Role of HOCO Chemistry in Syngas Combustion - Energy & Fuels

Subscriber access provided by GAZI UNIV

Article

The role of HOCO chemistry in syngas combustion Elna Johanna Kristina Nilsson, and Alexander A Konnov Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b02778 • Publication Date (Web): 03 Feb 2016 Downloaded from http://pubs.acs.org on February 9, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

The role of HOCO chemistry in syngas combustion E.J.K. Nilsson*, A.A. Konnov Division of Combustion Physics, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden KEYWORDS Syngas; kinetic mechanism; HOCO; combustion

ABSTRACT Chemical kinetic mechanisms for simulation of syngas (H2+CO) combustion are important for development of efficient practical applications like gas turbines. A useful syngas mechanism has to be able to accurately predict laminar burning velocities, ignition delays and oxidation of gas mixtures of varying composition over a range of temperatures and pressures. In the present work the performance of a new H2/CO combustion mechanism is analysed. The mechanism is built on reaction rate constants chosen from the most accurate available kinetic data, and this is thoroughly discussed. The mechanism is validated for a wide range of experimental data from the literature. Particular attention is paid to chemistry of the species HOCO, produced from CO+OH reaction and removed by decomposition or radical reactions. Most available syngas mechanisms do not include HOCO since it is only expected to be of importance at some extreme high pressure and low temperature conditions. The species is, however, essential in hierarchically extended mechanisms for small oxygenated hydrocarbons and its influence on the H2/CO subset of reactions need to be further understood to ensure accurate mechanism development for a range of fuels. In the present study it is found that

ACS Paragon Plus Environment

1

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 50

inclusion of the HOCO reaction subset does not alter the model predictions of laminar burning velocities, ignition delay times or oxidation. Sensitivity analysis reveals that HOCO production, its thermal decomposition and reaction with O2 is among the 20 most sensitive reactions for conditions of low temperatures and high CO concentrations, but with insignificant magnitude of the sensitivity compared to that of the major sensitive reactions.

INTRODUCTION Combustion chemistry of carbon monoxide, CO, and hydrogen gas, H2, is of importance in combustion research since the two species are present in the final oxidation steps for all hydrocarbon fuels. Mixtures of CO and H2 can also be used as a fuel and is then called synthesis gas or syngas. Syngas is a byproduct of some industrial processes and can be produced from a range of sources, which makes it a good choice for reliable and sustainable energy production. In recent years the need for reliable, clean and economically feasible fuels for, in particular, gas turbines has resulted in a research efforts towards further understanding of the combustion of syngas mixtures. A challenge in syngas combustion is the fact that syngases produced from various sources and processes have different compositions. As an example, nine selected syngas fuels in one study1 span concentrations of the fuel components CO and H2 in syngas from about 7 to 60% each, and in addition the mixtures contained CO2 (< 30%), water (< 20%), CH4 (< 10%), and also minor constituents like NH3. As a result, a chemical kinetic mechanism for simulations of syngas combustion needs to accurately predict conversion at various compositions of the main constituents H2 and CO, as well as the effects of addition of one or several of the other species in various amounts, in particular CO2 and H2O. To be useful for modeling of complex systems such as gas turbines the mechanism needs to capture variations in pressure (up to 30 atm), initial gas


2

Page 3 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

mixture temperature, dilution and fuel to oxygen ratio. To achieve this, a wide range of experimental data for flames, ignition and oxidation are required for validation purposes. The experimental efforts for determination of combustion characteristics of syngas are extensive, in particular for mixtures of the main constituents CO and H2. In recent years also studies considering the effects of dilution, temperature and pressure have been published. Laminar burning velocity measurements and ignition delays of syngas mixtures have most recently been reviewed by Lee et al.2, with a focus on data relevant for gas turbine conditions. Lee et al.2 pointed out that there is a need for further research regarding the effects of dilution by CO2 and H2O, and indeed several publications have recently focused on these diluents3-5. Syngas chemical kinetic mechanisms are commonly comprehensible in comparison to the models for heavier fuels and many perform well under various conditions. In a recent work by Olm et al.6 a number of syngas mechanisms have been tested against a large set of experimental data. It was concluded that the mechanisms of Healy et al.7, Starik et al.8, Li et al.9, Keromenes et al.10 and Davis et al.11 all showed overall good performance against the wide range of experimental data. A general trend is that the mechanisms do not reproduce well experimental ignition delays below 1000 K, which could be attributed to facility effects and thus the quality of the experimental data. For laminar burning velocities the mechanisms generally perform well at lower initial gas temperatures, fuel lean and CO rich conditions, and for highly diluted mixtures6. When N2 is the inert, the performance is worse compared to other diluents. Olm et al.6 also noted that for laminar burning velocities the agreement of models is best with experimental data from the heat flux and counterflow twin-flame methods. Recent efforts to improve efficiency and reduce NOx emissions in gas turbines have resulted in combustion at pressures up to 30 bar and temperatures below 1800 K, conditions that have been


3

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 50

experimentally visited for syngas flames by Burke et al.12. They showed that the peak in the mass burning rate for mixtures of H2 with CO or CO2 is at about 15 bar and then it decreases with increasing pressure. None of the chemical kinetics schemes tested by Burke et al.12 could reproduce this negative pressure dependence, but models did show very good agreement at the lower pressures. The combination of these experimental and simulated results imply that the chemical kinetics mechanisms do not correctly represent the high-P/low-T chemistry, either as a result of erroneous rate constant expressions, or missing reactions. It was reported that among the carbon containing reactions the mass burning rate is particularly sensitive to the reaction CO+OH=CO2+H12. This reaction is the main step converting CO to CO2, important in syngas mechanisms, and indeed in all mechanisms for hydrocarbon combustion. The reaction is commonly considered to give CO2 and H, but it is well known that the reaction proceeds via a chemically activated HOCO complex13. This intermediate can dissociate to give CO2+H or to give back the reactants CO+OH, but can also be collisionally deactivated to yield stable HOCO. The competition between these different fates of the HOCO intermediate manifests itself by an unusual temperature and pressure dependence of the reaction at low-temperature, high-pressure conditions13. The stable HOCO will under high pressure conditions mainly decompose to form CO+OH or CO2+H while at low temperatures also reaction with O2 becomes competitive14-15. In addition, a fraction of HOCO can undergo H-abstraction reactions by common radicals like OH, to mainly form CO2. The understanding of HOCO chemistry was in 2010 reviewed by Francisco et al.16. They pointed out the likely dependence on tunneling in the reaction of CO+OH, which was later confirmed in a theoretical study by Nguyen et al.17. Since at high pressures and low temperatures HOCO stabilization is favored, the question can be raised whether the inclusion of a subset of reactions for HOCO would affect the model


4

Page 5 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

prediction results at high pressures. None of the mechanisms reviewed by Olm et al.6 includes the species HOCO. The need for incorporating HOCO in syngas models has been discussed and it was often concluded that at common combustion conditions it does not improve the modeling results. Sivaramakrishnan et al.18 found anomalies between experimental and modelled CO conversion in shock tube experiments at 256 and 450 bars, but stated that inclusion of HOCO as a reaction product from CO+OH did not improve the modelling results. Only two recent syngas mechanisms, not covered in the evaluation by Olm et al.6, include simplified HOCO chemistry subsets; Rasmussen et al.15 and Goswami et al.19 both incorporated thermal dissociation of HOCO and reactions with OH and O2. As already mentioned the CO/H2 subset of reactions is an essential part of combustion mechanisms for all hydrocarbon species. For combustion of some small oxygenated species the HOCO chemistry has to be explicitly considered and the importance of these species increases as there is an interest in oxygenated biofuels. An example is formic acid combustion, where HOCO is a product of decomposition and H-abstraction from the acid20. A recent mechanism for ethyl propionate combustion also includes HOCO, which is produced by decomposition of an intermediate radical formed when the ethyl group is lost as a result of thermal decomposition 21. In these mechanisms production as well as loss of HOCO is mainly governed by thermal dissociation. In the recent formic acid combustion mechanism by Marshall and Glarborg several radical reactions of HOCO are also included14. The main reaction partners for HOCO are at higher temperatures O2 and at lower temperatures OH, with minor contribution from H, O and HO2. In Table 1 the reactions including HOCO, of possible relevance to syngas combustion, are listed. The table also presents which reactions are included in the oxygenated hydrocarbon


5

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

mechanisms mentioned above14-15,

19-21

Page 6 of 50

, and give the references to the sources of the rate

constants. In the present work we describe a new syngas mechanism including a subset for HOCO. The hydrogen subset in the mechanism has recently been updated36 and all rate constants for carbon containing species have been reviewed within the present work to build on up to date chemical kinetics data. The mechanism is validated to an extensive range of experimental data from the literature, including laminar burning velocities, ignition delays and flow reactor studies. The goals of the present work were: i) to build a CO/H2 subset of reactions that can be further extended to include reactions of oxygenated hydrocarbons such as acids and esters, ii) to investigate how the inclusion of the HOCO chemistry may affect a syngas mechanism behavior at various conditions, iii) to identify and further investigate the conditions (high P, low T) where HOCO may play notable role. In the following, the contemporary choice of the reaction rate constants is presented with the emphasis on their uncertainties. Then examples of the performance of the mechanism for simulations under various conditions are given, including predictions of ignition, oxidation and laminar burning velocities.

