Laminar Flame Speeds and Strain Sensitivities of Mixtures of H2 With CO, CO2and N2 at Elevated Temperatures

2007 ◽  
Author(s):  
J. Natarajan ◽  
T. Lieuwen ◽  
J. Seitzman
Keyword(s):  
Radiation Effects ◽  
Equivalence Ratio ◽  
Elevated Temperatures ◽  
Laminar Flame ◽  
Flame Speed ◽  
Bunsen Flame ◽  
Clear Trend ◽  
Numerical Predictions ◽  
Fuel Mixtures ◽  
Lean Conditions

Laminar flame speed and strain sensitivities have been measured for mixtures of H2/CO/CO2/N2/O2 with a wall stagnation flame technique at high preheat temperature (700 K) and lean conditions. The measurements are compared with numerical predictions based on two reaction mechanisms: GRI Mech 3.0 and a H2/CO mechanism (Davis et al.). For H2:CO 50:50 fuel mixtures, both models tend to over predict the temperature dependence of the flame speed especially at very lean conditions, which confirms the trend found in an earlier study employing a Bunsen flame technique. The predicted strain sensitivities are in good agreement with the measurements. For 50:50 H2:CO fuel mixtures diluted with 40% CO2, the amount of over prediction by the models is about the same as in the undiluted case, which suggests that radiation effects associated with CO2 addition are not important for this mixture at highly preheated lean condition. For low H2 content (5 to 20%) H2/CO fuel mixtures at 5 atm and fuel lean condition, the predicted unstrained flame speeds are in excellent agreement with the measurements, but the models fail to predicted the strain sensitivity as the amount of H2 increases to 20%. Results are also presented for pure H2 with N2 diluted air (O2:N2 1:9) over a range of equivalence ratios. At lean conditions, the models over predict the measured flame speed by as much as 30%, and the amount of over prediction decreases as the equivalence ratio increases to stoichiometric and rich condition. The measured strain sensitivities are three times higher than the model predictions at lean conditions. More importantly, the predicted strain sensitivities do not change with equivalence ratio for both models, while the measurements reveal a clear trend (decreasing and then increasing) as the fuel-air ratio changes from lean to rich.

Laminar Flame Speed Measurements of H2/CO/CO2 Mixtures Up to 15 atm and 600 K Preheat Temperature

2008 ◽  
Author(s):  
J. Natarajan ◽  
Y. Kochar ◽  
T. Lieuwen ◽  
J. Seitzman
Keyword(s):  
Temperature Dependence ◽  
Atmospheric Pressure ◽  
Radiation Effects ◽  
Laminar Flame ◽  
Elevated Pressure ◽  
Flame Speed ◽  
Preheat Temperature ◽  
Numerical Predictions ◽  
Kinetic Mechanisms ◽  
Fuel Mixtures

Laminar flame speeds of lean H2/CO/CO2 (syngas) fuel mixtures have been measured for a range of H2 levels (20–90% of the fuel) at pressures and reactant preheat temperatures relevant to gas turbine combustors (up to 15 atm and 600 K). A conical flame stabilized on a contoured nozzle is used for the flame speed measurement, which is based on the reaction zone area calculated from chemiluminescence imaging of the flame. A O2:He mixture (1:9 by volume) is used as the oxidizer, rather than standard air, in order to suppress the hydrodynamic and thermo-diffusive instabilities that become prominent at elevated pressure conditions for lean H2/CO fuel mixtures. All the measurements are compared with numerical predictions based on two leading kinetic mechanisms: the H2/CO mechanism of Davis et al. and the C1 mechanism of Li et al. The results generally agree with the findings of an earlier study at atmospheric pressure: 1) for low H2 content (<40%) fuels, the model predictions are in good agreement with measurements at both 300 K and 600 K preheat temperature; but 2) the models tend to over predict the temperature dependence of the flame speed for medium (∼40–60%) and high (> 60%) H2 content fuels, especially at very lean conditions. The elevated pressure (∼15 atm) results, however, reveal that the effect is less pronounced than at atmospheric pressure. The exaggerated temperature dependence of the current models may be due to errors in the temperature dependence used for so-called “low temperature” reactions that become more important as the preheat temperature is increased. The radiation effects associated with CO2 addition to the fuel (up to 40%) is found to be less important for medium and high H2 content syngas fuels at elevated pressure and preheat temperature.

