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Journal ArticleDOI

A 5-step reduced mechanism for combustion of CO/H2/H2O/CH4/CO2 mixtures with low hydrogen/methane and high H2O content

TL;DR: ZMN and NS acknowledge the funding through the Low Carbon Energy University Alliance Programme supported by Tsinghua University, China as mentioned in this paper, and also like to acknowledge the educational grant through the A.G. LeventisFoundation.
About: This article is published in Combustion and Flame.The article was published on 2013-01-01 and is currently open access. It has received 63 citations till now.

Summary (3 min read)

1. Introduction

  • Recent developments in gas-turbine power generation include the use of low calorific value fuels.
  • Generally, these mechanisms were developed systematically by introducing steady-state and/or partial equilibrium assumptions respectively for some species and reactions involved in a skeletal mechanism.
  • The hydrogen content is low in the BFG as noted earlier and one may like to mix it with small amounts of H2, CH4 and H2O or other gases containing high fractions of these species in order to enhance the BFG combustion characteristics.
  • To the best of their knowledge this is the first attempt to obtain a reduced mechanism for a multi-component fuel mixture with a good accuracy over a wide range of thermodynamic and thermo-chemical conditions.

2. Development of skeletal mechanism: Sensitivity analysis

  • The chemical kinetics of CO/H2 mixture oxidation has been investigated by numerous studies in the past and a sustained interest on the combustion of Syngas in gas turbines for power generation has led to publication of a dedicated volume on this topic in the Combustion Science and Technology journal in 2008.
  • Flame speed sensitivity analyses are conducted using the GRI [19], at high (20%) and zero water vapour content in the fuel mixture in order to (1) identify the most important reactions in each case and (2) to obtain a suitable skeletal mechanism for CO/H2/H2O mixtures.
  • CO2 has large sensitivities for both dry 9 and wet mixtures and OH + CO = H+ CO2 remains as the most important reaction with sensitivity nearly five times larger than for the HO2 reaction for CO consumption.
  • Thus, the effect of small CH4 amounts in the fuel mixture is adequately captured by the extra 9 reactions noted above, something which was neglected while developing reduced mechanism in a previous study [14].

3. Development of reduced chemistry

  • By removing certain intermediate species from the detailed mechanism, the computational effort is reduced as the number of ODEs that must be solved is decreased.
  • Intermediate species can be systematically identified and removed from the ODE system via two major sequential steps.
  • Second, further reduction of the skeletal mechanism results in a reduced mechanism.
  • For fast development of reduced chemistry, the interactive Computer Assisted Reduction Mechanism (CARM) algorithm [40, 43] was used for the automatic generation of reduced chemistry with the ability to produce source codes needed for computing the chemical sources.

4. Reduced mechanism

  • The same would apply in cases where Ar is the inert.
  • Also, for fine tuning of the reduced chemistry, the activation energy of reaction 2 in Table 3 was increased by 27.5%, a procedure similar to the correction factor employed by Boivin et al. [14] to correctly predict the ignition delay times.
  • The steady-state relationships can be written as dCA dt = ψA(ss, ss )− gA(ss, ss)CA = 0, where ψA(ss, ss) and gA(ss, ss) are functions of species both in steady-state, denoted by ss, and non steady-state, denoted by ss.
  • Since the current QSS species are not strongly coupled, the point iteration scheme is found to be sufficient for the present case.

5. Validation

  • Both the skeletal and reduced mechanisms are validated over wide range of conditions shown in Table 4, by comparing laminar flame speeds, ignition delay times and the flame structure with experimental results and/or the computational results obtained using the GRI Mech 3.0 [19].
  • The flame speeds are calculated using the PREMIX [45] code of the CHEMKIN package [46] including the thermal diffusion and multi-component formulation for the species’ diffusivities.
  • In the cases where no experimental data are available, the skeletal and the reduced mechanisms are validated against the predictions of the GRI Mech 3.0 [19] and so readers are cautioned while interpreting this particular comparison.
  • In calculating the ignition delay times with the reduced mechanism, the correction factor used in the study of Boivin et 18 al. [14] is employed.
  • This correction factor was originally developed in [47] from an analysis of the autoignition eigenvalue under lean conditions.

5.1. Premixed flames

  • Comparisons of computed flame speeds, sL, against available experimental data for the mixtures listed in Table 4 are presented in Figs. 1-10.
  • The above comparisons show that overall both the skeletal and the reduced mechanism give good agreement with the experimental data and the computations with the GRI Mech 3.0 [19].
  • The skeletal mechanism of [14] as implemented in this study, under-predicts the flame speeds for all equivalence ratios and the level of under-prediction increases with the H2O content in the fuel mixture.
  • Again there is a good agreement with the full GRI Mech 3.0 [19] and it is somewhat improved in the high pressure case, compared to the predictions of the methane-containing fuel mixture in Fig. 11.

