Modeling of burner-stabilized hydrogen/air flames using mathematically reduced reaction schemes

A mathematical technique is used to reduce several hydrogen/air reaction systems to one- and two-step schemes. The reduction technique is based on the use of intrinsic low-dimensional manifolds in composition space as introduced by Maas and Pope (1992). In this method it is assumed that the fastest reaction groups of the chemical source term are in steady-state. For a reaction mechanism that does not include HO2, a one-step reduced scheme is used for burner-stabilized hydrogen/air flame calculations. It appears that the one-step reduced scheme predicts the flame structure quite well for several values of the equivalence ratio and mass flow rates. The differences in flame temperature between the reduced scheme and full scheme calculations are less than 50 K. A one-step reduced scheme is also used for the reaction scheme including HO2. For this scheme, however, only low mass flow rates can be used, otherwise the flame will blow off. This is caused by the fact that the one-step scheme underestimates the adiabatic burning velocity considerably (Eggels, 1995). However, the one-step reduced scheme still predicts the main species guile well. For larger mass flow rates, close to the adiabatic mass burning rate, a two-step reduced scheme is used instead. The two-step scheme gives a significant improvement of the H-2/air flame structure, as expected.