Numerical and asymptotic analysis of ignition processes

Abstract

In this paper the transient process leading to ignition of a combustible mixture of lean hydrogen/air is studied using both Compu-tational Singular Perturbation (CSP) techniques as well as asymp-totic methods that allow us to deduce the most important regimes in the process as well as the characteristic times and the appropriate reduced kinetic mechanism involved. The CSP technique developed by Lam and co-workers has been used to follow closely the tempera-ture and species concentration evolution with time up to the ignition event. For lean mixtures, the most important intermedíate species is the atomic oxygen; the other radicals follow the quasi-steady state behavior. A closed form solution is then obtained for the ignition delay time, which compares very well with the numerical sohition with full kinetics.