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Flame Temperature (flame + temperature)
Selected AbstractsHydrogen utilization as a fuel: hydrogen-blending effects in flame structure and NO emission behaviour of CH4,air flameINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2007Jeong Park Abstract Hydrogen-blending effects in flame structure and NO emission behaviour are numerically studied with detailed chemistry in methane,air counterflow diffusion flames. The composition of fuel is systematically changed from pure methane to the blending fuel of methane,hydrogen through H2 molar addition up to 30%. Flame structure, which can be described representatively as a fuel consumption layer and a H2,CO consumption layer, is shown to be changed considerably in hydrogen-blending methane flames, compared to pure methane flames. The differences are displayed through maximum flame temperature, the overlap of fuel and oxygen, and the behaviours of the production rates of major species. Hydrogen-blending into hydrocarbon fuel can be a promising technology to reduce both the CO and CO2 emissions supposing that NOx emission should be reduced through some technologies in industrial burners. These drastic changes of flame structure affect NO emission behaviour considerably. The changes of thermal NO and prompt NO are also provided according to hydrogen-blending. Importantly contributing reaction steps to prompt NO are addressed in pure methane and hydrogen-blending methane flames. Copyright © 2006 John Wiley & Sons, Ltd. [source] Numerical study on flame structure and NO formation in CH4,O2,N2 counterflow diffusion flame diluted with H2OINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2004Dong-Jin Hwang Abstract Numerical study on flame structure and NO emission behaviour has been conducted to grasp chemical effects of added H2O on either fuel- or oxidizer-side in CH4,O2,N2 counterflow diffusion flames. An artificial species, which has the same thermodynamic, transport, and radiation properties of added H2O, is introduced to feasibly isolate the chemical effects. Special concern is focused on the important role of remarkably produced OH radicals due to chemical effects of added H2O on flame structure and NO emission. The reason why the difference of behaviours between the principal chain branching reaction rate and flame temperature appear is attributed to the drastic change of reaction step (R120) from the production to the consumption of OH. It is also, however, seen that the most important contribution of produced OH due to chemical effects of added H2O is through reaction step (R127). The importantly contributing reaction steps to NO production are also examined. The production rates of thermal NO and prompt NO are suppressed by chemical effects of added H2O. The contribution of the reaction steps related to HNO intermediate species to the production of prompt NO is also stressed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Comparative study of flame structures and NOx emission characteristics in fuel injection recirculation and fuel gas recirculation combustion systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2004Jeong Park Abstract A numerical study with momentum-balanced boundary conditions has been conducted to grasp the chemical effects of added CO2 to fuel- and oxidizer-sides on flame structure and NO emission behaviour in H2,O2 diffusion flames with varying flame location. A reaction mechanism is proposed to show better agreements with experimental results in CO2 -added hydrogen flames. Oxidizer-side dilution results in significantly higher flame temperatures and NO emission. Flame location is dramatically changed due to high diffusivity of hydrogen according to variation of the composition of fuel- and oxidizer-sides. This affects flame structure and NO emission considerably especially the chemical effects of added CO2. The present work also displays separately thermal contribution and prompt NO emission due to the chemical effects caused by thermal dissociation of added CO2 in NO emission behaviour. It is found that flame temperature and the flame location affect the contribution of thermal and prompt NO due to chemical effects considerably in NO emission behaviour. Copyright © 2004 John Wiley & Sons, Ltd. [source] Chemical effects of CO2 addition to oxidizer and fuel streams on flame structure in H2,O2 counterflow diffusion flamesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2003Jeong Park Abstract Numerical simulation of CO2 addition effects to fuel and oxidizer streams on flame structure has been conducted with detailed chemistry in H2,O2 diffusion flames of a counterflow configuration. An artificial species, which displaces added CO2 in the fuel- and oxidizer-sides and has the same thermochemical, transport, and radiation properties to that of added CO2, is introduced to extract pure chemical effects in flame structure. Chemical effects due to thermal dissociation of added CO2 causes the reduction flame temperature in addition to some thermal effects. The reason why flame temperature due to chemical effects is larger in cases of CO2 addition to oxidizer stream is well explained though a defined characteristic strain rate. The produced CO is responsible for the reaction, CO2+H=CO+OH and takes its origin from chemical effects due to thermal dissociation. It is also found that the behavior of produced CO mole fraction is closely related to added CO2 mole fraction, maximum H mole