On H2-O2 oxidation in several bath gases

The oxidation process of H/O mixtures has received a lot of attention since it represents the first step for the development of detailed kinetic schemes for complex fuels within the idea of their construction in a hierarchical structure. Although much effort has been dedicated to the definition of reliable and robust kinetic mechanisms for the H-O sub-system, still recently updated kinetic mechanisms for the H-O system have been proposed by several authors. While under traditional conditions, available kinetic schemes seem to perform properly, when moving towards the simulation of new combustion modes (i.e. MILD, Oxyfuel, LTC engine conditions) their performance is still under discussion. In particular, the presence of large amount of non-inert diluent species as HO and CO with high collisional efficiencies poses several problems, such as uncertainties on third body collisional efficiencies, the chemical kinetic description of reaction pressure dependence and "mixing rules". In this work, new experimental tests have been run for a lean H2-O2 mixture in several bath gases (mainly N2, CO2 and H2O) in a Jet Stirred Flow Reactor. Dynamic behaviors have been experimentally detected, with temperature oscillations within the control volume for N2 diluted mixtures. CO2 and H2O act as inhibitors of such phenomenologies. The performance of updated kinetic schemes in different environments is satisfactory when the diluent is N2, while some relevant discrepancies occur for mixtures diluted in other bath gases. Analyses of Rates of Reactions (RR) have allowed to identify the kinetic mechanism responsible for the onset and termination of instabilities. CO2 and H2O may suppress instabilities because of the enhanced role of termolecular reactions in virtue of their high third body collisional efficiencies.