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Zheng Chen - One of the best experts on this subject based on the ideXlab platform.
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effects of pressure rise rate on laminar Flame Speed under normal and engine relevant conditions
Combustion Theory and Modelling, 2020Co-Authors: Yiqing Wang, Jagannath Jayachandran, Zheng ChenAbstract:Laminar Flame Speed (LFS) is one of the most important physicochemical properties of a combustible mixture. At normal and elevated temperatures and pressures, LFS can be measured using propagating ...
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effects of radiation absorption on spherical Flame propagation and radiation induced uncertainty in laminar Flame Speed measurement
Proceedings of the Combustion Institute, 2017Co-Authors: Zheng ChenAbstract:Abstract Outwardly propagating spherical Flames are popularly used to measure the laminar Flame Speed, especially for high pressure conditions. Since radiation always exists in spherical Flame experiments, the accuracy of laminar Flame Speed measurement is inherently affected by radiation. In this study, the radiation-induced uncertainty in laminar Flame Speed measurement was investigated numerically. We focused on CO 2 diluted mixtures in which the radiation absorption effects are important. The outwardly propagating spherical Flames of different CO 2 diluted mixtures at a broad range of pressure up to 25 atm were simulated. Different fuels (hydrogen, methane, dimethyl ether and iso-octane) with different amounts of CO 2 dilution were considered and detailed chemistry was included in simulation. Two radiation models were used: one is the optically thin model considering only radiation emission and the other is the statistical narrow band model considering both radiation emission and absorption. The effects of radiation absorption on spherical Flame propagation and radiation-induced uncertainty in laminar Flame Speed measurement were quantified through comparison among results predicted by these two radiation models. It was found that for CO 2 diluted mixtures, radiation absorption has great impact on spherical Flame propagation: it greatly reduces the radiation-induced thermal and flow effects. The influence of radiation absorption was show to be stronger at higher pressure. When only radiation emission is considered and radiation absorption is neglected, the radiation-induced uncertainty in laminar Flame Speed measurement is substantially over-predicted for CO 2 diluted mixtures. When radiation absorption is included, the radiation-induced uncertainty in laminar Flame Speed measurement is nearly negligible (within 2.5%) for all the CO 2 diluted mixtures considered in this study.
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The constant-volume propagating spherical Flame method for laminar Flame Speed measurement
Science Bulletin, 2016Co-Authors: Faghih, Zheng ChenAbstract:Laminar Flame Speed is one of the most important intrinsic properties of a combustible mixture. Due to its importance, different methods have been developed to measure the laminar Flame Speed. This paper reviews the constant-volume propagating spherical Flame method for laminar Flame Speed measurement. This method can be used to measure laminar Flame Speed at high pressures and temperatures which are close to engine-relevant conditions. First, the propagating spherical Flame method is introduced and the constant-volume method (CVM) and constant-pressure method (CPM) are compared. Then, main groups using the constant-volume propagating spherical Flame method are introduced and large discrepancies in laminar Flame Speeds measured by different groups for the same mixture are identified. The sources of discrepancies in laminar Flame Speed measured by CVM are discussed and special attention is devoted to the error encountered in data processing. Different correlations among burned mass fraction, pressure, temperature and Flame Speed, which are used by different researchers to obtain laminar Flame Speed, are summarized. The performance of these correlations are examined, based on which recommendations are given. Finally, recommendations for future studies on the constant-volume propagating spherical Flame method for laminar Flame Speed measurement are presented.
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effects of radiation on the uncertainty of Flame Speed determination using spherically propagating Flames with co co2 h2o dilutions at elevated pressures
International Journal of Heat and Mass Transfer, 2015Co-Authors: Chae Hoon Sohn, Zheng ChenAbstract:Abstract This work investigates numerically the effects of spectral dependent radiation on laminar Flame Speed determination using spherically propagating CH4/air and H2/air Flames with CO/CO2/H2O dilutions at elevated pressures. Three different models, adiabatic, optically thin radiation, and fitted statistically narrow band correlated k (FSNB-CK) models, are employed. The effects of radiation-induced negative burned gas velocity, increased density ratio, and chamber confinement induced flow compression are investigated. It is found that compared to the FSNB-CK model, the adiabatic Flame model over-predicts the Flame Speed by 7% and the optically thin model makes more significant under-prediction. Moreover, this discrepancy increases with pressure. The results also show that a large negative velocity in the burned gas is induced by radiative heat loss and magnified further by the flow compression in a small combustion chamber. The radiation-induced negative burned gas velocity causes an under-estimation of Flame Speed. Moreover, radiation also increases the density ratio between the burned and the unburned gases. The use of the density ratio of adiabatic Flame also causes under-prediction of Flame Speed. Two radiation corrections taking into account of the negative burned gas velocity and the increased density ratio are recommended for Flame Speed determination using propagating spherical Flame for radiative mixtures. The corrections proposed in this study reduce the uncertainty of Flame Speed due to radiation.
