Low temperature combustion of methane/alkenes mixtures

The use of methane is commonly adopted as thermal diluent and chemical inhibitor in the partial oxidation of alkenes, in order to avoid the occurrence of unwanted reactions and full oxidation. Moreover, methane-alkene mixtures are commonly present in several industrial applications such as petrochemical processes. In this work, experimental data for pure ethylene and propylene flames in presence of air were collected, as first. Then the effect of alkenes addition on methane premixed flames was investigated. These fuel compositions were investigated by means of a heat flux burner at different gaseous compositions. The measurements were compared with experimental data retrieved from current literature as well as with the results of a detailed kinetic mechanism. The data collected in this work suggest the existence of two chemical regimes, resulting in a methane-dominated kinetic, in case of alkene addition lower than 20 %v/v, and alkene-dominated kinetic, in case of higher alkenes content. The production of soot precursors for methane combustion was found to be significantly increased by the addition of propylene. Finally, the maximum reactivity, expressed in terms of laminar burning velocity, undergoes a non-negligible shift toward a richer composition of methane in the presence of alkene. The agreement between the experimental data and numerical predictions allowed for further evaluation of the chemical interactions, product and heat profiles as a function of the initial composition. A criterion based on the flame structure was posed and successfully implemented to identify the temperature values giving unsafe or undesired conditions in the epoxidation processes. © 2019 Elsevier Ltd