Stationary state multiplicities in diffusive-reactive systems: Hydrogen versus heated air

This study investigates the existence of multiple stationary states in a system of nonpremixed, counterflowing hydrogen against heated air. Raman spectroscopy measurements of the water concentration show that up to three stable stationary states can exist for identical boundary conditions. The system is simulated using detailed kinetics and transport properties, and S-curve sensitivity is employed to identify the dominant chemistry. The response of the multiplicity regime to changes in the fuel concentration and system pressure is investigated by measuring the air temperatures corresponding to ignition and extinction for concentrations between 6-38% H₂ in N₂ (vol.) and pressures between 0.3-8 atm. The triple-solution multiplicity is found between 7- 25% H₂ in N₂ at 4 atm, and between -1.5-7 atm at 9% H₂ in N₂ and a constant pressureweighted strain rate of 300 s^-1 In addition, the response to changes in the strain rate is studied computationally for strain rates between 10 and 40, 000 s^-1 and for air boundary temperatures ranging between 950 and 1100 K. In the strain rate space, the triplestable- solution multiplicity extends from -100-10, 000 s^-1 at 9% H₂ in N₂ and 4 atm. The experimental results are found to agree well with the computational results.