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Effects of radiation on the uncertainty of Flame Speed determination using spherically propagating Flames with CO/CO2/H2O dilutions at elevated pressures
International Journal of Heat and Mass Transfer, 2015Co-Authors: Chae Hoon Sohn, Zheng ChenAbstract:Abstract This work investigates numerically the effects of spectral dependent radiation on laminar Flame Speed determination using spherically propagating CH4/air and H2/air Flames with CO/CO2/H2O dilutions at elevated pressures. Three different models, adiabatic, optically thin radiation, and fitted statistically narrow band correlated k (FSNB-CK) models, are employed. The effects of radiation-induced negative burned gas velocity, increased density ratio, and chamber confinement induced flow compression are investigated. It is found that compared to the FSNB-CK model, the adiabatic Flame model over-predicts the Flame Speed by 7% and the optically thin model makes more significant under-prediction. Moreover, this discrepancy increases with pressure. The results also show that a large negative velocity in the burned gas is induced by radiative heat loss and magnified further by the flow compression in a small combustion chamber. The radiation-induced negative burned gas velocity causes an under-estimation of Flame Speed. Moreover, radiation also increases the density ratio between the burned and the unburned gases. The use of the density ratio of adiabatic Flame also causes under-prediction of Flame Speed. Two radiation corrections taking into account of the negative burned gas velocity and the increased density ratio are recommended for Flame Speed determination using propagating spherical Flame for radiative mixtures. The corrections proposed in this study reduce the uncertainty of Flame Speed due to radiation.
Frederic Grisch - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation of laminar Flame Speed measurement for kerosene fuels: Jet A-1, surrogate fuel and its pure components
Energy & Fuels, 2018Co-Authors: Vincent Modica, Frederic GrischAbstract:The present work investigated the laminar Flame Speed measurement of kerosene-relevant fuel, including Jet A-1 commercial kerosene, and surrogate kerosene fuel and its pure components ( n -decane, n -propyl benzene, and propyl cyclohexane) using a high-pressure Bunsen Flame burner. The OH* chemiluminescence technique and the kerosene-PLIF technique were used for Flame contours detection in order to calculate the laminar Flame Speed. The experiments were first conducted for n -decane/air Flame at T = 400 K, φ = 0.6–1.3, and atmospheric pressure conditions in order to validate the whole experimental system and measurement methodology. The laminar Flame Speed of Jet A-1/air, surrogate/air, and pure kerosene component ( n -decane, n -propyl benzene, and propyl cyclohexane) was then measured under large operating conditions, including temperature T = 400–473 K, pressure P = 0.1–1.0 MPa, and equivalence ratio φ = 0.7–1.3. It was found that these three pure components of kerosene have very similar laminar Flame Speed. By comparing the experimental results of surrogate kerosene and Jet A-1 commercial kerosene, it was observed that the proposed surrogate kerosene, i.e., mixtures of 76.7 wt % n -decane, 13.2 wt % n -propyl benzene, and 10.1 wt % propyl cyclohexane, can appropriately reproduce the Flame Speed property of Jet A-1 commercial kerosene fuel. The experimental results were further compared with simulation results using a skeletal kerosene mechanism.
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laminar Flame Speed of lignocellulosic biomass derived oxygenates and blends of gasoline oxygenates
Fuel, 2017Co-Authors: Bjorn Rossow, Vincent Modica, Frederic GrischAbstract:Oxygenates present in partially hydro processed lignocellulosic-biomass pyrolysis oil to be component of second generation bio-fuels have been examined for their compact on the laminar Flame Speed of gasoline. Experiments were performed in an elevated pressure combustion vessel designed around a concept of a premixed Bunsen Flame. Laminar Flame Speed measurements were firstly conducted for neat oxygenate fuel (anisole, 4-methylanisole and ethylvalerate)/N-2/O-2 mixtures at conditions T = 423 K, P = 0.1 MPa and phi = 0.6-1.3. It has been observed that anisole has a higher Flame Speed compared to 4-methylanisole and ethylvalerate. Meanwhile, very similar values of Flame Speeds have been obtained for 4-mythlanisole and ethylvalerate fuels. To learn the potential effect of these oxygenates present in biofuels acting as drop-in additives on the petroleum-based gasoline fuel, a five components surrogate gasoline fuel (hexane, 2,3-dimethyl-2-butene, cyclohexane, isooctane, and toluene) was then proposed and validated by comparing its laminar Flame Speed with commercial gasoline. Laminar Flame Speeds measurements were finally performed for the blends mixed by the proposed surrogate gasoline and different percentage of oxygenates over a large working condition range including T = 400-473 K, phi = 0.61.3 and P = 0.1-0.8 MPa. The influence of studied oxygenates as additives on gasoline has been found to be negligible for values up to 10% (wt) which is insensitive to the variation of pressure and temperature. (C) 2017 Elsevier Ltd. All rights reserved.
