THEORY OF RADICAL-INDUCED IGNITION OF COUNTERFLOWING HYDROGEN VERSUS OXYGEN AT HIGH-TEMPERATURES

Ignition of hydrogen and oxygen in counterflow was studied using asymp totic methods for temperatures above that of crossover. Starting with seven elementary reaction steps, a reduced mechanism was derived using chemical steady-state approximations for the O and OH radicals. An al gebraic ignition criterion was derived using this mechanism which pred icts the ignition state as a function of the parameters defining the s ystem. This criterion successfully explains the behavior analogous to the ''first'' and ''second'' explosion limits observed in homogeneous hydrogen-oxygen mixtures. A bifurcation analysis was then performed to clarify the ignition behavior. This analysis demonstrated that an ign ition turning point can occur solely through the interaction of radica l species with no contribution from heat release. The source of this t urning was found to be the reaction H + HO2 --> 2OH, confirming result s from numerical calculations. Finally, the regimes in which abrupt or monotonic transition to an ignited state were recalculated including the effect of this reaction. (C) 1998 by The Combustion Institute.