Comparison of the modeling and experiments is analysed and

discussed in terms of the possible role of the HOCO chemistry.

REACTION MECHANISM The detailed reaction mechanism used in this study (excluding H/O subset36) is listed in Table 2. In the following, the sources of the rate constants are shortly outlined. Also temperature range over which the rate constants were determined and associated uncertainty are presented. An estimated uncertainty factor, UF, implies that the rate constant is expected to be in the range


6

Page 7 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

k/UF < k < k×UF. Additional check of the consistency of the kinetic and thermodynamic data was performed by comparison of the reverse rate constants with available measurements. The reverse rate constants for this purpose were calculated using the Mechmod code.37 All rate coefficients in the present work are given in cm3 - mole - s units, while activation energies are in cal/mole. In the following the reactions are numbered according to the full mechanism starting with the H/O mechanism36 consisting of 20 reactions.

Species, thermodynamic and transport parameters Thermodynamic data were taken from the recent database of Goos et al. 49 All reactions are reversible; in the modeling, the reverse rate constants are calculated from the forward rate constants and thermodynamic data by the Chemkin chemical interpreter code.50 The choice of the transport parameters implemented in the Chemkin package50 for flame modeling was discussed by Alekseev et al.36. Following recommendations of Brown et al.51 recently measured diffusion coefficients for OH and HO252 are adopted in the present model.

Reactions CO2 as collisional partner Reactions comprising updated hydrogen combustion mechanism and associated rate constants have been discussed recently by Alekseev et al.36 The interaction between H/O reactions and H/C/O reactions discussed in the present work is limited to termolecular processes where carboncontaining species may affect the rates as collisional partners.

To address this issue, one

additional channel of recombination of H atoms and molecular oxygen is included: H + O2 (+CO2) = HO2 (+CO2)

(5e).


7

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 50

with the low-pressure rate constant recommended by Vasu et al..38

Reactions of CO Reactions of CO mainly treat its conversion to CO2 as a result of reaction with various radicals, but in a mechanism with HOCO included also the recombination of CO and OH. The rate constant of reaction CO + O (+M) = CO2 (+M)

(21)

possesses unusual Arrhenius form that prompts Warnatz42 to recommend an expression with effective negative activation energy within 1000 - 3000 K and Baulch et al.53 with positive one within 250-500 K range. Troe23 derived both limiting low and high-pressure rate constants for the forward and reverse reactions and found significant non-Arrhenius behavior of the termolecular recombination. Westmoreland et al.54 focused their QRRK analysis on the lowpressure term of this pressure-dependent rate constant. At typical flame temperatures the lowpressure rate constant calculated by Westmoreland et al.54 is about one order of magnitude higher than that of Troe23. Allen et al.41 proposed to combine the low-pressure rate constant expression from Westmoreland et al.54 fit to modified Arrhenius form and high-pressure rate constant taken from Gardiner and Troe55 yet referring on Troe’s work23.

Since then this combination is

implemented in many combustion models9, 15, 19. Davis et al.11 evaluated uncertainty factor of this rate constant as 2, and in the optimization procedure proposed to multiply the rate constant of Allen et al.41 by a factor of 0.76. Keromnes et al.10 implemented both high and low-pressure terms of Allen et al.41, but with reductions by 25% and 13%, respectively. Jasper and Dawes39 revisited molecular dynamics of reaction (21) and calculated high-pressure limiting rate constant which is 7-35 times larger at 1000-5000 K than the rate constant obtained by Troe.23 An


8

Page 9 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

uncertainty of their calculations was evaluated as ±40%. In the present work the high-pressure rate constant of Jasper and Dawes39 is combined using a Lindemann fit with the low-pressure rate constant recommended by Tsang and Hampson40, which was used in the Konnov56 mechanism. Their recommendation is based on the rate constant of Baldwin et al.57 adopted by, e.g., Sun et al.58 The collisional efficiencies with respect to N2 are adopted from Warnatz42 and Allen et al.41 The uncertainty of this rate constant is still very high given the contradictory calculations mentioned above and is probably of a factor of 3. Temperature and pressure dependence of the rate constant of reaction CO + OH = CO2 + H

(22)

as well as the role of stabilized intermediate, HOCO, was a subject of many experimental and theoretical works. Baulch et al.46 summarized experimental studies and reviews prior to 2004 and accepted as recommendations the rate constants derived by Troe24 that in turn are largely based on the experiments and analysis of Fulle et al.25

However, the recommended rate

expressions cannot be directly used in the Chemkin interpreter due to complex high-pressure terms. To overcome this problem Sun et al.58 did not include the HOCO formation in their model, while Rasmussen et al.15 approximated the rate constants of reaction (22) and of reaction forming HOCO derived by Troe24 by bimolecular two-term expressions at different pressures. Senosiain et al.22, 26 and Joshi and Wang13 performed further theoretical studies of reactions (22) and CO + OH (+M) = HOCO (+M)

(23)

aimed at more accurate description and interpretation of available experimental data. Li et al.9 proposed modified Arrhenius expression for the rate constant of reaction (23) using least-squares fit to all experimental data and noted that this expression, adopted in the present work, is


9

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 50

approximately half-way between the theoretical results of Senosiain et al.26 and of Joshi and Wang13 indicating the remaining uncertainty below a factor of 1.2. Pressure-dependent rate constant of reaction (23) of Senosiain et al.26 is also implemented here. Reaction CO + O2 = CO2 + O

(24)

is only important in "dry" CO + O2 mixtures that is mixtures without hydrogen-containing species. Together with reaction (21) it governs very slow CO oxidation by oxygen. In the presence of traces of hydrogen, water or hydrocarbons, chain process develops fast with participation of H, OH, and HO2 radicals. That makes experimental determination of the rate constant of reaction (24) very difficult43, 59. Most of the contemporary combustion mechanisms implement rate constants suggested by Warnatz42 or by Tsang and Hampson40, both originating from the estimation of Baulch et al.53. In the present work the rate constant determined by Thielen and Roth43 is adopted with evaluated uncertainty of a factor of 3. Recent theoretical study60 essentially supported these measurements. A possible role of adduct formation in reaction CO + HO2 = CO2 + OH

(25)

similar to HOCO formed in reaction (23) was discussed quite some time ago.61 Yet it was not until recent demonstration of Mittal et al.62-63 that recommended rate constants of this reaction, e.g.40, are too high to reproduce autoignition delays of syngas in a rapid compression machine that the rate constant was revisited through theoretical calculations by Sun et al. al..44 In the present work as well as in the models of Keromnes et al.

10

58, 64

and You et

and Rasmussen et al.15

the expression derived by You et al.44 is adopted. The calculations44, 58 differ by a factor of 2-3 that indicates remaining uncertainty of the rate constant.


10

Page 11 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Reactions of HCO In mechanisms for hydrocarbon combustion HCO is an important intermediate linking the oxygenated hydrocarbons to CO, while in a pure syngas situation HCO is produced from CO. Kinetic experiments on HCO are often challenging and thus the experimental data are scarce. Baulch et al.46 reviewed several direct measurements including65-66 as well as preliminary results of Krasnoperov et al.67 of the rate constant of reaction HCO + M = H + CO + M

(26)

and preferred the expression of Friedrichs et al.66. Although typical uncertainties stated in these experimental studies are 30-40%, there is apparently no consensus between different groups68-71 and remaining uncertainty is still not better than of a factor of 2. Li et al.9 proposed modified Arrhenius expression for the rate constant of reaction (26) using least-squares fit to all experimental data and noted that this expression, adopted in the present work, is almost equidistant from the measurements reported by Timonen et al.65 and Friedrichs et al.66 Reaction HCO + H = CO + H2

(27)

as well as other reactions between HCO and radicals competes with reaction (26) removing H atoms which may participate in chain branching. The rate constant recommended by Baulch et al.46, 72 was approximately an average value of different experiments with evaluated uncertainty of a factor of 2. The classical trajectory calculations45 confirmed that the rate constant is nearly independent of temperature.

The calculated value, which is in very good agreement with

experiments of Friedrichs et al.66, is adopted in the present work with reduced uncertainty.


