S型管内超临界航空煤油的裂解与结焦研究

Pyrolysis and Coking Deposition of Aviation Kerosene under Supercritical Conditions in S-Bend Tubes

关键词:  S型管  热裂解  结焦  RP-3航空煤油  超临界

Key words:  S-bend tube  Pyrolysis  Coking deposition  RP-3 aviation kerosene  Supercritical

摘要:

再生主动冷却是超燃冲压发动机热防护的关键技术之一。为了探究冷却通道中弯管结构产生的二次流对碳氢燃料裂解与结焦特性的影响，使用S型圆管实验段进行了RP-3航空煤油超临界裂解结焦实验。重点考察了沿程壁温、产气率、气相产物分布以及S型管结焦沿程分布特征。实验结果表明：由于S型管的结构特点，沿程壁温和结焦分布均呈现出与直管相迥异的特征。在两个弯道区域，离心力产生的二次流加剧湍流混合，强化了局部换热，导致壁温下降。结焦率在弯道结构处出现小幅度局部峰值，在出口温度为700℃时，第二个弯道处平均结焦率比中间直管段提高了101%~170%。此外，还发现S型管产气率比直管更高，在出口温度为700℃时提高了10.2%~14.9%。而S型管的特殊结构对裂解的反应路径无明显影响，因此气相产物分布与直管并无明显差异。

Abstract:

Regenerative active cooling is one of the critical technologies of thermal protection for scramjet. An experiment on supercritical pyrolysis of RP-3 aviation kerosene was conducted in S-bend tubes to investigate the effects of secondary flow in the bend sections of the cooling channels on pyrolysis and coking deposition characteristics. The characteristics of wall temperature distribution along the tubes， gas yield， gas product distribution and coking distribution along the S-bend tubes were analyzed. Experimental results indicate that the distributions of the wall temperature and coking deposition are quite different from those of the straight tubes due to the structural characteristic of the S-bend tubes. Local heat transfer is strengthened by the turbulent mixing intensified through the secondary flow generated by the centrifugal force， leading to the decrease in the wall temperature at the bend sections of the S-bend tubes. And local peaking at a small scale can be observed in the coking rate at the bend sections， and the average coking rate at the second bend increases by 101%-170% compared with the middle straight section at the fluid outlet temperature of 700 ℃. Moreover， it can be also found that the gas yield of the S-bend tube is higher than that of the straight tube. The gas yield of the S-bend tube increases by 10.2%-14.9% compared with the straight tube at the fluid outlet temperature of 700 ℃. Meanwhile， the special structure of the S-shaped tube has no remarkable impact on the reaction path of pyrolysis， so the distribution of gas product is not obviously different from that of the straight tube.