 mm), is investigated for an amount of heat supplied upstream through the wall. The first objective is to determine the set of canonical problems that a reduced chemistry must accurately reproduce to simulate the flame/wall coupling under such circumstances. The second objective is to identify the major energy transport mechanisms at play, i.e. convective heat transfer in the gas or conductive in the solid wall. The stoichiometric methane-air flame numerical simulations performed include complex molecular transport and the fully coupled solving of heat transfer at and within the wall. Initially, the flame is stabilised by an inlet mass flow rate matching the flame burning velocity. A reference simulation is first performed with a comprehensive methane-air chemistry. Then, two chemistry reduction strategies targeting a different set of canonical problems are applied and the results compared to conclude on the necessary constraints for chemistry reduction under such flow configuration. Various heating intensities are considered and a minimum heating supply is found necessary to initiate a complete upstream flame translation. A specific attention is paid on the relative contributions of heat convection in the flow and heat conduction in the solid. The heat transfer mechanism triggering the flame movement is revealed to be mainly convective. The flame translation is found to be organised in two stages, with first a downstream movement due to fresh gases expansion because of heating by the wall, followed by the upstream propagation due to the enhancement of the burning rate by the preheating of the mixture. The shape, the flash back speed, and the final position of the flame vary with the amplitude of the heat flux brought to the external surface of the wall.

Experimental and kinetic modeling study of para-xylene chemistry in laminar premixed flames

The chemistry of para-xylene oxidation in laminar premixed flames has been analyzed using new experimental data on flame propagation at atmospheric pressure and flame structure of low-pressure stoichiometric flame. Atmospheric pressure laminar burning velocities of para-xylene + air flames were determined using the heat flux method at initial temperatures of 328 and 353 K over the equivalence ratio range of ϕ = 0.7–1.4 and of ϕ = 0.7–1.3, respectively. Temperature and mole fraction profiles of reactants, final products, and reactive and stable intermediate species have been measured in laminar premixed CH4/O2/N2 and CH4/1.5%C8H10/O2/N2 flames at low pressure (40 Torr) using thermocouple, molecular beam/mass spectrometry, and gas chromatography/mass spectrometry techniques. These new experimental results have been modeled with our previous model including sub-mechanisms for aromatics (benzene up to p-xylene) and aliphatic (C1 up to C7) oxidation. Good agreement has been observed for the profiles of the main species analyzed. Moreover, chemical pathways for common species in methane flame with and without 1.5% of benzene or 1.5% toluene investigated earlier under similar conditions were analysed and compared to the present flame doped with para-xylene. Key reactions of aromatics degradation in CH4/O2/N2 flames were identified and discussed. Burning velocities of para-xylene + air flames were also reproduced by the kinetic model.

Experimental Study and a Short Kinetic Model for High-Temperature Oxidation of Methyl Methacrylate

ABSTRACTSynthetic and natural polymeric esters find applications in transport and construction sectors, where fire safety is an important concern. One polymer that is widely used is poly (methyl methacrylate) (PMMA), which almost completely undergoes thermal decomposition into methyl methacrylate (its monomer) (MMA) at –C. In order to analyze the high-temperature gas-phase oxidation of PMMA, and thereby predict its fire behavior (such as burning rate, temperature of the material, and heat fluxes) with less computational effort, a compact kinetic model for the oxidation of its primary decomposition product, MMA, is most essential. This is accomplished in the present work by obtaining a reduced mechanism for MMA oxidation from a detailed mechanism from the Lawrence Livermore National Laboratories group.To extend the available data base for model validation and present validation data at atmospheric pressure conditions, for the first time, (i) detailed measurements of species profiles have been performed in stoichiometric laminar flat flames using flame sampling molecular beam mass spectrometry (MBMS) technique and (ii) laminar burning velocities have been obtained using the heat flux method for various unburnt mixture temperatures. Evaluating the model against these data sets point to the need to revise the kinetic model, which is achieved by adopting rate constants of key reactions among analogous molecules from recent literature. The updated compact kinetic model is able to predict the major species in the flat flame as well as the burning velocity of MMA satisfactorily. The final “short MMA mechanism” consists of 88 species and 1084 reactions.

