Dilution Effects in NAtural Gas Mild Combustion

The mild combustion conditions, i.e., high reactant preheating and dilution level, yield a high efficiency relying on an increase in thermal energy transfer and drastic reduction of pollutant emissions. In this work, an experimental characterization of methane oxidation in mild conditions was carried out in a simple laboratory-scale system as a function of dilution level, C/O ratio, and inlet temperature. The framework outlined by the experimental analyses underlines that extreme working conditions, very different from the ones used in traditional combustion processes, can lead to a very complex system behavior. Several thermokinetic regimes corresponding to static and dynamic conditions were recognized. An accurate characterization of the dynamic region was performed, identifying several temperature oscillation typologies. On the basis of the obtained results, the range of reliability of mild combustion processes were defined. It was pointed out that the range of dynamic behavior can be overcome by splitting the whole combustion process into two stages, where the first one evolves in diluted rich conditions.