To study the detonation limits of detonation

the gaseous detonation of stoichiometric ethylene/oxygen mixtures through narrow gaps with height of 1.0-4.0mm was experimentally studied by varying initial pressure of 0.004-0.04MPa. The soot film was utilized to record the cellular structure of detonation

and the high-speed cinematography was used to capture the flame. Results show that the smaller narrow gap height means the higher critical initial pressure for limits of detonation propagation. For unsteady detonation propagation modes near the detonation limits

including "stuttering" detonation and galloping detonation

the corresponding range of initial pressure becomes wider as the height of gap decreases. By considering both initial and boundary conditions

the ratio of hydraulic diameter to cellular width is found to be an appropriate sensitivity parameter to characterize the mixture. The range of this ratio for defining detonation limits in different narrow gap sizes is 0.326-0.403.