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Zhihua Wang - One of the best experts on this subject based on the ideXlab platform.
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investigation of flame and burner plate interaction during the heat flux method used for laminar Burning Velocity measurement
Fuel, 2020Co-Authors: Zhihua Wang, Yong He, Shixing Wang, Ran JiAbstract:Abstract The heat flux method has been used widely for measuring the laminar Burning Velocity S L . However, compared with ideal S L definition of freely-propagating, stretch-less and adiabatic, the data obtained by the heat flux method is usually not perfectly freely-propagating due to the interaction between the flame and burner plate, which can affect the accuracy of the measurement. Though this issue has caught attention by some researchers, it hasn’t been evaluated extensively by experiments so far. To fill this gap, this study specially investigated four experimentally obtained factors: the measured Burning Velocity, the measurement sensitivity, the stand-off distance and the flame thickness. The experiments were carried out with methane + air flames at 1 atm and 298 K, equivalence ratio 0.7–1.5. By changing the burner plate temperature, the extent of flame and burner plate interaction can be well controlled. After series of assumption, deduction, and comparison with experiment results, a half-quantitative equation was proposed, and the Burning Velocity of stretch-less adiabatic freely-propagating flame was extrapolated from the non-freely propagating experiment results, which shows good agreement with literature data and simulation results. Besides, the uncertainty caused by not considering the flame and burner plate interaction was also evaluated.
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parametrization of the temperature dependence of laminar Burning Velocity for methane and ethane flames
Fuel, 2019Co-Authors: Xinlu Han, Shixing Wang, Zhihua Wang, Ronald Whiddon, Alexander A KonnovAbstract:Abstract The power exponent α in the temperature dependence of laminar Burning Velocity S L S L 0 = T u T u 0 α is usually considered an empirical parameter extracted from measurements performed at different temperatures. In this paper an analytical derivation of α is proposed, calculating the power exponent from the overall activation energy as: α T u 0 → T u = E a 2 R · X + x . This relation is verified against experimental Burning Velocity data measured with the heat flux method and chemical kinetic models for flames with equivalence ratios, Φ , from 0.6 to 1.6 at up to 368 K unburned gas temperature and 1 a t m . Both methane and ethane were used as fuel. Laminar Burning Velocity predictions at elevated temperatures are made using proposed relation and the resulting values are in good agreement with existing data for methane flames up to 500 K. This indicates that the proposed mathematical derivation of α is accurate. In addition to providing a reliable extrapolation of the Burning Velocity at varying temperatures, isolating the temperature dependence of the power exponent α enables more accurate quantification of other factors, e.g., Φ , the unburned gas temperature and pressure, that influence laminar Burning Velocity. Additionally, it provides a simple means to evaluate the overall activation energy, E a .
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effect of hydrogen addition on laminar Burning Velocity of ch4 dme mixtures by heat flux method and kinetic modeling
Fuel, 2018Co-Authors: Zhihua Wang, Shixing Wang, Xinlu Han, Ronald Whiddon, Kefa CenAbstract:Abstract Laminar Burning velocities were measured by the heat flux method for premixed methane dimethyl-ether mixtures (CH4/DME) with air, at various mixture fractions from 100% CH4 to 100% DME with hydrogen addition of 0%, 20% and 40%. Experiments were carried out at atmospheric pressure and room temperature within an equivalence ratio range between 0.6 and 1.7. Four chemical kinetic mechanisms specifically created for DME combustion were validated against measured laminar Burning Velocity data, with Zhao’s mechanism providing accurate prediction for both CH4 and DME. Decreasing the DME/CH4 ratio in the fuel decreased the laminar Burning Velocity but the decreasing pattern behaved differently in rich flames. Enhancement of the laminar Burning Velocity by hydrogen addition was greater for 100% CH4 fuel than for 100% DME by 20–60% depending on the equivalence ratio and showed a non-monotonic behavior in rich CH4/DME flames. Reaction path and sensitivity analyses point at the increasing importance of CH3 than H and OH in rich flames with H2 addition. A strong linear correlation was indicated between laminar Burning Velocity and maximum concentration of [H + OH + CH3] radicals. This result indicates the importance of the CH3 radical in promoting combustion at rich equivalence ratios which is the reason for the non-monotonic laminar Burning Velocity enhancement by hydrogen addition.
