Multi-scale modeling of detonation formation with concentration and temperature gradients in n-heptane/air mixtures

Detonation initiation and ignition wave propagation in concentration stratified n-heptane/air mixtures with and without temperature gradient were numerically modeled using the correlated adaptive chemistry and transport method along with the hybrid multi-timescale method in a one-dimensional planar constant volume chamber. For concentration gradient only three combustion modes including spontaneous ignition detonation to spontaneous ignition transition and a fully developed detonation mode were observed corresponding to low critical and high concentration gradients respectively. The onset boundary of the three combustion modes is strongly influenced by the coupling between concentration and temperature gradients. At a given concentration gradient the temperature gradient can either promote or inhibit the detonation formations depending on the variation of the associated ignition delay times. The critical concentration gradient for detonation initiation was significantly modified by the existence of a temperature gradient and vice versa.