11

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 50

Recommendations of Warnatz42, Tsang and Hampson40, and Baulch et al.46,

72

for the rate

constants of reactions HCO + O = CO + OH

(28)

HCO + O = CO2 + H

(29)

are all the same and based on rather old experimental data never revisited since last 40 years. Remarkably no attempts to calculate these rate constants were found in the literature as well. Baulch et al.46 adopted the only experimental rate constant of reaction HCO+OH=CO+H2O

(30)

measured by Temps and Wagner47. The rate constant of reaction HCO + O2 = CO + HO2

(31)

possess quite large scattering especially at high temperatures.46 Baulch et al.46 modified the temperature dependence calculated by Hsu et al.48 to better match low-temperature measurements and argued that other channels of this reaction forming CO2 + OH or recombination to HCO3 are of little importance.

Later measurements of Colberg and

Friedrischs73 within temperature range 739 – 1108 K were found closer to the original expression of Hsu et al.48, which is therefore accepted in the present work. The uncertainty of this rate constant is probably close to a factor of 2 at high temperatures. Reactions between hydroperoxy radical and formyl radical HCO + HO2 = CO2 + OH + H

(32)

HCO + HO2 = CO + H2O2

(33)

have not been studied experimentally. Tsang and Hampson40 estimated the total rate constant to be close to the collisional limit and assigned it a high uncertainty of a factor of 5, this value is


12

Page 13 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

included in the present model for reaction (32). The second channel (33) is assumed to take place via direct hydrogen abstraction and therefore, by analogy to reaction (31)48, it is probably minor with a rate constant 10 times smaller. The rate constants for 2 channels HCO + HCO = CH2O + CO HCO + HCO = H2 + CO + CO

(34)

recommended by Tsang and Hampson40 are adopted in the present work. This overall rate constant is based on several experimental studies in good agreement. The branching ratio is based on the results of Horowitz and Calvert74, while the total rate constant is in excellent agreement with the measurements of Krasnoperov et al.71. The combination reaction forming (HCO)2 is generally considered to be unimportant40, 46 consistent with its rate constant of 1.66 E+11 suggested by Yee Quee and Thynne75. To limit the present kinetic mechanism by syngas only, reaction channel forming formaldehyde was not included here.

Reactions of HOCO Many kinetic schemes for syngas combustion do not include reaction (23) of HOCO formation and subsequent reactions of its decomposition HOCO (+M) = H + CO2 (+M)

(35)

and reactions of HOCO with other species arguing that stabilization is only important at very high pressures.15 HOCO, however, can easily be formed from formic acid, if present in a fuel, and even in reaction between CO and H2O2.32. Mechanisms for syngas and oxygenated hydrocarbons taking HOCO chemistry into account are presented in Table 1. The rate constant


13

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 50

of reaction (35) derived by Larson et al.27 and the same collisional efficiencies as for reactions (21) and (26) are adopted in the present work. Available measurements of the rate constants with HOCO are very limited, yet several theoretical studies have appeared recently.16 Reaction of HOCO with H atoms has two channels: HOCO + H = H2 + CO2

(36)

HOCO + H = H2O + CO

(37)

Dibble and Zeng76 performed RRKM/Master equation calculations and found that formation of H2O + CO accounts for about 90% of products irrespective of temperature. On the contrary, Yu and Francisco28 in their ab initio dynamic calculations revealed significant variation of the branching ratio with temperature. In the present work the calculated rate constants 28 were approximated by Arrhenius expressions presented in Table 2, yet attributing high uncertainty due to inconsistency with76. Yu et al.29 theoretically investigated possible products of reaction between HOCO and O atoms and concluded that reaction HOCO + O = OH + CO2

(38)

is the most important channel with the rate constant having rather weak temperature dependence. In the present work the calculated discrete values of the rate constant29 were approximated by Arrhenius expression as shown in Table 1. Although Yu et al.29 evaluated the uncertainty of the rate constant as ± 10%, in the present work an uncertainty factor of 1.5 is adopted. Yu et al.31 performed ab initio dynamic calculations of the thermal rate constant of reaction HOCO + OH = H2O + CO2

(39)


14

Page 15 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

from 250 to 800 K. They proposed a two-term expression in the range 180-850 K listed in Table 2, while noting that the calculations at temperatures around 400 K are off the expected Arrhenius behaviour. Due to this peculiarity the uncertainty of the rate constant is estimated to be of a factor of 2. The second channel of this reaction HOCO + OH = H2O2 + CO

(40)

was analyzed by Glarborg and Marshall32, who reinterpreted earlier experiments of Baldwin et al.77 on carbon monoxide-sensitized decomposition of hydrogen peroxide at 713 K. Extrapolation to a wider temperature range was guided by ab initio calculations. The rate constant derived by Glarborg and Marshall32 is much smaller than the earlier estimate of Rasmussen et al.15 and has probably an uncertainty of a factor of 2. The rate constant of reaction HOCO + O2 = HO2 + CO2

(41)

was measured only at room temperature34-35, 78, and the measurements are in agreement within overlapping uncertainties. Miyoshi et al.78 observed no pressure dependence and concluded that this fact suggests that the products of reaction (41) are HO2 and CO2, not a stabilized adduct. Poggi and Francisco79 performed ab initio calculations and came to the same conclusion. Yu and Muckerman33 extended these calculations using ab initio direct dynamics method and calculated thermal rate constant from 200 to 1000 K. Their value obtained at room temperature is in good agreement with the measurements of Petty et al.

35

, also preferred by Olkhov et al.80 in

interpretation of their experiments with HOCO. In the present work the results of Yu and Muckerman33 were approximated by the non-Arrhenius expression presented in Table 2. The uncertainty factor of this reaction was evaluated as 1.5 taking into account consistency of the experimental and modelling results.


15

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 50

Yu et al.30 investigated molecular dynamics of reaction between HOCO and HO2 and found that at room temperature the main channel is HOCO + HO2 = H2O2 + CO2

(42),

however branching ratio of HOC(O)O + OH formation is also significant (up to 15%). Temperature dependence of the rate constant was not investigated. In the present work only the channel (42) is considered with rather large uncertainty. Petty et al.35 found rather low upper limits for the rate constant of HOCO with CO; therefore this reaction was not considered in the present model. No attempt to “adjust” the reaction rate coefficients was made in the present work; however, possible modifications within the uncertainty factors listed in Table 1 will be discussed below in connection with the analysis of the mechanism performance.

MODELING DETAILS The Senkin code from the Chemkin Collection of Codes50 is used for the modeling of oxidation and self-ignition processes. Shock-tube and flow reactor measurements have been modeled as constant pressure adiabatic processes.

The Premix code from the Chemkin

Collection is used for the flame modeling. Multi-component diffusion and thermal diffusion options were taken into account. Adaptive mesh parameters were GRAD = 0.02 and CURV = 0.05. Typical number of grid points in the flame modeling was 500. Olm et al.6 tested 16 recent syngas mechanisms and concluded that the model by Keromnes et al.10 demonstrates very good performance for a wide range of experimental datasets. Keromnes et al.10 presented a very thorough validation, in particular against ignition delays, and also a comparison to the mechanisms of Li et al. 9, Davis et al.11, and the USC II81 mechanism. The


16

Page 17 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

mentioned mechanisms have different predictability to different types of data sets (ignition delays, flames, flow reactors) and parameter sets (P, T, composition). These differences were explained6 by the choice of chemical paths taken into account. In the following modeling using the recent mechanism of Keromnes et al.10 is included in all figures and, where relevant, the similarities or differences between the mechanisms are discussed.

RESULTS AND DISCUSSION The present mechanism was validated against a wide range of experimental data concerning ignition, oxidation and flames of syngas, with particular attention to laminar burning velocities. Variations in H2:CO ratio, pressure, temperature and diluents CO2, H2O and N2 were considered. For all cases it was investigated whether the HOCO subset was of importance by running the model with the HOCO reactions excluded. In particularly interesting cases sensitivity analysis was performed to further improve the understanding of the mechanism. In the following the performance of the mechanism is evaluated for laminar burning velocities, ignition in shock tubes and oxidation in flow reactors and shock tubes.

Laminar burning velocity Figure 1 presents laminar burning velocities at standard conditions for various H2:CO ratios, including pure hydrogen flames. For pure hydrogen the experimental datasets from a range of studies are in good agreement82-89, apart from Aung et al.89 at rich conditions. The present mechanism is in excellent agreement with the data for hydrogen+air flames and in particular with the recent study by Krejci et al.82 As seen in the zoom in, bottom panel of Figure 1, data by Krejci et al.82 are generally higher than other studies at lean conditions, which is supported by


17

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 50

modeling results using the present mechanism as well as that of Keromnes et al.10 For further discussion of the hydrogen subset of the present mechanism we refer to Alekseev et al.36. For the three different H2:CO ratios the agreement of the modeling with experiments82, 90-93 is generally good at lean and very rich conditions. At rich conditions the present mechanism gives laminar burning velocities 5-10 cm/s lower than the mechanism of Keromnes et al.10, which results in better agreement with experimental data.