Multiscale analysis of head-on quenching premixed turbulent flames

Multiscale analysis of wall-bounded turbulent premixed flames is performed using three-dimensional direct numerical simulation data of flame-wall interaction (FWI). The chosen configuration represents head-on quenching of a turbulent statistically planar stoichiometric methane-air flame by an isothermal inert wall. Different turbulence intensities and chemical mechanisms have been analyzed. A bandpass filtering technique is utilised to analyze the influence of turbulent eddies of varying size and the statistics of vorticity and strain rate fields associated with them. It is found that the presence of the flame does not alter the mechanism of vortex stretching in turbulent flows when the flame is away from the wall, but in the case of FWI, the mechanism of vortex stretching is altered due to a reduction in the contribution from non-local strain, and the small scales of turbulence start to contribute to the flame straining process. The results indicate that small scale eddies do not contribute to the tangential strain rate when the flames are away from the walls, whereas the contribution from the small scales to the tangential strain rate increases when the flame is in the vicinity of the wall. It is also found that the choice of chemical mechanism does not influence the underlying fluid mechanical processes involved in FWI.

Multi-environment PDF modeling for turbulent piloted premixed jet flames

The three-environment PDF approach has been applied to numerically investigate a series of the turbulent piloted premixed flames in the piloted premixed jet burner (PPJB). In this study, computations are made for three flames (PM1-100, PM1-150 and PM1-200). In terms of the unconditional means and conditional statistics, numerical results are reasonably well agreed with experimental data. At the central jet mixture fraction and temperature spaces, the predicted environment-conditional statistics at the near-injector region clearly identify the dual premixed flame modes established by the stoichiometric pilot flame and the lean premixed central jet. The present MEPDF approach together with the IEM micro-mixing model and the skeletal chemistry qualitatively predicts the ignition, local extinction and reignition process in the three-stream highly stretched piloted premixed flame even if there exist certain discrepancies. In terms of [CO][OH]|1400 K and temperature PDFs, the detailed discussions were also made for the effects of micro-mixing models (IEM, EIEM) and chemical mechanism (skeletal, GRI) on the local extinction and reignition characteristics.

Investigation of the Turbulent Near Wall Flame Behavior for a Sidewall Quenching Burner by Means of a Large Eddy Simulation and Tabulated Chemistry

Combustion will play a major part in fulfilling the world’s energy demand in the next 20 years. Therefore, it is necessary to understand the fundamentals of the flame–wall interaction (FWI), which takes place in internal combustion engines or gas turbines. The FWI can increase heat losses, increase pollutant formations and lowers efficiencies. In this work, a Large Eddy Simulation combined with a tabulated chemistry approach is used to investigate the transient near wall behavior of a turbulent premixed stoichiometric methane flame. This sidewall quenching configuration is based on an experimental burner with non-homogeneous turbulence and an actively cooled wall. The burner was used in a previous study for validation purposes. The transient behavior of the movement of the flame tip is analyzed by categorizing it into three different scenarios: an upstream, a downstream and a jump-like upstream movement. The distributions of the wall heat flux, the quenching distance or the detachment of the maximum heat flux and the quenching point are strongly dependent on this movement. The highest heat fluxes appear mostly at the jump-like movement because the flame behaves locally like a head-on quenching flame.

