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An eigenvalue-eigenvector analysis is used to extract meaningful kinetic information from linear sensitivity coefficients computed for several species of a reacting system at several time points. The main advantage of this method lies in its ability to reveal those parts of the mechanism which consist of strongly interacting reactions, and to indicate their importance within the mechanism. Results can be used to solve three general kinetic problems. Firstly, an objective condition for constructing a minimal reaction set is presented. Secondly, the uncovered dependencies among the parameters are shown to confirm or deny validity of quasi-steady-state assumptions under the considered experimental conditions. Thirdly, taking into account only sensitivities of observed species, the analysis is used to yield error estimates on unknown parameters determined from the experimental observations, and to suggest the parameters that should be kept fixed in the estimation procedure. To illustrate we chose the well-known hydrogen-bromine reaction and the kinetics of formaldehyde oxidation in the presence of co.

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A comprehensive chemical mechanism to describe the oxidation of methane has been developed, consisting of 351 irreversible reactions of 37 species. The mechanism also accounts for the oxidation kinetics of hydrogen, carbon monoxide, ethane, and ethene in flames and homogeneous ignition systems in a wide concentration range. It has been tested against a variety of experimental measurements of laminar flame velocities, laminar flame species profiles, and ignition delay times. The highest sensitivity reactions of the mechanism are discussed in detail and compared with the same reactions in the GRI, Chevalier, and Konnov mechanisms. Similarities and differences of the four mechanisms are discussed. The mechanism is available on the Internet as a fully documented CHEMKIN data file at the address

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A comprehensive and hierarchical optimization of a joint hydrogen and syngas combustion mechanism has been carried out. The Kéromnès et al. (Combust Flame, 2013, 160, 995–1011) mechanism for syngas combustion was updated with our recently optimized hydrogen combustion mechanism (Varga et al., Proc Combust Inst, 2015, 35, 589–596) and optimized using a comprehensive set of direct and indirect experimental data relevant to hydrogen and syngas combustion. The collection of experimental data consisted of ignition measurements in shock tubes and rapid compression machines, burning velocity measurements, and species profiles measured using shock tubes, flow reactors, and jet‐stirred reactors. The experimental conditions covered wide ranges of temperatures (800–2500 K), pressures (0.5–50 bar), equivalence ratios (ϕ = 0.3–5.0), and C/H ratios (0–3). In total, 48 Arrhenius parameters and 5 third‐body collision efficiency parameters of 18 elementary reactions were optimized using these experimental data. A large number of directly measured rate coefficient values belonging to 15 of the reaction steps were also utilized. The optimization has resulted in a H2/CO combustion mechanism, which is applicable to a wide range of conditions. Moreover, new recommended rate parameters with their covariance matrix and temperature‐dependent uncertainty ranges of the optimized rate coefficients are provided. The optimized mechanism was compared to 19 recent hydrogen and syngas combustion mechanisms and is shown to provide the best reproduction of the experimental data.

The determination of rate parameters of gas-phase elementary reactions is usually based on direct measurements. The rate parameters obtained in many independent direct measurements are then used in reaction mechanisms, which are tested against the results of indirect experiments, like time-to-ignition or laminar flame velocity measurements. We suggest a new approach that takes into account both direct and indirect measurements and optimizes all influential rate parameters. First, the domain of feasibility of the Arrhenius parameters is determined from all of the available direct measurements. Thereafter, the optimal Arrhenius parameters are sought within this domain to reproduce the selected direct and indirect measurements. Other parameters of a complex mechanism (third-body efficiencies, enthalpies of formation, parameters of pressure dependence, etc.) can also be taken into account in a similar way. A new fitting algorithm and a new method for error calculation were developed to determine the optimal mean values and the covariance matrix of all parameters. The approach is demonstrated on the calculation of Arrhenius parameters of reactions (R1): H + O 2 = OH + O and (R2): H + O 2 + M = HO 2 + M (low-pressure limit, M = N 2 or Ar). In total, 9 direct measurements for reaction (R1) (745 data points), 10 direct measurements for reaction (R2) (258 data points), and 11 ignition time measurements (79 data points) were taken into account. The application of the method resulted in the following rate parameters for the investigated reactions-(R1): A = 3.003 × 10 10 cm 3 mol −1 s −1 , n = 0.965, E/R = 6158 K (T = 950-3550 K) DETERMINATION OF RATE PARAMETERS BASED ON DIRECT AND INDIRECT MEASUREMENTS 285and (R2): A = 7.856 × 10 18 cm 6 mol −2 s −1 , n = −1.100, E/R = 0 K (low-pressure limit, M = N 2 , T = 300-1850 K). The optimized third-body efficiency of Ar relative to N 2 is m = 0.494 (standard deviation σ = 0.010). The uncertainty parameter f as a function of temperature was also calculated. Average uncertainty parameter values are f = 0.025 and 0.049 for reactions (R1) and (R2) (corresponding to 6% and 12%), respectively, which are much lower than those of the previous evaluations. C 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 284-302, 2012

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