Figure 1. Laminar burning velocities for flames of pure hydrogen and syngas mixtures in air at ambient temperature and pressure of 1 atm. Bottom panel is a zoom in at lean and stoichiometric conditions. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines). Color coding in terms of H2:CO composition: 100:0 – pink; 50:50 – blue; 25:75 – red; 5:95 – black.


18

Page 19 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Sensitivity analysis of both mechanisms have been performed at several equivalence ratios and is presented in the Supplemenatry material as Figures S3-S5. At intermediate equivalence ratios, around the peak in laminar burning velocity, the scatter of experimental data for H2:CO composition of 50:50 and 25:75 is significant, here the mechanism supports the experimental data of Burbano et al.93 and Krejci et al.82 suggesting higher laminar burning velocities than earlier studies. Burbano et al. argued that the discrepancy of their data with previous studies is likely a result of erroneous treatment of stretch corrections in some of the earlier datasets. The three experimental series at the lowest H2:CO ratio are in good agreement with each other and the modeling slightly over predicts the experimental laminar burning velocity. Based on the argument by Burbano et al.93 that some experimental datasets are too low, it could be inferred that the experimental data for 5:95 syngas mixtures are below the real laminar burning velocity and that the modeling prediction is indeed more accurate. Figure 2 shows the 20 most sensitive reactions at low, peak and high equivalence ratios for the present mechanism at high CO content (H2:CO 5:95), represented by the black lines in Figure 1. Production of HOCO (R23) and two reactions removing it (R37, R41) are present among 20 most sensitive reactions. The sensitivities are insignificant compared to that of the few most important reactions, but it is notable that the sensitivity for HOCO reactions is highest at the highest equivalence ratio, =5.0. The present mechanism with the HOCO subset excluded resulted in laminar burning velocities essentially indistinguishable from those of the full mechanism. At the most the difference is 0.44 cm/s (at =5.0) which is significantly smaller than the experimental uncertainty at these conditions and therefore considered negligible. For flames at standard conditions it can be concluded that the HOCO subset of reactions is not of significant importance but has some small contribution at high CO content at very rich conditions.


19

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 50

Figure 2. Flow rate sensitivity for 20 most important reactions of present mechanism for syngas mixture of composition H2:CO 5:95 at 298 K and 1 atm.

Figure 3. Mass burning rate as a function of pressure, experiments by Burke et al. 12 at =2.5 and flame temperature of 1600 K for different H2:CO compositions. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines).

Effect of pressure on mass burning rates of hydrogen and two different syngas mixtures flames at =2.5, experimentally studied by Burke et al.12, is presented in Figure 3. In contrast to other mechanisms (see discussion by Burke et al.12) the present mechanism predicts a decrease in mass


20

Page 21 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

burning rate at higher pressures, for the syngas flames. As evident from Figure 3 the peak pressure and the magnitude of the decrease are not perfectly reproduced and mass burning rates are generally under predicted at high CO content and over predicted at high H2 content. As discussed by Burke et al.12 mass burning rates generally becomes more sensitive to reaction rate constants at high pressures and one of the reactions that is playing a significant role is CO+OH, indicating that HOCO chemistry might become important.

Figure 4. Effect of pressure at initial gas mixture temperature 298 K and H2:CO 50:50. Oxidizer mixture is O2:He 1:7. Experimental data from Krejci et al.82, Natarajan et al.94 and Sun et al.58. Modeling: present mechanism (full drawn lines); Keromnes et al. 10 (dashed lines).

Figure 4 presents the effect of pressure on equimolar H2:CO (50:50) composition of the fuel mixture at 5 and 10 atm. The modeling is in good agreement with the datasets by Krejci et al

82

and Natarajan et al.94 while Sun et al.58 are generally lower. Modeling using the mechanism of Keromes et al.10 is lower than the present mechanism and in better agreement with Sun et al.58 results. Sun et al.58 also present data at H2:CO ratio of 5:95 up to 40 atm pressure, these measurements are presented in Figure 5, where one can see that the present mechanism is in


21

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 50

good agreement with the data at the highest pressure but yields overpredictions at other pressures, just like for the 50:50 mixtures. At all pressures the mechanism essentially succeeds in reproducing the low laminar burning velocities at rich conditions where the mechanism of Keromnes et al.10 shows over predictions.

Figure 5. Effect of pressure at high CO content, H2:CO 5:95. Oxidizer mixture is O2:He 1:7. Experimental data from Sun et al.58. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines).

Laminar burning velocities are expected to increase with increasing initial gas mixture temperature. In the evaluation of syngas mechanisms by Olm et al.6 it is highlighted that for laminar burning velocities the mechanisms tested generally perform worse at elevated temperatures. Figure 6 presents the laminar burning velocities for 50:50 mixtures of H2:CO at 1 atm and different initial temperatures with experimental data from studies by Singh et al.95, Lapalme et al.5 and Natarajan et al.94. An increasing divergence between experiments and modeling is seen as temperature increases, the same trend was seen for other mechanisms presented in the paper by Singh et al.95, who modelled using the GRI 3.096, San Diego97 and


22

Page 23 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Davis98 mechanisms. In the narrow range of lean equivalence ratios covered by more than one experimental studies it is apparent that at elevated temperatures there are discrepancies between the experimental studies, with the highest values in satisfying agreement with modeling. This could indicate that the deviation between modeling and experiments at high preheat temperatures and equivalence ratios is at least partly a result of unknown experimental uncertainties.For the modeling presented in Figure 6 the present mechanism with the HOCO subset excluded resulted in laminar burning velocities indistinguishable from those of the full mechanism.

Figure 6. Effect of initial gas mixture temperature for H2:CO 50:50 at 1 atm. Experimental data from Singh et al.95, Lapalme et al.17 and Natarajan et al.94. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines).

The effect of dilution of syngas mixtures with the inert N2 or the low reactivity species CO2 and H2O, are of importance since these three gases can be present in syngas mixtures from industrial processes, and are expected to inhibit laminar burning velocities. Figure 7 present the effect of N2 dilution from 0-60% of an equimolar H2:CO mixture, with experimental data from


23

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 50

studies of Prathap et al.99 and Burbano et al.93. As previously discussed the data of Burbano et al. are comparably high, in this case in agreement with the modeling.

Figure 7. Effect of N2 dilution at standard conditions. H2:CO is 50:50. Experimental data from Burbano et al.93 and Prathap et al.99. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines).

Dilution by CO2 has been shown to strengthen the pressure and temperature dependence of the laminar burning velocities of hydrogen flames98, 100. To further investigate the capability of the present mechanism for CO2 dilution these flames were modeled and the results are presented in Figure 8. The present mechanism is in excellent agreement with both high and low pressure flames for initial gas mixture temperature of 298 K, with slight overprediction at the higher temperature, as commonly seen and discussed in relation to Figure 6 above. In turn, Figure 9 shows the 20 most sensitive reactions for the 353 K case depicted in Figure 10. Two reactions for conversion between CO and CO2 are manifested, R21 and R22, which shows that the diluent CO2 at these conditions also participates as a reacting chemical species.


24

Page 25 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 8. Laminar burning velocity as a function of pressure for hydrogen burning in an O2+CO2 diluent. Experimental data from Li et al.100 and Burke et al.12 at =2.5 and flame temperature of 1600 K. Modeling: present mechanism (full drawn lines); Keromnes et al. 10 (dashed lines).

Figure 9. Flow rate sensitivity for 20 most important reactions of present mechanism for hydrogen burning in O2+CO2, at initial gas mixture temperature of 353 K and pressures of 5, 15 and 25 atm.

Dilution with CO2 and H2O decreases the reactivity of syngas mixtures as well. The effects are illustrated by experimental data for laminar burning velocities by Xie et al.4 in Figure 10 for


25

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 50

50:50 syngas mixtures at 1 atm and 373 K, where CO2 decreases laminar burning velocity more than H2O. The present mechanism reproduces the trend in decrease for CO2 as well as H2O, but generally over predicts the results.

Figure 10. Effect of dilution by 15% H2O or CO2 at 1 atm and 373 K. H2:CO 50:50. Experimental data from Xie et al.4. Modeling: present mechanism (full drawn lines); Keromnes et al. 10 (dashed lines).

