Ignition with stagnation flow

As an illustration, consider the stagnation flow over a catalytic surface during an ignition event. The inlet flow is steady, but the surface temperature increases as power through the platinum-foil surface increases. At a certain temperature the catalytic ignition occurs very rapidly. The flow configuration and conditions, which are taken from Deutschmann [101], are u n — 8 cm/s, Tln = 300 K, with an inlet mixture of 3% CH4, 3% O2, and 94% N2. The inlet-to-surface separation is L = 5 cm, and the surface Pt sites are initially covered... 

Figure 3.7 Catalytic ignition temperatures over rhodium. (A) Stagnation-flow experiments and (B) experiments (symbols) and stagnation-flow simulations for two surface mechanisms (solid-line screening mechanism, dashed-line optimized mechanism). Panel (A) is adapted from Bar et al. (2013) (with permission) and panel (B) is adapted from Mhadeshwar and Vlachos (2005) (with permission).

The ignition criteria for stagnation-point flow Semenov-Frank-Kamenetski or van t Hoff (with X, Song and L.D. Schmidt). Combust. Sci. Tech. 75, 311-331 (1991). 

As mentioned in Section 2.1, the development of surface reaction mechanisms proceeds with optimization of theoretical reaction parameters through comparisons with measurements obtained in a variety of reactors. Catalytic ignition of hydrogen over noble metals has been extensively investigated in stagnation point flow geometries. 

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