Numerical study of the detonation structure in rich H2-NO2/N2O4 and very lean H2-N2O mixtures

In some mixtures and under certain conditions, detonation soot records show substructures. In nitromethane and nitrogen tetroxide mixtures, particular cellular structures can be observed. This kind of structures has been reported as the so-called double cellular structure. One-and two-dimensional simulations of detonation have shown that the double cellular structure is related to a non-monotonous energy release. Two-step energy release is also observed in rich H-2-NO2/N2O4 and in very lean H-2-N2O mixtures. The present study aims at the investigation of the effect of the energy release profile on the detonation structure in these two mixtures through numerical simulations. The origin of the non-monotonous energy release is explained in both-mixtures using one-dimensional simulations with detailed chemistry. Reduced kinetic schemes are obtained and used to perform two-dimensional simulations. It is shown that in rich H-2-NO2/N2O4 mixtures, the double cellular structure appears, whereas in very lean H-2-N2O mixtures, classical substructures are observed. Both behaviours are explained based on ZND calculations and previous stability results. Phenomenological considerations led the authors to link the formation of the double cellular structure with the appearance of a large scale instability mode (a super cellular structure).