Control Methods And Mechanisms On High-pressure Transient Combustion Stability Of Bulk-loaded Liquid Propellant

Combustion instability of bulk-loaded energetic liquid in the high temperature and high pressure environment is a bottleneck for the development of this propulsion technology. In this dissertation, course of combustion stability research of bulk-loaded energetic liquid was reviewed. Based on the research status at the present time, combined the characteristics of combustion and propulsion of bulk-loaded energetic liquid, factors effect the combustion instability were discussed, a control method to improve the combustion stability by confine and induce effects of chamber boundary was put forward, correlative research of mechanisms, experiments and theories was carried out. The main contents and research results were illustrated as follows.I. Experiments on the expanding and mixing process of high-temperature gas jet in bulk-loaded liquidBased on the cold status experimental method which separates the flow and combustion process, a experimental system was set up to observe the interaction of high-pressure hot gas jet with bulk-loaded liquid. Cylindrical and multi-stage stepped wall chamber were designed. By high speed video system, the interaction process of hot gas jet with bulk-loaded liquid was recorded, especially the expanding profile and entrainment process of Taylor cavity in the multi-stage stepped wall chamber was observed. Turbulent mixing characteristics of gas and liquid were analyzed, the effects of chamber configuration and early ignition condition to the jet expanding process were discussed. These experiments show that Taylor and Helmholtz instability emerge at the interface of gas and liquid in the expanding process of gas jet, resulting in the mixing at the interface of gas and liquid. In the cylindrical chamber, gas jet expand rapidly in the axial direction, meanwhile gas jet expand slowly in the radial direction, which result in the Helmholtz instability effect becoming the main mixing mechanism of gas and liquid, there was obvious randomicity in the gas jet expanding process. In the stepped-wall chamber, radial turbulence intensity was enhanced when gas jet reach the step, Taylor cavity filled in the chamber boundary rapidly, the randomicity in the gas jet expanding process was reduced to a certain extent, and Helmholtz instability effect was reduced also. The effects of stepped-wall chamber to the gas jet expanding process can be expressed by parameterâ–³D/L, whenâ–³D/L was little, the axial expanding speed was great. Gas jet expanding process was related with stepped-wall chamber geometry and jet intensity, Controlling the expanding process of gas jet can be achieved in some extent by adjusting these parameters. Detention effect of chamber cover result in back flow of jet, interface of gas and liquid break up randomly, that complicate the mixing process between high-speed gas and liquid.II. Numerical simulation of gas jet expanding in the bulk-loaded liquidA2D axisymmetric gas-liquid two-phase turbulent flow model was developed. The jet expansion processes in the stepped-wall, conical and cylindrical chamber were calculated. The experiments and numerical simulation results show that chamber wall shape has obvious effect on the high-pressure combustion-gas jet expansion in the bulk-loaded liquid. Vortex emerges at the chamber steps, which induces the Taylor cavity to expand radially then restrains Kelvin-Helmholtz instability at the interface between the gas and liquid. When stepped-wall chamber size matches with Taylor cavity expansion, the chamber wall shape can delay the development of combustion in stability. The2D axisymmetric gas-liquid two-phase turbulent flow model has the capacity to describe the characteristics of combustion-gas jet expansion, and Taylor cavity expanding profile and expanding velocity coincide with the experiments. The numerical simulation can obtain the mechanisms of gas-liquid interface evolvement such as liquid breakup and vortex form, while these mechanisms were difficult to obtain only through experiments at present.III. Experiments on the combustion and propulsion in the multi-stage stepped-wall chamberAn experimental system was designed, based on the transient measurement technology of pressure, combustion and propulsion experiments in the cylindrical and stepped-wall chamber were carried out at the pressure from200MPa to500MPa. Through signal analysis and feature extraction of transient pressure data, the oscillation of combustion pressure was analyzed, the effects of chamber shape and liquid propellant type to combustion stability were discussed. Experiments show that the combustion and propulsion process of bulk-loaded liquid propellant have non-linear characteristics. Spectrum analysis of pressure signal illustrates the chaos property in the propulsion system. Using stepped-wall chamber is useful to deduce the pressure oscillation and can improve the combustion and propulsion stability of bulk-loaded energetic liquid. The quantity of steps and parameterâ–³D/L have effects on the combustion and propulsion stability. Improveâ–³D/L can reduce magnitude of pressure oscillation, and steps should have an optimal amount. Also there are stability differences in the combustion and propulsion process for different liquid propellant. â…£. Numerical simulation of combustion and propulsion process of bulk-loaded liquid propellantA bulk parameter model was developed, calculated muzzle velocity coincides with experiments, which indicates that bulk parameter model can inflect the holistic characteristic. But for the pressure oscillation observed in the experiments, bulk parameter model seems helpless. So a more complicated2D axisymmetric flow and combustion model based on the multi-phase hydrodynamics and turbulence combustion theory. Numerical simulation was carried out for the cylindrical and multi-stage stepped-wall chamber. Some characteristics of combustion and propulsion process, such as gas cavity expansion and liquid acceleration were shown. Parameter profiles such as mass fraction, temperate and pressure were obtained. The2D model can simulate the pressure oscillation. The numerical simulation results of stepped-wall chamber coincide with experiments. Thus the control effect of stepped-wall chamber to the combustion stability is demonstrated through numerical simulation.By experiments and numerical simulation, control mechanisms of using stepped-wall chamber to enhance radial expansion and improve combustion and propulsion stability were illustrated. The research results are significant to achieving stable combustion in the bulk-loaded liquid propellant gun.