A large set of experimental data was accumulated for hydrogen combustion: ignition measurements in\ud shock tubes (770 data points in 53 datasets) and rapid compression machines (229/20), concentra-\ud tion–time profiles in flow reactors (389/17), outlet concentrations in jet-stirred reactors (152/9) and\ud flame velocity measurements (631/73) covering wide ranges of temperature, pressure and equivalence\ud ratio. The performance of 19 recently published hydrogen combustion mechanisms was tested against\ud these experimental data, and the dependence of accuracy on the types of experiment and the experimen-\ud tal conditions was investigated. The best mechanism for the reproduction of ignition delay times and\ud flame velocities is Kéromnès-2013, while jet-stirred reactor (JSR) experiments and flow reactor profiles\ud are reproduced best by GRI3.0-1999 and Starik-2009, respectively. According to the reproduction of all\ud experimental data, the Kéromnès-2013 mechanism is currently the best, but the mechanisms NUIG-\ud NGM-2010, ÓConaire-2004, Konnov-2008 and Li-2007 have similarly good overall performances. Several\ud clear trends were found when the performance of the best mechanisms was investigated in various cat-\ud egories of experimental data. Low-temperature ignition delay times measured in shock tubes (below\ud 1000 K) and in RCMs (below 960 K) could not be well-predicted. The accuracy of the reproduction of\ud an ignition delay time did not change significantly with pressure and equivalence ratio. Measured H\ud 2\ud and O\ud 2\ud concentrations in JSRs could be better reproduced than the corresponding H\ud 2\ud O profiles. Large dif-\ud ferences were found between the mechanisms in their capability to predict flow reactor data. The repro-\ud duction of the measured laminar flame velocities improved with increasing pressure and total diluent\ud concentration, and with decreasing equivalence ratio. Reproduction of the flame velocities measured\ud using the flame cone method, the outwardly propagating spherical flame method, the counterflow\ud twin-flame technique, and the heat flux burner method improved in this order. Flame cone method data\ud were especially poorly reproduced. The investigation of the correlation of the simulation results revealed\ud similarities of mechanisms that were published by the same research groups. Also, simulation results cal-\ud culated by the best-performing mechanisms are more strongly correlated with each other than those of\ud the weakly performing ones, indicating a convergence of mechanism development. An analysis of sensi-\ud tivity coefficients was carried out to identify reactions and ranges of conditions that require more atten-\ud tion in future development of hydrogen combustion models. The influence of poorly reproduced\ud experiments on the overall performance was also investigated

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.