# The Period of Ignition Delay for Methane-Air Mixture with Hydrogen and Ethylene Additives
## 3 Analysis of Existing Kinetic Mechanisms
In [41], the delay time, excitation, and ignition times for CH\({}_{4}\)-air mixtures are given, which were simulated using the kinetic mechanisms GRI-Mesh3.0 and developed by the authors Mesh_56.54. The created kinetic mechanism showed satisfactory agreement with GRI-Mesh3.0 and experiments. The authors focused on the key reactions affecting the ignition period of the mixture, which made the Mesh_56.54 mechanism suitable for three-dimensional numerical simulation of the engine. It should be noted that the work used experimental data which were taken from the published literature. As for the ignition and combustion of hydrogen, according to [42; 43], the ignition of hydrogen can be described with high reliability by the mechanisms GRI-Mesh 3.0 and Keromnes-2013 at pressures up to 16 bar and hydrogen content below 40%. Attempts to improve the coincidence in the dynamics of hydrogen ignition are outlined in [44; 45; 46], where the author's kinetic mechanism, the Konnov mechanism, is presented. The results of [47] showed that this mechanism could be extended for an approximate description of the ignition of ethylene, and the Konnov mechanism gives the best quality coincidence in the size of the detonation cell [48]. According to [49], the USC Mesh II model gives good agreement between the calculated ignition delay period and experiment in a wide range of parameters, while the SERDP PAH model 0.1-only at rich fuel mixtures and low pressures. Let us consider the state of the problem in terms of ignition modeling of mixed fuels with air. The work [50] represents the particular interest, where the study of the ignition delay period of CH\({}_{4}\) + H\({}_{2}\) with air was carried out under the conditions realized in internal combustion engines. The assessment results were based on numerical simulations using the kinetic mechanisms GRI-Mesh 3.0, AramcoMech 1.3, and USC Mech 2.0. The most consistent with the experimental data was the USC Mech 2.0 mechanism. According to [50; 51], the USC Mech 2.0 model gives the best agreement with the experiment. With increasing pressure and temperature, better agreement with the experiment was obtained using the AramcoMech 1.3 model [52]. The results of the study showed that the increase in the proportion of hydrogen reduces the ignition delay period by two orders of magnitude. Analysis of chemical reactions showed that the limiting factors of the ignition rate are the concentrations of CH\({}_{4}\) and O\({}_{2}\). The leading role at low temperatures is played by the reaction with the participation of H and O\({}_{2}\) and at high temperatures by HO\({}_{2}\) and H\({}_{2}\)O\({}_{2}\). The aim of the study [53] was to obtain a simplified kinetic combustion mechanism for the mixture of H\({}_{2}\) + CH\({}_{4}\) in air to reduce computational costs when simulating the processes of ignition and combustion in internal combustion engines. The proposed kinetic mechanism, partially ignoring the reverse reactions, showed satisfactory agreement with the experimental data. It should be noted that the laminar flame velocity of stoichiometric methane-hydrogen-air mixtures were studied using numerical simulations in the range of initial temperatures of 300-600 K. It is shown that modern kinetic models allow to accurately descript the combustion of such mixtures, and at low hydrogen concentrations (H\({}_{2}\) < 50%), a simple global mechanism is sufficient. In the investigated range of initial temperatures, hydrogen weakly affects the laminar flame velocity when its concentration in the mixture is less than 50%. Only a more significant proportion of hydrogen in the fuel gives the beginning of a rapid increase in the investigated value; however, as the initial temperature increases, the effect of the hydrogen content on the combustion rate decreases. The work [54] considers the rate of laminar combustion of the mixture H\({}_{2}\) + CH\({}_{4}\) + air. The proportion of hydrogen in the fuel mixture varied from 0 to 1 at \(\varphi\) = 0.8, 1.0, and 1.2.