fraction and its position, and maximum flame temperature and its position. Copyright © 2003 John Wiley & Sons, Ltd. [source] Chemical effect of diluents on flame structure and NO emission characteristic in methane-air counterflow diffusion flameINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2002Jeong Park Abstract The dilution effect of air stream according to agent type on flame structure and NO emission behaviour is numerically simulated with detailed chemistry in CH4/air counterflow diffusion flame. The volume percentage of diluents (H2O, CO2, and N2) in air stream is systematically changed from 0 to 10. The radiative heat loss term, based on an optically thin model, is included to clearly describe the flame structure and NO emission behaviour especially at low strain rates. The effect of dilution of air stream on the decrease of maximum flame temperature varies as CO2>H2O>N2, even if heat capacity of H2O is the highest. It is also found that the addition of CO2 shows the tendency towards the reduction of flame temperature in both the thermal and chemical sides, while the addition of H2O enhances the reaction chemically and restrains it thermally due to a super-equilibrium effect of the chain carrier radicals caused by the breakdown of H2O in high-temperature region. The comparison of the nitrogen chemical reaction pathway between the cases of the addition of CO2 and H2O clearly displays that the addition of CO2 is much more effective to reduce NO emission. Copyright © 2002 John Wiley & Sons, Ltd. [source] Thermal and chemical contributions of added H2O and CO2 to major flame structures and NO emission characteristics in H2/N2 laminar diffusion flameINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2002Seung-Gon Kim Abstract Numerical simulation with detailed chemistry has been carried out to clearly discriminate the thermal and chemical contributions of added diluents (H2O and CO2) to major flame structures and NO emission characteristics in H2/N2 counterflow diffusion flame. The pertinence of GRI, Miller,Bowman, and their recent modified mechanisms are estimated for the combined fuel of H2, CO2, and N2. A virtual species X, which displaces the individual CO2 and H2O in the fuel sides, is introduced to separate chemical effects from thermal effects. In the case of H2O addition the chain branching reaction, H + O2 , O + OH is considerably augmented in comparison with that in the case of CO2 addition. It is also seen that there exists a chemically super-adiabatic effect in flame temperature due to the breakdown of H2O. The reaction path of CH2O,CH2OH,CH3 and the C1-branch reactions become predominant due to the breakdown of CO2. In NO emission behaviour super-equilibrium effects caused by the surplus chain carrier radicals due to the breakdown of added H2O are more superior to the enhanced effects of prompt NO with the breakdown of added CO2. Especially, it is noted that thermal NO emission is directly influenced by the chemical super-equilibrium effects of chain carrier radicals in the case of H2O addition. As a result the overall NO emission in the case of the addition of H2O is higher than that in the case of CO2 addition. Copyright © 2002 John Wiley & Sons, Ltd. [source] NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/ArINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2002Jeong Park Abstract Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. [source] Nanoparticle formation through solid-fed flame synthesis: Experiment and modelingAICHE JOURNAL, Issue 4 2009W. Widiyastuti Abstract The preparation of silica nanoparticles through solid-fed flame synthesis was investigated experimentally and theoretically. Monodispersed submicrometer- and micrometer-sized silica powders were selected as solid precursors for feeding into a flame reactor. The effects of flame temperature, residence time, and precursor particle size were investigated systematically. Silica nanoparticles were formed by the nucleation, coagulation, and surface growth of the generated silica vapors due to the solid precursor evaporation. Numerical modeling was conducted to describe the mechanism of nanoparticle formation. Evaporation of the initial silica particles was considered in the modeling, accounting for its size evolution. Simultaneous mass transfer modeling due to the silica evaporation was solved in combination with a general dynamics equation solution. The modeling and experimental results were in agreement. Both results showed that the methane flow rate, carrier gas flow rate, and initial particle size influenced the effectiveness of nanoparticle formation in solid-fed flame synthesis. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Atmospheric Pressure Synthesis of Heavy Rare Earth Sesquioxides Nanoparticles of the Uncommon Monoclinic PhaseJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Bing Guo We report, for the first time, the atmospheric pressure synthesis of nonagglomerated nanoparticles (20,60 nm in diameter) of the uncommon monoclinic phase of some heavy rare earth sesquioxides RE2O3 (RE=Dy, Ho, Er, Tm, and Yb). The RE2O3 nanoparticles, prepared by a flame synthesis process, were characterized by X-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy. Monoclinic nanoparticles were formed when the flame temperature was sufficiently high; lower temperatures led to the formation of the normal cubic (C-type) phase. We explain the formation of the uncommon monoclinic phase on the basis of pressure,temperature