Uncertainty of the rate parameters of several important elementary reactions of the H2 and syngas combustion systems

Nagy, Tibor; Valkó, Éva; Sedyó, Inez; Zsély, István Gy.; Pilling, Michael J.; Turányi, Tamás

doi:10.1016/j.combustflame.2015.01.005

Cited by 67 publications

(54 citation statements)

References 59 publications

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“…Here, the reaction of formaldehyde + OH is important across the whole temperature range, but particularly so at the highest temperature. The sensitivity analysis also shows that the reactions of HO 2 dominate above 780 K. Nagy et al [42] highlighted uncertainties of a factor of 2.5 in the reaction rate for HO 2 The isomerisation reactions from RO 2 to QOOH are of lower importance here than fuel + OH which contrasts with the behaviour of smaller molecules [43]. However, they do feature for both iso-octane and n-heptane channels across the range of temperatures studied, and thus uncertainties in the temperature dependence of these reactions could affect the prediction of NTC behaviour.…”

Section: The Representation Of the Reference Gasoline Via The Trf Surmentioning

confidence: 98%

The influence of n -butanol blending on the ignition delay times of gasoline and its surrogate at high pressures

Agbro

Tomlin

Lawes

et al. 2017

Fuel

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The influence of blending n-butanol at 20% by volume on the ignition delay times for a reference gasoline was studied in a rapid compression machine (RCM) for stoichiometric fuel/air mixtures at 20 bar and 678 K-858 K. Delay times for the blend lay between those of stoichiometric gasoline and stoichiometric n-butanol across the temperature range studied. At lower temperatures, delays for the blend were however, much closer to those of n-butanol than gasoline despite n-butanol being only 20% of the mixture. Under these conditions n-butanol acted as an octane enhancer over and above what might be expected from a simple linear blending law. The ability of a gasoline surrogate, based on a toluene reference fuel (TRF), to capture the main trends of the gasoline/ n-butanol blending behaviour was also tested within the RCM. The 3-component TRF based on a mixture of toluene, n-heptane and iso-octane was able to capture the trends well across the temperature range studied. Simulations of ignition delay times were also performed using a detailed blended nbutanol/TRF mechanism based on the adiabatic core assumption and volume histories from the experimental data. Overall, the model captured the main features of the blending behaviour, although at the lowest temperatures, predicted ignition delays for stoichiometric n-butanol were longer than those observed. A bruteforce local sensitivity analysis was performed to evaluate the main chemical processes driving the ignition behaviour of the TRF, n-butanol and blended fuels. The reactions of fuel + OH dominated the sensitivities at lower temperatures, with H abstraction from nn-butanol and the blend. At higher temperatures the decomposition of H 2 O 2 and reactions of HO 2 and that of formaldehyde with OH became critical, in common with the ignition behaviour of other fuels. Remaining uncertainties in the rates of these key reactions are discussed.

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Section: The Representation Of the Reference Gasoline Via The Trf Surmentioning

confidence: 98%

The influence of n -butanol blending on the ignition delay times of gasoline and its surrogate at high pressures

Agbro

Tomlin

Lawes

et al. 2017

Fuel

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“…Articles reporting the results of direct measurements provide the values of the measured rate coefficient of an elementary reaction at various temperatures, pressures, and possibly using different bath gases. A new systematic method for the determination of the prior uncertainty domain of the Arrhenius parameters has been applied to 22 reactions of the H 2 /CO system by Nagy et al . Applying this method to the ethanol combustion system, all direct measurements and theoretical determinations of the rate coefficient were collected for each elementary reaction investigated from the NIST Chemical Kinetics Database and from review articles .…”

Section: Rate Parameters To Be Optimized Their Prior Uncertainty Dommentioning

confidence: 99%

“…A collection of data used for the estimation of the prior uncertainty limits can be found in the Supporting Information. The prior uncertainty limits were determined by using the computer codes u‐Limits , UBAC and JPDAP that can be downloaded from the ReSpecTh webpage . Values of prior (and posterior) f ( T ) limits for each optimized reaction can be found in Table .…”

Section: Rate Parameters To Be Optimized Their Prior Uncertainty Dommentioning

confidence: 99%

Development of an Ethanol Combustion Mechanism Based on a Hierarchical Optimization Approach

Olm

Varga

Valkó

et al. 2016

Int. J. Chem. Kinet.