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effect of h2 co ratio and n2 co2 dilution rate on laminar Burning Velocity of syngas investigated by direct measurement and simulation
Fuel, 2015Co-Authors: Zhihua Wang, Wubin Weng, K F CenAbstract:Laminar Burning velocities of syngas/air premixed flames, varying with H2/CO ratio (from 5/95 to 75/25) and N2 or CO2 dilution rate (from 0% to 60%), were accurately measured using a Teflon coated Heat Flux burner and OH-PLIF based Bunsen flame method. Experiments were carried out at atmospheric pressure and room temperature, with fuel/air equivalence ratios ranging from fuel-lean to fuel-rich. Coupled with experimental data, three chemical kinetic mechanisms, namely GRI-Mech 3.0, USC Mech II and Davis H2–CO mechanism, were validated. All of them can provide good prediction for the laminar Burning Velocity. The laminar Burning Velocity variations with H2 and dilution gas contents were systematically investigated. For given dilution gas fraction, the laminar Burning Velocity reduction rate was enhanced as H2/CO ratio increasing. Effects of the syngas components and equivalence ratio variation on the concentrations of radical H and OH were also studied. It appears that there is a strong linear correlation between the laminar Burning Velocity and the maximum concentration of the H radical in the reaction zone for syngas. This characteristic is exclusively different from that in methane air premixed flame. These findings indicated that the high thermal diffusivity of the H radical played an important role in the laminar Burning Velocity enhancement and affected the laminar Burning Velocity reduction rate under dilution condition.
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effect of n 2 co2 dilution on laminar Burning Velocity of h 2 co o 2 oxy fuel premixed flame
International Journal of Hydrogen Energy, 2015Co-Authors: Wubin Weng, Zhihua Wang, Yong He, Ronald Whiddon, Yajun Zhou, Zhongshan LiAbstract:The dilution effect of N-2/CO2 on the laminar Burning Velocity of H-2-CO-O-2 mixtures was investigated. The dilution fraction of N-2 and CO2 in the unburned mixtures varied from 0% to 70% and 0%-50%, respectively, and H-2 content in H-2-CO fuels altered from 5% to 100%. All the studies were carried out at standard laboratory conditions (1 atm, 298 K) with equivalence ratio changing from 0.6 to 2.0. The Heat flux method and OH-PLIF (Planar Laser-Induced Fluorescence) based Bunsen flame method were employed to measure the laminar Burning velocities. The Li mechanism was used in simulations, due to its good prediction of laminar Burning velocities. Based on extensive experimental results, the correlations between dilution fraction and laminar Burning Velocity reduction rate were analyzed. It was found that, for a given dilution fraction, the reduction in laminar Burning Velocity is largely independent equivalence ratio and fuel H-2-CO mole fraction. This behavior does not extend to all fuels, e.g. methane. Exploiting the lack of dependence on equivalence ratio and fuel composition, a unified correlation equation was proposed which can be used to predict the laminar Burning velocities of H2CO fuels for given fuel component, dilution rate and equivalence ratio. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. (Less)
Alexander A Konnov - One of the best experts on this subject based on the ideXlab platform.
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parametrization of the temperature dependence of laminar Burning Velocity for methane and ethane flames
Fuel, 2019Co-Authors: Xinlu Han, Shixing Wang, Zhihua Wang, Ronald Whiddon, Alexander A KonnovAbstract:Abstract The power exponent α in the temperature dependence of laminar Burning Velocity S L S L 0 = T u T u 0 α is usually considered an empirical parameter extracted from measurements performed at different temperatures. In this paper an analytical derivation of α is proposed, calculating the power exponent from the overall activation energy as: α T u 0 → T u = E a 2 R · X + x . This relation is verified against experimental Burning Velocity data measured with the heat flux method and chemical kinetic models for flames with equivalence ratios, Φ , from 0.6 to 1.6 at up to 368 K unburned gas temperature and 1 a t m . Both methane and ethane were used as fuel. Laminar Burning Velocity predictions at elevated temperatures are made using proposed relation and the resulting values are in good agreement with existing data for methane flames up to 500 K. This indicates that the proposed mathematical derivation of α is accurate. In addition to providing a reliable extrapolation of the Burning Velocity at varying temperatures, isolating the temperature dependence of the power exponent α enables more accurate quantification of other factors, e.g., Φ , the unburned gas temperature and pressure, that influence laminar Burning Velocity. Additionally, it provides a simple means to evaluate the overall activation energy, E a .
