Flammability limits of methane/alkene mixtures in air

The knowledge of alkane/alkene chemical interactions in gaseous mixtures are fundamental for several industrial applications as they represent the main compounds of the pyrolysis gas produced in stream cracking process, or in the oxidative coupling of methane, or even as component of biogas. However, reliable and comprehensive empirical correlations for the estimation of flammability limits for complex fuel mixtures are still to be developed. More in particular, the additivity correlations (e.g. Le Chatelier’s rule) are not suitable or uncertain when alkanes are mixed with saturated hydrocarbon species. In this work, the flammability limits for binary mixtures of ethylene or propylene in air, either pure or in mixture with methane were defined by experimental and numerical analysis. The experimental data were evaluated by means of the heat flux burner method, which is able to reduce the effect of the flame stretching and the related uncertainties. The obtained results were compared with the corresponding experimental data retrieved in the current literature, when available, and with the data calculated by the most common empirical correlations. The data were also compared with numerical estimations obtained by fully validated detailed kinetic model suitable for light compounds oxidative chemistry. To estimate the flammability limits, the limiting laminar burning velocity theory has been adopted. The agreement between experimental data and numerical results was evaluated by means of statistical approach.