Figure 11 presents effects of CO2 dilution at standard conditions for equimolar fuel mixtures, the lower panel being a zoom in at the leaner conditions. With the lower CO2 percentages, 10% and 20%, the measurements by Burbano et al.93 are generally higher than the modeling while the results by Lapalme et al.5 and Prathap et al.101 are generally lower. The same trend is true at the non-diluted conditions, uppermost line in Figure 11. Laminar burning velocities for cases with higher CO2 fractions, from experiments by Ratna Kishore et al.102, are overpredicted for 40% and 50% CO2, but in better agreement at the highest CO2 fraction, 60%. It should be noted here that the datasets by Burbano et al.93 and Kishore et al.102 disagree with each other. As seen in Figure 1 for undiluted syngas and Figure 7 for N2 diluted syngas, the data of Burbano et al.93 are


26

Page 27 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

generally higher at intermediate equivalence ratios, compared to other datasets. They used a burner stabilized conical flame combined with Schlieren imaging and explained the discrepancy with other studies as failure of stretch correction in the closed vessel studies. It is noted, however, that when corrections are made as suggested by Burke et al.103 the results of Burbano et al. are still slightly higher compared to other literature data. Figure S20 in the Supporting Information presents the effect of 60% CO2 dilution for varying hydrogen content, agreement with the modeling is the best at highest CO fraction. Sensitivity analysis reveals that at none of the investigated N2 or CO2 dilution conditions evaluated here reactions of HOCO are among the 20 most sensitive reactions.

Figure 11. Effect of CO2 dilution in the range 0-60% at standard conditions. H2:CO is 50:50. Bottom panel is a zoom for better view of data at lower equivalence ratios. Experimental data


27

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 50

from Ratna Kishore et al.102, Prathap et al.101, Lapalme et al.5.Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines).

The effect of H2O on laminar burning velocity is shown in Figure 12 for H2:CO of 5:95. At the higher equivalence ratios the effect of H2O addition is stronger. H2O addition up to 15% increase the laminar burning velocity while further addition decrease it. The peak velocities occur at 15% H2O dilution, where laminar burning velocities are 20-40% higher compared to the undiluted cases. The model overprediction seen in Figure 12 is most certainly to a large extent a result of the elevated (323 K) initial gas mixture temperature and it is not clear whether the discrepancy also has some origin in reactions including H2O. It is, however, clear that the modeling capture the general trend in increase and decrease of laminar burning velocity with increasing water content. Sensitivity analysis reveals that the subset of reactions with HOCO is not important at any of the investigated conditions for water dilution.

Figure 12. Effect of various fractions of H2O in a syngas mixture with H2:CO 5:95 at 1 atm and 323 K. Experimental data from Das et al.104. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines).


28

Page 29 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Ignition delays Ignition delay times for syngas mixtures can be expected to be dependent on H2:CO ratio, pressure, and possibly on equivalence ratio. In the following these aspects are investigated. Sensitivity analysis was performed with the brute force method applied using the ignition delay program of A. Kazakov105. Ignition delays of syngas mixtures of high H2 and high CO contents, from Kalitan et al.106, are presented in Figure 13 for an equivalence ratio of 0.5 at pressures of about 1.1 atm. The present mechanism with and without the HOCO subset and the mechanism of Keromnes et al.10 give essentially indistinguishable results. An example of the small impact of HOCO chemistry is that at 950 K and 1 atm for the 5:95 syngas mixture the ignition delay time is longer by only about 1.3% when HOCO subset is included in the present mechanism.

Figure 13. Ignition delays for syngas mixtures of H2:CO 80:20 and 5:95, in air at pressures about 1.1 atm and =0.5, by Kalitan et al.106. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines).

Important chemistry for most of the cases are the hydrogen subset but at high CO and low temperature ignition delays become increasingly sensitive to the CO subset, implying that


29

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 50

HOCO chemistry might start to play a role. From sensitivity analysis at 950 K presented in Figure 14 it is seen that the production of HOCO from CO2+OH is among the 20 most sensitive reactions for the mixture with high CO content, but with an insignificant sensitivity compared to that of the major sensitive reactions.

Figure 14. 20 reactions most sensitive to OH production for the 80:20 and 5:95 syngas mixtures at 1.1 atm, 950 K and =0.5. Modeling using the present mechanism.

Figure 15. Ignition delays at pressure of about 1.8 atm for two syngas mixtures in air. Experimental data from Thi et al.107. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines).


30

Page 31 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 15 present ignition delays determined by Thi et al.107 at =0.3, 1.0 and 1.5 at pressures of about 1.8 atm, for H2:CO 33:67, and at =0.3 for H2:CO 70:30. Ignition delays from experiment seem to be independent on equivalence ratio while slightly dependent on H2:CO ratio, where the higher CO content mixture ignites slower. Modeling with both the present mechanism and that of Keromnes et al.

10

suggests a small dependence on equivalence ratio and

is in good agreement with experiments at the lean conditions, in particular at high temperatures. Sensitivity analysis shows complete dominance of reactions of H with O2, reactions including HOCO are among the 20 most sensitive reactions but with sensitivity coefficients of negligible magnitude compared to the most sensitive reactions, see Supporting Information Figure S28.

Figure 16. Ignition delay for various syngas mixtures in air at pressure 1.1 and 14.5 atm, by Kalitan et al.106. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines).

Ignition delays at 1.1 and 14.5 atm for H2:CO of 5:95, from the experimental study of Kalitan et al.106 are presented in Figure 16, to elucidate the pressure dependence. The mechanism


31

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 50

predictions are in good agreement with experiments at atmospheric pressure but overestimate ignition delays at the higher pressure. No differences were seen when the mechanism was used with and without HOCO subset. Sensitivity analysis shown in Figure 17 reveals that at the higher pressure sensitivity coefficients are significantly lower than at the lower pressure presented in Figure 14, but with HOCO production (R23) among the 20 most sensitive reactions.

Figure 17. 20 reactions most sensitive to OH production for the 5:95 syngas mixture at 14.5 atm, 950 K and =0.5. Modeling using the present mechanism.

Figure 18 present ignition delays for equivalence ratio 0.3 at pressures of 2, 10 and 20 atm. Again agreement is good at the low pressure, while at higher pressures the mechanisms overpredict ignition delays at higher temperatures. Sensitivity analysis at 1000 K, Figure 19, have HOCO reactions among the 20 most sensitive but with very low sensitivity compared to the most important reactions. Sensitivity coefficients decrease with increasing pressure but with reactions of H+O2 as the most important for all pressures. Reaction of CO and OH to produce CO2 has a positive sensitivity for the lowest pressure, but shifts to negative sensitivity at higher


32

Page 33 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

pressures. Overall it is clear that ignition delay times for syngas mixtures at various conditions are not affected by the HOCO subset of reactions.

Figure 18. Ignition for a syngas mixture with H2:CO 33:67 and phi=0.3 at several pressures. Symbols represent experimental data by Thi et al.107. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines).

Figure 19. 20 reactions most sensitive to OH production for syngas mixture of composition H2:CO 5:95, at about 1.9, 9.5 and 20 atm, 1000 K and =0.3. Modeling using the present mechanism.


33

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 50

Species profiles in flow reactors and shock tubes Experimental studies of CO oxidation in flow reactors and shock tubes have been performed with and without addition of H2,18 CO2110 and H2O108,

109, 110

. Sivaramakrishnan et al.18

investigated CO oxidation in the presence of H2 in a shock tube over a wide pressure range from 24 to 450 atm. Species profiles of CO, CO2 and O2 are presented in Figure 20 for pressure of 43 atm and =1.0, for other conditions see Figures S35-37 and S39-40 of Supporting Information. The present mechanism and that of Keromnes et al.10 generally underestimate CO conversion but are in good agreement with each other at 24 and 43 bar. At the higher pressures of 256 and 450 atm the mechanism of Keromnes et al.10 is in better agreement with the experiment than the present mechanism. In general the modeling show later onset of oxidation than the experimental data. This is particularly obvious for O2 profiles that in the experiments start to decrease rather early, while in the simulations the O2 decrease occurs at the same time as CO decrease and CO2 production. The HOCO subset does not improve model predictions, as previously noted by Sivaramakrishnan et al.18

Figure 20. Species profiles from from oxidation of H2:CO mixture of about 30:70 in a shock tube at 43 atm18 (diamonds). Modeling: present mechanism (triangles); Keromnes et al.10 (stars).


34

Page 35 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 21. Effect of pressure on mole fraction profiles of CO from a flow reactor study by Kim et al.108. T=1040 K. Initial composition CO:O2:H2O:N2 1.0:0.5:0.65:97.85. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines). Mole fraction profiles from modeling shifted to coincide with experimental data at 50% consumption of CO.