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Laminar Burning Velocity of lean H2-CO mixtures at elevated pressure using the heat flux method
International Journal of Hydrogen Energy, 2014Co-Authors: M. Goswami, R.j.m. Bastiaans, Alexander A Konnov, Laurentius P H De GoeyAbstract:Laminar Burning Velocity measurements of 50:50 and 85:15% (by volume) H2-CO mixtures with O2-N2 and O2-He oxidizers were performed at lean conditions (equivalence ratio from 0.5 to 1) and elevated pressures (1 atm-9 atm). The heat flux method (HFM) is employed for determining the laminar Burning Velocity of the fuel-oxidizer mixtures. HFM creates a one-dimensional adiabatic stretchless flame which is an important prerequisite in defining the laminar Burning Velocity. This technique is based on balancing the heat loss from the flame to the burner with heat gain to the unburnt gas mixture, in a very simple way, such that no net heat loss to the burner is obtained. Instabilities are observed in lean H2-CO flames with nitrogen as the bath gas for pressures above 4 atm. Stable flames are obtained with helium as the bath gas for the entire pressure range. With the aim to cater stringent conditions for combustion systems such as gas turbines, an updated H2-CO kinetic mechanism is proposed and validated against experimental results. The scheme was updated with recent rate constants proposed in literature to suit both atmospheric and elevated pressures. The proposed kinetic model agrees with new experimental results. At conditions of high pressure and lean combustion, reactions H + O2 = OH + O and H + O2 (+M) = H2 (+M) compete the most when compared to other reactions. Reaction H + HO2 = OH + OH contributes to OH production, however, less at high-pressure conditions. At higher CO concentrations and leaner mixtures an important role of reaction CO + OH = CO2 + H is observed in the oxidation of CO. Copyright ?? 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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the effect of elevated pressures on the laminar Burning Velocity of methane air mixtures
Combustion and Flame, 2013Co-Authors: Mayuri M Goswami, Sander C R Derks, Kris K Coumans, Willemyn J Slikker, Marcelo H De Andrade Oliveira, Rob Bastiaans, C C M Luijten, Philipus L H De Goey, Alexander A KonnovAbstract:In spite of the large amount of research spent on the evaluation of the high pressure dependence of laminar Burning Velocity of methane + air flame, there still exists a large uncertainty in the data for various reasons. In order to reduce the scatter to acceptable levels, the Heat Flux Method (HFM), known as a potential method with high accuracy, has been extended to higher pressures. New measurements of the laminar Burning Velocity of methane + air flames are presented. Non-stretched planar flames were stabilized on a perforated plate burner which was placed in a high pressure environment. The experimental results are reported for a pressure range between 1 and 5 atm. The equivalence ratio was varied from 0.8 to 1.4. Comparisons with several recent literature sources (experiments) show good agreement. An exhaustive literature survey was performed to study the numerous existing laminar Burning Velocity correlations for its pressure dependence. It is indicated from the literature that many of the deduced correlations use stretched laminar Burning Velocity results. Many used only few data points for the pressure behavior and correlations and therefore show wide discrepancies. As the heat flux method furnishes quality results with reduced errors, the results were further utilized in deducing a power-law pressure dependence. Numerical simulations were also performed using two widely used chemical reaction mechanisms, which were further involved in comparing correlations. The proposed power exponent beta(1) shows a non-monotonic behavior at equivalence ratio around 1.4 in experiments and simulations. Through species and reaction flux analysis it was observed that CH3 consumption through various reactions remain pressure dependent and show non-monotonic behavior at equivalence ratio around 1.4. (c) 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved. (Less)
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temperature dependence of the laminar Burning Velocity of methanol flames
Energy & Fuels, 2012Co-Authors: Jeroen Vancoillie, Sebastian Verhelst, Moah Christensen, Elna Heimdal Nilsson, Alexander A KonnovAbstract:To better understand and predict the combustion behavior of methanol in engines, sound knowledge of the effect of the pressure, unburned mixture temperature, and composition on the laminar Burning Velocity is required. Because many of the existing experimental data for this property are compromised by the effects of flame stretch and instabilities, this study was aimed at obtaining new, accurate data for the laminar Burning Velocity of methanol air mixtures. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. The heat flux method was used to determine Burning velocities under conditions when the net heat loss from the flame to the burner is zero, Equivalence ratios and initial temperatures of the unburned mixture ranged from 0.7 to 1.5 and from 298 to 358 K, respectively. Uncertainties of the measurements were analyzed and assessed experimentally. The overall accuracy of the Burning velocities was estimated to be better than +/-1 cm/s. In lean conditions, the correspondence with recent literature data was very good, whereas for rich mixtures, the deviation was larger. The present study supports the higher Burning velocities at rich conditions, as predicted by several chemical kinetic mechanisms. The effects of the unburned mixture temperature on the laminar Burning Velocity of methanol were analyzed using the correlation u(L) = u(L0)(T-u/T-u0)(alpha). Several published expressions for the variation of the power exponent alpha with the equivalence ratio were compared against the present experimental results and calculations using a detailed oxidation kinetic model. Whereas most existing expressions assume a linear decrease of alpha with an increasing equivalence ratio, the modeling results produce a minimum in alpha for slightly rich mixtures. Experimental determination of alpha was only possible for lean to stoichiometric mixtures and a single data point at phi = 1.5. For these conditions, the measurement data agree with the modeling results. (Less)
