A local criterion for distinguishing detonation and deflagration for pressure gain combustion

Detonation and deflagration waves are compared and distinguished for hydrogen/air mixtures. Chemical explosive mode analysis (CEMA) showed that detonation is characterized by higher chemical explosive mode eigenvalues and undergoes radical explosion after the shock wave. CEMA showed that the H radical makes the largest contribution to the chemical explosive mode and can be used as an ignition indicator. A characteristic Damköhler number (Dac,H) is then defined as the ratio of the H radical peak chemical production to peak diffusion rates. The deflagration mode consistently shows a Dac,H of O(1) at a wide range of operating conditions, while detonation shows a higher contribution of chemistry relative to diffusion that increases with pressure [i.e. O(100) for P = 1 bar and O(1000) for P = 10 bar]. This behavior is due to the different ignition and flame propagation mechanisms for detonation compared to deflagration. The criterion is applied to one-dimensional detonation and deflagration propagating flames and to the non-premixed Air Force Research Laboratory (AFRL)'s 6-inch Rotating detonation engine over a wide range of pressures and equivalence ratios. Analysis shows that the criterion can detect successfully the detonation front and contact burning by deflagration.