Abstract: In the thermal stability test of the pulsing condition of 25N bipropellant thruster, 16% of those cases were affected by the high temperature overheating problem of the injector head in the sudden transition of thruster steady-state temperature distribution. This study investigated in-depth mechanism analysis for this problem in order to remove application restrictions and risks in those specific pulse working modes by optimizing the thermal conductive characteristics of the thruster. The droplet impact experiment was carried out to research the development of spray droplets impinging the coating wall under different conditions. Once the cooling film goes into the Leidenfrost state, it can be very difficult to make the effective heat transfer with the hot chamber wall and it influences the efficiency of cooling film. Through the thermal simulation using Amesim, it was clear that the formation of the cooling film of the thruster can be strongly affected due to the variable impact between the atomized droplets and coating wall, under the influence of thermo-soakback phenomena. That can consequently lead to the second plateau state of thruster from the normal first state, which was a recurrence of the failure characteristic in the thermal stability test. According to this mechanism, the structural thermal conductivity of injector was improved by thickening as 1.5 times as the frame connection structure of injector, weakening the heat flux burden of the liquid film to suppress its generation of Leidenfrost state. After improvement, it was validated that the thermal stability and reliability of thruster in the pulse working mode can be enhanced significantly in this way, getting the success rate of thermal stability tests up to 100%.

Key words: Bipropellant 25N thruster;Heat transfer;Liquid film;Thermal stability;Structural thermal conductivity

摘要： 在离心式双组元25N推力器的脉冲工况温度稳定性试验中，有16%的工况均发生了推力器稳态温度跃迁导致的喷注器头部高温过热的问题。本研究针对该问题开展了深入的机理分析，并通过优化推力器局部传热特性以消除其对于特殊脉冲工况的应用限制和风险。通过液滴撞壁试验，分析了不同条件下推进剂液膜发展的规律和机理：一旦壁面温度达到了莱登弗斯特温度以后，液滴与壁面的换热能力将大幅下降，严重影响液膜冷却的效率。通过Amesim软件进行的传热仿真进一步表明，一旦因为热回浸现象导致雾化液滴与涂层壁面的作用机制发生变化，进而影响冷却液膜的形成，就会使推力器的温度分布从正常的第一稳态进入无液膜的第二高温稳态。仿真结果基本复现了热稳定性试验中出现的故障模式。针对该故障机理改进了喷注器的结构导热性，将喷注器的花篮连接结构的导热面积增加了1.5倍，可以有效分担液膜的热流负担，抑制液膜进入莱登弗斯特态，使得推力器的脉冲工作可靠性大幅提高，令温度稳定性试验的通过率提升至100%。

关键词: 双组元25N推力器;传热;液膜;热稳定性;结构导热性