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investigation of combustion enhancement by ozone additive in ch 4 air flames using direct laminar Burning Velocity measurements and kinetic simulations
Combustion and Flame, 2012Co-Authors: Zhihua Wang, Marcus Aldén, L Yang, Zhiwei Sun, Kefa Cen, Alexander A KonnovAbstract:The effect of ozone additive on the enhancement of the Burning Velocity for premixed methane-air flames is investigated by both experimental measurements and kinetic simulations. Laminar Burning velocities with and without O(3) were directly measured using the Heat Flux method. The O(3) molecules were introduced into the system by a dielectric-barrier-discharge ozone generator installed in the O(2) gas line, which provided prompt control of on/off of the O(3) feed into the system, enabling a precise comparison of the measured Burning Velocity with and without ozone additives. Noticeable Burning Velocity enhancement was observed at off-stoichiometric conditions rather than stoichiometric conditions. With 3730 ppm O(3) additive in the oxidizer, experimental data shows similar to 8% Burning Velocity increase in fuel-rich mixtures and similar to 3.5% Burning Velocity increase for the stoichiometric mixture. With 7000 ppm ozone additive in the oxidizer, maximum similar to 16% Burning Velocity increase was observed at fuel-lean conditions while similar to 9.0% was found at fuel-rich conditions. An O(3) kinetic mechanism involving 16 elementary reactions together with the GRI-Mech 3.0 was composed and validated through CHEMKIN calculations, which gives good predictions of the Burning velocities with and without O(3) additives. Extra O radicals contributed by O(3) molecules in the pre-heat zone initiate and accelerate the chain-branching reactions and consequently increase the Burning Velocity. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved. (Less)
M.r. Ravi - One of the best experts on this subject based on the ideXlab platform.
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effects of dilution with carbon dioxide on the laminar Burning Velocity and flame stability of h2 co mixtures at atmospheric condition
Combustion and Flame, 2012Co-Authors: Chockalingam Prathap, Anjan Ray, M.r. RaviAbstract:Abstract The objective of this investigation was to study the effect of dilution with CO 2 on the laminar Burning Velocity and flame stability of syngas fuel (50% H 2 –50% CO by volume). Constant pressure spherically expanding flames generated in a 40 l chamber were used for determining unstretched Burning Velocity. Experimental and numerical studies were carried out at 0.1 MPa, 302 ± 3 K and ϕ = 0.6–3.0 using fuel-diluent and mixture-diluent approaches. For H 2 –CO–CO 2 –O 2 –N 2 mixtures, the peak Burning Velocity shifts from ϕ = 2.0 for 0% CO 2 in fuel to ϕ = 1.6 for 30% CO 2 in fuel. For H 2 –CO–O 2 –CO 2 mixtures, the peak Burning Velocity occurred at ϕ = 1.0 unaffected by proportion of CO 2 in the mixture. If the mole fraction of combustibles in H 2 –CO–O 2 –CO 2 mixtures is less than 32%, then such mixtures are supporting unstable flames with respect to preferential diffusion. The analysis of measured unstretched laminar Burning velocities of H 2 –CO–O 2 –CO 2 and H 2 –CO–O 2 –N 2 mixtures suggested that CO 2 has a stronger inhibiting effect on the laminar Burning Velocity than nitrogen. The enhanced dilution effect of CO 2 could be due to the active participation of CO 2 in the chemical reactions through the following intermediate reaction CO + OH ↔ CO 2 + H.
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adiabatic Burning Velocity and cellular flame characteristics of h2 co co2 air mixtures
Combustion and Flame, 2011Co-Authors: Ratna V Kishore, M.r. RaviAbstract:Abstract The objective of this work was to study the effect of dilution with carbon dioxide on the adiabatic Burning Velocity of syngas fuel (with various H2/CO ratios)-air(21% O2–79% N2 by volume) mixtures along with detailed understanding of cellular flame structures. Heat flux method with a setup similar to that of de Goey and co-workers [1] was used for measurement of Burning velocities. Validation experiments were done for H2 (5%)–CO (95%)–air and H2 (5%)–CO (45%)–CO2 (50%)–air mixtures at various equivalence ratios and the results were in good agreement with published data in the literature. The mixtures considered in this work had 1:4, 1:1 and 4:1 H2/CO ratio in the fuel and 40%, 50% and 60% CO2 dilution. The Burning Velocity increased significantly with the increase in H2 content in mixture of H2–CO with fixed CO2 dilution. The Burning Velocity reduced remarkably with carbon dioxide dilution in H2–CO mixture due to reduction in heat release, flame temperature and thermal diffusivity of the mixture. The location of peak adiabatic Burning Velocity shifted from ϕ = 1.6 for 40% CO2 to ϕ = 1.2 for 60% CO2, whereas it remained unchanged with variation of H2:CO ratio (4:1, 1:1 and 1:4) at a given CO2 dilution. A comparison of experiments and simulations indicated that the Davis et al. [2] mechanism predicted Burning velocities well for the most of experimental operating conditions except for rich conditions. For some lean mixtures, flames exhibited cellular structures. In order to explain the structures and generate profiles of various field variables of interest, computations of three dimensional porous burner stabilized cellular flames were performed using commercial CFD software FLUENT. Simulations for lean H2 (25%)–CO (25%)–CO2 (50%)–air mixtures (ϕ = 0.6 and 0.8) produced cellular flame structures very similar to those observed in the experiments. It was found that the in the core region of a typical cell, stretch rate was positive, the volumetric heat release rate was high and the net reaction rate for the reaction O + H2 ⇄ H + OH and the net consumption rate of H2 were both high.
