What connects ignition and deflagration? -- On explosive transition of deflagration

Abstract

The general relation between ignition and deflagration analyses was studied theoretically and computationally. Simple analysis showed that the temporal evolutions of normalized fuel mass fraction and the normalized temperature in a 0D homogeneous ignition are equivalent to the spatial evolutions of those in a 1D laminar premixed flame at Lewis number of unity if a spatio-temporal transformation of the flame is applied. Furthermore, computations showed that the degree of reduction in normalized fuel mass fraction in the preheat zone was found to be in the following order: when the Lewis number is less than unity, when the Lewis number is unity (= ignition), and when the Lewis number is greater than unity. This suggested that ignition in the preheat zone near the explosive transition can only occur for 1D laminar premixed flames with Lewis number greater than unity. In summary, the characteristic times of ignition and flame propagation can be of the same order of magnitude in premixed gases compressed by piston in engines or shock waves, and thus the Lewis number determines the existence of premixed flame structure under such conditions.