scholarly journals Laminar Flame Characteristics of Premixed Methanol–Water–Air Mixture

Energies ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 6504
Author(s):  
Zhennan Zhu ◽  
Kun Liang ◽  
Xinwen Chen ◽  
Zhongwei Meng ◽  
Wenbin He ◽  
...  
Keyword(s):  
Internal Combustion Engines ◽  
Laminar Flame ◽  
Burning Velocity ◽  
Molar Fraction ◽  
Stoichiometric Ratio ◽  
Gaseous State ◽  
Promising Alternative ◽  
Water Fraction ◽  
Flame Instability ◽  
Preferential Diffusion

Methanol is hygroscopic in a gaseous state and is a promising alternative fuel for internal combustion engines. It is understood that adding water can improve the antiknock performance for spark ignition engines, but this will also affect the flame speed and stability. In this work, laminar flame characteristics of methanol/water/air mixtures were experimentally investigated at a temperature range of 380–450 K, a pressure range of 1–4 bar, and water fractions (vaporous water molar fraction in the water–methanol fuel gas) of 0–40%. The results show that laminar burning velocity increases with temperature but decreases with pressure. The burning velocity decreases linearly with water fraction at a stoichiometric ratio. For rich mixtures and high pressures, the laminar flames tend to be more sensitive to stretch and, thus, more prone to being unstable. Increasing the water fraction can slightly increase the Markstein length. Increasing the initial pressure enhances the general flame instability, while increasing the initial temperature suppresses the general flame instability. Increasing the water fraction can lead to a decreasing thermal expansion ratio and an elevated flame thickness, both of which can lead to a suppression of hydrodynamic instability. An increase in the water fraction decreases the Lewis number, resulting in preferential diffusion instability. There is no direct relationship between the onset of cellularity and general flame instability.

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 Effect of Hydrogen Content and Dilution on Laminar Burning Velocity and Stability Characteristics of Producer Gas-Air Mixtures

2008 ◽  
Vol 2008 ◽  
pp. 1-8 ◽  
Author(s):  
V. Ratna Kishore ◽  
M. R. Ravi ◽  
Anjan Ray
Keyword(s):  
Hydrogen Content ◽  
Alternative Fuels ◽  
Burning Velocity ◽  
Operating Conditions ◽  
Producer Gas ◽  
Laminar Burning Velocity ◽  
High Hydrogen ◽  
Promising Alternative ◽  
Preferential Diffusion ◽  
Wide Range

Producer gas is one of the promising alternative fuels with typical constituents of H2, CO, CH4, N2, and CO2. The laminar burning velocity of producer gas was computed for a wide range of operating conditions. Flame stability due to preferential diffusional effects was also investigated. Computations were carried out for spherical outwardly propagating flames and planar flames. Different reaction mechanisms were assessed for the prediction of laminar burning velocities of CH4, H2, H2-CO, and CO-CH4and results showed that the Warnatz reaction mechanism with C1 chemistry was the smallest among the tested mechanisms with reasonably accurate predictions for all fuels at 1 bar, 300 K. To study the effect of variation in the producer gas composition, each of the fuel constituents in ternary CH4-H2-CO mixtures was varied between 0 to 48%, while keeping diluents fixed at 10% CO2and 42% N2by volume. Peak burning velocity shifted fromϕ=1.6to 1.1 as the combined volumetric percentage of hydrogen and CO varied from 48% to 0%. Unstable flames due to preferential diffusion effects were observed for lean mixtures of fuel with high hydrogen content. The present results indicate that H2has a strong influence on the combustion of producer gas.

Experimental Study on the Influence of Pressure and Temperature on the Burning Velocity and Markstein Number of Jet A-1 Kerosene

2010 ◽  
Author(s):  
Vlade Vukadinovic ◽  
Peter Habisreuther ◽  
Nikolaos Zarzalis
Keyword(s):  
Experimental Study ◽  
Flame Front ◽  
Laminar Flame ◽  
Burning Velocity ◽  
Laminar Burning Velocity ◽  
Laser Method ◽  
Gaseous State ◽  
Markstein Number ◽  
Laminar Flame Front ◽  
Front Stability