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adiabatic Burning Velocity and cellular flame characteristics of h2 co co2 air mixtures
Combustion and Flame, 2011Co-Authors: Ratna V Kishore, M.r. Ravi, Anjan RayAbstract:Abstract The objective of this work was to study the effect of dilution with carbon dioxide on the adiabatic Burning Velocity of syngas fuel (with various H2/CO ratios)-air(21% O2–79% N2 by volume) mixtures along with detailed understanding of cellular flame structures. Heat flux method with a setup similar to that of de Goey and co-workers [1] was used for measurement of Burning velocities. Validation experiments were done for H2 (5%)–CO (95%)–air and H2 (5%)–CO (45%)–CO2 (50%)–air mixtures at various equivalence ratios and the results were in good agreement with published data in the literature. The mixtures considered in this work had 1:4, 1:1 and 4:1 H2/CO ratio in the fuel and 40%, 50% and 60% CO2 dilution. The Burning Velocity increased significantly with the increase in H2 content in mixture of H2–CO with fixed CO2 dilution. The Burning Velocity reduced remarkably with carbon dioxide dilution in H2–CO mixture due to reduction in heat release, flame temperature and thermal diffusivity of the mixture. The location of peak adiabatic Burning Velocity shifted from ϕ = 1.6 for 40% CO2 to ϕ = 1.2 for 60% CO2, whereas it remained unchanged with variation of H2:CO ratio (4:1, 1:1 and 1:4) at a given CO2 dilution. A comparison of experiments and simulations indicated that the Davis et al. [2] mechanism predicted Burning velocities well for the most of experimental operating conditions except for rich conditions. For some lean mixtures, flames exhibited cellular structures. In order to explain the structures and generate profiles of various field variables of interest, computations of three dimensional porous burner stabilized cellular flames were performed using commercial CFD software FLUENT. Simulations for lean H2 (25%)–CO (25%)–CO2 (50%)–air mixtures (ϕ = 0.6 and 0.8) produced cellular flame structures very similar to those observed in the experiments. It was found that the in the core region of a typical cell, stretch rate was positive, the volumetric heat release rate was high and the net reaction rate for the reaction O + H2 ⇄ H + OH and the net consumption rate of H2 were both high.
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adiabatic Burning Velocity of h2 o2 mixtures diluted with co2 n2 ar
International Journal of Hydrogen Energy, 2009Co-Authors: Ratna V Kishore, Anjan Ray, Ringkhang Muchahary, M.r. RaviAbstract:Abstract Global warming due to CO 2 emissions has led to the projection of hydrogen as an important fuel for future. A lot of research has been going on to design combustion appliances for hydrogen as fuel. This has necessitated fundamental research on combustion characteristics of hydrogen fuel. In this work, a combination of experiments and computational simulations was employed to study the effects of diluents (CO 2 , N 2 , and Ar) on the laminar Burning Velocity of premixed hydrogen/oxygen flames using the heat flux method. The experiments were conducted to measure laminar Burning Velocity for a range of equivalence ratios at atmospheric pressure and temperature (300 K) with reactant mixtures containing varying concentrations of CO 2 , N 2 , and Ar as diluents. Measured Burning velocities were compared with computed results obtained from one-dimensional laminar premixed flame code PREMIX with detailed chemical kinetics and good agreement was obtained. The effectiveness of diluents in reduction of laminar Burning Velocity for a given diluent concentration is in the increasing order of argon, nitrogen, carbon dioxide. This may be due to increased capabilities either to quench the reaction zone by increased specific heat or due to reduced transport rates. The lean and stoichiometric H 2 /O 2 /CO 2 flames with 65% CO 2 dilution exhibited cellular flame structures. Detailed three-dimensional simulation was performed to understand lean H 2 /O 2 /CO 2 cellular flame structure and cell count from computed flame matched well with the experimental cellular flame.