Figure 21 present the effect of variation in pressure on CO mole profiles in flow reactor oxidation of CO+O2+H2O mixture highly diluted by N2 at 1040 K and =1.0. The present mechanism makes excellent predictions of mole fraction profiles at the lower pressures but overpredicts CO at 6.5 and 9.6 atm. No difference in results was obtained when the mechanism was applied without the HOCO subset. Figure 22 presents CO, CO2 and H2O profiles at atmospheric pressure and 1032 K for CO oxidation at =0.88 here the agreement between experiments and modeling and between two mechanisms is excellent. At these conditions HOCO subset was shown not to affect the results. Oxidation in a flow reactor is highly sensitive to temperature, which is shown in Figure 23 where CO mole fraction profiles for two flow reactor experiments only 10 K apart show significant difference in CO conversion.


35

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 50

Figure 22. Mole fraction profiles from a flow reactor study by Yetter et al.109. P=1 atm, T=1032 K. Initial composition CO:O2:H2O:N2 0.96:0.55:0.56:97.93. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines). Mole fraction profiles from modeling shifted to coincide with experimental data at 50% consumption of CO.

Figure 23. Mole fraction profiles of CO from a flow reactor study at 1 atm, by Yetter et al.109. Initial

composition

CO:O2:H2O:N2

0.895:0.438:1.235:97.432

at

952K

and

0.95:0.442:1.324:97.329 at 943K. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines). Mole fraction profiles from modeling shifted to coincide with experimental data at 50% consumption of CO.


36

Page 37 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 24 presents CO consumption profiles from a flow reactor study by Abian et al. 110 at H2O fractions of 0.1%. Parameters varied are the CO2 content (0 and 25%) and the equivalence ratio (=0.5 and 2.0). CO conversion is complete at the low equivalence ratio with no additional CO2. CO2 presence suppresses the CO conversion for rich as well as lean conditions. At 10% H2O content (shown in Figure S40) CO conversion is more complete but for rich conditions still significantly suppressed by CO2. Model predictions are in qualitative agreement for the different mixtures, but with the best agreement at the lower water content. In the presence of CO2, CO concentrations start to build up at higher temperatures, a trend that is seen in the experiments as well as modeling but with stronger increase in the modeling.

Figure 24. Conversion of CO in a flow reactor at atmospheric pressure, by Abian et al.110. Gas mixture include 0.1% H2O and 0 or 25% of CO2 at rich and lean conditions, balance gas was N2. Modeling: present mechanism (full drawn lines); Keromnes et al.10 (dashed lines).

Conclusions


37

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 50

A detailed kinetic mechanism for syngas combustion has been presented and evaluated in the present work. The reaction rate constants were chosen based on a review of all available literature. Reactions involving HOCO chemistry were included in the mechanism to allow coupling of the mechanism to subsets relevant to combustion of oxygenated species such as acids and esters. A thorough investigation of the performance of the mechanism for syngas combustion reveal that HOCO chemistry is not to any significant extent involved in under the conditions visited here; T=850-2500 K, P=1-450 atm and H2:CO ratios ranging from pure H2 to high CO content (5:95). From simulations using the mechanism with and without the HOCO reaction subset it is seen that the model predictions are essentially identical. The conditions where HOCO reactions appear among the 20 most sensitive reactions is typically high CO content and low temperatures. The sensitivity coefficients for HOCO reactions are, however, insignificant compared to the coefficients for the main sensitive reactions. The mechanism is in generally good agreement with experimental data for flames, ignition and oxidation of syngas. In comparison to the mechanism of Keromnes et al.10 it is concluded that the mechanisms show overall similar capability, with the present mechanism in better agreement with experimental laminar burning velocities at rich conditions. The present mechanism is, in contrast to the majority of the previously published mechanisms, able to predict a decrease in mass burning rate with pressure, experimentally determined by Burke et al.12.

TABLES. Table 1. Reactions included in the mechanisms including HOCO chemistry, and references used. Target fuel

Syngas

Syngas

Syngas

Formic

Ethyl Propiona

Formic


38

Page 39 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Present mech.

Reference

Acid

te

BattinLeclerc et al. 20

Farooq et Marshall and al. 21 Glarborg

24-25

22

adjusted

26

24-25

27

adjusted

24-25

Goswa Rasmusse mi et al. n et al. 15 19

23

Acid

14

23 CO+OH(+M)=HOCO(+M)

22

35 HOCO(+M)=H+CO2(+M)

27

36 HOCO+H=H2+CO2

28

28

37 HOCO+H= H2O+CO

28

28

38 HOCO+O=OH+CO2

29

30

39 HOCO+OH= H2O+CO2

31

40 HOCO+OH= H2O2+CO

32

31

31

15,31

Estimate

rev 32

41 HOCO+O2=HO2+CO2

33

42 HOCO+HO2= H2O2+CO2

30

33

34

35

33 30

Table 2. H/C/O kinetic mechanism, units are cm3 - mole - s - cal - K, k = ATn exp(-Ea/RT). UF uncertainty factor. No

Reaction

A

n

Ea

T, K

UF

Source

5e

H+O2(+CO2)=HO2 (+CO2)

4.66E+12

0.44

0

300-2000

1.2

38

Low pressure limit:

4.20E+18

-0.86

0

800-1300

38

CO+O(+M)=CO2 (+M)

4.00E+15

-0.96

9837

1000-5000 3

39

Low pressure limit:

6.16E+14

0.0

3000

300-2500

40

21

3

41-42

Enhanced third-body efficiencies (relative to N2): H2=2.5, H2O=12, CO=1.9, CO2=3.8, Ar=0.87 22

CO+OH=CO2+H

2.23E+05

1.90

-1160

400-3500

1.1

9

23

CO+OH(+M)=HOCO(+M)

1.20E+07

1.83

-236.0

800-2000

1.2

22


39

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Low pressure limit:

Page 40 of 50

7.20E+25

-3.85

1550.0

22

Fcent = 0.6 24

CO+O2=CO2+O

5.06E+13

0.0

63190

1700-3500 3

43

25

CO+HO2=CO2+OH

1.57e+05

2.18

17940

300-2500

3

44

26

HCO+M=H+CO+M

4.75E+11

0.66

14870

300-2500

2

9 41-42


HCO+H=CO+ H2

1.20E+14

0.0

0.0

200-1000

1.2

45

28

HCO+O=CO+OH

3.00E+13

0.0

0.0

300-2500

2

46

29

HCO+O=CO2+H

3.00E+13

0.0

0.0

300-2500

2

46

30

HCO+OH=CO+ H2O

1.10E+14

0.0

0.0

296-2500

2

46-47

31

HCO+O2=CO+HO2

1.20E+10

0.807

-727.0

300-3000

2

48

32

HCO+HO2=CO2+OH+H

3.00E+13

0.0

0.0

300-2500

5

40

33

HCO+HO2=CO+ H2O2

3.00E+12

0.0

0.0

300-2500

5

see text

34

HCO+HCO=H2+CO+CO

3.00E+12

0.0

0.0

300-2500

1.5

40

35

HOCO(+M)=H+CO2 (+M)

1.74E+12

0.307

32930

200-2200

2

27

Low pressure limit:

2.29E+26

-3.02

35070

200-2200

2

27 41-42


HOCO+H= H2+CO2

4.07E+17

-1.38

597

200-1000

3

28

37

HOCO+H= H2O+CO

1.96E+14

-0.06

1634

200-1000

3

28

38

HOCO+O=OH+CO2

2.95E+12

0.17

-69.9

200-1000

1.5

29

39

HOCO+OH= H2O+CO2

4.56E+12

0.0

-89

180-850

2

31

+

9.54E+06

2.0

-89

180-850

2

31

40

HOCO+OH= H2O2+CO

3.90E+05

2.09

5444

500-2000

2

32

41

HOCO+O2=HO2+CO2

1.38E+10

0.842

160

200-1000

1.5

33

42

HOCO+HO2= H2O2+CO2

3.00E+13

0.0

0

300

2.5

30


40

Page 41 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

ASSOCIATED CONTENT Supporting Information. Extended compilation of validation cases and corresponding sensitivity analyses. AUTHOR INFORMATION Corresponding Author Phone: +46 46 222 1403 E-mail: [email protected] ACKNOWLEDGMENT Financial support of the Centre for Combustion Science and Technology (CECOST) is gratefully acknowledged. REFERENCES (1)

Chacartegui, R.; Torres, M.; Sanchez, D.; Jimenez, F.; Munoz, A.; Sanchez, T. Fuel

Process. Technol. 2011, 92 (2), 213-220. (2)

Lee, H. C.; Jiang, L. Y.; Mohamad, A. A. Int. J. Hydrogen Energy 2014, 39 (2), 1105-

1121. (3)

Xie, Y. L.; Wang, J. H.; Xu, N.; Yu, S. B.; Zhang, M.; Huang, Z. H. Energy Fuels 2014,

28 (5), 3391-3398. (4)

Xie, Y.; Wang, J.; Xu, N.; Yu, S.; Huang, Z. Int. J. Hydrogen Energy 2014, 39 (7), 3450-

3458.