5.2. Autoignition

  • Figure 21 compares the computed ignition delay times (with the correction factor in Eq. 3 applied) with the experimental results of Kalitan et al. [55] for CO/H2 mixtures over a range of conditions listed in Table 4.
  • Overall, the agreement is very good for both low and high pressures and for the entire range of temperatures considered.
  • Figure 22 compares ignition delay times computed for a CO2-diluted mixture to the measured values in [28] at different pressures.
  • The reduced mechanism shows good agreement with the experimental data for the entire temperature range.
  • As noted in [28] using sensitivity analysis, the most important reactions at the conditions tested were the chain-branching reactions and the three body recombination reaction H + O2 + CO2 = HO2 + CO2.

6. Speed up times

  • Table 5 shows the time in seconds taken for each run for each of the conditions shown in Table 4.
  • The flame speeds were calculated using the PREMIX code [45] with thermal diffusion and a multi-component formulation for the species’ diffusivities, in a 2.5 cm domain with adaptive grid.
  • It is clear that both the skeletal and reduced mechanisms reduced the computational time significantly compared to the GRI Mech 3.0 [19], while maintaining the same level of accuracy.
  • In particular for case 3 the skeletal mechanism is about 50 times faster and the reduced mechanism about 300 times faster.

7. Conclusions

  • A 5-step reduced chemical kinetic mechanism involving 9 species for accurate prediction of the combustion characteristics of multi-species fuel mixtures of CO/H2/H2O/CH4/CO2, having low hydrogen/methane and high water vapour content is derived.
  • These two mechanisms are tested for their ability to predict laminar flame speeds, flame structure and ignition delay times over a wide range of pressure, temperature and fuel mixture composition.
  • It is also worth to note that these conditions are relevant for stationary gas-turbines for power generation.
  • Furthermore, it is found that use of the reduced mechanism decreases the computational time significantly compared to the GRI Mech 3.0, while maintaining a a very good degree of accuracy.
  • ZMN also likes to acknowledge the educational grant through the A.G. Leventis Foundation.

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Journal ArticleDOI
TL;DR: In this paper, the authors carried out the molecular dynamics simulations of the PVTx properties of the H2O-CO2-H2 mixtures in the near-critical and supercritical regions of water to generate 600 datasets at 750-1150 K and 4.0-443.5 MPa.

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Cites background from "A 5-step reduced mechanism for comb..."

  • ...[14] Nikolaou ZM, Chen J-Y, Swaminathan N....

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  • ...Moreover, H2O, CO2, and H2, as most common substances in both nature and industry, the PVTx properties of their mixtures have great potential applications in thermochemical processes [14] and environmental engineering [15]....

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Journal ArticleDOI
TL;DR: In this paper, the authors evaluate the predictive capabilities of selected detailed, reduced and global syngas chemical mechanisms by comparing the numerical results with experimental laminar flame speed values of lean premixed syngga flames.
Abstract: The implementation of reduced syngas combustion mechanisms in numerical combustion studies has become inevitable in order to reduce the computational cost without compromising the predictions’ accuracy. In this regard, the present study evaluates the predictive capabilities of selected detailed, reduced and global syngas chemical mechanisms by comparing the numerical results with experimental laminar flame speed values of lean premixed syngas flames. The comparisons are carried out at varying equivalence ratios, syngas compositions, operating pressures, and preheat temperatures to represent a range of operating conditions of modern fuel flexible combustion systems. NOX emissions predicted by the detailed mechanism, GRI-Mech. 3.0, are also used to study the accuracy of the selected mechanisms under these operating conditions. Moreover, the selected mechanisms’ accuracy in predicting the laminar flame thickness, species concentrations of the reactants, and OH profiles at different equivalence ratios and syngas compositions are investigated as well. The laminar flame speed is generally observed to increase with increasing equivalence ratio, hydrogen content in the syngas, and preheat temperature, while it is decreased with increasing operating pressure. This trend is followed by all mechanisms understudy. The global mechanisms of Watanabe-Otaka and Jones-Lindstedt for syngas are consistently observed to over-predict and under-predict the laminar flame speed up to an average of 60% and 80%, respectively. The reduced mechanism of Slavinskaya has an average error of less than 20% which is comparable to the average error of the GRI-Mech. 3.0. It however overpredicts the flame thickness by up to 30% when compared to GRI-Mech. 3.0. The NO prediction by Li mechanism and the reduced mechanisms are observed to be within 10% prediction range of the GRI-Mech. 3.0 at intermediate equivalence ratio (φ = 0.7) up to stoichiometry. Moving towards more lean conditions, there is significant difference between the GRI-Mech. 3.0 NO prediction and those of the reduced mechanisms due to relative importance of the prompt NOX at lower temperature compared to thermal NOX that is only accounted for by the GRI-Mech. 3.0.

