Experimental and Numerical Analysis of Laminar Burning Velocity of Binary and Ternary Hydrocarbon/H2 Mixtures (original) (raw)
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Energies
The flammable hydrogen-blended methane–air and natural gas–air mixtures raise specific safety and environmental issues in the industry and transportation; therefore, their explosion characteristics such as the explosion limits, explosion pressures, and rates of pressure rise have significant importance from a safety point of view. At the same time, the laminar burning velocities are the most useful parameters for practical applications and in basic studies for the validation of reaction mechanisms and modeling turbulent combustion. In the present study, an experimental and numerical study of the effect of hydrogen addition on the laminar burning velocity (LBV) of methane–air and natural gas–air mixtures was conducted, using mixtures with equivalence ratios within 0.90 and 1.30 and various hydrogen fractions rH within 0.0 and 0.5. The experiments were performed in a 14 L spherical vessel with central ignition at ambient initial conditions. The LBVs were calculated from p(t) data, det...
Proceedings of The Combustion Institute, 2005
The aim of the present work was to characterize both the effects of pressure and of hydrogen addition on methane/air premixed laminar flames. The experimental setup consists of a spherical combustion chamber coupled to a classical shadowgraphy system. Flame pictures are recorded by a high speed camera. Global equivalence ratios were varied from 0.7 to 1.2 for the initial pressure range from 0.1 to 0.5 MPa. The mole fraction of hydrogen in the methane + hydrogen mixture was varied from 0 to 0.2. Experimental results were compared to calculations using a detailed chemical kinetic scheme (GRIMECH 3.0). First, the results for atmospheric laminar CH4/air flames were compared to the literature. Very good agreements were obtained both for laminar burning velocities and for burned gas Markstein length. Then, increasing the hydrogen content in the mixture was found to be responsible for an increase in the laminar burning velocity and for a reduction of the flame dependence on stretch. Transport effects, through the reduction of the fuel Lewis number, play a role in reducing the sensitivity of the fundamental flame velocity to the stretch. Finally, when the pressure was increased, the laminar burning velocity decreased for all mixtures. The pressure domain was limited to 0.5 MPa due to the onset of instabilities at pressures above this value.
Processes
Methane is one of the most common gaseous fuels that also exist in nature as the main part of the natural gas, the flammable part of biogas or as part of the reaction products from biomass pyrolysis. In this respect, the biogas and biomass installations are always subjected to explosion hazards due to methane. Simple methods for evaluating the explosion hazards are of great importance, at least in the preliminary stage. The paper describes such a method based on an elementary analysis of the cubic law of pressure rise during the early stages of flame propagation in a symmetrical cylindrical vessel of small volume (0.17 L). The pressure–time curves for lean, stoichiometric and rich methane–air mixtures were recorded and analyzed. From the early stages of pressure–time history, when the pressure increase is equal to or less than the initial pressure, normal burning velocities were evaluated and discussed. Qualitative experiments were performed in the presence of a radioactive source o...
Revue Roumaine de Chimie
Computed burning velocities of C2H6-air, C2H4-air and C2H2-air stoichiometric flames with variable initial pressure and temperature obtained by a detailed numerical modeling are compared to those measured or previously reported burning velocities obtained from transient pressure-time records during explosions in spherical vessels with central ignition. Correlations in the form of S-u/S-u.ref = (p/pref)(v)(T-u/T-u,T-ref)(mu)describe well the burning velocity dependence on pressure and temperature of all mixtures, for both experimental and computed data. The bane coefficient, v, was further used for calculation of the overall reaction order, n, found to vary within 1.3 and 1.8 for the examined hydrocarbons. The burning velocity dependence on the average flame temperature was used to calculate the overall activation energy of the oxidation, E-a,specific for each flame. The change of flame initial conditions (pressure and temperature) was found to determine important changes of the flam...
The enhanced combustion properties of hydrogen as well as worldwide concerns due to global warming are acting together as the major driving force to a future hydrogen-based economy. However this will not be a step change and the blends of hydrogen and hydrocarbons must be looked as a transition solution to a purely hydrogen-based economy [1]. In the present study, numerical investigations of a wider range of fuel/air mixtures which includes H 2 -hydrocarbon blends have been carried out for the unstretched laminar burning velocities, S L0 at STP conditions using detailed reaction mechanisms. For this purpose, different reaction mechanisms are combined with the combustion simulation package Cosilab [2]. Comparative studies with experimental data from several independent investigations show that San Diego mechanism [3] predicts S L0 of H 2 /air mixtures very well while Konnov v0.5 [4] is the most valid mechanism for CH 4 /air mixtures. QMech [5] shows good agreement for C 3 H 8 /air mi...
Explosion behavior of hydrogen–methane/air mixtures
Journal of Loss Prevention in the Process Industries, 2012
The effects of enriching natural gas with hydrogen on local flame extinction, combustion instabilities and power output have been widely studied for both stationary and mobile systems. On the contrary, the issues of explosion safety for hydrogenemethane mixtures are still under investigation.