41

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 50

(5)

Lapalme, D.; Seers, P. Int. J. Hydrogen Energy 2014, 39 (7), 3477-3486.

(6)

Olm, C.; Zsély, I. G.; Varga, T.; Curran, H. J.; Turányi, T. Combust. Flame 2015, 162

(5), 1793-1812. (7)

Healy, D.; Kalitan, D. M.; Aul, C. J.; Petersen, E. L.; Bourque, G.; Curran, H. J. Energy

Fuels 2010, 24, 1521-1528. (8)

Starik, A. M.; Titova, N. S.; Sharipov, A. S.; Kozlov, V. E. Combust. Explos. Shock

Waves 2010, 46 (5), 491-506. (9)

Li, J.; Zhao, Z. W.; Kazakov, A.; Chaos, M.; Dryer, F. L.; Scire, J. J. Int. J. Chem. Kinet.

2007, 39 (3), 109-136. (10) Keromnes, A.; Metcalfe, W. K.; Heufer, K. A.; Donohoe, N.; Das, A. K.; Sung, C.-J.; Herzler, J.; Naumann, C.; Griebel, P.; Mathieu, O.; Krejci, M. C.; Petersen, E. L.; Pitz, W. J.; Curran, H. J. Combust. Flame 2013, 160 (6), 995-1011. (11) Davis, S. G.; Joshi, A. V.; Wang, H.; Egolfopoulos, F. Proc. Combust. Inst. 2005, 30, 1283-1292. (12) Burke, M. P.; Chaos, M.; Dryer, F. L.; Ju, Y. Combust. Flame 2010, 157 (4), 618-631. (13) Joshi, A. V.; Wang, H. Int. J. Chem. Kinet. 2006, 38 (1), 57-73. (14) Marshall, P.; Glarborg, P. Proc. Combust. Inst. 2015, 35 (1), 153-160. (15) Rasmussen, C. L.; Hansen, J.; Marshall, P.; Glarborg, P. Int. J. Chem. Kinet. 2008, 40 (8), 454-480.


42

Page 43 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(16) Francisco, J. S.; Muckerman, J. T.; Yu, H. G. Accounts Chem. Res. 2010, 43 (12), 15191526. (17) Nguyen, T. L.; Xue, B. C.; Weston, R. E.; Barker, J. R.; Stanton, J. F. J. Phys. Chem. Lett. 2012, 3 (11), 1549-1553. (18) Sivaramakrishnan, R.; Comandini, A.; Tranter, R. S.; Brezinsky, K.; Davis, S. G.; Wang, H. Proc. Combust. Inst. 2007, 31 (1), 429-437. (19) Goswami, M.; Bastiaans, R. J. M.; Konnov, A. A.; de Goey, L. P. H. Int. J. Hydrogen Energy 2014, 39 (3), 1485-1498. (20) Battin-Leclerc, F.; Konnov, A. A.; Jaffrezo, J. L.; Legrand, M. Combust. Sci. Technol. 2008, 180 (2), 343-370. (21) Farooq, A.; Davidson, D. F.; Hanson, R. K.; Westbrook, C. K. Fuel 2014, 134, 26-38. (22) Senosiain, J. P.; Musgrave, C. B.; Golden, D. M. Int. J. Chem. Kinet. 2003, 35 (9), 464474. (23) Troe, J. Symp. Int. Combust. Proc. 1975, 15, 667-680. (24) Troe, J. Proc. Combust. Instit. 1998, 27, 167-175. (25) Fulle, D.; Hamann, H. F.; Hippler, H.; Troe, J. J. Chem. Phys. 1996, 105 (3), 983-1000. (26) Senosiain, J. P.; Klippenstein, S. J.; Miller, J. A. Proc. Combust. Inst. 2005, 30, 945-953. (27) Larson, C. W.; Stewart, P. H.; Golden, D. M. Int. J. Chem. Kinet. 1988, 20 (1), 27-40. (28) Yu, H.-G.; Francisco, J. S. J. Chem. Phys. 2008, 128 (24), 244315.


43

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 44 of 50

(29) Yu, H.-G.; Muckerman, J. T.; Francisco, J. S. J. Chem. Phys. 2007, 127 (9). (30) Yu, H.-G.; Poggi, G.; Francisco, J. S.; Muckerman, J. T. J. Chem. Phys. 2008, 129 (21). (31) Yu, H. G.; Muckerman, J. T.; Francisco, J. S. J. Phys. Chem. A 2005, 109 (23), 52305236. (32) Glarborg, P.; Marshall, P. Chemical Physics Letters 2009, 475 (1-3), 40-43. (33) Yu, H. G.; Muckerman, J. T. J. Phys. Chem. A 2006, 110 (16), 5312-5316. (34) Nolte, J.; Grussdorf, J.; Temps, E.; Wagner, H. G. Z. Naturforsch. A Phys.l Sci. 1993, 48 (12), 1234-1238. (35) Petty, J. T.; Harrison, J. A.; Moore, C. B. J. Phys. Chem. 1993, 97 (43), 11194-11198. (36) Alekseev, V. A.; Christensen, M.; Konnov, A. A. Combust. Flame 2015, 162 (5), 18841898. (37) Kovacs, T.; Zsely, I. G.; Kramarics, A.; Turanyi, T. J. Anal. Appl. Pyrol. 2007, 79 (1-2), 252-258. (38) Vasu, S. S.; Davidson, D. F.; Hanson, R. K. Energy Fuels 2011, 25 (3), 990-997. (39) Jasper, A. W.; Dawes, R. J. Chem. Phys. 2013, 139 (15). (40) Tsang, W.; Hampson, R. F. J. Phys. Chem. Ref. Data 1986, 15 (3), 1087-1279. (41) Allen, M. T.; Yetter, R. A.; Dryer, F. L. Combust. Flame 1997, 109 (3), 449-470. (42) Warnatz, J., Rate coefficients in the C/H/O system. Springer-Verlag: New York, 1984.


44

Page 45 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(43) Thielen, K.; Roth, P. Ber. Bunsen-Ges.-Phys. Chem. Chem. Phys. 1983, 87 (10), 920-925. (44) You, X.; Wang, H.; Goos, E.; Sung, C.-J.; Klippenstein, S. J. J. Phys. Chem. A 2007, 111 (19), 4031-4042. (45) Troe, J.; Ushakov, V. J. Phys. Chem. A 2007, 111 (29), 6610-6614. (46) Baulch, D. L.; Bowman, C. T.; Cobos, C. J.; Cox, R. A.; Just, T.; Kerr, J. A.; Pilling, M. J.; Stocker, D.; Troe, J.; Tsang, W.; Walker, R. W.; Warnatz, J. J. Phys. Chem. Ref. Data 2005, 34 (3), 757-1397. (47) Temps, F.; Wagner, H. G. Ber. Bunsen-Ges.-Phys. Chem. Chem. Phys. 1984, 88 (4), 415418. (48) Hsu, C. C.; Mebel, A. M.; Lin, M. C. J. Chem. Phys. 1996, 105 (6), 2346-2352. (49) Goos, E.; Burcat, A.; Ruscic, B. Extended Third Millenium Ideal Gas and Condensed Phase Thermochemical Database for Combustion with updates from Active Thermochemical Tables. received from Elke Goos, [email protected] April 2015. (50) CHEMKIN 10112, Reaction Design: San Diego, 2011. (51) Brown, N. J.; Bastien, L. A. J.; Price, P. N. Prog. Energy Combust. Sci. 2011, 37 (5), 565-582. (52) Ivanov, A. V.; Trakhtenberg, S.; Bertram, A. K.; Gershenzon, Y. M.; Molina, M. J. J. Phys. Chem. A 2007, 111 (9), 1632-1637.