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15 Jun 2019-Fuel
TL;DR: In this article, two detailed kinetic mechanisms, namely AramcoMech 2.0 and recently updated Konnov mechanism, were validated using available measurements of ignition delay times and laminar burning velocities for hydrogen, methane and hydrogen+methane fuel mixtures.

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Journal ArticleDOI
24 May 2021
TL;DR: In this paper, a review of detailed, reduced, and global kinetic mechanisms of importance for CFD of methane combustion is presented, and procedures of relevance to model development are outlined.
Abstract: 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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Journal ArticleDOI
25 Jun 2019-Energies
TL;DR: In this paper, the effects of H2 and CH4 concentrations on the ignition delay time and laminar flame speed during the combustion of CH4/H2 and multicomponent syngas mixtures using a novel constructed reduced Syngas chemical kinetics mechanism.
Abstract: This study investigated the effects of H2 and CH4 concentrations on the ignition delay time and laminar flame speed during the combustion of CH4/H2 and multicomponent syngas mixtures using a novel constructed reduced syngas chemical kinetics mechanism. The results were compared with experiments and GRI Mech 3.0 mechanism. It was found that mixture reactivity decreases and increases when higher concentrations of CH4 and H2 were used, respectively. With higher H2 concentration in the mixture, the formation of OH is faster, leading to higher laminar flame speed and shorter ignition delay time. CH4 and H2 concentrations were calculated at different pressures and equivalence ratios, showing that at high pressures CH4 is consumed slower, and, at different equivalence ratios CH4 reacts at different temperatures. In the presence of H2, CH4 was consumed faster. In the conducted two-stage sensitivity analysis, the first analysis showed that H2/CH4/CO mixture combustion is driven by H2-based reactions related to the consumption/formation of OH and CH4 recombination reactions are responsible for CH4 oxidation. The second analysis showed that similar CH4-based and H2 -based reactions were sensitive in both, methane- and hydrogen-rich H2/CH4 mixtures. The difference was observed for reactions CH2O + OH = HCO + H2O and CH4 + HO2 = CH3 + H2O2, which were found to be important for CH4-rich mixtures, while reactions OH + HO2 = H2O + O2 and HO2 + H = OH + OH were found to be important for H2-rich mixtures.

12 citations

References
More filters
ReportDOI
01 Sep 1989

3,517 citations


"A 5-step reduced mechanism for comb..." refers methods in this paper

  • ...The flame speeds are calculated using the PREMIX [45] code of the CHEMKIN package [46] including thermal diffusion and multi-component formulation for the species’ diffusivities....

    [...]

  • ...Ignition delay times are calculated using a constant volume reactor solver of the CHEMKIN package [46]....

    [...]

01 Jan 1998
TL;DR: In this paper, a Fortran computer program that computes species and temperature profiles in steady-state burner-stabilized and freely propagating laminar flames is described.
Abstract: This report documents a Fortran computer program that computes species and temperature profiles in steady-state burner-stabilized and freely propagating premixed laminar flames. The program accounts for finite rate chemical kinetics and multicomponent molecular transport. After stating the appropriate governing equations and boundary conditions, we discuss the finite difference discretization and the Newton method for solving the boundary value problem. Global convergence of this algorithm is aided by invoking time integration procedures when the Newton method has convergence difficulties. The program runs in conjunction with preprocessors for the chemical reaction mechanism and the transport properties. Transport property formulations include the option of using multicomponent or mixtureaveraged formulas for molecular diffusion. Discussion of two example problems illustrates many of the program's capabilities.

1,533 citations


"A 5-step reduced mechanism for comb..." refers methods in this paper

  • ...The flame speeds were calculated using the PREMIX code [45] with thermal diffusion and a multicomponent formulation for the species’ diffusivities, in a 2.5 cm domain with adaptive grid....

    [...]

  • ...The flame speeds are calculated using the PREMIX [45] code of the CHEMKIN package [46] including thermal diffusion and multi-component formulation for the species’ diffusivities....

    [...]

  • ...The flame speeds were calculated using the PREMIX code [45] with thermal diffusion and a multicomponent formulation for the species’ diffusivities, in a 2....

    [...]

  • ...Table 5 Time in s of the run for each condition using PREMIX [45] with thermal and multicomponent diffusion....

    [...]

