# The Period of Ignition Delay for Methane-Air Mixture with Hydrogen and Ethylene Additives
## 3 Analysis of Existing Kinetic Mechanisms  
A detailed kinetic mechanism of ignition and combustion of hydrocarbons with air was proposed in [33] and subsequently developed in other works. Today, detailed mechanisms can contain a few hundred to several thousand components. The number of forward and reverse reactions can exceed \(10^{4}\). Such a large number of components and reactions complicates the practical use of detailed kinetic mechanisms in modern calculations of the flow fields of combustion chambers of propulsion and power plants, taking into account the spatial configuration and turbulent nature of the flow [34]. In addition, the validation of detailed kinetic mechanisms remains an important task and has not yet been fully resolved. In practice, the most popular and validated are reduced kinetic mechanisms, which make it possible to describe fuel combustion in a selected range of conditions without a significant loss of modeling accuracy in comparison with the original detailed mechanism. At the moment, there are a large number of reduced kinetic mechanisms describing the ignition and combustion of hydrocarbons. We will conduct some preliminary analyses of them based on research by other authors. The most common reduced kinetic mechanisms are [35]: GRI-Mech 3.0, USC Mech II, ARAMCO, FFCM, as well as their modifications. Less common are the author's reduced mechanisms, which can give a higher agreement with experiments for special problems. Since in our work, the ignition delay period of methane-air mixtures with additions of ethylene and hydrogen is investigated, the analysis of the reduced kinetic mechanisms describing the combustion of these gases is carried out. It should be emphasized that there are no experimental data on the ignition of CH\({}_{4}\) + H\({}_{2}\) + C\({}_{2}\)H\({}_{4}\) mixture with air; therefore, a preliminary selection of the kinetic model and comparison of the results with the experiment was carried out for the process of ignition of individual substances (CH\({}_{4}\) and H\({}_{2}\)), as well as a mixture of CH\({}_{4}\) + H\({}_{2}\) with air. Let us consider the process of methane ignition. Work [36] is based on measuring the laminar flame velocity and the ignition delay period of methane-air mixtures at elevated pressures and temperatures in a constant volume bomb and shock tube. In this work, three kinetic mechanisms are compared with experimental data: GRI-Mech 3.0, USC Mech II, Aramco Mech I.3. As a result of the analysis of the data obtained, the authors proposed a formula describing the dependence of the ignition delay period on the main characteristics of the mixture before ignition. However, the presented calculation method gives discrepancies with experimental data at high pressures. Good agreement of the calculation results with experiments on the ignition of mixtures of hydrogen with air, methane with air, and natural gas with air were obtained for the kinetic models ARAMCO and FFCM. The results are presented in papers [37; 38; 39]. A special place is occupied by the results of [40], in which a noticeable discrepancy with other works with similar experimental conditions occurs. The measurement of the ignition delay period for methane-air mixtures was carried out behind reflected shock waves. The experiments were conducted at a fixed pressure of 1.8 MPa and fuel excess ratios of 0.5 and 1.0 in the temperature range of 800-1000 K. In this work, calculations were also performed using four well-known kinetic mechanisms: UBC Mech 2.1, GRI-Mech 3.0, Aramco Mech 2.0, and USC Mech 2.0. The results of calculations fulfilled using the UBC Mech 2.1 model coincided most closely with the experiment. As an explanation, the author suggests that at high temperatures, the ignition of a near-stoichiometric mixture of methane with air occurs in four stages:  
- induction of deflagration;  
- stable deflagration;  
- transformation between deflagration and detonation;  
- detonation.