45

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 46 of 50

(53) Baulch, D. L.; Drysdale, D. D.; Duxbury, J.; Grant, S. L., Evaluated kinetic data for high temperature reactions. Vol. 3. Homogeneous gas phase reactions of O2-O3 systems, the CO-O2H2 system and of sulfur-containing species. Butterworths: London, 1976. (54) Westmoreland, P. R.; Howard, J. B.; Longwell, J. P.; Dean, A. M. Aiche Journal 1986, 32 (12), 1971-1979. (55) Troe, J.; Gardiner, W. C., In Combustion Chemistry, Springer-Verlag: New York, 1984; pp 171-196. (56) Konnov, A. A. Combust. Flame 2009, 156 (11), 2093-2105. (57) Baldwin, R. R.; Jackson, D.; Melvin, A.; Rossiter, B. N. Int. J. Chem. Kinet. 1972, 4 (3), 277-292. (58) Sun, H.; Yang, S. I.; Jomaas, G.; Law, C. K. Proc. Combust. Inst. 2007, 31, 439-446. (59) Sutherland, J. W.; Patterson, P. M.; Klemm, R. B. Brookhaven Nat. Lab.: Upton, NY, 1992. (60) Sharipov, A.; Starik, A. J. Phys. Chem. A 2011, 115 (10), 1795-1803. (61) Volman, D. H. J. Photochem. Photobiol. A 1996, 100 (1-3), 1-3. (62) Mittal, G.; Sung, C. J.; Fairweather, M.; Tomlin, A. S.; Griffiths, J. F.; Hughes, K. J. Proc. Combust. Inst. 2007, 31, 419-427. (63) Mittal, G.; Sung, C.-J.; Yetter, R. A. Int. J. Chem. Kinet. 2006, 38 (8), 516-529. (64) Sun, H.; Law, C. K. Theochem-J. Mol. Struct. 2008, 862 (1-3), 138-147.


46

Page 47 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(65) Timonen, R. S.; Ratajczak, E.; Gutman, D.; Wagner, A. F. J. Phys. Chem. 1987, 91 (20), 5325-5332. (66) Friedrichs, G.; Herbon, J. T.; Davidson, D. F.; Hanson, R. K. Phys. Chem. Chem. Phys. 2002, 4 (23), 5778-5788. (67) Krasnoperov, L. N.; Chesnokov, E. N.; Stark, H.; Ravishankara, A. R. J. Phys. Chem. A 2004, 108 (52), 11526-11536. (68) Hippler, H.; Krasteva, N.; Striebel, F. Phys. Chem. Chem. Phys. 2004, 6 (13), 3383-3388. (69) Krasnoperov, L. N. Phys. Chem. Chem. Phys. 2005, 7 (9), 2074-2076. (70) Hippler, H.; Krasteva, N.; Striebel, F. Phys. Chem. Chem. Phys. 2005, 7 (9), 2077-2079. (71) Krasnoperov, L. N.; Chesnokov, E. N.; Stark, H.; Ravishankara, A. R. Proc. Combust. Inst. 2005, 30 (1), 935-943. (72) Baulch, D. L.; Cobos, C. J.; Cox, R. A.; Esser, C.; Frank, P.; Just, T.; Kerr, J. A.; Pilling, M. J.; Troe, J.; Walker, R. W.; Warnatz, J. J. Phys. Chem. Ref. Data 1992, 21 (3), 411-734. (73) Colberg, M.; Friedrichs, G. J. Phys. Chem. A 2006, 110 (1), 160-170. (74) Horowitz, A.; Calvert, J. G. Int. J. Chem. Kinet. 1978, 10 (7), 713-732. (75) Quee, M. J. Y.; Thynne, J. C. J. Ber. Bunsen-Ges. Phys. Chem. 1968, 72 (2), 211-217. (76) Dibble, T. S.; Zeng, Y. Chemical Physics Letters 2010, 495 (4-6), 170-174. (77) Baldwin, R. R.; Walker, R. W.; Webster, S. J. Combust. Flame 1970, 15 (2), 167-172. (78) Miyoshi, A.; Matsui, H.; Washida, N. J. Chem. Phys. 1994, 100 (5), 3532-3539.


47

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 48 of 50

(79) Poggi, G.; Francisco, J. S. J. Chem. Phys. 2004, 120 (11), 5073-5080. (80) Olkhov, R. V.; Li, Q.; Osborne, M. C.; Smith, I. W. M. Phys. Chem. Chem. Phys. 2001, 3 (20), 4522-4528. (81) Wang, H.; You, X.; Joshi, A.; Davis, S. G.; Laskin, A.; Egolfopoulos, F.; Law, C. K. USC Mech Version II. High-Temperature Combustion Reaction Model of H2/CO/C1-C4 Compounds. http://ignis.usc.edu/USC_Mech_II.htm. (82) Krejci, M. C.; Mathieu, O.; Vissotski, A. J.; Ravi, S.; Sikes, T. G.; Petersen, E. L.; Kermones, A.; Metcalfe, W.; Curran, H. J. J. Eng. Gas Turb. Power 2013, 135 (2), 21503. (83) Tse, S. D.;Zhu, D. L.;Law, C. K. Proc. Combust. Inst. 2000 28(2): 1793-1800. (84) Dowdy, D. R.;Smith, D. B.;Taylor, S. C.;Williams, A. Symp. Int. Combust. Proc. 1991, 23(1), 325-332. (85) Law, C. K.;Peters, B.;Rogg, B. Reduced Kinetic Mechanisms for Applications in Combustion Systems. Berlin/Heidelberg 1993, Springer. 15: 15-26. (86) Egolfopoulos, F. N.; Law, C. K. Symp. Int. Combust. Proc. 1991, 23 (1), 333-340. (87) Wu, C. K.;Law, C. K. Symp. Int. Combust. Proc. 1985, 20(1), 1941-1949 (88) Vagelopoulos, C. M.;Egolfopoulos, F. N.;Law, C. K. Symp. Int. Combust. Proc. 1994, 25(1), 1341-1347 (89) Aung, K. T.; Hassan, M. I.; Faeth, G. M. Combust. Flame 1997, 109 (1-2), 1-24. (90) Scholte, T. G.;Vaags, P. B. Combust. Flame 1959, 3(4), 511-524.


48

Page 49 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(91) McLean, I. C.;Smith, D. B.;Taylor, S. C. Symp. Int. Combust. Proc. 1994, 25(1), 749757. (92) Sun, H.; Yang, S. I.; Jomaas, G.; Law, C. K. Proc. Combust. Inst. 2007, 31, 439-446. (93) Burbano, H. J.; Pareja, J.; Amell, A. A. Int. J. Hydrogen Energy 2011, 36 (4), 3232-3242. (94) Natarajan, J.; Lieuwen, T.; Seitzman, J. Combust. Flame 2007, 151 (1-2), 104-119. (95) Singh, D.; Nishiie, T.; Tanvir, S.; Qiao, L. Fuel 2012, 94 (1), 448-456. (96) Smith, G. P.; Golden, D. M.; Frenklach, M.; Moriarty, J.; Eiteneer, B.; Goldenberg, M.; Bowman, C. T.; Hanson, R. K.; Song, S.; Gardiner, J. W. C.; Lissianski, V.; Qin , Z. GRI-Mech 3.0. http://www.me.berkeley.edu/gri_mech/. (97) Petrova, M. V.; Williams, F. A. Combust. Flame 2006, 144 (3), 526-544. (98) Davis, S. G.; Law, C. K. Combust. Sci. Technol. 1998, 140 (1-6), 427-449. (99) Prathap, C.; Ray, A.; Ravi, M. R. Combust. Flame 2008, 155 (1-2), 145-160. (100) Li, X.; You, X.; Wu, F.; Law, C. K. Proc. Combust. Inst. 2015, 35 (1), 617-624. (101) Prathap, C.; Ray, A.; Ravi, M. R. Combust. Flame 2012, 159 (2), 482-492. (102) Kishore, V. R.; Ravi, M. R.; Ray, A. Combust. Flame 2011, 158 (11), 2149-2164. (103 Burke, M. P.; Chen, Z.; Ju, Y.; Dryer, F. L. Combust. Flame 2009, 156 (4), 771-779. (104) Das, A. K.; Kumar, K.; Sung, C.-J. Combust. Flame 2011, 158 (2), 345-353. (105) Kazakov, A. (2004) Igdelay v 1.0 code, personal communication.


49

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 50 of 50

(106) Kalitan, D. M.; Mertens, J. D.; Crofton, M. W.; Petersen, E. L. J.Propul. Power 2007, 23 (6), 1291-1303. (107) Thi, L. D.; Zhang, Y. J.; Huang, Z. H. Int. J. Hydrogen Energy 2014, 39 (11), 6034-6043. (108) Kim, T. J.; Yetter, R. A.; Dryer, F. L. Symp. Int. Combust. 1994, 25 (1), 759-766. (109) Yetter, R. A.; Dryer, F. L.; Rabitz, H. Combust. Sci. Technol. 1991, 79 (1-3), 129-140. (110) Abian, M.; Gimenez-Lopez, J.; Bilbao, R.; Alzueta, M. U. Proc. Combust. Inst. 2011, 33, 317-323.


50

Role of HOCO Chemistry in Syngas Combustion - Energy & Fuels

Recommend Documents