Laminar Flame Speeds and Strain Sensitivities of Mixtures of H2∕O2∕N2 at Elevated Preheat Temperatures

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
J. Natarajan ◽  
T. Lieuwen ◽  
J. Seitzman
Keyword(s):  
Kinetic Model ◽  
Temperature Dependence ◽  
Reasonable Agreement ◽  
Room Temperature ◽  
Laminar Flame ◽  
Flame Speed ◽  
Numerical Predictions ◽  
Hydrogen Flame ◽  
Measured Strain ◽  
Lean Conditions

Laminar flame speeds and strain sensitivities of mixtures of H2 and air or air highly diluted with N2 (O2:N2 1:9) have been measured for a range of equivalence ratios at high preheat conditions (∼700K) using a nozzle generated, 1D, laminar, wall stagnation flame. The measurements are compared with numerical predictions based on three detailed kinetic models (GRIMECH 3.0, a H2∕CO mechanism from Davis et al. (2004, “An Optimized Kinetic Model of H2∕CO Combustion,” Proc. Combust. Inst., 30, pp. 1283–1292) and a H2 mechanism from Li et al. (2004, “An Updated Comprehensive Kinetic Model of Hydrogen Combustion,” Int. J. Chem. Kinet., 36, pp. 566–575)). Sensitivity of the measurements to uncertainties in boundary conditions, e.g., wall temperature and nozzle velocity profile (plug or potential), is investigated through detailed numerical simulations and shown to be small. The flame speeds and strain sensitivities predicted by the models for preheated reactants are in reasonable agreement with the measurements for mixtures of H2 and standard air at very lean conditions. For H2 and N2 diluted air, however, all three mechanisms significantly overpredict the measurements, and the overprediction increases for leaner mixtures. In contrast, the models underpredict flame speeds for room temperature mixtures of H2 with both standard and N2 diluted air, based on comparisons with measurements in literature. Thus, we find that the temperature dependence of the hydrogen flame speed as predicted by all the models is greater than the actual temperature dependence (for both standard and diluted air). Finally, the models are found to underpredict the measured strain sensitivity of the flame speed for H2 burning in N2 diluted air, especially away from stoichiometric conditions.

Laminar Flame Speed Experiments of Alternative Liquid Fuels

2019 ◽  
Author(s):  
Charles L. Keesee ◽  
Bing Guo ◽  
Eric L. Petersen
Keyword(s):  
Equivalence Ratio ◽  
Laminar Flame ◽  
Initial Conditions ◽  
Synthetic Jet ◽  
Flame Speed ◽  
Liquid Fuels ◽  
Jet Fuels ◽  
Data Sets ◽  
Laminar Flame Speed ◽  
Best Parameter

Abstract New laminar flame speed experiments have been collected for multiple alternative liquid fuels. Understanding the combustion characteristics of these synthetic fuels is an important step in developing new chemical kinetics mechanisms that can be applied to real fuels. Included in this study are two synthetic Jet fuels: Syntroleum S-8 and Shell GTL. The precise composition of these fuels is known to change from sample to sample. Since these are low vapor pressure fuels, there are additional uncertainties in their introduction into gas-phase mixtures, leading to uncertainty in the mixture equivalence ratio. An in-situ laser absorption technique was implemented to verify the procedure for filling the vessel and to minimize and quantify the uncertainty in the experimental equivalence ratio. The diagnostic utilized a 3.39-μm HeNe laser in conjunction with Beer’s Law. The resulting spherically expanding flame experiments were conducted over a range of equivalence ratios from φ = 0.7 to φ = 1.5 at initial conditions of 1 atm and 403 K in the high-temperature, high-pressure constant-volume vessel at Texas A&M University. The experimental results show that both fuels have similar flame speeds with a peak value just under 60 cm/s. However, it is shown that when comparing the results from different data sets for these real fuels, equivalence ratio is not necessarily the best parameter to use. Fuel mole fraction may be a better parameter to use as it is independent of the average fuel molecule or fuel surrogate used to calculate equivalence ratio in these real fuel/air mixtures.

