The Onset of Detonation Behind Shock Waves of Moderate Intensity in Gas Phase

The shock-to-detonation transition (SDT) in gaseous n-heptane/oxygen/argon mixtures has been experimentally studied, using a shock tube, at low initial pressure (2–4 kPa) for a better understanding of the deflagration-to-detonation transition process. The detonation is generated by a precursory shock wave (PSW), with a Mach number smaller than that of the self-sustained detonation. Pressure (P2) and temperature (T2) behind incident shock waves have been accurately determined from the PSW velocity. The transition occurs in the measurement zone located between 3.20 m and 3.65 m from the shock tube diaphragm. The auto-ignition of mixture behind PSW is immediately followed by the onset of a combustion wave, which propagates at near Chapman–Jouguet (CJ) detonation velocity in the mixture carried at P2, T2 conditions. Consequently, the pressure peak can reach 350 times the initial pressure during the transition. The combustion wave merges with the PSW to form an overdriven detonation propagating in the initial ...