Catalytic Ignition and Extinction of Very Fuel-Lean Hydrogen-Air Mixtures on Platinum Surfaces

摘要

Surface ignition and extinction of very fuel-lean hydrogen-air mixtures on platinum surfaces were modeled using a detailed surface kinetic mechanism and transport phenomena. A stagnation-point flow geometry was employed to study the effect of heat flux, flow velocity, and composition on the surface ignition and extinction. The temperature and concentration on platinum surfaces as well as the coverage of surface species were also explored to evaluate the role of gas-phase chemistry. It was shown that the platinum surface can be poisoned by different adsorbates, and the dynamic process of surface ignition and extinction is associated with a phase transition from one poisoning species to another. For certain temperatures, multiple poisoned states of the surface coexist. Comparisons of simulations with experiments were carried out, and the results revealed that the self-inhibition of hydrogen surface ignition is caused by poisoning of platinum by atomic hydrogen.