scholarly journals Experimental and Numerical Investigation on the Laminar Flame Speed of CH4/O2 Mixtures Diluted With CO2 and H2O

2010 ◽  
Author(s):  
A. N. Mazas ◽  
D. A. Lacoste ◽  
T. Schuller
Keyword(s):  
Laminar Flame ◽  
Burning Velocity ◽  
Molar Fraction ◽  
Fuel Combustion ◽  
Flame Speed ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Laminar Flame Speed ◽  
Numerical Predictions ◽  
Linear Decrease

The effects of CO2 and H2O addition on premixed oxy-fuel combustion are investigated with experiments and numerical simulations on the laminar flame speed of CH4/O2/CO2/H2O(v) and CH4/O2/N2/H2O(v) mixtures, at atmospheric pressure and for a reactants inlet temperature Tu = 373 K. Experiments are conducted with steady laminar conical premixed flames over a range of operating conditions representative of oxy-fuel combustion with flue gas recirculation. The relative O2-to-CO2 and O2-to-N2 ratios, respectively defined as O2/(O2+CO2) (mol.) and O2/(O2+N2) (mol.), are varied from 0.21 to 1.0. The equivalence ratio of the mixtures ranges from 0.5 to 1.5, and the steam molar fraction in the reactive mixture is varied from 0 to 0.45. Laminar flame speeds are measured with the flame area method using a Schlieren apparatus. Experiments are completed by simulations with the PREMIX code using the detailed kinetic mechanism GRI-mech. 3.0. Numerical predictions are found in good agreement with experimental data for all cases explored. It is also shown that the laminar flame speed of CH4/O2/N2 mixtures diluted with steam H2O(v) features a quasi-linear decrease when increasing the diluent molar fraction, even at high dilution rates. Effects of N2 replacement by CO2 in wet reactive mixtures are then investigated. A similar quasi-linear decrease of the flame speed is observed for CH4/O2/CO2 H2O-diluted flames. For a similar flame speed in dry conditions, results show a larger reduction of the burning velocity for CH4/O2/N2/H2O mixtures than for CH4/O2/CO2/H2O mixtures, when the steam molar fraction is increased. Finally, it is observed that the laminar flame speed of weakly (CO2, H2O)-diluted CH4/O2 mixtures is underestimated by the GRI-mech 3.0 predictions.

scholarly journals Laminar flame speed of soy and canola biofuels

2012 ◽  
Vol 4 (5) ◽  
pp. 75-83 ◽  
Author(s):  
Juan-Sebastián Gómez-Meyer ◽  
Subramanyam R Gollahalli ◽  
Ramkumar N. Parthasarathy ◽  
Jabid-Eduardo Quiroga
Keyword(s):  
Flame Propagation ◽  
Equivalence Ratio ◽  
Laminar Flame ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Thermochemical Property ◽  
Laminar Flame Speed ◽  
Hot Air ◽  
Maximum Value ◽  
Canola Oils

In this article, the flame speed values determined experimentally for laminar premixed flames of the vapors of two biofuels in air are presented. The laminar flame speed is a fundamental thermochemical property of fuels, and is essential for analyzing the flame propagation in practical devices, even those employing turbulent flames. The fuels obtained from transesterification of soy and canola oils are tested. Also, the diesel flames are studied to serve as a baseline for comparison. The experiments are performed with a tubular burner; pre-vaporized fuel is mixed with hot air and is ignited. The flame speed is determined at fuel-equivalence ratios of 1; 1,1 and 1,2 by recording the geometry of the flame. The experimental results show that the flame speed of biofuels is lower by about 15% than that of diesel. Also, the maximum value of flame speed is obtained at an equivalence ratio of approximately 1,1.

