Formation mechanism of backpressure waves in a pulse detonation ramjet

Backpressure is one of the key challenges limiting the engineering applications of the Pulse Detonation Ramjet (PDR). In this work, the formation mechanism of backpressure is studied through comprehensive experiments and simulations. The research results prove that backpressure is primarily caused by the formation of strong upstream-propagating shock waves. These waves result from the interaction of compression waves generated by backflow flames, in addition to those produced when the compression waves at the flame front collide with the obstacle walls, which then propagate upstream. Once the flame velocity exceeds the speed of sound, the backflow flames no longer generate upstream-propagating compression waves. Furthermore, the study confirms that variations in operational parameters, such as the equivalence ratio and airflow rate, have minimal impact on backpressure strength when the obstacle configuration is kept unchanged. Therefore, optimizing the configuration of obstacles in the initial sections, where the flame speed remains subsonic relative to the reactants, can effectively suppress backflow flame development and diminish the strength of upstream-propagating compression waves. This approach contributes to a reduction in the isolator length and the engine weight, significantly enhancing the engineering applicability of PDR systems.