Reduction of the deflagration-to-detonation transition distance and time in a tube with regular shaped obstacles

Abstract

209 Here, we suggest, for the first time, use of regular obstacles of special shape for acceleration of deflagra- tion-to-detonation transition (DDT). As shown by cal- culations and experiments, such obstacles make it pos- sible to considerably decrease the DDT length and time as compared to regular rectangular obstacles. The new method of acceleration of the DDT can be used for designing compact combustion chambers of air-breath- eling ignition pulse. In this case, the mixture was ignited by several, rather than one, electric dischargers mounted along the tube. The careful synchronization of the electric discharge with the shock wave (SW) arrival at the cross section of each discharger ensured detona- tion in a smooth-walled tube at very short distances, with the overall ignition energy being considerably lower than the energy of direct detonation initiation by a single discharge. In (6), based on a survey of the experiments in (4, 5), an important conclusion was drawn: classical experiments on DDT in tubes with reg- ular obstacles can also be considered as detonation ini- tiation by a traveling ignition pulse, at least, at the final stages of the process after the SW has formed. In this case, the forced ignition of a mixture near the SW front is not necessary; rather, the autoignition of the mixture takes place due to SW reflection from the obstacles. The ignition delay, determined by the SW intensity and the SW compression phase duration, plays the same role as the forced ignition delay in the experiments in (4, 5). Thus, the closer to the SW front the autoignition region is ("synchronization" of autoignition with the SW arrival) and the larger this region is, the more favor- able the conditions for fast DDT in a tube with regular obstacles. Such an interpretation of the classical exper- iments on DDT opens up new possibilities for reducing the detonation run-up distance and time. One such pos- sibility was considered for the first time in (7). In the present work, the results of calculations of DDT in channels with regular obstacles were described and compared with experimental results.