For accurate prediction of the laminar flame front propagation the influence of the stretch effect on the burning velocity has to be considered. Thus, only burning velocity and Markstein number together give complete information about the laminar flame front behavior. The Markstein number quantifies the influence of the stretch effect on the burning velocity and accordingly, indicates the flame front stability. Due to the analogy between the laminar and the turbulent flames these two parameters, laminar burning velocity and Markstein number must be also considered as essential for describing the turbulent flame front stability [1]. Nevertheless, the experimental data of commercial liquid fuels regarding these parameters are scarce, especially at elevated pressure. Combustion characteristics (laminar burning velocity and Markstein number) of Kerosene Jet A-1 are investigated experimentally in an explosion bomb vessel. For this purpose an optical laser method is employed based on the Mie-scattering of the laser light by smoke particles. Unlike analogous experiments conducted with gaseous fuels [1], the major challenge connected with the present experiments arises from the liquid state of the investigated fuel at ambient condition. Thus, a main difficulty in the present experiments is pre-evaporation of the fuel and achieving of homogeneous gaseous fuel/air mixture prior to ignition. This is solved by mounting a heating system into the walls of the bomb vessel that provides a homogeneous temperature distribution in the vessel and therewith of the mixture itself. The experimental investigation is practically done through the following steps: heating the vessel up to the requested temperature; filling the vessel with an appropriate mixture by the partial pressure method (providing a fuel in gaseous state through the liquid fuel injection and its instantaneous evaporation due to the elevated temperature); attaining an uniform mixture by means of fans; ignition and acquisition of the data; post-processing and data analyses. Within the experimental study influence on the burning velocity and Markstein number of three crucial parameters — initial temperature, initial pressure and mixture composition — are investigated. Observed results for the burning velocity and Markstein number follow the theoretically expected tendencies resulting from the variation of the initial parameters in almost all cases. Where that was not the case the reasons for discrepancies are discussed. Impact of the results on emissions influenced by different operating modes of jet turbines is considered. Due to the common substitution of the kerosene with n-decane in numerical simulations their burning velocities are compared.

Analysis of Premixed Laminar Combustion of Methane With Noble Gases as a Working Fluid

2021 ◽  
Author(s):  
Mammadbaghir Baghirzade ◽  
Md Nayer Nasim ◽  
Behlol Nawaz ◽  
Jonathan Aguilar ◽  
Martia Shahsavan ◽  
...  
Keyword(s):  
Internal Combustion Engines ◽  
Noble Gases ◽  
Laminar Flame ◽  
Burning Velocity ◽  
Diagnostic Technique ◽  
Methane Combustion ◽  
Working Fluid ◽  
Driving Mechanism ◽  
Hydrodynamic Instabilities ◽  
Premixed Laminar

Abstract Hydrodynamic and diffusional-thermal instabilities affect the flame dynamics, which result in non-planar flame fronts with self-accelerating cellularities and wrinkles. In premixed flames, the driving mechanism for perturbations is hydrodynamic instabilities, which are associated with thermal expansion. Under high-pressure conditions, such as in spark-ignition engines, the flame curvature and morphology might be influenced by the hydrodynamic instabilities. This study focuses on the replacement of nitrogen with a noble gas (argon and krypton) as the working fluid in the premixed combustion of methane to investigate its effect on flame stability and dynamics. The utilization of noble gases can also enhance the ideal thermal efficiency of internal combustion engines due to the higher specific heat ratio they possess and may also reduce the NOx emissions markedly because of the lack of nitrogen in the working fluid. The experiments are conducted for various equivalence ratios (φ = 0.8, 1.0, 1.2) in a constant volume combustion chamber (CVCC) at atmospheric and elevated initial pressures and atmospheric temperature. As an outcome of this study, to understand the influence of krypton on methane combustion, spherically propagating flames are analyzed in terms of the laminar flame burning velocity, cellular instability, unburned gas Markstein length, and flame morphology utilizing a Z-type Schlieren optical diagnostic technique and fractal analysis, which is a promising approach to analyze flame surfaces. The fractal dimension of the flame fronts is calculated by a box-counting algorithm. The results are compared against the previously examined case studies in which argon was used as the primary working fluid.

scholarly journals Laminar Burning Velocity of Biogas-Containing Mixtures. A Literature Review

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 996
Author(s):  
Venera Giurcan ◽  
Codina Movileanu ◽  
Adina Magdalena Musuc ◽  
Maria Mitu
Keyword(s):  
Gas Turbines ◽  
Internal Combustion Engines ◽  
Fossil Fuels ◽  
Combustion Engine ◽  
Burning Velocity ◽  
Internal Combustion ◽  
Electricity Production ◽  
Engine Fuel ◽  
Laminar Burning Velocity ◽  
Waste Products