Laminar Flame Speed Experiments of Alternative Liquid Fuels

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Charles L. Keesee ◽  
Bing Guo ◽  
Eric L. Petersen
Keyword(s):  
Equivalence Ratio ◽  
Laminar Flame ◽  
Initial Conditions ◽  
Synthetic Jet ◽  
Flame Speed ◽  
Liquid Fuels ◽  
Jet Fuels ◽  
Laminar Flame Speed ◽  
Synthetic Fuels ◽  
Best Parameter

Abstract New laminar flame speed experiments have been collected for two alternative liquid fuels. Understanding the combustion characteristics of these synthetic fuels is an important step in developing new chemical kinetics mechanisms that can be applied to real fuels. Included in this study are two synthetic Jet fuels: Syntroleum S-8 and Shell GTL. The precise composition of these fuels is known to change from sample to sample. Since these are low-vapor pressure fuels, there are additional uncertainties in their introduction into gas-phase mixtures, leading to uncertainty in the mixture equivalence ratio. An in-situ laser absorption technique was implemented to verify the procedure for filling the vessel and to minimize and quantify the uncertainty in the experimental equivalence ratio. The diagnostic utilized a 3.39-μm HeNe laser in conjunction with Beer's law. The resulting spherically expanding, laminar flame experiments were conducted over a range of equivalence ratios from φ = 0.7 to φ = 1.5 at initial conditions of 1 atm and 403 K in the high-temperature, high-pressure (HTHP) constant-volume vessel at Texas A&M University. The experimental results show that both fuels have similar flame speeds with a peak value just under 60 cm/s. However, it is shown that when comparing the results from different datasets for these real fuels, equivalence ratio may not be the best parameter to use. Fuel mole fraction may be a better parameter to use as it is independent of the average fuel molecule or fuel surrogate used to calculate equivalence ratio in these real fuel/air mixtures.

Experimental Study on Laminar Flame Speeds and Markstein Length of Methane-Air Mixtures at Atmospheric Conditions

2014 ◽  
Vol 699 ◽  
pp. 714-719
Author(s):  
Alaeldeen Altag Yousif ◽  
Shaharin Anwar Sulaiman
Keyword(s):  
High Speed ◽  
Equivalence Ratio ◽  
Laminar Flame ◽  
Burning Velocity ◽  
Ambient Pressure ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
Atmospheric Conditions ◽  
Laminar Burning Velocity ◽  
Markstein Length

Accurate value of laminar flame speed is an important parameter of combustible mixtures. In this respect, experimental data are very useful for modeling improvement and validating chemical kinetic mechanisms. To achieve this, an experimental characterization on spherically expanding flames propagation of methane-air mixtures were carried out. Tests were conducted in constant volume cylindrical combustion chamber to measure stretched, unstretched laminar flame speed, laminar burning velocity, and flame stretch effect as quantified by the associated Markstein lengths. The mixtures of methane-air were ignited at extensive ranges of lean-to-rich equivalence ratios, under ambient pressure and temperature. This is achieved by high speed schlieren cine-photography for flames observation in the vessel. The results showed that the unstretched laminar burning velocity increased and the peak value of the unstretched laminar burning velocity shifted to the richer mixture side with the increase of equivalence ratio. The flame propagation speed showed different trends at different equivalence ratio for tested mixtures. It was found that the Markstein length was increased with the increase of equivalence ratio.

