Extinction of strained premixed flames of hydrogen/air/steam mixture: Local equilibrium temperature and local equivalence ratio

The effect of steam addition on the structure and extinction of hydrogen/ai r premixed flames is investigated numerically with a detailed kinetic mecha nism by adopting both counterflow and stagnation-point flow configurations as model problems. For a specified equivalence ratio of hydrogen/air mixtur e, the flames in a stagnation-point flow can be maintained to higher steam content compared to those in a counterffow. This can be explained based on the local strain rates defined at the location of maximum heat release rate . The effects of preferential diffusion and reaction incompleteness caused by flame stretch and the effect of steam addition on flame extinction can b e successfully quantified by adopting a local equilibrium temperature, whic h can be determined from chemical equilibrium calculation using the tempera ture and concentrations of a local mixture in a flow field. The structure o f near-stoichiometric flames with the variation in steam content can be suc cessfully explained by introducing a local equivalence ratio.