Bifurcation Behavior of Premixed Hydrogen/Air Mixtures in a Continuous Stirred Tank Reactor

ABSTRACT

Ignitions, extinctions, and Hopf bifurcations are studied in the oxidation of premixed hydrogen/air mixtures in a continuous stirred tank reactor using detailed kinetics. One- and two- parameter bifurcation diagrams are constructed using numerical bifurcation theory to examine the roles of composition, temperature, pressure, residence time, preheating of reactants, and wall reactions in reactor stability. The stability of stationary branches is determined using local stability analysis. We have found that chemical autocatalysis drives isothermal ignition, extinction, and oscillations at high pressures and low residence times. C-shaped and Z-shaped pressure-temperature (P-T) diagrams are observed reminiscent of the explosion limits of hydrogen/oxygen mixtures in closed vessels. Mass transfer outflow becomes important on the first branch (low pressures) of a P-T diagram, but kinetic coupling controls ignition and extinction limits on the intermediate branch (high pressures). We have found that reaction exothermicity controls ignition at high pressures. Periodic oscillations have been observed under certain conditions. It is shown that ignition and extinction can be oscillatory, and two extinctions, one oscillatory and one from stable solutions, can exist under certain conditions.

Key Words:

• Ignition
• extinction
• oscillations
• hydrogen
• bifurcation
• stirred reactor