Finding the concentration limits of combustion on the basis of the analysis of the diffusion-thermal instability of the flame. Methane–air–diluent mixture

This paper describes the method for calculating the concentration limits of combustion with the use of equations for the boundaries of the diffusion-thermal stability. The key parameter responsible for the existence of the combustion limits is the heat effect of the gas mixture combustion. The thermal effect and the equation of the boundary of the diffusion-thermal stability are used to determine the minimum flame temperature below which combustion is not possible. A significant impact on the concentration limits is produced by the heat capacity of the components of the mixture if it is strongly dependent on temperature. For the upper and lower concentration limits, the minimum flame temperature generally varies and depends on the relative concentration and properties of the diluent. The theoretical methods for calculating the concentration limits are tested according to the experimental data on the combustion of the methane–air–diluent mixture.