Hydrogen cloud explosion evaluation under inert gas atmosphere

This paper is aimed at evaluating the hydrogen cloud explosion under inert gas atmosphere experimentally and numerically. The results demonstrate that only under Ar, N2 and CO2 atmosphere, the lean and stoichiometric hydrogen flame tends to be unstable. The Markstein length of Ar, N2 and CO2 is less than zero and the decreasing order is Ar, N2 and CO2. Except for CO2, the average flame propagation velocity, maximum explosion pressure, maximum pressure rise rate, positive pressure impulse and explosion pressure attenuation decrease monotonously in the order of He, Ar and N2. For various equivalence ratios and inert gases, the explosion pressure releases into the far field at the sound speed and attenuates with distance. Due to the fact that the explosion pressure is closely related to laminar burning velocity, the explosion pressure suppression by inert gas is revealed by analyzing the factors affecting laminar burning velocity. As equivalence ratio increases, the adiabatic flame temperature plays a more important role in affecting laminar burning velocity than thermal diffusivity. For different inert gases, the effect of thermal diffusivity on laminar burning velocity is obviously greater than adiabatic flame temperature. Besides, the third-body effect of various inert gases increases gradually until Φ = 1.4. and then decreases with increasing equivalence ratio. For a given equivalence ratio, the increasing order of third-body effect is He, Ar and CO2.

Heat transfer investigations on impinging flame jets of a multi-port convex burner

Multi-port curved surface burners are used in industrial boilers, preheating of large diameter pipes, textile industries, preheating of cylindrical metal billets and other industrial applications. The present work reports the heat transfer characteristics of convex shaped burner with 49 inline ports arranged in an array of 7 each. The methane-air premixed flame jets are impinged on the concave surface of a curved plate placed with radial spacing of 12 mm. Two different burners with port diameters of 2 mm and 3 mm with pitch to diameter ratio of 2.33 are used. The flame jet is studied for Reynolds number (Re) ranging from 75 to 200 and equivalence ratio of 0.9–1.5. The characterisation is done by impinging the pre-characterised air jets of various flow rates on the rear surface and capturing the wall temperature. The wall temperature is analysed to get the distributions of Nusselt number and effectiveness. The variation of coefficient of variance of Nusselt number, average Nusselt number and thermal efficiency is reported in the present work. The Nusselt number and effectiveness distributions increase with the increase in mixture Reynolds number. For a fixed mixture Reynolds number, the optimum heat transfer is obtained for stoichiometric flame. The thermal efficiency and average heat transfer of 2 mm port diameter is observed to be 18–25% higher as compared with burner with port diameter of 3 mm. Correlations are developed to predict the average Nusselt number, average effectiveness, coefficient of variance (COV) of Nusselt number distribution and thermal efficiency.

Flame Curvature Distribution in High Pressure Turbulent Bunsen Premixed Flames

The flame curvature statistics of turbulent premixed Bunsen flames have been analysed in this paper using a Direct Numerical Simulation (DNS) database of turbulent Bunsen flames at ambient and elevated pressures. In order to be able to perform a large parametric study in terms of pressure, heat release parameter, turbulence conditions and nozzle diameter, a single step Arrhenius type irreversible chemistry has been used for the purpose of computational economy, where thermo-chemical parameters are adjusted to match the behavior of stoichiometric methane-air flames. This analysis focuses on the characterization of the local flame geometry in response to turbulence and hydro-dynamic instability. The shape of the flame front is found to be consistent with existing experimental data. Although the Darrieus Landau instability promotes cusp formation, a qualitatively similar flame morphology can be observed for hydro-dynamically stable flames. A criterion has been suggested for the curvature PDF to become negatively skewed.

Direct Numerical Simulation of Head-On Quenching of Statistically Planar Turbulent Premixed Methane-Air Flames Using a Detailed Chemical Mechanism

