Detonation as combustion in a supersonic flow of a combustible mixture

The classical models of steady propagation of combustion and detonation waves in a combustible mixture describe the increase in the system entropy to a maximum value in the case of deflagration (subsonic) combustion of the mixture driven by slow processes of heat conduction and diffusion. In the detonation (supersonic) regime, however, where one of the leading roles belongs to the bow shock wave, the models predict that the combustible system after completion of the chemical reaction “chooses” the minimum increase in entropy. These predictions are inconsistent with the formulation of chemical thermodynamics that the entropy of the system reaches its maximum value after the spontaneous irreversible chemical reaction is finalized and the equilibrium state is established. It is shown in the present study that the predictions of the classical models on the minimum increase in entropy in the case of detonation are eliminated if detonation is considered as a process of combustion of a mixture preliminary subjected to an irreversible process of compression and heating of the initial mixture in the bow shock wave (chemical spike) with a corresponding increase in entropy of the initial mixture and subsequent energy release from the mixture in an irreversible process of mixture conversion to chemical reaction products.