Investigation On Propagation Property Of Flame And Pressure Wave In Rotating Detonation Engine

Rotating detonation engine(RDE)is a new type of propulsion device based on detonation,which is characterized with fast heat release,high thermal cycling efficiency and simple structure,and has attracted worldwide attention in recent years.In this paper,experiments and also the numerical simulations are carried out in H2/air RDE to investigate the propagation characteristics of flame and pressure wave in the engine.During the experiment,by changing the equivalence ration,the mass flow rate,the axial length of the combustor,the width of the combustor annular gap,the nozzle configuration and the injection area of oxidant,and also by conducting long-time experiment,the unstable working mode and stable working mode were obtained.Combined with pressure signal,ion signal and high-speed photography,the flame and pressure wave under different working modes were analyzed.In the numerical simulation,four different nozzle configurations were used.The internal flow field structure and working characteristics of RDE were analyzed under different mass flow rate.Based on the results of experiment and simulation,the following conclusions are drawn:In the ignition process,the flame of the outer wall and the inner wall develop faster than the middle flame.In the ensuing double-wave collision process,the flame is decoupled from the pressure wave first and then coupling.In the shut-down process,the ion signal peak,pressure peak and the pressure wave speed gradually decrease.Flame and pressure wave are decoupled and extinguished after a period of coupling.In the longitudinal pulse detonation mode,the pressure wave moves axially at a high frequency.As the pressure wave propagates toward the exit,the intensity attenuates gradually and decays when it propagate toward the entrance,but enhances near the entrance and promotes the next cycle.As the length of the combustor increases,the frequency of the longitudinal pulse detonation wave decreases.What's more,the acoustic coupling phenomenon occurs when the equivalence ratio is relatively low and the length of the combustor is large.Annular gap width of combustor and oxidant injection area have great impact on the operating characteristics of rotating detonation wave.When the combustor annular gap width is constant,with the decreasing of the area of oxidant injection,the stable propagation of single-wave,co-directional two-wave and four-wave collision modes are sequentially obtained.The detonation wave velocity,pressure peak and ion signal peak gradually decrease in the order of single wave,double wave and four-wave collision.Under the stable operation mode of RDE,the flame is coupled with the pressure wave.In addition,pressure wave collision are observed during the single-wave and double-wave alternation and detonation wave steering,and both of the pressure peak and the ion signal peak are smaller during the transition.With the extension of working time,the detonation products presenting in the wave-front increases,while the velocity of the detonation wave decreases slightly,and finally tend to stabilize.Part of the detonation product in the detonation wave-front mixture is one of the causes of the detonation wave speed loss.For the RDE without nozzle and with divergent nozzle,as the mass flow rate increases,the detonation wave height increases first and then decreases and the average Mach number at exit increases gradually.Moreover,higher the mass flow rate is,closer the velocity of detonation wave is to the theoretical C-J velocity.For the RDE with convergent nozzle and Laval nozzle,as the mass flow rate increases,the detonation wave height decreases,while the average Mach number at exit almost unchanged.Compared to the RDE without nozzle and with divergent nozzle,the detonation wave pressure,temperature and the average total pressure at the exit increase,while the detonation wave height and velocity decrease.