同轴喷嘴自发激励高频燃烧不稳定性试验研究

Experimental Investigation for Spontaneous High Frequency Combustion Instability of a Coaxial Injector

为增进对液氧煤油火箭发动机同轴离心喷嘴燃烧不稳定性过程的理解,在大气环境下进行了同轴离心喷嘴的自发激励燃烧不稳定性试验。试验采用单喷嘴敞口模拟燃烧室,高温的氧气和空气混合物从同轴喷嘴的直流喷嘴喷注,高温的煤油蒸气从同轴喷嘴的离心喷嘴喷注。通过逐步改变氧化剂流量使模拟燃烧室内产生自发激励高频燃烧不稳定性,使用脉动压力传感器和黑白高速相机记录稳定和不稳定燃烧工况下的脉动压力和火焰。研究发现:气气同轴离心喷嘴的自发激励高频燃烧不稳定过程呈现"滞后"现象;不稳定工况下的火焰均为脱口火焰,火焰特征长度约等于喷嘴出口到脱口火焰团上沿的距离;气气同轴离心喷嘴燃烧不稳定性的发生原因可以被认为是因混合特征时间与声学特征时间相关。

Spontaneous combustion instability is investigated experimentally by using an open-end subscale chamber for a coaxial swirl injector operated under the atmospheric environment. Hot air-GOX mixture and hot kerosene vapor are injected respectively by a jet injector and a swirl injector. Spontaneous combustion instability is excited by changing flow rate of oxidizer step by step. The flame is directly detected by use of a high-speed gray CCD camera and the dynamic pressure is measured by using a dynamic pressure sensor. Hysteresis of combustion instability is present in the hot fire tests. And the flame under the combustion instability operating conditions is always lift-off flame. And it is found that the characteristic length of flame is approximately equal to the distance between the injector faceplate and the upside of lift-off flame lump. An instability mechanism can be explained by use of the correlation between the characteristic mixing time and the characteristic acoustic time.