Currently, the use of fossil fuels is very high and existing nature reserves are rapidly depleted. Therefore, researchers are turning their attention to find renewable fuels that have a low impact on the environment, to replace these fossil fuels. Biogas is a low-cost alternative, sustainable, renewable fuel existing worldwide. It can be produced by decomposition of vegetation or waste products of human and animal biological activity. This process is performed by microorganisms (such as methanogens and sulfate-reducing bacteria) by anaerobic digestion. Biogas can serve as a basis for heat and electricity production used for domestic heating and cooking. It can be also used to feed internal combustion engines, gas turbines, fuel cells, or cogeneration systems. In this paper, a comprehensive literature study regarding the laminar burning velocity of biogas-containing mixtures is presented. This study aims to characterize the use of biogas as IC (internal combustion) engine fuel, and to develop efficient safety recommendations and to predict and reduce the risk of fires and accidental explosions caused by biogas.

scholarly journals The effect of thermal expansion on diffusion flame instabilities

2010 ◽  
Vol 647 ◽  
pp. 453-472 ◽  
Author(s):  
M. MATALON ◽  
P. METZENER
Keyword(s):  
Thermal Expansion ◽  
Diffusion Flame ◽  
Initial Mixture ◽  
Surprising Result ◽  
Flame Instability ◽  
Preferential Diffusion ◽  
The Stability ◽  
Flame Instabilities ◽  
Comprehensive Characterization

In this paper we examine the effect of thermal expansion on the stability of a planar unstrained diffusion flame and provide a comprehensive characterization of diffusive-thermal instabilities while realistically accounting for density variations. The possible patterns that are likely to be observed as a result of differential and preferential diffusion are identified for a whole range of parameters including the distinct Lewis numbers associated with the fuel and oxidizer, the initial mixture strength and the flow conditions. Although we find that thermal expansion has a marked influence on flame instability, it does not play a crucial role as it does in premixed combustion. It primarily affects the parameter regime associated with the onset of the instabilities and the growth rate of the unstable modes. Perhaps the most surprising result is that its has a different influence on the various modes of instability – a destabilizing influence on the formation of cellular structures and a stabilizing influence on the onset of oscillations.

A Laminar Burning Velocity Correlation for Hydrogen/Air Mixtures Valid at Spark-Ignition Engine Conditions

2003 ◽  
Author(s):  
Sebastian Verhelst ◽  
Roger Sierens
Keyword(s):  
Chemical Kinetics ◽  
Laminar Flame ◽  
Burning Velocity ◽  
Spark Ignition ◽  
Flame Speed ◽  
Spark Ignition Engine ◽  
Laminar Flame Speed ◽  
Spark Ignition Engines ◽  
Laminar Burning Velocity ◽  
Velocity Correlation

During the development of a quasi-dimensional simulation programme for the combustion of hydrogen in spark-ignition engines, the lack of a suitable laminar flame speed formula for hydrogen/air mixtures became apparent. A literature survey shows that none of the existing correlations covers the entire temperature, pressure and mixture composition range as encountered in spark-ignition engines. Moreover, there is ambiguity concerning the pressure dependence of the laminar burning velocity of hydrogen/air mixtures. Finally, no data exists on the influence of residual gases. This paper looks at several reaction mechanisms found in the literature for the kinetics of hydrogen/oxygen mixtures, after which one is selected that corresponds best with available experimental data. An extensive set of simulations with a one-dimensional chemical kinetics code is performed to calculate the laminar flame speed of hydrogen/air mixtures, in a wide range of mixture compositions and initial pressures and temperatures. The use of a chemical kinetics code permits the calculation of any desired set of conditions and enables the estimation of interactions, e.g. between pressure and temperature effects. Finally, a laminar burning velocity correlation is presented, valid for air-to-fuel equivalence ratios λ between 1 and 3 (fuel-to-air equivalence ratio 0.33 < φ < 1), initial pressures between 1 bar and 16 bar, initial temperatures between 300 K and 800 K and residual gas fractions up to 30 vol%. These conditions are sufficient to cover the entire operating range of hydrogen fuelled spark-ignition engines.