phase equilibria, and the extra internal pressure induced by surface curvature of the nanoparticles. [source] Prediction of flammability speciation for the lower alkanes, carboxylic acids, and estersPROCESS SAFETY PROGRESS, Issue 1 2007M. Palucis Abstract A Gibbs energy minimization procedure is used to predict the flammability envelopes of alkanes, carboxylic acids, and acetates. In addition to providing the calculated adiabatic flame temperature (CAFT), the product profiles reveal regions of incomplete combustion products and the onset of methane formation above 0.0001 mole fraction. Temperatures at the predicted onset of methane production appear to be closely related to the temperature at the upper flammability limit (UFL). Although a fixed CAFT value could be related to the lower flammability limit (LFL), it was found that this was not the case with the UFL and only for acetic acid could a single CAFT value of 1200K be used to conservatively predict the flammable region. Rather, in general, a single CAFT value could not conservatively predict the upper flammable region. The predictions also reveal local maxima and minima in the concentrations of reaction products. These maps of incomplete combustion products for the flammability region predict that incomplete combustion products are produced at fuel/oxygen ratios significantly below the fuel/oxygen stoichiometric ratio. This region decreases as the limiting oxygen concentration is approached. © 2006 American Institute of Chemical Engineers Process Saf Prog, 2006 [source] Numerical study on NO formation in CH4,O2,N2 diffusion flame diluted with CO2INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2005Dong-Jin Hwang Abstract Numerical study with momentum-balanced boundary conditions has been conducted to grasp chemical effects of added CO2, to either fuel- or oxidizer-side on flame structure and NO emission behaviour in CH4,O2,N2 diffusion flames. Cautious investigation is made for the comparison among the behaviours of principal chain branching and important H-removal key reactions. This describes successfully the reason why flame temperatures for fuel-side dilution are higher than those for oxidizer-side dilution. The role of the principal chain branching reaction is also recognized to be important even in the change of major flame structure caused by chemical effects. The importantly contributing reaction steps to NO production are examined. The reduced production rates of thermal NO and prompt NO due to chemical effects are much more remarkable for fuel-side dilution. It is also found that the reaction step, H+NO+M=HNO+M plays a decisive role of the formation and destruction of prompt NO. Copyright © 2005 John Wiley & Sons, Ltd. [source] Further uses of the heat of oxidation in chemical hazard assessmentPROCESS SAFETY PROGRESS, Issue 1 2003Laurence G. Britton Flammability: The "net heat of oxidation" technique described in an earlier publication is extended to predicting the lower flammable limits, lower limit flame temperatures, and limiting oxygen concentrations of chlorinated organic fuels having H:Cl ratios greater than unity. A new Rule is derived for predicting the effect of initial temperature on the lower flammable limits and limiting oxygen concentrations of organic fuels. It is suggested that this Rule be used in preference to the modified "Burgess-Wheeler" Rule. The effect of initial pressure is discussed. Instability: Net heats of oxidation (kcal/mol oxygen) for a series of disparate fuel groups are compared with ",HD," the maximum heat of decomposition (cal/g) calculated using CHETAH methodology. Given the reasonable assumption that CHETAH's "maximum heat of decomposition" cannot exceed the net heat of combustion ",HC," examination is made as to whether the ratio of these parameters (each expressed in units of kcal/mol), coined the "Reaction Heat Ratio" (RH), provides a useful new indicator for instability assessment. Of these parameters, the net heat of oxidation (,HC/S) is the best indicator to help assign NFPA Instability Ratings. However, ,HC/S cannot generally be used to assign ratings for organo-peroxides. Also, its performance as an indicator for hazardous polymerization depends on the ,HC/S difference between the reacting monomer and the polymer product, so it should become increasingly unreliable as the monomer ,HC/S approaches -100 kcal/mol oxygen. The ranking method tacitly assumes organic polymers to have a constant heat of oxidation of about -100 kcal/mol oxygen. Errors in this assumption must invalidate the ranking approach where ,HC/S differences are small. Finally, separate "cut-offs" must be used at each NFPA Instability Rating for organo-nitrates versus other organics containing combinations of CHON atoms. Additional materials need to be examined to extend this preliminary analysis. The net heat of oxidation would be a useful additional output parameter of the CHETAH program, if only for its application in flammability assessment. No conclusions are drawn regarding the usefulness of net heat of oxidation or RH in conducting CHETAH hazard assessments, since this procedure requires consideration of several variables. However, the analysis may be helpful to the ASTM E 27.07 subcommittee responsible for developing the program. For example, the -,HD , 700 cal/g cut-off used to assign a "high" CHETAH hazard rating typically corresponds to organic materials rated NFPA 1, the second to lowest hazard rating. [source] | ||||||||||