Experimental and numerical investigation of the catalytic ignition of mixtures of hydrogen and oxygen on platinum

Catalytic ignition of mixtures of H-2 + O-2 has been studied, with emphasis on the dynamics behavior, by measuring and simulating the temporal evolution from the kinetically controlled regime (i.e., prior to ignition) to the state controlled by mass transport after ignition. In the experiments, different non flammable mixtures of H-2 + O-2 (with N-2 as diluent) react catalytically to form H2O on a Pt-wire at a total pressure of 1 atm. The transient behavior from the ignition point to the state controlled by mass transport was measured via the temperature of the Pt-wire. These zero flow experiments were simulated by a code which describes reacting flows with diffusion, heat balance and detailed surface kinetics. The evolution of the catalyst's temperature, the surface coverages and the gradients in the reactants' concentrations and temperature were calculated. Good agreement was obtained between the experiments and the simulations. The results provide new insight into both the mechanism of catalytic ignition and the relative importance of reaction kinetics and mass transfer at different stages. Catalytic ignition of H-2 + O-2 is primarily governed by coupling between: (i) the heat balance, (ii) the kinetics of adsorption of H-2 and O-2, and (iii) the desorption kinetics of H-2. The model presented can be applied to ignition or combustion, where heterogeneous processes are coupled to those in the gaseous phase. (C) 1997 by The Combustion Institute.