scholarly journals Model Comparisons of Flow and Chemical Kinetic Mechanisms for Methane–Air Combustion for Engineering Applications

2021 ◽  
Vol 11 (9) ◽  
pp. 4107
Author(s):  
Di He ◽  
Yusong Yu ◽  
Yucheng Kuang ◽  
Chaojun Wang
Keyword(s):  
Experimental Data ◽  
Mixture Fraction ◽  
Radiation Heat Transfer ◽  
Kinetic Mechanism ◽  
Reynolds Stress Model ◽  
Chemical Kinetic ◽  
Transfer Model ◽  
Molecular Mixing ◽  
Jet Flame ◽  
Kinetic Mechanisms

The reasonably accurate numerical simulation of methane–air combustion is important for engineering purposes. In the present work, the validations of sub-models were carried out on a laboratory-scale turbulent jet flame, Sandia Flame D, in comparison with experimental data. The eddy dissipation concept (EDC), which assumes that the molecular mixing and subsequent combustion occur in the fine structures, was used for the turbulence–chemistry interaction. The standard k-ε model (SKE) with the standard or the changed model constant C1ε, the realizable k-ε model (RKE), the shear-stress transport k-ω model (SST), and the Reynolds stress model (RSM) were compared with the detailed chemical kinetic mechanism of GRI-Mech 3.0. Different reaction treatments for the methane–air combustion were also validated with the available experimental data from the literature. In general, there were good agreements between predictions and measurements, which gave a good indication of the adequacy and accuracy of the method and its further applications for industry-scale turbulent combustion simulations. The differences between predictions and measured data might have come from the simplifications of the boundary settings, the turbulence model, the turbulence–reaction interaction, and the radiation heat transfer model. For engineering predictions of methane–air combustion, the mixture fraction probability density function (PDF) model for the partially premixed combustion with RSM is recommended due to its relatively low simulation expenses, acceptable accuracy predictions, and quantitatively good agreement with the experiments.

Combustion Simulation of Propane/Oxygen (With Nitrogen/Argon) Mixtures Using Rate-Controlled Constrained-Equilibrium

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Guangying Yu ◽  
Hameed Metghalchi ◽  
Omid Askari ◽  
Ziyu Wang
Keyword(s):  
Experimental Data ◽  
Energy System ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Oxygen Mixture ◽  
Free Valence ◽  
Wide Range ◽  
Constrained Equilibrium ◽  
Rate Controlled ◽  
Good Agreement

The rate-controlled constrained-equilibrium (RCCE), a model order reduction method, has been further developed to simulate the combustion of propane/oxygen mixture diluted with nitrogen or argon. The RCCE method assumes that the nonequilibrium states of a system can be described by a sequence of constrained-equilibrium states subject to a small number of constraints. The developed new RCCE approach is applied to the oxidation of propane in a constant volume, constant internal energy system over a wide range of initial temperatures and pressures. The USC-Mech II (109 species and 781 reactions, without nitrogen chemistry) is chosen as chemical kinetic mechanism for propane oxidation for both detailed kinetic model (DKM) and RCCE method. The derivation for constraints of propane/oxygen mixture starts from the eight universal constraints for carbon-fuel oxidation. The universal constraints are the elements (C, H, O), number of moles, free valence, free oxygen, fuel, and fuel radicals. The full set of constraints contains eight universal constraints and seven additional constraints. The results of RCCE method are compared with the results of DKM to verify the effectiveness of constraints and the efficiency of RCCE. The RCCE results show good agreement with DKM results under different initial temperature and pressures, and RCCE also reduces at least 60% CPU time. Further validation is made by comparing the experimental data; RCCE shows good agreement with shock tube experimental data.

scholarly journals Simulation of a GOx-GCH4 Rocket Combustor and the Effect of the GEKO Turbulence Model Coefficients

Aerospace ◽  
2021 ◽  
Vol 8 (11) ◽  
pp. 341
Author(s):  
Evgeny Strokach ◽  
Victor Zhukov ◽  
Igor Borovik ◽  
Andrej Sternin ◽  
Oscar J. Haidn
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Turbulence Model ◽  
Chemical Kinetic ◽  
Wall Heat Flux ◽  
Combustion Model ◽  
Combustion Chambers ◽  
Separation Parameter ◽  
Kinetic Mechanisms ◽  
Stable Performance

