Catalytic ignition of very lean mixtures of hydrogen

This paper deals with transient ignition of very lean hydrogen/air mixtures by thin catalytic wire in a natural convection environment. Modeling is accomplished via a reduced set of heterogeneous kinetic processes which include dissociative adsorption and desorption of both reactants, three fast surface reactions of the Langmiur–Hinshelwood type and the desorption reaction of the adsorbed product. For equivalence ratios smaller than a critical value (which in this case is 0.22), the ignition process shows a dual character, depending on the initial conditions for the surface coverages at the wire. Besides the classical thermal ignition mechanism, there is another branch called in this paper the equi-adsorption regime (EAR), characterized by equal adsorption rates of both reactants. In this regime, the overall reaction rates are very much higher than in the thermal regime, producing the combustion process at relatively low temperatures, even at room temperatures. A closed form solution for the overall reaction rate has obtained in this regime. This mechanism is appropriate to remove even traces of hydrogen in critical environments.