Ignition and extinction of flames near surfaces: Combustion of H 2 in air

Abstract

The ignition and extinction characteristics in homogeneous combustion of H 2 in air close to inert surfaces are studied with detailed chemistry involving 19 reversible reactions and 9 species. Flame structures for gases impinging on planar surfaces with stagnation point flow are computed using numerical bifurcation theory. Two-parameter bifurcation diagrams are constructed as functions of equivalence ratio and strain rate. It is shown that up to five multiple solutions can coexist for some conditions. When three steady states coexist, the species in abundance are HO 2 and H 2O 2 at ignition and H, O, and OH at extinction. Isothermal walls, heated (constant power) walls, adiabatic walls, and symmetric counterflow jets are compared to examine the role of different stagnation surfaces on ignition and extinction for planar and axisymmetric flow. Implications of heterogeneous catalytic processes on ignition and extinction are also considered by examining surfaces that are sinks or sources for particular intermediate species.