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Laminar Flame Speed of lignocellulosic biomass-derived oxygenates and blends of gasoline/oxygenates
Fuel, 2017Co-Authors: Bjorn Rossow, Vincent Modica, Frederic GrischAbstract:Oxygenates present in partially hydro processed lignocellulosic-biomass pyrolysis oil to be component of second generation bio-fuels have been examined for their compact on the laminar Flame Speed of gasoline. Experiments were performed in an elevated pressure combustion vessel designed around a concept of a premixed Bunsen Flame. Laminar Flame Speed measurements were firstly conducted for neat oxygenate fuel (anisole, 4-methylanisole and ethylvalerate)/N-2/O-2 mixtures at conditions T = 423 K, P = 0.1 MPa and phi = 0.6-1.3. It has been observed that anisole has a higher Flame Speed compared to 4-methylanisole and ethylvalerate. Meanwhile, very similar values of Flame Speeds have been obtained for 4-mythlanisole and ethylvalerate fuels. To learn the potential effect of these oxygenates present in biofuels acting as drop-in additives on the petroleum-based gasoline fuel, a five components surrogate gasoline fuel (hexane, 2,3-dimethyl-2-butene, cyclohexane, isooctane, and toluene) was then proposed and validated by comparing its laminar Flame Speed with commercial gasoline. Laminar Flame Speeds measurements were finally performed for the blends mixed by the proposed surrogate gasoline and different percentage of oxygenates over a large working condition range including T = 400-473 K, phi = 0.61.3 and P = 0.1-0.8 MPa. The influence of studied oxygenates as additives on gasoline has been found to be negligible for values up to 10% (wt) which is insensitive to the variation of pressure and temperature. (C) 2017 Elsevier Ltd. All rights reserved.
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effects of pressure and preheating temperature on the laminar Flame Speed of methane air and acetone air mixtures
Fuel, 2016Co-Authors: Yi Wu, Vincent Modica, Bjorn Rossow, Frederic GrischAbstract:Abstract Laminar Flame Speeds of acetone/air mixtures have been investigated at elevated temperature and high pressure conditions in regards to the importance of this intermediate oxygenated molecule in hydrocarbon oxidation. Experiments were performed in an elevated pressure combustion vessel specifically designed around a concept of a premixed Bunsen Flame. In a first step, measurements of the laminar Flame Speed of gaseous CH4/air mixtures were performed with OH chemiluminescence and OH-PLIF methodologies and compared with literature data in order to validate the experimental setup. The effects of the preheating temperature (373–523 K), pressure (0.1–1.0 MPa) and equivalence ratio (0.6–1.3) on the laminar Flame Speed of acetone/air mixtures were then examined. The experiments were finally complemented and compared with numerical simulations conducted with Cosilab commercial software package using published detailed chemical kinetic mechanisms for proposing a correlation relationship of the acetone/air laminar Flame Speed with pressure, temperature and equivalence ratio.
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Effects of pressure and preheating temperature on the laminar Flame Speed of methane/air and acetone/air mixtures
Fuel, 2016Co-Authors: Vincent Modica, Bjorn Rossow, Frederic GrischAbstract:Laminar Flame Speeds of acetone/air mixtures have been investigated at elevated temperature and high pressure conditions in regards to the importance of this intermediate oxygenated molecule in hydrocarbon oxidation. Experiments were performed in an elevated pressure combustion vessel specifically designed around a concept of a premixed Bunsen Flame. In a first step, measurements of the laminar Flame Speed of gaseous CH4/air mixtures were performed with OH center dot chemiluminescence and OH-PLIF methodologies and compared with literature data in order to validate the experimental setup. The effects of the preheating temperature (373-523 K), pressure (0.1-1.0 MPa) and equivalence ratio (0.6-1.3) on the laminar Flame Speed of acetone/air mixtures were then examined. The experiments were finally complemented and compared with numerical simulations conducted with Cosilab commercial software package using published detailed chemical kinetic mechanisms for proposing a correlation relationship of the acetone/air laminar Flame Speed with pressure, temperature and equivalence ratio. (C) 2016 Elsevier Ltd. All rights reserved.