scholarly journals A New Metaheuristic Inspired by the Vapour-Liquid Equilibrium for Continuous Optimization

2018 ◽  
Vol 8 (11) ◽  
pp. 2080 ◽  
Author(s):  
Enrique Cortés-Toro ◽  
Broderick Crawford ◽  
Juan Gómez-Pulido ◽  
Ricardo Soto ◽  
José Lanza-Gutiérrez
Keyword(s):  
Equilibrium State ◽  
Optimization Problem ◽  
Optimization Problems ◽  
Molar Fraction ◽  
Chemical System ◽  
Decision Variable ◽  
Liquid Equilibrium ◽  
Acceptance Probability ◽  
Promising Alternative ◽  
Highly Nonlinear

In this article, a novel optimization metaheuristic based on the vapour-liquid equilibrium is described to solve highly nonlinear optimization problems in continuous domains. During the search for the optimum, the procedure truly simulates the vapour-liquid equilibrium state of multiple binary chemical systems. Each decision variable of the optimization problem behaves as the molar fraction of the lightest component of a binary chemical system. The equilibrium state of each system is modified several times, independently and gradually, in two opposite directions and at different rates. The best thermodynamic conditions of equilibrium for each system are searched and evaluated to identify the following step towards the solution of the optimization problem. While the search is carried out, the algorithm randomly accepts inadequate solutions. This process is done in a controlled way by setting a minimum acceptance probability to restart the exploration in other areas to prevent becoming trapped in local optimal solutions. Moreover, the range of each decision variable is reduced autonomously during the search. The algorithm reaches competitive results with those obtained by other stochastic algorithms when testing several benchmark functions, which allows us to conclude that our metaheuristic is a promising alternative in the optimization field.

Effect of CO2 Dilution on the Laminar Burning Velocities of Premixed Methane/Air Flames at Elevated Temperature

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
B. C. Duva ◽  
L. E. Chance ◽  
E. Toulson
Keyword(s):  
Elevated Temperature ◽  
San Diego ◽  
Research University ◽  
Laminar Flame ◽  
Experimental Testing ◽  
Burning Velocity ◽  
Chemical Kinetic ◽  
Fortran Program ◽  
Elementary Reactions ◽  
Kinetic Mechanisms

Abstract With increased interest in reducing emissions, the staged combustion concept for gas turbine combustors is gaining in popularity. For this work, the effect of CO2 dilution on laminar burning velocities of premixed methane/air flames was investigated at elevated temperature through both experiments and numerical simulations. Validation of the experimental setup and methodology was completed through experimental testing of methane/air mixtures at 1 bar and 298 K. Following validation, high temperature experiments were conducted in an optically accessible constant volume combustion chamber at 1 bar and 473 K. Laminar burning velocities of premixed methane/air flames with 0%, 5%, 10%, and 15% CO2 dilution were determined using the constant pressure method enabled via schlieren visualization of the spherically propagating flame front. Results show that laminar burning velocities of methane/air mixtures at 1 bar increase by 106–145% with initial temperature increases from 298 K to 473 K. Additions of 5%, 10%, and 15% CO2 dilution at 1 bar and 473 K cause a 30–35%, 51–54%, and 66–68% decrease in the laminar burning velocity, respectively. Numerical results were obtained with CHEMKIN (Kee et al., 1985, “PREMIX: A Fortran Program for Modeling Steady Laminar One-Dimensional Premixed Flames,”) using the GRI-Mech 3.0 (Smith et al., 2019) and the San Diego (“Chemical-Kinetic Mechanisms for Combustion Applications,” San Diego Mechanism Web Page, Mechanical and Aerospace Engineering (Combustion Research), University of California at San Diego, San Diego, CA) mechanisms. It is concluded that the GRI-Mech 3.0 (Smith et al.., 2019) better captures the general overall trend of the experimental laminar flame speeds of methane/air/CO2 mixtures at 1 bar and 473 K. Additionally, the dilution, thermal-diffusion, and chemical effects of CO2 on the laminar burning velocities of methane/air mixtures were investigated numerically by diluting the mixtures with both chemically active and inactive CO2 following the determination of the most important elementary reactions on the burning rate through sensitivity analysis. Finally, it was shown that CO2 dilution suppresses the flame instabilities during combustion, which is attributable to the increase in the burned gas Markstein length (Lb) with the addition of diluent.

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