Measurements of laminar burning velocities for natural gas–hydrogen–air mixtures
Combustion and Flame, 2006
Laminar flame characteristics of natural gas-hydrogen-air flames were studied in a constant-volume bomb at normal temperature and pressure. Laminar burning velocities and Markstein lengths were obtained at various ratios of hydrogen to natural gas (volume fraction from 0 to 100%) and equivalence ratios (φ from 0.6 to 1.4). The influence of stretch rate on flame was also analyzed. The results show that, for lean mixture combustion, the flame radius increases with time but the increasing rate decreases with flame expansion for natural gas and for mixtures with low hydrogen fractions, while at high hydrogen fractions, there exists a linear correlation between flame radius and time. For rich mixture combustion, the flame radius shows a slowly increasing rate at early stages of flame propagation and a quickly increasing rate at late stages of flame propagation for natural gas and for mixtures with low hydrogen fractions, and there also exists a linear correlation between flame radius and time for mixtures with high hydrogen fractions. Combustion at stoichiometric mixture demonstrates the linear relationship between flame radius and time for natural gas-air, hydrogen-air, and natural gas-hydrogen-air flames. Laminar burning velocities increase exponentially with the increase of hydrogen fraction in mixtures, while the Markstein length decreases and flame instability increases with the increase of hydrogen fractions in mixture. For a fixed hydrogen fraction, the Markstein number shows an increase and flame stability increases with the increase of equivalence ratios. Based on the experimental data, a formula for calculating the laminar burning velocities of natural gas-hydrogen-air flames is proposed.
International Journal of Hydrogen Energy, 2009
Hydrogen Laminar burning velocity Markstein length Sensitivity analysis Flame structure a b s t r a c t An experimental and numerical study on laminar burning characteristics of the premixed methane-hydrogen-air flames was conducted at room temperature and atmospheric pressure. The unstretched laminar burning velocity and the Markstein length were obtained over a wide range of equivalence ratios and hydrogen fractions. Moreover, for further understanding of the effect of hydrogen addition on the laminar burning velocity, the sensitivity analysis and flame structure were performed. The results show that the unstretched laminar burning velocity is increased, and the peak value of the unstretched laminar burning velocity shifts to the richer mixture side with the increase of hydrogen fraction. Three regimes are identified depending on the hydrogen fraction in the fuel blend. They are: the methane-dominated combustion regime where hydrogen fraction is less than 60%; the transition regime where hydrogen fraction is between 60% and 80%; and the methane-inhibited hydrogen combustion regime where hydrogen fraction is larger than 80%. In both the methane-dominated combustion regime and the methane-inhibited hydrogen combustion regime, the laminar burning velocity increases linearly with the increase of hydrogen fraction. However, in the transition regime, the laminar burning velocity increases exponentially with the increase of hydrogen fraction in the fuel blends. The Markstein length is increased with the increase of equivalence ratio and is decreased with the increase of hydrogen fraction. Enhancement of chemical reaction with hydrogen addition is regarded as the increase of H, O and OH radical mole fractions in the flame. Strong correlation is found between the burning velocity and the maximum radical concentrations of H and OH in the reaction zone of the premixed flames.
International Journal of Hydrogen Energy, 2009
Hydrogen Laminar burning velocity Markstein length Sensitivity analysis Flame structure a b s t r a c t An experimental and numerical study on laminar burning characteristics of the premixed methane-hydrogen-air flames was conducted at room temperature and atmospheric pressure. The unstretched laminar burning velocity and the Markstein length were obtained over a wide range of equivalence ratios and hydrogen fractions. Moreover, for further understanding of the effect of hydrogen addition on the laminar burning velocity, the sensitivity analysis and flame structure were performed. The results show that the unstretched laminar burning velocity is increased, and the peak value of the unstretched laminar burning velocity shifts to the richer mixture side with the increase of hydrogen fraction. Three regimes are identified depending on the hydrogen fraction in the fuel blend. They are: the methane-dominated combustion regime where hydrogen fraction is less than 60%; the transition regime where hydrogen fraction is between 60% and 80%; and the methane-inhibited hydrogen combustion regime where hydrogen fraction is larger than 80%. In both the methane-dominated combustion regime and the methane-inhibited hydrogen combustion regime, the laminar burning velocity increases linearly with the increase of hydrogen fraction. However, in the transition regime, the laminar burning velocity increases exponentially with the increase of hydrogen fraction in the fuel blends. The Markstein length is increased with the increase of equivalence ratio and is decreased with the increase of hydrogen fraction. Enhancement of chemical reaction with hydrogen addition is regarded as the increase of H, O and OH radical mole fractions in the flame. Strong correlation is found between the burning velocity and the maximum radical concentrations of H and OH in the reaction zone of the premixed flames.
Burning velocity of methane-hydrogen mixtures at elevated pressures and temperatures
Russian Journal of Physical Chemistry B, 2013
The effect of the initial pressure, temperature, and equivalence ratio on a number of combustion characteristics of methane-air mixtures with hydrogen additives in a closed vessel is experimentally studied. Experiments are conducted at 1, 5, and 10 atm and temperatures from 22 to 300°C. The hydrogen content in the fuel is 0, 10, and 20 vol %. The fuel equivalence ratio varies from 0.6 to 1.0. The limitations imposed by buoyancy on measurements of the laminar burning velocity by the constant volume bomb method with recording of pressure-time histories are analyzed. It is shown that the laminar burning velocity can be appre ciably increased by adding no less than 20 vol % of hydrogen to the fuel.