Suppression of premature ignition in the premixed inlet flow of a shcramjet

The problem of premature ignition in a shock-induced combustion ramjet (shcramjet) inlet is addressed. Previous studies of fuel injection in the inlet have developed fuel injectors and inlet configurations that maximize the mixing efficiency in a shcramjet inlet while maintaining inlet losses at a minimum. A chemically reacting study of the recommended shcramjet inlet configurations finds premature ignition to occur primarily in the boundary layer in the last 15% of the inlet, spreading into the core flow before the inlet exit. Both gaseous nitrogen and additional hydrogen are then injected into the inlet flowfield in an attempt to suppress the flame. Premature ignition is suppressed most feasibly by the injection of additional hydrogen through a backward-facing step (slot injector) located just before the second inlet shock, such that the global equivalence ratio of the premixed flow exiting the inlet is one. The performance of the original inlet remains unaltered, and the frictional force on the inlet wall is reduced by 10% due to the hydrogen slot injection. All turbulent, chemically reacting, three-dimensional, mixing flowfields are solved using the WARP code, which solves the Favre- averaged Navier-Stokes equations closed by the Wilcox kω turbulence model and the Wilcox dilatational dissipation correction. Chemical kinetics are modeled by a 9-species, 20-reaction model by Jachimowski.