# The Period of Ignition Delay for Methane-Air Mixture with Hydrogen and Ethylene Additives
## 1 Introduction
It was also noted that the addition of hydrogen significantly reduced the radius of curvature of the flame surface. The particular influence of the hydrogen effect on the diffusion flame shape is presented in [17]. When adding hydrogen to methane, the concentration gradients of reactive particles in front of the flame increase, though the flame length decreases. This factor indicates the intensification of chemical reactions through the addition of hydrogen. The intensification of the ignition and combustion of methane upon the addition of hydrogen was also confirmed by the results of [18], where quantitative data were obtained on the spreading rate of deflagration flame in air + methane + hydrogen mixtures with different contents of H\({}_{2}\). When burning fuel-air mixtures in constant cross-section channels, it should be noted that the addition of hydrogen to methane leads not only to an increase in the spreading velocity of the flame front but also to a change in its shape [19; 20; 21]. Due to the rapid oxidative reactions of hydrogen, combustion is stabilized in the boundary layer near the channel wall. In this case, the shape of the flame passes from the V-shaped, characteristic of methane combustion, to the M-shaped. The stabilization effect of the M-shaped flame is enhanced along with an increase in the proportion of hydrogen and an increase in the wall temperature. The practical use of methane and hydrogen mixtures as a fuel for internal combustion engines is considered in [22; 23; 24; 25; 26] and in [27; 28; 29] for power plants based on boiler and turbine devices. In these works, it was shown that the addition of hydrogen (less than 10%) made it possible to reduce NOx emissions and improve the characteristics of power plants due to an increase in the flame spreading rate and homogenization of the mixture in the working zone due to high diffusion of hydrogen. In addition to hydrogen, other additives to methane are currently being considered to increase its flammability [30] and combustion efficiency. One of these additives is ethylene, which is less explosive and denser than hydrogen. Considering these advantages, as well as its high manufacturability and widespread use in industry, the use of C\({}_{2}\)H\({}_{4}\) as a combustion-intensifying additive for methane can be considered for different power plants. These factors initiated additional studies of the combustion of mixtures CH\({}_{4}\) + C\({}_{2}\)H\({}_{4}\) + air. For example, the study of the combustion rate of a mixture CH\({}_{4}\) + C\({}_{2}\)H\({}_{4}\) + air is given in [31]. In this work, the detonation of mixtures with an excess fuel ratio in the range from 0.72 to 1.3 and with a volume fraction of ethylene from 0% to 100% at ambient temperature and pressure in a closed chamber was experimentally investigated. The results showed that ethylene increases the maximum chamber pressure, and the derivative of pressure changes over time. This is due to the reduction in the ignition induction time and the increase in the relative time interval, which is characterized by so-called \"fast combustion\". To describe the combustion of the fuel mixture, three characteristic modes are chosen, depending on the ethylene content:  
1. combustion mode with a predominance of methane (volumetric ethylene content less than 30%);
2. transient mode (volumetric ethylene content from 30% to 70%);
3. combustion mode with a predominance of ethylene (volumetric ethylene content more than 70%). Some experimental data on the ignition delay of methane, ethylene, propylene and their mixtures at high pressures are presented in [32]. As shown in this work, the presence of ethylene makes it possible to accelerate the methane combustion reactions. It should be emphasized that the variety of experimental settings and methods for processing empirical data do not allow direct comparison with quantitative results presented by different authors. The example of this difference will be discussed below.