On the methane negative temperature coefficient behavior in MILD combustion conditions. Water and carbon dioxide effects.

concept in the field and diluted, by means of internal or external recirculation of exhausted gases, to realize a thermal efficient process and drastically reduce pollutants formation. Under such operative conditions, the evolution of the oxidation process is significantly affected by mixture high inlet sensible enthalpy, low reactants concentration, and the presence of conspicuous amount of water and carbon dioxide. The paper aims to study the methane oxidation process under MILD combustion conditions in presence of different diluent species. Previous experimental studies, performed in a tubular flow reactor, using CH4/O2 mixtures diluted in nitrogen, revealed the existence of a Negative Temperature Coefficient (NTC) behavior. Therefore, the attention has been devoted to such peculiar phenomenology. Several simulations were carried out by means of commercial codes and different kinetic schemes available in literature and the analyses were extended to mixtures diluted with different diluents, namely carbon dioxide and water. Reaction path diagrams, sensitivity and Rates Of Production analyses were realized to understand the methane NTC behavior and the chemical influence of diluent species on auto-ignition characteristic times. Keywords - Methane oxidation, MILD combustion, Negative Temperature Coefficient, Auto-ignition delay time.