In this study, a single injector methane-oxygen rocket combustor is numerically studied. The simulations included in this study are based on the hardware and experimental data from the Technical University of Munich. The focus is on the recently developed generalized k–ω turbulence model (GEKO) and the effect of its adjustable coefficients on the pressure and on wall heat flux profiles, which are compared with the experimental data. It was found that the coefficients of ‘jet’, ‘near-wall’, and ‘mixing’ have a major impact, whereas the opposite can be deduced about the ‘separation’ parameter Csep, which highly influences the pressure and wall heat flux distributions due to the changes in the eddy-viscosity field. The simulation results are compared with the standard k–ε model, displaying a qualitatively and quantitatively similar behavior to the GEKO model at a Csep equal to unity. The default GEKO model shows a stable performance for three oxidizer-to-fuel ratios, enhancing the reliability of its use. The simulations are conducted using two chemical kinetic mechanisms: Zhukov and Kong and the more detailed RAMEC. The influence of the combustion model is of the same order as the influence of the turbulence model. In general, the numerical results present a good or satisfactory agreement with the experiment, and both GEKO at Csep = 1 or the standard k–ε model can be recommended for usage in the CFD simulations of rocket combustion chambers, as well as the Zhukov–Kong mechanism in conjunction with the flamelet approach.

Theoretical Investigation of Autoignition of Combustible Gas Mixtures in Rapid Compression Machines

2002 ◽  
Author(s):  
Shaoping Shi ◽  
Daniel Lee ◽  
Sandra McSurdy ◽  
Michael McMillian ◽  
Steven Richardson ◽  
...  
Keyword(s):  
Experimental Data ◽  
Theoretical Investigation ◽  
Ignition Delay ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Reaction Scheme ◽  
Independent Manner ◽  
Elementary Reactions ◽  
Chemical Kinetic Mechanism ◽  
Rapid Compression

In any theoretical investigation of ignition processes in natural gas reciprocating engines, physical and chemical mechanisms must be adequately modeled and validated in an independent manner. The Rapid Compression Machine (RCM) has been used in the past as a tool to validate both autoignition models as well as turbulent mixing effects. In this study, two experimental cases were examined. In the first experimental case, the experimental measurements of Lee and Hochgreb (1998a) were chosen to validate the simulation results. In their experiments, hydrogen/oxygen/argon mixtures were used as reactants. In the simulations, a reduced chemical kinetic mechanism consisting of 10 species and 19 elementary reactions coupled to a CFD software, Fluent 6, was used to simulate the autoignition. The ignition delay from the simulation agreed very well with that from the experimental data of Lee and Hochgreb, (1998b). In the second case, experimental data derived from an RCM with two opposed, pneumatically driven pistons (Brett et al., 2001) were used to study the autoignition of methane/oxygen/argon mixtures. The reduced chemical kinetic mechanism DRM22, derived from the GRI-Mech reaction scheme coupled to Fluent 6, was applied in the simulations. The DRM22 scheme included 22 species and 104 reactions. When methane/oxygen/argon mixture were simulated for the RCM, the ignition delay deviated about 15% from the experimental results. The simulation approaches as well as the validation results are discussed in detail in this paper. The paper also discusses an evaluation of reduced reaction models available in the literature for subsequent Fluent modeling.

