Effect of diluents on methane oxidation in a jet stirred flow reactor

Advanced combustion technologies, such as MILD, LTC (Low Temperature Combustion) reduce emission of pollutants by controlling system working temperatures to values not critical to promote the formation of several classes of pollutants. To access this temperature range, a significant dilution of reactants is required. At the same time, reactants have to be preheated to sustain the oxidation process. Such conditions are achieved by a strong recirculation of exhaust gases. Such a strategy implies that high contents of CO2 and H2O interact with reactants oxidation chemistry. In order to characterize this aspect of the combustion processes under diluted conditions, experimental tests were carried out for methane/oxygen mixtures in presence of N2, CO2 and H2O in a quartz Jet Stirred Flow Reactor (JSFR), at atmospheric pressure, over the temperature range 790- 1215 K, from fuel lean to rich conditions and at a residence time of 0.5 s. Temperature and species concentration measurements suggest that the oxidation of methane may be significantly altered by CO2 and H2O in dependence of mixture inlet temperatures and equivalence ratios. Numerical analyses were performed to explore the interaction of diluents with the oxidation chemistry of methane. Results suggested that such species alter the main radical branching mechanisms, i.e. in termolecular reactions as a third body species with high collisional efficiency or directly participating in bimolecular reactions.