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investigation of nitrogen dilution effects on the laminar Burning Velocity and flame stability of syngas fuel at atmospheric condition
Combustion and Flame, 2008Co-Authors: Chockalingam Prathap, Anjan Ray, M.r. RaviAbstract:Abstract The objective of this investigation was to study the effect of dilution with nitrogen on the laminar Burning Velocity and flame stability of syngas fuel (50% H 2 –50% CO by volume)–air (21% O 2 –79% N 2 by volume) mixtures. The syngas fuel composition considered in this work comprised x % N 2 by volume and ( 100 − x )% an equimolar mixture of CO and H 2 . The proportion x (i.e., %N 2 ) was varied from 0 to 60% while the H 2 /CO ratio was always kept as unity. Spherically expanding flames were generated by centrally igniting homogeneous fuel–air gas mixtures in a 40-L cylindrical combustion chamber fitted with optical windows. Shadowgraphy technique with a high-speed imaging camera was used to record the propagating spherical flames. Unstretched Burning Velocity was calculated following the Karlovitz theory for weakly stretched flames. Also, Markstein length was calculated to investigate the flame stability conditions for the fuel–air mixtures under consideration. Experiments were conducted for syngas fuel with different nitrogen proportions (0–60%) at 0.1 MPa (absolute), 302 ± 3 K , and equivalence ratios ranging from 0.6 to 3.5. All the measurements were compared with the numerical predictions obtained using RUN-1DL and PREMIX with a contemporary chemical kinetic scheme. Dilution with nitrogen in different proportions in syngas resulted in (a) decrease in laminar Burning Velocity due to reduction in heat release and increase in heat capacity of unburned gas mixture and hence the flame temperature, (b) shift in occurrence of peak laminar Burning Velocity from ϕ = 2.0 for 0% N 2 dilution to ϕ = 1.4 for 60% N 2 dilution, (c) augmentation of the coupled effect of flame stretch and preferential diffusion on laminar Burning Velocity, and d) shift in the equivalence ratio for transition from stable to unstable flames from ϕ = 0.6 for 0% N 2 dilution to ϕ = 1.0 for 60% N 2 dilution. The present work also indicated that if the fuel mole fraction in the wide range of fuel–air mixtures investigated is less than 22%, then those fuel mixtures are in the unstable regime with regard to preferential diffusion.
Hideaki Kobayashi - One of the best experts on this subject based on the ideXlab platform.
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turbulent Burning Velocity of ammonia oxygen nitrogen premixed flame in o2 enriched air condition
Fuel, 2020Co-Authors: Genya Hashimoto, Khalid Hadi, Nozomu Hashimoto, Akihiro Hayakawa, Hideaki Kobayashi, Osamu FujitaAbstract:Abstract Ammonia is a promising hydrogen-energy carrier as well as a carbon-free fuel. However, turbulent Burning behavior of ammonia flame had yet to be sufficiently studied. In this work, laminar and turbulent Burning velocities of ammonia/oxygen/nitrogen flames were investigated under the condition of oxygen enrichment. The turbulent Burning Velocity of ammonia/oxygen/nitrogen mixtures was found to increase with increasing turbulence intensity. The ratio of the turbulent Burning Velocity to stretched laminar Burning Velocity, Utr/UN, increased with the turbulence Karlovitz number. However, because of the diffusional–thermal instability effect, given the same turbulent Karlovitz numbers, Utr/UN in ammonia-lean cases is larger than in ammonia-rich cases. These findings indicate that consideration of the effects of diffusional–thermal instability and of the turbulence is important for the prediction of turbulent flame propagation Velocity in ammonia combustion fields.
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Burning Velocity and flame structure of ch4 nh3 air turbulent premixed flames at high pressure
International Journal of Hydrogen Energy, 2019Co-Authors: Akinori Ichikawa, Akihiro Hayakawa, Yuji Naito, Taku Kudo, Hideaki KobayashiAbstract:Abstract Ammonia is one of the most promising alternative fuels. In particular, ammonia combustion for gas turbine combustors for power generation is expected. To shift the fuel for a gas turbine combustor to ammonia step-by-step, the partial replacement of natural gas by ammonia is considered. To reveal the turbulent combustion characteristics, CH4/NH3/air turbulent premixed flame at 0.5 MPa was experimentally investigated. The ammonia ratio based on the mole fraction and lower heating value was varied from 0 to 0.2. The results showed that the ratio of the turbulent Burning Velocity and unstretched laminar Burning Velocity decreased with an increase in the ammonia ratio. The reason for this variation is that the flame area decreased with an increase in the ammonia ratio as the flame surface density decreased and the fractal inner cutoff increased. The volume fractions in the turbulent flame region were almost the same with ammonia addition, indicating that combustion oscillation can be handled in a manner similar to that for the case of natural gas for CH4/NH3/air flames.