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A detailed multi-purpose reaction mechanism for ethanol combustion was developed for the use in high-fidelity numerical simulations describing ignition, flame propagation and species concentration profiles with high accuracy. Justified by prior analysis, an optimization of 44 Arrhenius parameters of 14 crucial elementary reactions using several thousand direct and indirect measurement data points was performed, starting from the ethanol combustion mechanism of Saxena and Williams (2007). The final optimized mechanism was compared to 13 reaction mechanisms frequently used in ethanol combustion with respect to their accuracy in reproducing the various types of experimental data.

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“…Many of the general ideas are traceable to the early work of Frenklach , which was further developed as solution mapping methods , and later used in optimizations of methane combustion chemistry . Numerous researchers have since suggested other mathematical techniques to optimize rate constants by comparison of available experimental data with model predictions . Such methods commonly employ a starting chemical reaction set with a preassigned set of uncertainties in the model rate constants; parameter values are then adjusted on the basis of mathematical formalisms that compare experimental and model results.…”

Section: Introductionmentioning

confidence: 99%

“…Recent work on uncertainty quantification in combustion models includes that of Nagy and Turanyi , and Nagy et al , who considered uncertainties related to the temperature dependence of Arrhenius parameters. Prager et al examined the effects of correlations in rate rules, for which little or no experimental data are available and found improvement in modeled ignition delay times when correlations were considered; Cai and Pitsch have considered similar effects in the optimization of models of n ‐pentane combustion.…”

Section: Introductionmentioning

confidence: 99%

The Importance of Relative Reaction Rates in the Optimization of Detailed Kinetic Models

Manion

McGivern

2016

Int J of Chemical Kinetics

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Numerous mathematical tools intended to adjust rate constants employed in complex detailed kinetic models to make them consistent with multiple sets of experimental data have been reported in the literature. Application of such model optimization methods typically begins with the assignment of uncertainties in the absolute rate constants in a starting model, followed by variation of the rate constants within these uncertainty bounds to tune rate parameters to match model outputs to experimental observations. The present work examines the impact of including information on relative reaction rates in the optimization strategy, which is not typically done in current implementations. It is shown that where such rate constant data are available, the available parameter space changes dramatically due to the correlations inherent in such measurements. Relative rate constants are typically measured with greater relative accuracy than corresponding absolute rate constant measurements. This greater accuracy further reduces the available parameter space, which significantly affects the uncertainty in the model outcomes as a result of kinetic parameter uncertainties. We demonstrate this effect by considering a simple example case emulating an ignition event and show that use of relative rate measurements leads to a significantly smaller uncertainty in the output ignition delay time in comparison with results based on absolute measurements. This is true even though the same range of absolute rate constants is sampled in each case. Implications of the results with respect to the maintenance of physically realistic kinetics in optimized models are discussed, and suggestions are made for the path forward in the refinement of detailed kinetic models. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. Int J Chem Kinet 48: [358][359][360][361][362][363][364][365][366] 2016

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Uncertainty of the rate parameters of several important elementary reactions of the H2 and syngas combustion systems

Cited by 67 publications

References 59 publications

The influence of n -butanol blending on the ignition delay times of gasoline and its surrogate at high pressures

The influence of n -butanol blending on the ignition delay times of gasoline and its surrogate at high pressures

Development of an Ethanol Combustion Mechanism Based on a Hierarchical Optimization Approach

The Importance of Relative Reaction Rates in the Optimization of Detailed Kinetic Models

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