Investigations On Fluidic Nozzle For Pulse Detonation Rocket Engines

Detonation-based engines possess great potentials on higher heat release rate,greater thermodynamic efficiency and more compact heat release chamber than the conventional propulsion devices.Therefore,application of detonation to propulsion attracts lot of attentions.Attentions were paid to the exhaust process analysis and optimal nozzle design of the pulse detonation rocket engine(PDRE)in the present study.A fluidic nozzle has been proposed to take full advantages of energy release and enhance the propulsive performance,and theoretical and experimental investigations were carried out for the validation of this method.(1)The exhaust process and optimal converging/diverging area ratios of a nozzle were theoretically analyzed.Pressure and velocity fluctuations of the exhaust flow were considered to be the major issues.A key-point method concluding four design points(the von-Neumann spike point,the C-J point,the platform state point and the fill state point)was proposed for the nozzle design of a PDRE.Optimal converging/diverging area ratios for various fuel/oxidizer mixtures have been calculated.(2)Experiments have been carried out to investigate the impact of exit nozzles on the operation and the propulsive performance of a valveless PDRE under wide operating frequencies.Gasoline and oxygen-enriched air were used as fuel and oxidizer.Two detonation tubes and twenty-one nozzles with different shapes were employed in this study.It was observed that nozzles with converging sections decreased the highest operating frequency,even the engine can not operate normally with nozzles whose contraction ratios are larger than four.The expansion ratio almost has no impact on the operation of the valveless PDRE,but the thrust decreases when the expansion ratios of diverging nozzles are larger than five.Most converging nozzles increase the thrust,especially when the fill fractions were greater than one,while most diverging nozzles increase the thrust when the fill fractions were smaller than one.A maximum thrust increase of 25% has been obtained when nozzles were utilized.(3)A fluidic solution which employs nitrogen flows in the nozzle throat and divergent section has been propsed and tested experimentally.The fluidic nozzle was validated to be an effective method to adjust its area ratios according to the incoming flow.The effective convergent area ratio varied from 2.0 to 2.2,and the divergent one varied from 5.0 to 1.8.It was proved that the propulsive performance of a PDRE was observably improved by utilizing the fluidic nozzle.A maximum average thrust increase of 137.8% was obtained in proper conditions.(4)The wave structures and pressure histories inside the fluidic nozzle were investigated,single and muti cycle operations were both considered.Based on the results,it was indicated that the effective area ratio was effectively adjusted according to the primary flow when secondary injections were utilized and then the over-expanded loss was reduced.It was also indicated that the injected flow changed the cone-shaped nozzle to a similar bell-shaped one.Therefore,it helps to reduce the thrust loss and enhance the propulsive performance.The injections also changed the direction of the exhausted gas,so it was validated to be a vector propulsion method.(5)The effect of secondary oxidizer injection on the operation and propulsive performance of a PDRE was investigated.Firstly,the stratified fuel distribution effect was introduced and discussed.Then a secondary oxidizer injection solution for reducing pressure and velocity fluctuations of the burned gas is explored.Experiments have been carried out to test the operation and propulsion features.With the injections,remarkable reductions of pressure and velocity fluctuations of the burned gas were obtained(-50.7% for the pressure reduction,and-43.3% for the velocity reduction).Obvious thrust enhancements were also achieved,and the stratified fuel distribution effect,after-burning effect,and partial-fill effect are considered to be the major reasons which bring these enhancements.Furthermore,the stratified fuel distribution effect dominates at lower operating frequencies(in over-filling conditions),while the afterburning effect,together with partial-fill effect provides most of the increase at higher frequencies(in partial-filling conditions).By the combination of fluidic nozzle,a maximum thrust increase of 70.4%was achieved.