Mathematical Imaging of Piloted Diffusion Methane-Air Flames Under Anisotropic Scalar Dissipation Rates

2005 ◽  
Author(s):  
Mohsen M. Abou-Ellail ◽  
Karam R. Beshay ◽  
David R. Halka
Keyword(s):  
Diffusion Flame ◽  
Dissipation Rate ◽  
Mixture Fraction ◽  
Flame Temperature ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Scalar Dissipation ◽  
Elementary Reactions ◽  
Chemical Kinetic Mechanism ◽  
Limiting Value

The present work is a numerical simulation of the, piloted, non-premixed, methane–air flame structure in a new mathematical imaging domain. This imaging space has the mixture fraction of diffusion flame Z1 and mixture fraction of pilot flame Z2 as independent coordinates to replace the usual physical space coordinates. The predications are based on the solution of two–dimensional set of transformed second order partial differential conservation equations describing the mass fractions of O2, CH4, CO2, CO, H2O, H2 and sensible enthalpy of the combustion products which are rigorously derived and solved numerically. A three–step chemical kinetic mechanism is adopted. This was deduced in a systematic way from a detailed chemical kinetic mechanism by Peters (1985). The rates for the three reaction steps are related to the rates of the elementary reactions of the full reaction mechanism. The interaction of the pilot flame with the non-premixed flame and the resulting modifications to the structure and chemical kinetics of the flame are studied numerically for different values of the scalar dissipation rate tensor. The dissipation rate tensor represents the flame stretching along Z1, the main mixture fraction, and in the perpendicular direction, along Z2, the pilot mixture fraction. The computed flame temperature contours are plotted in the Z1-Z2 plane for fixed values of the dissipation rate along Z1 and Z2.These temperature contours show that the flame will become unstable when the dissipate rates along Z1 and Z2 increase, simultaneously, to the limiting value for complete flame extinction of 45 s−1. However, the diffusion flame will extinguish for dissipate rates less than 20 1/s, if unpiloted. It is also noticed that the flame will remain stable if the dissipation rate along Z2 is increased to the limiting value, while the dissipation rate, along Z2, remains constant at a value less than 30 s−1.

Modeling spray combustion using multi-component surrogate fuels

2021 ◽  
pp. 095765092110025
Author(s):  
Tao Yang ◽  
Ran Yi ◽  
Qiaoling Wang ◽  
Chien-Pin Chen
Keyword(s):  
Chemical Properties ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Spray Combustion ◽  
Surrogate Fuels ◽  
Diesel Fuels ◽  
Constant Volume Chamber ◽  
Kinetic Mechanisms ◽  
Lift Off ◽  
Evaporation Models

Kerosene and diesel fuels involved in spray combustion operations are complex fuels composed of a wide and diverse variety of hydrocarbon components. For practical numerical modeling of the evaporation and combustion phenomena in a combustor, well-designed surrogates fuels that can mimic the real fuel thermal and chemical properties can be utilized. In this study, predictions and validations of the influence of fuel on the liquid and vapor penetration characteristics within a constant-volume chamber were first performed utilizing a benchmark m-xylene/ n-dodecane, Jet-A, and diesel surrogate fuels. Then, simulations of reacting spray of a bi-component m-xylene/ n-dodecane fule, and a four-component Jet-A surrogate fuel ( n-dodecane (C12H26), iso-cetane (C16H34), trans-decalin (C10H18) and toluene (C7H8)) were studied aided by skeleton chemical kinetic mechanisms available from the literature. The results of ignition delay time, lift-off length, radicals, and the mass fraction histories of fuel species were comprehensively used to assess the performance of relevant thermophysical and chemical sub-models. Two different chemical mechanisms were compared in detail to investigate the effect of the chemical kinetics model on the flame structures and spray characteristics. It has been found that the spray ignition of multi-component fuels is remarkably influenced by the chosen chemical kinetic mechanism and less affected by the droplet evaporation models.

scholarly journals Chemical Kinetic Mechanism Study on Premixed Combustion of Ammonia/Hydrogen Fuels for Gas Turbine Use

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Hua Xiao ◽  
Agustin Valera-Medina
Keyword(s):  
Experimental Data ◽  
Gas Turbine ◽  
Ignition Delay ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Sensitivity Analyses ◽  
Mechanism Study ◽  
Combustion Chemistry ◽  
Chemical Mechanisms ◽  
Ignition Delay Times