A three-dimensional compressible Direct Numerical Simulation (DNS) analysis has been carried out for head-on quenching of a statistically planar stoichiometric methane-air flame by an isothermal inert wall. A multi-step chemical mechanism for methane-air combustion is used for the purpose of detailed chemistry DNS. For head-on quenching of stoichiometric methane-air flames, the mass fractions of major reactant species such as methane and oxygen tend to vanish at the wall during flame quenching. The absence of text {OH} at the wall gives rise to accumulation of carbon monoxide during flame quenching because text {CO} cannot be oxidised anymore. Furthermore, it has been found that low-temperature reactions give rise to accumulation of text {HO}_{2} and mathrm {H}_{2}mathrm {O}_{2} at the wall during flame quenching. Moreover, these low temperature reactions are responsible for non-zero heat release rate at the wall during flame-wall interaction. In order to perform an in-depth comparison between simple and detailed chemistry DNS results, a corresponding simulation has been carried out for the same turbulence parameters for a representative single-step Arrhenius type irreversible chemical mechanism. In the corresponding simple chemistry simulation, heat release rate vanishes once the flame reaches a threshold distance from the wall. The distributions of reaction progress variable c and non-dimensional temperature T are found to be identical to each other away from the wall for the simple chemistry simulation but this equality does not hold during head-on quenching. The inequality between c (defined based on text {CH}_{4} mass fraction) and T holds both away from and close to the wall for the detailed chemistry simulation but it becomes particularly prominent in the near-wall region. The temporal evolutions of wall heat flux and wall Peclet number (i.e. normalised wall-normal distance of T = 0.9 isosurface) for both simple and detailed chemistry laminar and turbulent cases have been found to be qualitatively similar. However, small differences have been observed in the numerical values of the maximum normalised wall heat flux magnitude left ({Phi }_{max } right )_{mathrm {L}} and the minimum Peclet number (Pe_{min })_{mathrm {L}} obtained from simple and detailed chemistry based laminar head-on quenching calculations. Detailed explanations have been provided for the observed differences in behaviours of left ({Phi }_{max }right )_{mathrm {L}} and (Pe_{min })_{mathrm {L}}. The usual Flame Surface Density (FSD) and scalar dissipation rate (SDR) based reaction rate closures do not adequately predict the mean reaction rate of reaction progress variable in the near-wall region for both simple and detailed chemistry simulations. It has been found that recently proposed FSD and SDR based reaction rate closures based on a-priori DNS analysis of simple chemistry data perform satisfactorily also for the detailed chemistry case both away from and close to the wall without any adjustment to the model parameters.

Sound generation by turbulent premixed flames

This paper presents a numerical study of the sound generated by turbulent, premixed flames. Direct numerical simulations (DNS) of two round jet flames with equivalence ratios of 0.7 and 1.0 are first carried out. Single-step chemistry is employed to reduce the computational cost, and care is taken to resolve both the near and far fields and to avoid noise reflections at the outflow boundaries. Several significant features of these two flames are noted. These include the monopolar nature of the sound from both flames, the stoichiometric flame being significantly louder than the lean flame, the observed frequency of peak acoustic spectral amplitude being consistent with prior experimental studies and the importance of so-called ‘flame annihilation’ events as acoustic sources. A simple model that relates these observed annihilation events to the far-field sound is then proposed, demonstrating a surprisingly high degree of correlation with the far-field sound from the DNS. This model is consistent with earlier works that view a premixed turbulent flame as a distribution of acoustic sources, and provides a physical explanation for the well-known monopolar content of the sound radiated by premixed turbulent flames.

Dimensionally reduced modeling of nitric oxide formation for premixed methane-air flames with ammonia content

The paper presented an experimental and numerical study on a combustion process of ammonia doped methane flames with the NH3 content in the fuel from 1% up to 5%. Tests were performed with an atmospheric pressure axisymmetric burner for stoichiometric mixtures and fuel-lean conditions (φ = 0.63, 0.71, 0.83, 1.0) with the substrates preheating up to 573 K. Numerical modelling involved three reduced dimensionally combustion models (0D IdealGasReactor, 1D FreeFlame, 1D BurnerFlame) with four detailed reaction mechanisms for the hydrocarbons and nitrogen chemistry (GRI 3.0, SanDiego, Konnov 0.6 and Tian). Comparison of the 0D/1D calculations results with a complete burner geometry modelling (3D Ansys EDC) was performed for GRI 3.0.Experimental study shown that nitric oxide emission increased with the increase of NH3 content in the introduced fuel, however transition from NH3 to NO was incomplete and trend was not linear for the rising ammonia share. Doubling of the ammonia content in the fuel from 2.5% to 5% resulted in a rise of NO emission by only 55.5% (from 946 to 1471 ppmv) for the lean mixtures and by 48% (from 1451 to 2148 ppmv) for the stoichiometric conditions.The numerical analysis results were in a good agreement with the experimental results for the lean mixtures and ammonia content up to 1% for all investigated combustion models and the kinetic reaction mechanisms. Trends of the nitric oxide emission obtained with the stoichiometric flames were valid for 1D models. However overall values were over predicted for an adiabatic 1D FreeFlame calculations and under predicted for 1D BurnerFlame, which showed a sensitivity of the nitrogen chemistry to the process temperature. Analysis with the 3D Ansys EDC model and GRI 3.0 provided the most accurate results up to 2.5% of the NH3 share in the fuel with a maximum relative differences values to the experimental results from 10% up to 24% for the lean and the stoichiometric conditions respectively.

