Initiation of an upstream propagating detonation wave near the open end of the detonation tube operating in the valveless and purgeless scheme

Controllable and sustainable operations are the basic need for the practical pulse detonation engines (PDEs). Previous works have demonstrated that the valveless and purgeless scheme is beneficial to achieve high frequency detonations. However, steady deflagration often arises in the implementation of a long duration operation, especially when the more reactive fresh mixture is employed. To this end, three types of detonation tubes, named as type-A, type-B, and type-C, in which an upstream propagating detonation wave will be produced are experimentally investigated. In this study, the detonation wave is initiated near the open end of the detonation tube through the deflagration to detonation transition (DDT) process, and thus, the fresh reactive mixture was consumed by the upstream propagating detonation wave. Experimental results indicate that the detonation cycles can be maintained by utilizing the upstream detonation waves, and the sustainability has been dramatically improved. Especially, the available oxygen volume fraction of the oxidizer is improved to about 80% for the type-C detonation tube. In addition, the propulsive performance has been improved by 9.5% utilizing the upstream propagating detonation wave in the type-C detonation tube, and meanwhile the fluctuation of the thrust during the detonation cycle can be decreased.