Experimental study of the effect of CO2 on propane oxidation in a Jet Stirred Flow Reactor

The use of advanced combustion technologies (MILD, oxy-fuel combustion) is among the most promising methods to reduce emission of pollutants, as the system working temperatures are enough low to boost 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 exhausted gases. Such a strategy implies that high contents of CO2 and/or H2O interact with the reactants oxidation chemistry. In order to characterize this aspect of the combustion processes under diluted conditions, experimental tests were carried out for propane/oxygen/nitrogen mixtures in presence of variable amounts of CO2 in a quartz Jet Stirred Flow Reactor (JSFR). Experiments were realized at atmospheric pressure, over the temperature range 720–1100 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 propane is significantly altered by CO2 in dependence of mixture inlet temperatures and equivalence ratios. Numerical simulations pointed out that kinetic models are not able to correctly reproduce the experimental results. Further numerical analyses were performed to explore the interaction of CO2 with the oxidation chemistry of propane. Results suggested that such a species alters 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.