EXPERIMENTAL AND NUMERICAL INVESTIGATION OF THE CATALYTIC IGNITION OFMIXTURES OF HYDROGEN AND OXYGEN ON PLATINUM

Catalytic ignition of mixtures of H-2 + O-2 has been studied, with emp hasis on the dynamics behavior, by measuring and simulating the tempor al evolution from the kinetically controlled regime (i.e., prior to ig nition) to the state controlled by mass transport after ignition. In t he 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 t he 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 detail ed surface kinetics. The evolution of the catalyst's temperature, the surface coverages and the gradients in the reactants' concentrations a nd temperature were calculated. Good agreement was obtained between th e experiments and the simulations. The results provide new insight int o 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 appli ed to ignition or combustion, where heterogeneous processes are couple d to those in the gaseous phase. (C) 1997 by The Combustion Institute.