To explore the potential of ammonia-based fuel as an alternative fuel for future power generation, studies involving robust mathematical, chemical, thermofluidic analyses are required to progress toward industrial implementation. Thus, the aim of this study is to identify reaction mechanisms that accurately represent ammonia kinetics over a large range of conditions, particularly at industrial conditions. To comprehensively evaluate the performance of the chemical mechanisms, 12 mechanisms are tested in terms of flame speed, NOx emissions and ignition delay against the experimental data. Freely propagating flame calculations indicate that Mathieu mechanism yields the best agreement within experimental data range of different ammonia concentrations, equivalence ratios, and pressures. Ignition delay times calculations show that Mathieu mechanism and Tian mechanism yield the best agreement with data from shock tube experiments at pressures up to 30 atm. Sensitivity analyses were performed in order to identify reactions and ranges of conditions that require optimization in future mechanism development. The present study suggests that the Mathieu mechanism and Tian mechanism are the best suited for the further study on ammonia/hydrogen combustion chemistry under practical industrial conditions. The results obtained in this study also allow gas turbine designers and modelers to choose the most suitable mechanism for combustion studies.

scholarly journals Formation of secondary aerosols over Europe: comparison of two gas-phase chemical mechanisms

2011 ◽  
Vol 11 (2) ◽  
pp. 583-598 ◽  
Author(s):  
Y. Kim ◽  
K. Sartelet ◽  
C. Seigneur
Keyword(s):  
Gas Phase ◽  
Organic Aerosols ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Chemical Mechanisms ◽  
Kinetic Mechanisms ◽  
Chemical Kinetic Mechanism ◽  
The Impact ◽  
Phase Chemical ◽  
Inorganic And Organic

Abstract. The impact of two recent gas-phase chemical kinetic mechanisms (CB05 and RACM2) on the formation of secondary inorganic and organic aerosols is compared for simulations of PM2.5 over Europe between 15 July and 15 August 2001. The host chemistry transport model is Polair3D of the Polyphemus air-quality platform. Particulate matter is modeled with a sectional aerosol model (SIREAM), which is coupled to the thermodynamic model ISORROPIA for inorganic species and to a module (MAEC) that treats both hydrophobic and hydrophilic species for secondary organic aerosol (SOA). Modifications are made to the gas-phase chemical mechanisms to handle the formation of SOA. In order to isolate the effect of the original chemical mechanisms on PM formation, the addition of reactions and chemical species needed for SOA formation was harmonized to the extent possible between the two gas-phase chemical mechanisms. Model performance is satisfactory with both mechanisms for speciated PM2.5. The monthly-mean difference of the concentration of PM2.5 is less than 1 μg m−3 (6%) over the entire domain. Secondary chemical components of PM2.5 include sulfate, nitrate, ammonium and organic aerosols, and the chemical composition of PM2.5 is not significantly different between the two mechanisms. Monthly-mean concentrations of inorganic aerosol are higher with RACM2 than with CB05 (+16% for sulfate, +11% for nitrate, and +10% for ammonium), whereas the concentrations of organic aerosols are slightly higher with CB05 than with RACM2 (+22% for anthropogenic SOA and +1% for biogenic SOA). Differences in the inorganic and organic aerosols result primarily from differences in oxidant concentrations (OH, O3 and NO3). Nitrate formation tends to be HNO3-limited over land and differences in the concentrations of nitrate are due to differences in concentration of HNO3. Differences in aerosols formed from aromatic SVOC are due to different aromatic oxidation between CB05 and RACM2. The aromatic oxidation in CB05 leads to more cresol formation, which then leads to more SOA. Differences in the aromatic aerosols would be significantly reduced with the recent CB05-TU mechanism for toluene oxidation. Differences in the biogenic aerosols are due to different oxidant concentrations (monoterpenes) and different particulate organic mass concentrations affecting the gas-particle partitioning of SOA (isoprene). These results show that the formulation of a gas-phase chemical kinetic mechanism for ozone can have significant direct (e.g., cresol formation) and indirect (e.g., oxidant levels) effects on PM formation. Furthermore, the incorporation of SOA into an existing gas-phase chemical kinetic mechanism requires the addition of reactions and product species, which should be conducted carefully to preserve the original mechanism design and reflect current knowledge of SOA formation processes (e.g., NOx dependence of some SOA yields). The development of chemical kinetic mechanisms, which offer sufficient detail for both oxidant and SOA formation is recommended.

