Ignition of H2-NO2/N2O4 Mixtures Under Volumetric Expansion Conditions

The competition between chemical energy release rate and volumetric expansion related to shock wave’s dynamics is of primary importance for a number of situations relevant to explosion safety. While studies have been performed on this topic over the years, they have been limited to mixtures with monotonous energy release profile. In the present study, the ignition of H2-NO2/N2O4 mixtures, which exhibit a single-step or a two-step energy release rate profile depending on the equivalence ratio, has been investigated under volumetric expansion conditions. The rate of expansion has been calculated using the Taylor-Sedov solution and accounted for using 0-D numerical simulations with time-dependent specific volume. The results were analyzed in terms of a Damkohler number defined as the ratio of the expansion to ignition times. For mixtures with non-monotonous energy release rate profiles, two critical Damkohler numbers can be identified, one for each of the steps of energy release. It was also shown that the fluid element which is the most likely to ignite corresponds to the one behind a shock propagating at the Chapman-Jouguet velocity. The thermo-chemical dynamics have been analyzed about the critical conditions using energy release rate per reaction, rate of production and sensitivity analyses.