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experimental and numerical study of the laminar Burning Velocity of ch4 nh3 air premixed flames
Combustion and Flame, 2018Co-Authors: Ekenechukwu C Okafor, Akihiro Hayakawa, Akinori Ichikawa, Yuji Naito, Taku Kudo, Sophie Colson, Hideaki KobayashiAbstract:Abstract With the renewed interest in ammonia as a carbon-neutral fuel, mixtures of ammonia and methane are also being considered as fuel. In order to develop gas turbine combustors for the fuels, development of reaction mechanisms that accurately model the Burning Velocity and emissions from the flames is important. In this study, the laminar Burning Velocity of premixed methane–ammonia–air mixtures were studied experimentally and numerically over a wide range of equivalence ratios and ammonia concentrations. Ammonia concentration in the fuel, expressed in terms of the heat fraction of NH3 in the fuel, was varied from 0 to 0.3 while the equivalence ratio was varied from 0.8 to 1.3. The experiments were conducted using a constant volume chamber, at 298 K and 0.10 MPa. The Burning Velocity decreased with an increase in ammonia concentration. The numerical results showed that the kinetic mechanism by Tian et al. largely underestimates the unstretched laminar Burning Velocity owing mainly to the dominance of HCO (+H, OH, O2) = CO (+H2, H2O, HO2) over HCO = CO + H in the conversion of HCO to CO. GRI Mech 3.0 predicts the Burning Velocity of the mixture closely however some reactions relevant to the Burning Velocity and NO reduction in methane–ammonia flames are missing in the mechanism. A detailed reaction mechanism was developed based on GRI Mech 3.0 and the mechanism by Tian et al. and validated with the experimental results. The temperature and species profiles computed with the present model agree with that of GRI Mech 3.0 for methane–air flames. On the other hand, the NO profile computed with the present model agrees with Tian et al.’s mechanism for methane–ammonia flames with high ammonia concentration. Furthermore, the burned gas Markstein length was measured and was found to increase with equivalence ratio and ammonia concentration.
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laminar Burning Velocity and markstein length of ammonia air premixed flames at various pressures
Fuel, 2015Co-Authors: Akihiro Hayakawa, Taku Kudo, Takashi Goto, Rentaro Mimoto, Yoshiyuki Arakawa, Hideaki KobayashiAbstract:Abstract Ammonia is expected to be useful not only as a hydrogen-energy carrier but also as a carbon-free fuel. In order to design an ammonia fueled combustor, fundamental flame characteristics of ammonia must be understood. However, knowledge of the characteristics of ammonia/air flames, especially at the high pressures, has been insufficient. In this study, the unstretched laminar Burning Velocity and the Markstein length of ammonia/air premixed flames at various pressures up to 0.5 MPa were experimentally clarified for the first time. Spherically propagating premixed flames, which propagate in a constant volume combustion chamber, were observed using high-speed schlieren photography. Results indicate that the maximum value of unstretched laminar Burning velocities is less than 7 cm/s within the examined conditions and is lower than those of hydrocarbon flames. The unstretched laminar Burning Velocity decreases with the increase in the initial mixture pressure, tendency being the same as that of hydrocarbon flames. The burned gas Markstein length increases with the increase in the equivalence ratio, the tendency being the same as that of hydrogen/air flames and methane/air flames. The burned gas Markstein lengths at 0.1 MPa are higher than those at 0.3 MPa and 0.5 MPa. However, the values of burned gas Markstein length at 0.3 MPa and 0.5 MPa are almost the same. In addition, numerical simulations using CHEMKIN-PRO with five detailed reaction mechanisms which are presently applicable for the ammonia/air combustion were also conducted. However, qualitative predictions of unstretched laminar Burning Velocity using those reaction mechanisms are inaccurate. Thus, further improvements of reaction mechanisms are essential for application of ammonia/air premixed flames.
