In order to solve the problem of shock wave initiation within a short range

a flame focusing structure with a shock wave focusing flame was designed

and the flow field inside the structure was studied by numerical simulation. Results showed that the acceleration region was an important region for the acceleration of flame instability

and the local energy explosion caused by the energy convergence in the focusing region was the key factor for the acceleration of deflagration to detonation transition. In this region

the vortex induced by the geometrical structure can enhance the focusing and hinder the shock wave back into the accelerating region. The transition region of the detonation wave from the over driving state to the stable detonation state was mainly realized in the stable region.The temperature and pressure fluctuations on the central axis were caused by the focusing action of the focusing cavity

and the temperature and pressure changes of the detonation front were caused by the three wave point motions.