Numerical investigation of the effect of jet intensity from internal jet tube on detonation initiation characteristics

Abstract

Detonation initiation is one of the key problems in the application of pulse detonation engine (PDE). In recent years, the experimental research and numerical simulation results of multi-point jet initiation show that multi-point jet initiation can expand ignition energy and accelerate Deflagration-to-Detonation Transition (DDT) process. However, it will bring some difficulties to the actual implementation process due to the increase in the number of jet tubes. In order to reduce the number of ignition sources and keep multiple jets, this paper proposed a new structure of jet tube, in which the jet tube was inserted into the detonation tube, and multiple jets were generated by opening holes at the jet tube wall. The effect of the jet intensity propagated from the jet tube through the jet hole on the detonation initiation characteristics was studied by changing the initial pressure of the ignition zone. Stoichiometric hydrogen-air mixture was used. The simulation results indicated that the jet intensity had a great influence on the characteristics of detonation wave. When the initial pressure was 0 or 0.2 MPa, the stable detonation wave could not be initiated due to the jet intensity was weak. When the initial pressure of ignition zone reached 0.4 MPa, the intensity of the jet propagating from the jet tube was obviously strengthened. Then, a local detonation point was generated near the center axis of the jet tube at about x = 20 mm and developed into detonation wave. The detonation wave attenuated into quasi-Chapman-Jouguet (C-J) detonation wave, and the coupling of pressure and temperature gradually declined through the transversal jet hole. Finally, high pressure points were formed near the wall of the detonation tube, interacted at the center of the detonation tube, and a plane detonation wave was generated through reflection from the wall of the detonation tube. As the initial pressure of ignition zone continued to increase to 0.6 MPa, the development process of detonation wave was similar to that of 0.4 MPa, but the jet intensity was further improved, which made the distance and time of DDT significantly shortened. In addition, multi-stage jets could obviously reduce DDT distance and time compared with the transverse jet.