高背压等离子点火器及其液体燃料点火特性实验研究

Experiment Researches of High Back Pressure Plasma Ignitor and Liquid Fuel Ignition Characteristics

关键词:  液体火箭发动机  等离子体  点火器  背压  发射光谱  液体推进剂

Key words:  Liquid rocket engine  Plasma  Ignitor  Back pressure  Emission spectrum  Liquid propellant

摘要:

航天应用的液体火箭发动机及燃烧型加热器燃烧室室压高、燃料流量大、温度低、有重复启动需求，实现安全可靠点火的难度较大。针对这些需求，研究了一种采用高背压设计的电弧等离子体点火器。实验研究了Ar，N₂气体工质在高进气压力下的伏安特性，发现N₂在宽压力范围内适用于点火。发射光谱分析表明，在高达数MPa的进气压力下，Ar，N₂等离子体射流电子密度符合局部热力学平衡判据（LTE判据），点火能量集中。N₂等离子体整体温度低于Ar，但阳极喷口附近温度高于Ar，N₂等离子体射流火焰长，卷吸沿程空气造成射流平均温度偏低，但有助于低温液体推进剂的蒸发混合和强化点火。等离子体射流引起了臭氧和氮氧化物的形成，具有促进点火和化学反应的作用。背压提高引起电源输出电压升高，提高供气压力和电流，有助于点火器在高背压环境中稳定电压。燃烧型空气加热器燃烧室的点火实验发现，采用N₂等离子体喷注面中心点火，可以在短时间内完成酒精-空气和酒精-液氧-空气的点火，最高燃烧室室压接近5MPa时，点火器仍能稳定工作，多次使用电极烧蚀不明显，在液体火箭发动机的重复可靠点火方面具有很好的应用前景。

Abstract:

Combustion chamber of cryogenic liquid rocket engine and air heater has characteristics of high pressure， heavy flow of cryogenic fuels and demands repeated starts， for which the safety and reliable ignition is difficult. A high back pressure plasma ignitor meeting with these requirements was designed and studied. The voltage-current characteristics of Ar and N₂ working at high inlet pressures were studied by experiments and results showed that N₂ worked well within a wide pressure range. Emission spectrum diagnose showed that the electron density of Ar，N₂ plasma jets reached the local thermodynamic equilibrium（LTE） criterion and showed concentrated ignition power under inlet pressures of several MPa. The average temperature of N₂ plasma was lower than that of Ar， while just the reverse at the anode outlet. N₂ plasma jet lasted longer in atmosphere， sucking and mixing the air， which resulted in the temperature drop but would accelerate the evaporation， mixture and ignition of cryogenic liquid fuels. The plasma caused the formation of active particles like ozone and oxynitride， which would also promote the ignition and chemical reactions. Higher back pressure caused higher output voltage， and raising inlet pressure and current helped to stabilize the output voltage under high back pressure. Ignition experiments in the combustion chamber of combustion-type air heater showed that N₂ plasma could ignite the alcohol-air and alcohol-LOX-air within a short period when placed in the center of the injection surface. The ignitor worked stably even the back pressure reached 5MPa， and repeated operations caused slightly electrode erosion， showing prospects in reliable and repeated ignition of liquid rocket engine.