scholarly journals Modelling of Self-Ignition in Spark-Ignition Engine Using Reduced Chemical Kinetics for Gasoline Surrogates

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 157 ◽  
Author(s):  
Ahmed Faraz Khan ◽  
Philip John Roberts ◽  
Alexey A. Burluka
Keyword(s):  
Chemical Kinetics ◽  
Octane Number ◽  
Kinetic Mechanism ◽  
Spark Ignition ◽  
Chemical Kinetic ◽  
Spark Ignition Engine ◽  
Detailed Chemical Kinetics ◽  
Kinetic Predictions ◽  
Kinetic Mechanisms

A numerical and experimental investigation in to the role of gasoline surrogates and their reduced chemical kinetic mechanisms in spark ignition (SI) engine knocking has been carried out. In order to predict autoignition of gasoline in a spark ignition engine three reduced chemical kinetic mechanisms have been coupled with quasi-dimensional thermodynamic modelling approach. The modelling was supported by measurements of the knocking tendencies of three fuels of very different compositions yet an equivalent Research Octane Number (RON) of 90 (ULG90, PRF90 and 71.5% by volume toluene blended with n-heptane) as well as iso-octane. The experimental knock onsets provided a benchmark for the chemical kinetic predictions of autoignition and also highlighted the limitations of characterisation of the knock resistance of a gasoline in terms of the Research and Motoring octane numbers and the role of these parameters in surrogate formulation. Two approaches used to optimise the surrogate composition have been discussed and possible surrogates for ULG90 have been formulated and numerically studied. A discussion has also been made on the various surrogates from the literature which have been tested in shock tube and rapid compression machines for their autoignition times and are a source of chemical kinetic mechanism validation. The differences in the knock onsets of the tested fuels have been explained by modelling their reactivity using semi-detailed chemical kinetics. Through this work, the weaknesses and challenges of autoignition modelling in SI engines through gasoline surrogate chemical kinetics have been highlighted. Adequacy of a surrogate in simulating the autoignition behaviour of gasoline has also been investigated as it is more important for the surrogate to have the same reactivity as the gasoline at all engine relevant p − T conditions than having the same RON and Motored Octane Number (MON).

scholarly journals Evaluation of Chemical Kinetic Mechanisms for Methane Combustion: A Review from a CFD Perspective

Fuels ◽  
2021 ◽  
Vol 2 (2) ◽  
pp. 210-240
Author(s):  
Niklas Zettervall ◽  
Christer Fureby ◽  
Elna J. K. Nilsson
Keyword(s):  
Model Development ◽  
Computational Cost ◽  
Informed Choice ◽  
Methane Combustion ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Cfd Modeling ◽  
Computational Time ◽  
Wide Range ◽  
Kinetic Mechanisms

Methane is an important fuel for gas turbine and gas engine combustion, and the most common fuel in fundamental combustion studies. As Computational Fluid Dynamics (CFD) modeling of combustion becomes increasingly important, so do chemical kinetic mechanisms for methane combustion. Kinetic mechanisms of different complexity exist, and the aim of this study is to review commonly used detailed, reduced, and global mechanisms of importance for CFD of methane combustion. In this review, procedures of relevance to model development are outlined. Simulations of zero and one-dimensional configurations have been performed over a wide range of conditions, including addition of H2, CO2 and H2O, and the results are used in a final recommendation about the use of the different mechanisms. The aim of this review is to put focus on the importance of an informed choice of kinetic mechanism to obtain accurate results at a reasonable computational cost. It is shown that for flame simulations, a reduced mechanism with only 42 irreversible reactions gives excellent agreement with experimental data, using only 5% of the computational time as compared to the widely used GRI-Mech 3.0. The reduced mechanisms are highly suitable for flame simulations, while for ignition they tend to react too slow, giving longer than expected ignition delay time. For combustible mixtures with addition of hydrogen, carbon dioxide, or water, the detailed as well as reduced mechanisms generally show as good performance as for the corresponding simulations of pure methane/air mixtures.

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