Deflagration to detonation transitions and strong deflagrations in alkane and alkene air mixtures

Abstract Deflagration to detonation transitions and strong deflagrations for a large range of stoichiometric alkane (CH 4 , C 2 H 6 , C 3 H 8 , C 4 H 10 ) and air mixtures and alkene (C 2 H 4 , C 3 H 6 , C 4 H 8 ) and air mixtures have been studied systematically by varying surface roughness via the introduction of Shchelkin spirals. The use of such spirals, rather than repeated obstacles such as orifice plates, is preferred, as improved acceleration and higher flame speeds are obtained due to reduced momentum losses. The results obtained indicate that deflagration to detonation transitions (DDT) and quasi-detonations can be obtained for all fuels tested. Using short obstacles it is demonstrated that quasi-stable strong deflagrations of considerable duration, supported only by a smooth-walled tube, can easily be established and typically serve as a basis for further acceleration and transition to detonation. The effects of different obstacle exit velocities on the duration of the strong deflagration phase and on DDT parameters have been investigated. By further increasing the obstacle length, DDT via quasi-detonations has been investigated and it is demonstrated that the relative detonability of the fuels under strongly turbulent conditions differs systematically from that obtained in smooth tube experiments.