Numerical Study of the Effect of hydrogen addition on the laminar flame speed and premixed flame structure of biogas

In this work, the laminar flame speed and flame structure of biogas/H2 fuel mixtures were studied numerically from pure biogas to biogas with an addition of 15% H2 in volume by using the CHEMKIN software with the GRIMECH 2.11 kinetic mechanism. The effect of hydrogen addition to biogas on laminar flame speed and flame structure has been studied as well as the variation of the aeration rate from stoichiometric conditions to lean conditions. The trends in laminar flame speed results obtained are explained by means of numerical results on temperature profile and heat release rate. CO, CO2 and NO profiles are also observed for the different mixtures studied. Hydrogen addition in biogas flames shows an important effect, especially in zones near stoichiometric flames, decreasing its effects in lean mixtures combustion.

Experimental studies of nitromethane flames and evaluation of kinetic mechanisms

The present work reports new experimental data for premixed flames of nitromethane, CH3NO2, at atmospheric pressure, and an evaluation of two contemporary kinetic mechanisms based on these new flame studies as well as previously published experimental data on laminar burning velocity and ignition. Flames of nitromethane + air at lean (ϕ = 0.8) and rich (ϕ = 1.2) conditions were stabilized on a flat-flame burner, where profiles of CH2O, CO and NO were obtained using laser-induced fluorescence and temperature profiles using coherent anti-Stokes Raman spectroscopy. Laminar burning velocities for nitromethane + O2 + CO2 were measured using the heat flux method for ϕ = 0.8–1.3 at 348 K and ϕ = 0.8–1.6 at 358 K, and an oxidizer composition of 35% O2 and 65% CO2. In addition, the effect of the oxidizer composition was examined for a stoichiometric flame at 358 K by varying oxygen fraction from 30% to 40%. The mechanism by Mathieu et al. (Fuel 2016, 182, 597), previously not validated for flames, was able to reproduce experimental laminar burning velocities for nitromethane + air, but under predicted new results for CH3NO2 + O2 + CO2 mixtures. The mechanism by Brequigny et al. (Proc. Combust. Inst. 2014, 35, 703) under predicted experimental laminar burning velocities significantly at all investigated conditions. Previous studies have shown that none of the mechanisms can accurately predict ignition delay time over a wide range of conditions with respect to pressure, temperature, diluent and dilution ratio. The evaluation of the mechanisms reveals that the understanding of nitromethane combustion is at the present time not sufficient to produce a widely applicable mechanism.

Experimental and Numerical Study of Ethyl Valerate Flat Flames at Low Pressure

ABSTRACTThree flat flames of ethyl valerate (C7H14O2) at different equivalence ratios, 0.81, 0.95, and 1.31, have been stabilized at 55 mbar and analyzed using gas chromatography. Based on the experimental results, a detailed kinetic model of ethyl valerate combustion, containing 211 species and 1368 reactions, has been elaborated. The model predictions agree well with the experimental results for the temperature range of 1100–2000 K. In the lean flame, the main decomposition pathways leads to C7H14O2 → CH3(CH2)3COOCHCH3 → CH3CHO → CH3CO → CH3 → CH2O → HCO. For the stoichiometric flame, the ethyl valerate consumption pathway produces C7H14O2 → C4H9COOH → CH3CHCH2CH2COOH → C4H7COOH → CH2COOH → CH2CO → CH3 → CH2O → HCO. In the rich flame, from ethyl valerate to pentenoic acid (C4H7COOH), the decomposition pathway is the same as in the stoichiometric flame. The pentenoic acid leads to the formation of C2H4 via C4H6 and C3H6. Finally, the new model has been tested on the experimental data obtained in a jet-stirred reactor at high pressure (10 atm) and low temperatures (560–1160 K). The mechanism predicts fairly well all the species, except H2 and C2H2. Future work should improve the mechanism to extend its validity range up to high pressure and low temperature range.

