Pulsating detonative combustion in n-heptane/air mixtures under off-stoichiometric conditions

Numerical simulations of one-dimensional pulsating detonation in off-stoichiometric n-heptane/air mixtures are conducted by solving the reactive Navier–Stokes equations with a skeletal chemical mechanism. The effects of mixture equivalence ratio, initial pressure and temperature on pulsating detonations are studied. The results show that the pulsating instabilities in n-heptane/air mixtures are strongly affected by equivalence ratio. It is seen that pulsating instability only occurs in the fuel-lean or fuel-rich cases, whereas stable detonation is obtained for near-stoichiometric mixtures. Low-frequency pulsating detonations with single mode are observed, and decoupling / coupling of the reaction front and leading shock front occur periodically during the pulsating detonation propagation. The heat release and flame structure at the reaction front of the fuel-lean case differ from those in the fuel-rich case, and thus affects the DDT process of the reaction front. The pulsating detonation frequency is considerably influenced by equivalence ratio, initial pressure and temperature. The results of chemical explosive mode analysis and budget analysis of energy equation reveal that the mixture between the reaction front and shock front is highly explosive and thermal diffusion would promote the periodic dynamics of the reaction front and shock front. It is also found that the chemical explosion mode in the induction zone consists of two parts, i.e. the autoignition dominated reaction immediately behind the leading shock front and a following propagating reaction front.