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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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Citations
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Journal ArticleDOI
TL;DR: In this article, the origins of PSR non-equilibrium behavior are elucidated by analyzing the relevance of the reaction steps involved in the CO/O2 kinetic mechanism, deriving and assessing analytical expressions reproducing the PSR results, and examining asymptotic limit solutions emphasizing a possible cause of the nonequilibrium behaviour observed.
Abstract: The observed origins of non-equilibrium behavior, even for relatively large residence times in perfectly stirred reactors (PSRs) burning fuel-rich mixtures, are addressed. These PSR deviations from chemical equilibrium are characterized by using PSR-based results of CO/O2 reacting mixtures. Accordingly, the origins of the PSR non-equilibrium behavior are elucidated by (i) analyzing the relevance of the reaction steps involved in the CO/O2 kinetic mechanism, (ii) deriving and assessing analytical expressions reproducing the PSR results, and (iii) examining asymptotic limit solutions emphasizing a possible cause of the non-equilibrium behavior observed. The main results highlight that the PSR non-equilibrium behavior is controlled by a competition between (i) the rate of progress variable backward component of the CO + O + M ⇌ CO2 + M reaction and (ii) the ratio between the reactor inlet O2 molar concentration and the reactor residence time. Thus, even when the reactor is operating in a region of te...

3 citations


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

  • ...They are employed, for instance, in (i) the study or derivation of detailed (LeCong andDagaut, 2007, 2008) and reduced (Mallampalli et al., 1998; Nikolaou et al., 2013; Sung et al., 2001) chemical kinetic mechanisms, (ii) the prediction of pollutant formation (Adhikari et al....

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  • ...They are employed, for instance, in (i) the study or derivation of detailed (LeCong andDagaut, 2007, 2008) and reduced (Mallampalli et al., 1998; Nikolaou et al., 2013; Sung et al., 2001) chemical kinetic mechanisms, (ii) the prediction of pollutant formation (Adhikari et al., 2016; Amzin and Cant,…...

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Journal ArticleDOI
TL;DR: In this paper, the authors proposed a reduction strategy and used it to obtain a reduced kinetic mechanism for the methyl butanoate (MB, $$C_3H_7COOCH_3$$¯¯¯¯ ) for biodiesel fuels.
Abstract: The computational treatment of detailed kinetic reaction mechanisms for combustion is expensive, especially in the case of biodiesel fuels. In this way, great efforts in the search of techniques for the development of reduced kinetic mechanisms have been observed. As Methyl Butanoate (MB, $$C_3H_7COOCH_3$$ ) is an essential model frequently used to represent the ester group of reactions in saturated methyl esters of large chain, this paper proposes a reduction strategy and uses it to obtain a reduced kinetic mechanism for the MB. The reduction strategy consists in the use of artificial intelligence to define the main chain and produce a skeletal mechanism, apply the traditional hypotheses of steady-state and partial equilibrium, and justify these assumptions through an asymptotic analysis. The main advantage of the strategy employed here is to reduce the work required to solve the system of chemical equations by two orders of magnitude for MB, since the number of reactions is decreased in the same order.

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  • ...The skeletalmechanismused to develop the reducedmechanism strongly influences the stiffness of the latter [40]....

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Journal ArticleDOI
TL;DR: In this article, a single species X can be introduced, representing either HO 2 for high temperature ignition or H 2 O 2 for low-temperature ignition, to develop an algorithm that covers the entire range of ignition, flame propagation, and combustion conditions, without a significant degradation of accuracy, for hydrogen-air systems.

3 citations

Journal ArticleDOI
TL;DR: In this paper, the sensitivity of elementary reaction to combustion rate was analyzed by using one dimensional laminar premixed reactor model, and the reduced 18-step mechanism which is specified to 0.1-3 Mpa was used to solve the lack of reduced BFG mechanism under elevated pressure environment in numerical simulation.
Abstract: To solve the lack of reduced Blast furnace gas (BFG) mechanism under elevated pressure environment in numerical simulation, the present paper analyzes the sensitivity of every elementary reaction to combustion rate by using one dimensional laminar premixed reactor model. The steps with sensitivities larger than 0.1 are selected and the chemical kinetic parameters are revised by the method of weighted least squares fitting. The reduced 18-step mechanism which is specified to 0.1-3 Mpa is validated for laminar flame speeds, ignition delay times with available experiment data and GRI3.0 mechanism. Moreover, both the reduced and DRM-22 mechanisms are introduced into an experimental burner and an industrial gas turbine combustor simulation. The results of temperature and main species distribution illustrate that the 18-step mechanism is able to give a reasonable prediction combustion simulation. The 18-step mechanism lays the foundation of further studying the combustion of the low calorific value fuels at high pressure conditions.

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Journal ArticleDOI
21 Sep 2018
TL;DR: In this paper, a deconvolution-modelled variance is used as an input in the flamelet models for modeling the filtered progress variable rate in large eddy simulations of turbulent and reacting flows.
Abstract: A novel approach for modeling the progress variable reaction rate in Large Eddy Simulations of turbulent and reacting flows is proposed. This is done in the context of two popular flamelet models which require the progress variable variance as input. The approach is based on using a recently proposed deconvolution method for modeling the variance. The deconvolution-modeled variance, is used as an input in the flamelet models for modeling the filtered progress variable rate. The assessment of the proposed approach is conducted a priori using direct numerical simulation data of turbulent premixed flames. For the conditions tested in this study, deconvolution does not introduce a significant bias in the flamelet models' predictions, while a quantitatively good prediction of the progress variable rate is obtained for both flamelet models considered.

2 citations

References
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"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....

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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.

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"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....

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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

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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

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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...

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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.