Journal ArticleDOI
TL;DR: In this paper, a new experimental profile of stable species concentrations is reported for formaldehyde oxidation in a variable pressure flow reactor at initial temperatures of 850-950 K and at constant pressures ranging from 1.5 to 6.0 atm.
Abstract: New experimental profiles of stable species concentrations are reported for formaldehyde oxidation in a variable pressure flow reactor at initial temperatures of 850–950 K and at constant pressures ranging from 1.5 to 6.0 atm. These data, along with other data published in the literature and a previous comprehensive chemical kinetic model for methanol oxidation, are used to hierarchically develop an updated mechanism for CO/H2O/H2/O2, CH2O, and CH3OH oxidation. Important modifications include recent revisions for the hydrogen–oxygen submechanism (Li et al., Int J Chem Kinet 2004, 36, 565), an updated submechanism for methanol reactions, and kinetic and thermochemical parameter modifications based upon recently published information. New rate constant correlations are recommended for CO + OH = CO2 + H (R23) and HCO + M = H + CO + M (R24), motivated by a new identification of the temperatures over which these rate constants most affect laminar flame speed predictions (Zhao et al., Int J Chem Kinet 2005, 37, 282). The new weighted least-squares fit of literature experimental data for (R23) yields k23 = 2.23 × 105T1.89exp(583/T) cm3/mol/s and reflects significantly lower rate constant values at low and intermediate temperatures in comparison to another recently recommended correlation and theoretical predictions. The weighted least-squares fit of literature results for (R24) yields k24 = 4.75 × 1011T0.66exp(−7485/T) cm3/mol/s, which predicts values within uncertainties of both prior and new (Friedrichs et al., Phys Chem Chem Phys 2002, 4, 5778; DeSain et al., Chem Phys Lett 2001, 347, 79) measurements. Use of either of the data correlations reported in Friedrichs et al. (2002) and DeSain et al. (2001) for this reaction significantly degrades laminar flame speed predictions for oxygenated fuels as well as for other hydrocarbons. The present C1/O2 mechanism compares favorably against a wide range of experimental conditions for laminar premixed flame speed, shock tube ignition delay, and flow reactor species time history data at each level of hierarchical development. Very good agreement of the model predictions with all of the experimental measurements is demonstrated. © 2007 Wiley Periodicals, Inc. 39: 109–136, 2007

707 citations

Journal ArticleDOI
01 Jan 2005
TL;DR: In this paper, a H2-CO kinetic model was proposed to predict a wide variety of H2 and CO combustion data, from global combustion properties (shock-tube ignition delays, laminar flame speeds, and extinction strain rates) to detailed species profiles during H 2 and CO oxidation.
Abstract: We propose a H2–CO kinetic model which incorporates the recent thermodynamic, kinetic, and species transport updates relevant to high-temperature H2 and CO oxidation. Attention has been placed on obtaining a comprehensive and kinetically accurate model able to predict a wide variety of H2–CO combustion data. The model was subject to systematic optimization and validation tests against reliable H2–CO combustion data, from global combustion properties (shock-tube ignition delays, laminar flame speeds, and extinction strain rates) to detailed species profiles during H2 and CO oxidation in flow reactor and in laminar premixed flames.

626 citations

Journal ArticleDOI
TL;DR: In this paper, a consensus value of the appearance energy of the O−H bond energy was derived from a mass-selected photoionization measurements, pulsed-field-ionization photoelectron spectroscopy measurements, and photo-electron-photoion coincidence measurements.
Abstract: In a recent letter (J. Phys. Chem. A, 2001, 105,1), we argued that, although all major thermochemical tables recommend a value of (OH) based on a spectroscopic approach, the correct value is 0.5 kcal/mol lower as determined from an ion cycle. In this paper, we expand upon and augment both the experimental and theoretical arguments presented in the letter. In particular, three separate experiments (mass-selected photoionization measurements, pulsed-field-ionization photoelectron spectroscopy measurements, and photoelectron-photoion coincidence measurements) utilizing the positive ion cycle to derive the O−H bond energy are shown to converge to a consensus value of the appearance energy AE0(OH+/H2O) = 146117 ± 24 cm-1 (18.1162 ± 0.0030 eV). With the most accurate currently available zero kinetic energy photoionization value for the ionization energy IE(OH) = 104989 ± 2 cm-1, corroborated by a number of photoelectron measurements, this leads to D0(H−OH) = 41128 ± 24 cm-1 = 117.59 ± 0.07 kcal/mol. This corres...

453 citations

Frequently Asked Questions (2)
Q1. What are the contributions in "A 5-step reduced mechanism for combustion of co/h2/h2o/ch4/co2 mixtures with low hydrogen/methane and high h2o content" ?

In this study a 5-step reduced chemical kinetic mechanism involving 9 species is developed for combustion of Blast Furnace Gas ( BFG ), a multi-component fuel containing CO/H2/CH4/CO2, typically with low hydrogen, methane and high water fractions, for conditions relevant for stationary gas-turbine combustion. 

The computational results are compared to experimental measurements of the flame speeds available in the literature for a wide range of pressure, 1-20 atm., temperature, 298- 700 K and thermo-chemical conditions. The authors thank the reviewers for suggesting many validation data which helped to show the robustness of the mechanisms over wide range of conditions for flame speeds and autoignition delay times.