Satoru Ishizuka - One of the best experts on this subject based on the ideXlab platform.
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Further investigation on the enhancement of Flame Speed in vortex ring combustion
Proceedings of the Combustion Institute, 2013Co-Authors: Satoru Ishizuka, Toshiyuki Yamashita, Daisuke ShimokuriAbstract:Abstract Enhancement of Flame Speed in vortex ring combustion has been investigated experimentally. The Flame Speed and the maximum tangential velocity for each vortex ring were simultaneously measured with a PIV system and a high Speed camera. To vary the extent of the enhancement, methane/hydrogen mixtures were used. Furthermore, rich mixtures were used as a source of vortex ring so that the situation of the experiment and the results could be applied more directly to practical use. Results have confirmed that enhancement of Flame Speed does occur in vortex ring combustion of rich methane/hydrogen mixtures in air. The extent of the enhancement becomes larger as the hydrogen content is increased. The Flame Speed reaches about twice as high as the maximum tangential velocity for pure hydrogen. Based on momentum conservation across the Flame, a simple equation on the ratio of the Flame Speed to the maximum tangential velocity has been obtained, which has shown that the Flame Speed enhancement can be explained successfully by considering the spherically expanding type premixed combustion behind the Flame. The pressure rise of a spherically expanding type premixed Flame can explain the Flame Speed enhancement observed in the present rich methane/hydrogen vortex ring combustion.
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Enhancement of Flame Speed in vortex rings of rich hydrogen/air mixtures in air
Proceedings of the Combustion Institute, 2000Co-Authors: Satoru Ishizuka, Kiminori Koumura, Ryo HasegawaAbstract:Using a laser Doppler velocimetry, relationships between the Flame Speed, V f , and the maximum tangential velocity, V θmax , in vortex ring combustion of hydrogen/air mixtures have been rigorously obtained. Results in the air atmosphere show that the slopes in the V f − V θmax , plane are almost unity for lean mixtures, whereas the slope increases, contrary to the vortex bursting theory, with an increase in the equivalence ratio for rich mixtures. The Flame Speeds for lean mixtures are in good agreement with the back-pressure drive Flame propagation theory, whereas the Flame Speeds for rich mixtures become much higher than the values given by the back-pressure drive Flame propagation theory and approach the predictions of the vortex bursting theory. To clarify the basic cause of the enhancement of Flame Speed, further measurements have been made in a nitrogen atmosphere. Results show that the Flame Speeds for rich mixtures are lowered and they are in good agreement with the back-pressure drive Flame propagation theory. Thus, it is confirmed that the enhancement of Flame Speed in air is attributed to the combustion of excess hydrogen with the ambient air. The mechanism for the enhancement of Flame Speed has been discussed on the basis of a steady-state Flame propagation model for vortex ring combustion. It is shown that if we assume that the excess hydrogen is burned with a turbulent burning velocity, which is proportional to the maximum tangential velocity, and that the pressure behind the Flame is additionally raised, then the increase in slope in the V f − V θmax plane can be well described.
C E Paillard - One of the best experts on this subject based on the ideXlab platform.
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spherical expanding Flames in h2 n2o ar mixtures Flame Speed measurements and kinetic modeling
International Journal of Hydrogen Energy, 2009Co-Authors: Nabiha Chaumeix, R Mevel, F Lafosse, G Dupre, C E PaillardAbstract:Abstract Although ignition of hydrogen–nitrous oxide mixtures is a serious issue for nuclear waste storage and semi-conductor manufacturing, available Flame Speed data have not been recently updated and thermodiffusive stability is not known. In order to palliate this, the Flame Speed of a hydrogen–nitrous oxide mixture diluted in Ar (60% mol) was measured in a spherical bomb as a function of equivalence ratio. The initial pressure and temperature were held constant around ambient conditions. It is shown that the unstretched Flame Speed of the hydrogen–nitrous oxide mixture is relatively low for a hydrogen-based mixture, with a maximum of 56 cm/s for the stoichiometric condition. Further, hydrogen–nitrous oxide–argon Flames appear unstable with respect to thermodiffusive effects at an equivalence ratio of 1. The downward flammability limit of hydrogen–nitrous oxide–argon was observed for hydrogen content of 8 mol%. The modeling of these experimental data has been performed with three recently developed models. All kinetic schemes give satisfactory predictions of the experimentally observed data. Sensitivity and reaction pathway analysis have demonstrated that the dynamic of the system is dominated by the reaction N2O + H = N2 + OH which governs the rate of energy release.
