Investigation On Propagation Characteristics Of Detonation Wave In Continuous Rotating Detonation Engine

The continuous rotating detonation engine has the advantages of compact structure,high thermal cycle efficiency,self-pressurization,large thrust-to-weight ratio,etc.It has become a research hotspot in recent years and has broad application prospects in aerospace propulsion systems.In this paper,the rocket-type continuous rotating detonation engine was taken as the research object.The gaseous hydrogen and liquid gasoline were applied as fuel,respectively,while the air and oxygen-enriched air were used as oxidizers.Experiments and numerical simulations were carried out to explore the detonation characteristics and thrust performance of continuous rotating detonation engines.In order to study the initiation and propagation characteristics of H2/air continuous rotating detonation wave,a series of experiments were carried out under different conditions.According to the experiments,it found that after ignition,the rotating detonation wave could not be formed directly but after a complex,transitory period.Moreover,the equivalence ratio and the total mass of the propellant both have certain influences on the formation of detonation wave,especially the equivalence ratio.With the increase of the equivalence ratio or the total mass flow of the propellant,the detonation wave exhibits different propagation modes,and the average propagation velocity of the detonation wave increase first and then decrease.In addition,there exists an optimal condition to make detonation wave propagate most steadily.With the effect of lateral expansion,the angle of downstream oblique shock wave decreases slowly in the axial direction.As the equivalence ratio increases,the bending degree of the oblique shock wave gradually increases.However,with increase of the total mass flow rate,the bending degree of the oblique shock first increases and then decreases.Meanwhile,the average thrust of engine increases linearly.A theoretical model of gas-liquid two-phase continuous rotating detonation was established.The flow field of that with gasoline and oxygen-rich air as oxidizer was simulated based on the two-dimensional CE/SE method.The calculation results show that:(1)As the axial length of the combustion chamber elongates,the outlet pressure,temperature,density and circumferential velocity all decrease,the axial velocity increases gradually,and the average thrust density along with the fuel specific impulse of the engine increases first and then decreases.(2)There exists a critical circumferential length for combustion chamber to form a self-sustaining propagation wave.As the circumferential length increases,the inlet detonation parameters increase,while the average thrust density and fuel specific impulse decrease gradually.(3)Increasing the injection pressure of the oxygen-enriched air can increase the inlet pressure and outlet flow field parameters,accordingly promote the average thrust density and the fuel specific impulse.(4)With the increase of the fuel droplet radius,the pressure,temperature and speed of detonation wave reduce,and detonation wave appears unstable gradually.When the droplet radius increases to 70μm,the detonation wave cannot form.(5)When the equivalence ratio increases,the detonation pressure and the temperature peak both increase first and then decrease,while the detonation wave velocity increases gradually.The average thrust density increases with the equivalence ratio,while the fuel specific impulse is almost inversely proportional to the equivalence ratio.On the basis of two-dimensional theory,a three-dimensional theoretical model of gas-liquid two-phase continuous rotating detonation was established.The three-dimensional flow field of continuous rotating detonation was simulated by the three-dimensional CE/SE method.Due to the special configuration of the annular combustion chamber,the inner wall surface has a diverging effect,and the outer wall surface has a converging effect,so that the detonation strength near the outer wall is higher than that near the inner wall,ensuring the angular velocity at the front of detonation wave remains uniform and the rotating detonation propagates self-sustainingly.As the width of the combustion chamber increases,the difference of pressure peaks between the inner and outer wall surfaces increases slowly.The mass flow rate and total thrust increase linearly,while the fuel specific impulse decreases slowly.Two sets of gas-liquid two-phase continuous rotating detonation engines with radial and axial fuel injection were taken.The initiation and self-sustaining propagation of two-phase continuous rotating detonation wave with gasoline and oxygen-enriched air were realized successfully.The propagation characteristics and formation mechanism of detonation wave in different propagation modes were analyzed.And the effects of combustion chamber width,nozzle configuration and oxidant injection area on the propagation characteristics of two-phase detonation wave were studied.During the experiment,it is found that when the combustion chamber width is reduced,the pressure waveform oscillates more serious,and the propagation velocity of the detonation wave decreases.Under the conditions of contraction nozzle and Laval nozzle,the engine mainly works in mixed mode and single-wave mode,respectively.However,at the condition of expansion nozzle,the detonation wave mainly propagates in the double-wave collision mode,which is consistent with the straight nozzle.After installing the nozzle,the propagation velocity of the detonation wave increases,especially for the contraction nozzle and the Laval nozzle.When the oxidizer injection area increases from 456.9mm2 to 620mm2,the propagation mode of detonation wave varies from the mixed mode to the single-wave mode,and the detonation wave becomes more stable.With the increase of the oxidizer injection area,there appears a low frequency oscillation in the high-frequency pressure of the combustion chamber.When the injection area of oxidizer increases further to 799mm2,it is difficult to form a stable self-sustaining detonation wave in the combustion chamber.Experimental investigation on the thrust measurement of gas-liquid two-phase continuous rotating detonation engine was carried out.The thrust performance and oscillation characteristics of the engine are analyzed in detail in the double-wave collision mode,single-wave mode,mixed mode and deflagration mode,respectively.It is found that the thrust under different modes has not only the high-frequency oscillation,but also the low-frequency oscillation similar to sinusoidal oscillation.Under wider combustion chamber conditions,the thrust and specific impulse of the engine are relatively low.As the width of the combustion chamber decreases,the thrust and specific impulse of the engine increase significantly,but the thrust stability deteriorates.Compared with no nozzle,the thrust and fuel specific impulse are both promoted by the three nozzles,among which the thrust performance with the contraction nozzle is the most remarkable and the most stable.In this paper,the effects of propellant equivalent ratio and total mass flow on the detonation and propagation characteristics of H2/air continuous rotating detonation waves were clarified.The self-sustaining propagation mechanism of two-phase continuous rotating detonation was revealed.The propagation characteristics of detonation wave and the promotion mechanisms of thrust performance under different nozzles were analyzed.The research was of great significance to improve the performance of continuous rotating detonation engine,so as to realize the engineering application.