CO2-DRIVEN OSCILLATIONS IN METHANE MILD COMBUSTION

The aim of the work is to numerically study the oxidation process of methane in typical condition of MILD combustion in systems highly diluted in CO2. Simulations have been performed in a perfect stirred flow reactor at atmospheric pressure. The analyses have been realized as function of the main parameters of the system, namely mixture inlet temperatures, mixture compositions and reactor heat loss coefficient values. Previous experimental and numerical works carried out in a non-adiabatic perfect stirred flow reactor showed a complex dynamic behavior of methane/oxygen systems highly diluted in nitrogen or steam. More specifically, thermo-kinetics temperature oscillations were observed. The main result obtained with respect to previous works is that the presence of carbon dioxide in the combustion system leads to the establishment of temperature oscillations even for adiabatic conditions, so that temperature oscillations are kinetic-driven. In fuel lean conditions the CO/CO2 equilibrium inter-conversion plays a key role in the establishment of dynamic behavior; in rich fuel conditions the CH3 recombination path, active at relatively high working temperatures, modulates temperature oscillations. In agreement with previous works, in case of non-adiabatic systems, temperature oscillations are influenced by the heat loss towards the surrounding.