Multi-Dimensional CFD Simulations of Knocking Combustion in a CFR Engine

2017 ◽  
Author(s):  
Pinaki Pal ◽  
Yunchao Wu ◽  
Tianfeng Lu ◽  
Sibendu Som ◽  
Yee Chee See ◽  
...  
Keyword(s):  
Experimental Data ◽  
Flame Front ◽  
Octane Number ◽  
Equivalence Ratio ◽  
Laminar Flame ◽  
Equation Model ◽  
Flame Speed ◽  
Lookup Table ◽  
Laminar Flame Speed ◽  
Skeletal Mechanism

Knock is a major impediment to achieving higher efficiency in Spark-Ignition (SI) engines. The recent trends of boosting, downsizing and downspeeding have exacerbated this issue by driving engines toward higher power density and higher load duty cycles. Apart from the engine operating conditions, fuel anti-knock quality is a major determinant of the knocking tendency in engines, as quantified by its octane number (ON). The ON of a fuel is based on an octane scale which is defined according to the standard octane rating methods for Research Octane Number (RON) and Motor Octane Number (MON). These tests are performed in a single cylinder Cooperative Fuel Research (CFR) engine. In the present work, a numerical approach was developed based on multidimensional computational fluid dynamics (CFD) to predict knocking combustion in a CFR engine. The G-equation model was employed to track the propagation of the turbulent flame front and a multi-zone model based on temperature and equivalence ratio was used to capture auto-ignition in the endgas ahead of the flame front. Furthermore, a novel methodology was developed wherein a lookup table generated from a chemical kinetic mechanism could be employed to provide laminar flame speed as an input to the G-equation model, instead of using empirical correlations. To account for fuel chemistry effects accurately and lower the computational cost, a compact 121-species primary reference fuel (PRF) skeletal mechanism was developed from a more detailed gasoline surrogate mechanism using the directed relation graph assisted sensitivity analysis (DRGASA) reduction technique. Extensive validation of the skeletal mechanism was performed against experimental data available in the literature for both homogeneous ignition delay and laminar flame speed. The skeletal mechanism was used to generate the lookup tables for laminar flame speed as a function of pressure, temperature and equivalence ratio. The engine CFD model incorporating the skeletal mechanism was employed to perform numerical simulations under RON and MON conditions for different PRFs. Parametric tests were conducted at different compression ratios and the predicted values of critical compression ratio (at knock onset), delineating the boundary between “no knock” and “knock”, were found to be in good agreement with the available experimental data. The virtual CFR engine model was, therefore, demonstrated to be capable of adequately capturing the sensitivity of knock propensity to fuel chemistry.

scholarly journals Structure and Laminar Flame Speed of an Ammonia/Methane/Air Premixed Flame under Varying Pressure and Equivalence Ratio

2021 ◽  
Author(s):  
Rodolfo C. Rocha ◽  
Shenghui Zhong ◽  
Leilei Xu ◽  
Xue-Song Bai ◽  
Mário Costa ◽  
...  
Keyword(s):  
Equivalence Ratio ◽  
Laminar Flame ◽  
Flame Speed ◽  
Premixed Flame ◽  
Laminar Flame Speed

scholarly journals The adiabatic flame temperature and laminar flame speed of methane premixed flames at varying pressures

2019 ◽  
pp. 220-227
Author(s):  
Ahmad Sakhrieh
Keyword(s):  
Equivalence Ratio ◽  
Initial Temperature ◽  
Laminar Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Pressure Increase ◽  
Stoichiometric Ratio ◽  
Laminar Flame Speed ◽  
Adiabatic Flame Temperature ◽  
Percent Increase

This paper studies the influence of equivalence ratio, pressure and initial temperature on adiabatic flame temperature and laminar flame speed of methane-air mixture. The results indicate that adiabatic flame temperature is weakly correlated with pressure. The adiabatic flame temperature increases only by about 50?C as a result of 30 bar pressure increase. The flame speed is inversely proportional to pressure. The maximum adiabatic flame temperature and flame speed occur at the stoichiometric ratio, ?=1. The percent increase in the flame speed was about 400% when the initial temperature of the mixture is increased from 25?C to 425?C.

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