Single detonation in stoichiometric ethylene/oxygen mixtures was experimentally studied at initial pressure (5-45kPa) to achieve change rule of detonation initiation distance (DID) of detonation wave in narrow gap. The narrow gap detonation tube was formed by the cross-section with width of 10mm

height of 1.0

2.2

2.9

4.0mm

and length of 1220mm. Detonation initiation position was decided by soot records and high-speed digital imaging. Effect law of initial pressure and narrow gap height on detonation initiation distance was achieved. The results indicate that: (1) detonation initiation distance is reduced with the increase of narrow gap height at initial pressure of 10-20kPa; (2) detonation initiation distance initially decreases with increase of narrow gap height and then increases at initial pressure of 25-40kPa

and increases at initial pressure of 45kPa with the increase of narrow gap height; (3) compositing the influence of initial pressure and the narrow gap height

non-dimensional empirical formula for detonation initiation distance varying with initial pressure and narrow gap height is achieved.