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laminar Burning Velocity and markstein length of ammonia hydrogen air premixed flames at elevated pressures
International Journal of Hydrogen Energy, 2015Co-Authors: Akinori Ichikawa, Akihiro Hayakawa, Taku Kudo, Yuichi Kitagawa, K Kunkuma D A Somarathne, Hideaki KobayashiAbstract:Abstract Ammonia shows promise not only as a hydrogen-energy carrier but also as a carbon-free fuel. However, combustion intensity of ammonia must be improved to enable its application to practical combustors. In order to achieve this, hydrogen-added ammonia/air flames were experimentally and numerically investigated at elevated pressures up to 0.5 MPa. The hydrogen ratio, which is defined as the hydrogen concentration in the fuel mixture, was varied from 0 to 1.0. The unstretched laminar Burning Velocity and Markstein length of spherically propagating laminar flames were experimentally evaluated. The results showed that, unstretched laminar Burning Velocity increases non-linearly with an increase in the hydrogen ratio. The Markstein length varies non-monotonically with an increase in the hydrogen ratio. The unstretched laminar Burning Velocity, and the Markstein length decrease with an increase in the initial mixture pressure. Although the decrease in the Markstein length is larger when the initial mixture pressure increases from 0.1 to 0.3 MPa, the values of Markstein lengths at 0.5 MPa are almost the same as those at 0.3 MPa.
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effects of co2 n2 dilution on laminar Burning Velocity of stoichiometric dme air mixture at elevated temperatures
Journal of Hazardous Materials, 2017Co-Authors: Abdul Naseer Mohammed, Khalid A Juhany, Sudarshan Kumar, Ratna V Kishore, Akram MohammadAbstract:Abstract The laminar Burning Velocity of CO2/N2 diluted stoichiometric dimethyl ether (DME) air mixtures is determined experimentally at atmospheric pressure and elevated mixture temperatures using a mesoscale high aspect-ratio diverging channel with inlet dimensions of 25 mm × 2 mm. In this method, planar flames at different initial temperatures (Tu) were stabilized inside the channel using an external electric heater. The magnitude of Burning velocities was acquired by measuring the flame position and initial temperature. The mass conservation of the mixture entering the inlet and the stationary planar flame front is applied to obtain the laminar Burning Velocity. Laminar Burning Velocity at different initial mixture temperatures is plotted with temperature ratio ( T u / T u , o ) , where a reference temperature (Tu,o) of 300 K is used. Enhancement in the laminar Burning Velocity is observed with mixture temperature for DME-air mixtures with CO2 and N2 dilutions. A significant decrease in the Burning Velocity and slight increase in temperature exponent of the stoichiometric DME-air mixture was observed with dilution at same temperatures. The addition of CO2 has profound influence when compared to N2 addition on both Burning Velocity and temperature exponent.
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effect of n2 co2 dilution on laminar Burning Velocity of h2 air mixtures at high temperatures
International Journal of Hydrogen Energy, 2013Co-Authors: Santosh Kumar Paidi, Mohammad Akram, Amrutha Bhavaraju, Sudarshan KumarAbstract:Abstract The laminar Burning velocities of H2–air mixtures diluted with N2 or CO2 gas at high temperatures were obtained from planar flames observed in externally heated diverging channels. Experiments were conducted for an equivalence ratio range of 0.8–1.3 and temperature range of 350–600 K with various dilution rates. In addition, computational predictions for Burning velocities and their comparison with experimental results and detailed flame structures have been presented. Sensitivity analysis was carried out to identify important reactions and their contribution to the laminar Burning Velocity. The computational predictions are in reasonably good agreement with the present experimental data (especially for N2 dilution case). The Burning Velocity maxima was observed for slightly rich mixtures and this maxima was found to shift to higher equivalence ratios (Ф) with a decrease in the dilution. The effect of CO2 dilution was more profound than N2 dilution in reducing the Burning Velocity of mixtures at higher temperatures.
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laminar Burning Velocity of methane air mixtures at elevated temperatures
Energy & Fuels, 2013Co-Authors: Mohammad Akram, Priyank Saxena, Sudarshan KumarAbstract:The measured and computed laminar Burning velocities of methane–air mixtures at higher mixture temperatures are reported in this paper. The experiments and computations were performed for a wide range of mixture temperatures and equivalence ratios. The unburned mixture temperature ranges from 370 to 650 K. Computational predictions of Burning velocities were carried out with GRI-Mech 3.0, San Diego mechanism, and Konnov mechanism for methane–air mixtures. The measured Burning velocities match very well with the numerical predictions for all mixture temperatures and existing experimental results for mixtures at ambient temperature. Another contribution of the present work is the variation of the measured power-law temperature exponent with mixture equivalence ratios. The maximum Burning Velocity (even at high mixture temperatures) and minimum temperature exponent magnitudes were observed to exist for slightly richer mixtures.
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laminar Burning Velocity of propane co2 n2 air mixtures at elevated temperatures
Energy & Fuels, 2012Co-Authors: Mohammad Akram, Ratna V Kishore, Sudarshan KumarAbstract:The laminar Burning Velocity of pure and diluted high-temperature propane–air mixtures is extracted from the planar flames stabilized in the preheated mesoscale diverging channel. The experiments w...
