Development of a Joint Hydrogen and Syngas Combustion Mechanism Based on an Optimization Approach

Abstract

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.

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

“…The global parameter optimization method applied here has been described in detail . Its use has been successfully demonstrated in various articles . The optimal set of parameters was obtained by the minimization of the following objective function:where…”

“…The mechanism of Saxena and Williams was chosen as a starting point for the development of an initial mechanism based on its overall satisfying performance in predicting the collected measurement data and its suitable size. The H 2 /CO core of the original mechanism was replaced by the optimized syngas mechanism developed in our earlier work . As a consequence, the excited radical OH* was added to the mechanism.…”

“…A complete overview of all important reactions for each type of measurement can be found in Table F of the Supporting Information. Note that several of the most important reactions are part of the H 2 /CO subsystem and have previously been optimized . These reactions were not selected for (re)optimization to preserve mechanism hierarchy.…”

“…Typically validated for a restricted range of applications and/or conditions, it can be observed that most of these mechanisms, to a greater or lesser extent, fail at reproducing certain experimental data outside their range of validation. The aims of this work are to develop a robust and well‐performing detailed mechanism suited for multiple purposes related to ethanol combustion following a hierarchical mechanism optimization approach that was previously employed in the optimization of hydrogen and syngas combustion mechanisms and to demonstrate the usefulness of this method for more complex systems such as ethanol combustion.…”

“…This solution decreases computational costs and guarantees that a new mechanism also provides good results for the combustion of smaller fuels, since the relevant chemistry is not modified. In other words, the hierarchy of combustion systems is maintained and larger mechanisms are fully “backward compatible.” For this reason, the H 2 /CO chemistry optimized in a previous work of our group remained unchanged, despite the fact that several reactions in the H 2 /CO subsystem are important for the modeling of ethanol combustion, particularly in freely propagating premixed flames (see Table F of the Supporting Information).…”