Swetaprovo Chaudhuri - One of the best experts on this subject based on the ideXlab platform.
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scaling of turbulent Flame Speed for expanding Flames with markstein diffusion considerations
Physical Review E, 2013Co-Authors: Swetaprovo Chaudhuri, Chung King LawAbstract:In this paper we clarify the role of Markstein diffusivity, which is the product of the planar laminar Flame Speed and the Markstein length, on the turbulent Flame Speed and its scaling, based on experimental measurements on constant-pressure expanding turbulent Flames. Turbulent Flame propagation data are presented for premixed Flames of mixtures of hydrogen, methane, ethylene, n-butane, and dimethyl ether with air, in near-isotropic turbulence in a dual-chamber, fan-stirred vessel. For each individual fuel-air mixture presented in this work and the recently published iso-octane data from Leeds, normalized turbulent Flame Speed data of individual fuel-air mixtures approximately follow a Re-T,f(0.5) scaling, for which the average radius is the length scale and thermal diffusivity is the transport property of the turbulence Reynolds number. At a given Re-T,Re-f, it is experimentally observed that the normalized turbulent Flame Speed decreases with increasing Markstein number, which could be explained by considering Markstein diffusivity as the leading dissipation mechanism for the large wave number Flame surface fluctuations. Consequently, by replacing thermal diffusivity with the Markstein diffusivity in the turbulence Reynolds number definition above, it is found that normalized turbulent Flame Speeds could be scaled by Re-T,M(0.5) irrespective of the fuel, equivalence ratio, pressure, and turbulence intensity for positive Markstein number Flames.
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turbulent Flame Speed scaling for expanding Flames with markstein diffusion considerations
arXiv: Fluid Dynamics, 2012Co-Authors: Swetaprovo Chaudhuri, Chung K LawAbstract:In this work we clarify the role of Markstein diffusivity on turbulent Flame Speed and it's scaling, from analysis and experimental measurements on constant-pressure expanding Flames propagating in near isotropic turbulence. For all C0-C4 hydrocarbon-air mixtures presented in this work and recently published C8 data from Leeds, the normalized turbulent Flame Speed data of individual mixtures approximately follows the recent theoretical and experimental $Re_{T,f}^{0.5} $ scaling, where the average radius is the length scale and thermal diffusivity is the transport property. We observe that for a constant $Re_{T,f} $, the normalized turbulent Flame Speed decreases with increasing Markstein Number. This could be explained by considering Markstein diffusivity as the large wavenumber, Flame surface fluctuation dissipation mechanism. As originally suggested by the theory, replacing thermal diffusivity with Markstein diffusivity in the turbulence Reynolds number definition above, the present and Leeds dataset could be scaled by the new $Re_{T,M}^{0.5} $irrespective of the fuel considered, equivalence ratio, pressure and turbulence intensity for positive Mk Flames over a large range of Damk\"ohler numbers.
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Spectral formulation of turbulent Flame Speed with consideration of hydrodynamic instability.
Physical review. E Statistical nonlinear and soft matter physics, 2011Co-Authors: Swetaprovo Chaudhuri, V'yacheslav Akkerman, Chung K LawAbstract:Effects of Darrieus-Landau (DL) instability on the structure and propagation of turbulent premixed Flame fronts are considered. By first hypothesizing separation of time scales of instability and turbulence, we estimate whether the instability can develop in the presence of turbulence of given flow rms-velocity and integral length scale. As a result, we modify the standard turbulent premixed combustion regime diagram by introducing new boundaries, limiting the domain where the instability influences the global Flame shape and Speed. Based on this analysis, a "turbulence-induced DL cutoff" as a function of turbulence and instability parameters is introduced, which when combined with a turbulent Flame Speed without DL instability yields the turbulent Flame Speed accounting for the instability. The consumption turbulent Flame Speed for no DL instability is formulated from the spectral closure of the G equation, thus accounting for the scale-dependent "turbulent" nature of the problem. Finally, an analytical form of the turbulent Flame Speed is derived, which is found to agree well with the corresponding experimentally measured turbulent Flame Speed from literature over wide ranges of normalized turbulence intensities and length scales.