Assessment of uncertainties of laminar flame speed of premixed flames as determined using a Bunsen burner at varying pressures

Laminar methane/air premixed flames at different pressures in a newly developed high-pressure Bunsen flame rig are studied using detailed numerical simulations and laser diagnostics. In the numerical simulations, one-dimensional and two-dimensional axisymmetric configurations were considered employing detailed transport properties and chemical kinetic mechanisms. In the measurements, OH PLIF was employed. The aims are to improved the understanding of the structures of the flames at varying pressures, to measure the laminar flame speed at different pressures, and to quantify the accuracy of the Bunsen flame method for measurement of laminar flame speed at different pressures. The stoichiometric and fuel-rich flames were found to exhibit a two-reaction-zone structure: an inner premixed flame in which the fuel was converted to CO and H2, and an outer diffusion flame in which CO and H2 were oxidized further to form combustion products. With increasing pressure, the inner premixed flame becomes thinner and the flame as a whole has the tendency to become unstable. Using the numerical and the experimental data, the methods of flame-cone-angle and flame-area were used to extract the laminar flame speed for different equivalence ratios and pressures. The flame-cone-angle method showed slightly better accuracy than the flame-area method did. The accuracy of both methods became lower under high pressure conditions. The inlet velocity of the burner was shown to affect the accuracy of the extracted laminar flame speed. For a stoichiometric atmospheric flame it was found that the most suitable inlet velocity for the fuel/air mixture was about 6 times the laminar flame speed, yielding a flame length about 7 times the radius of the burner. With appropriate flame length, the mid-height of the flame showed a rather low flame stretch rate, the laminar flame speed being in close agreement with the unstretched laminar flame speed, the error being less than 6% for the flames that were studied.

Experimental and numerical investigation of the chemical reaction kinetics in H2/CO syngas flame at a pressure of 1–10 atm

The structure of a premixed stoichiometric flame of syngas (H2/CO/O2/Ar = 0.0667/0.0667/0.0667/0.8) stabilized on a flat burner at a pressure of 5 atm was studied experimentally and by numerical simulation. The mole fraction profiles of the reactants (H2, CO, and O2) and the major (H2O and CO2) and intermediate (O, OH, HO2, and H2O2) combustion products were measured by molecular beam mass spectrometry. The experimental data were compared with those calculated using three detailed chemical-kinetic mechanisms proposed in the literature for oxidation of a H2/CO mixture. Good agreement was found between the results of the experiment and simulation. Calculations of the structure of the flame of the same composition at a pressure of 1 and 10 atm were performed to establish the effect of the pressure on the chemical reaction kinetics in the syngas flame. The results were explained by kinetic analysis of the mechanisms.

Electric Field Modified Bunsen Flame with Variable Anode Placement

A methane–air Bunsen flame was tested under dc electric field forcing with different ring anode sizes and locations. The anodes were placed within the flame to far outside the flame, both axially and radially. The focus of the work is to understand the limit of electrode placement and its effect on the flame under a dc field. A stoichiometric flame with voltages up to 9.1 kV was tested. The electrical current and flame height were measured as a function of the bias voltage and anode location. Plasma density measurements of the unmodified flame at various axial locations were used to corroborate that anode placement at regions of high electron density caused the largest reductions in flame height. The results showed the anodes closest to the burner at 35 mm caused the largest reduction (24%) in flame height. The effect of the electric field on flame height decreased as the anode moved farther downstream of the flame or radially outward. For the same voltage, larger currents were also observed for anodes close to the burner, whereas anodes placed far outside of the flame had minimal effects on current and, consequently, on the flame height. These differences are due to the variable electron density at the anode, which limits the net current collected and the strength of the field.