Flame propagation and detonation initiation distance of ethylene/oxygen in narrow gap

Abstract

Flame propagation and detonation initiation distances (DID) of the ethylene/oxygen mixture in different narrow gaps at initial operating pressure 5–50kPa were experimentally investigated with soot track records and high-speed digital imaging. The narrow gaps were combined with some channels, the width of 1.0mm, 2.2mm, 2.9mm, 4.0mm, the height of 10mm, 20mm, 30mm and the length of 1220mm. The correlations of the DID on initial pressure and gap size were discussed. While the initial pressure was different in macro-scale tube, the effect of minimum hydraulic diameter and boundary layer on acceleration of flame during the process of deflagration-to-detonation transition (DDT) and DID in narrow gap has obviously different variation trend. Compared with large scale tube, the boundary layer plays an important role in flame acceleration process, which causes different change rule of DID in the narrow gap. The overdriven detonation waves decrease to steady detonation wave at about 2000m/s in three kinds of gap with different height. The flame speed rose sharply from 340m/s to 2760m/s along approximately 30mm distance in W=30mm gap, significantly higher than Chapman-Jouguet (C-J) speed 2326m/s. The process of flame development and DDT were presented and the variation trends of DID with the height or width of gap at different initial pressure were gained. The influence of width-height ratio on DID gradually weaken with increase of the initial pressure.