The new generation of intelligent satellites is now in urgent demand for bipropellant thrusters in minimum impulse mode without limitation. Thruster's impulse performance involving combustion efficiency and impulse repeatability strongly correlates to transient spray atomization. Accordingly, the transient spray atomization under impulse working condition is investigated to optimize thruster dynamic response. In order for thrusters to work reliably in short-impulse mode and to further improve

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... s impulse repeatability, the solenoid valve must be improved firstly to achieve high-speed switch with stable flow supply. In the simulation using OpenFOAM, the differences in switch speed, valve stroke and throttle layout are all investigated in comparison and optimization. The fluctuating flowrate provided from the solenoid outlet can be further used as boundary conditions to study downstream swirl injector atomization. Based on the interFoam solver and 2D wedge physical model, spray simulations of MMH (monomethyl hydrazine) and NTO (nitrogen tetroxide) propellants under fluctuating condition are conducted. When the upstream flowrate stabilizes faster, the atomization stability can also be enhanced, thereby improving the impulse repeatability of thrusters in combustion. Atomization is rather unstable when upstream flowrate fluctuates violently, but this fluctuation can enhance the primary breakup of droplets. Compared with MMH spray, NTO spray from outer swirl injector is more sensitive to different upstream fluctuation. Throttle layout plays the most significant roles in transient spray development. In the short-impulse firing test, the thruster with improved high-speed solenoid valve can just work under the impulse time of 4ms with poor repeatability. But this repeatability can be improved with the increase of impulse time, and satisfy the requirement at impulse command of 8ms. This experimental result made a good agreement with the simulation, thus showing that only when transient atomization of MMH spray and NTO spray both develop into the steady state in 5ms after valve opening, the impulse performance is able to be reliably achieved.