The Effect of Flow Velocity on Ignition and Extinction in Homogeneous-Heterogeneous Combustion

Abstract

Ignition and extinction points are calculated for homogeneous-heterogeneous combustion of a premixed propane-air stream in stagnation point flow over a platinum surface as functions of inlet gas velocity and composition and power input to the catalyst surface using global rate expressions for the homogeneous and surface reactions. Curves of surface temperature and surface concentration of fuel and oxygen at the ignition and extinction points are computed at several compositions in the fuel-lean regime. [gnition and extinction of the surface reaction and autothermal behavior are found over a very broad range of velocities. Homogeneous ignition occurs only at relatively low velocities. As the velocity increases from 0.5 cm/s to 50 cm/s, autothermal behavior is supported by leaner mixtures, and the autothermal surface temperature increases substantially. Inlet compositions leaner than 1.4% propane cannot support autothermal operation at any velocity. Homogeneous ignition takes place at higher surface temperatures as the velocity is increased, while the range of compositions that exhibit homogeneous ignition shrinks markedly as velocity increases.