| In the task of space launching, during the period of launching preparation there is always a large quantity of hydrogen leaking out from the liquid rocket engine in a short time before its ignition and being emitted into the air. Taking effective measures to cope with the emission gas is of great importance to guarantee the safety of launch site and spacecraft.By drawing lessons from the international processing styles to solve the problem, direct combustion method to handle the cryogenic hydrogen emitted from the engine was adopted. In this paper, the advantages and disadvantages of four ignition methods of high temperature heat source-hot jet,flame and ignition engine jet were compared and analyzed. On the basis of comprehensive comparison of common ignition sources and ignition ability, the final ignition method was determined, that is, using high temperature two-phase jet flow field from the ignition motor which contains a large number of metal particles as the ignition source of hydrogen Emitted by Rocket EngineThe numerical simulation of ignition motor’s high speed multiphase exhaust plume flow field was performed by using FLUENT software. Euler-Lagrange approach was employed. For gas phase, compressible Navier-Stokes equation set was solved. Particle trajectory model was used to describe particle phase. Temperature, velocity field and particle distribution with high temperature was obtained in the exhaust plume. Meanwhile, the installation form of ignition motor was designed and optimized, including its location, number, combination structure of ignition motor, in order to get the best plan to ensure the reliability of successful ignition.Finally, the three-dimensional transient simulation of the low temperature hydrogen diffusion combustion process with variable flow temperature was carried out by means of fluid modeling and simulation software. The spatial distribution and variation of combustion products concentration, temperature and thermal radiation was analyzed to provide a reference for the safe discharge of low temperature hydrogen and the thermal protection of the surrounding equipment.The study finds that the minimum ignition energy of hydrogen is an order of magnitude of mj. When the ignition temperature is greater than 1100K, the temperature requirements for hydrogen ignition is basically met. The particle diameter has great influence on the temperature of gas and particle phase. When the jet contains a variety of particles with different diameters,1100K gas isothermal surface along the direction of the jet length is about 1.1 m. When particles with a diameter of 50 microns are emitted from the outlet 4.6m far away,their temperature is still higher than 1100K;Particles with a diameter of 20 microns can be cooled to 1100K when they are emitted from the outlet 2.7m far away. Under the same circumstances,particles with a diameter of 10 microns can move to a position far from the nozzle 1.9m;particles with a diameter of 5 microns can move to a position far from the nozzle 1.4m.In the jet field,there is a temperature region in which the emitted hydrogen can be ignited and the two phase jet can be used as a medium for hydrogen ignition. Under the condition of multiple and even numbered ignition motors installation, when the angle between two jet orifices is 147.350, the high temperature region formed by the interaction of the high temperature flow field after stable work can meet the requirement of the critical ignition temperature of hydrogen ignition. In the early stages of combustion, the influence of the flame is mainly concentrated in the space below the nozzle to above the diversion trench. As the development of combustion process, combustion products will spread to the area above the hydrogen nozzle exit plane under the action of buoyancy. Heat insulation and fire prevention measures should be made surrounding and above the exhaust nozzle. |
PDF Full Text Request