高超声速进气道的裂解碳氢燃料提前喷注研究

Pre-Injection of Cracked Hydrocarbon Fuel in Hypersonic Inlets

关键词:  高超声速进气道  裂解碳氢燃料  激波系控制  掺混效率

Key words:  Hypersonic inlet  Cracked hydrocarbon fuel  Shock control  Mixing efficiency

摘要:

高超声速进气道的裂解碳氢燃料提前喷注一方面可以显著增加燃料的有效掺混长度，另一方面也可以实现对进气道激波和流场的控制。以替代裂解碳氢燃料C12H24为喷注气体，采用数值工具模拟高超声速二元进气道在飞行高度为26km时的工作状态，开展了马赫5设计状态无燃料喷注和马赫6超额定状态带燃料喷注的两类流场分析，重点研究燃料对波系的控制和燃料的自身掺混。通过调节五喷嘴的燃料喷注压力发现，按照马赫5设计的高超声速进气道在马赫6时同样可以实现完全激波贴口，燃料在进气道内通过多重外压缩激波作用也实现了与空气的完全掺混。同时，冷壁温条件下进气道内仅出现少量近壁燃烧，CO₂产物的质量百分比仅在10-7量级，进气道出口的总压恢复系数相较无化学反应时下降2.5%，但仍维持在0.5左右。还对比了五喷嘴、三喷嘴、五喷嘴后移和90°单喷嘴结构下进气道流场以及掺混效率的区别，结果表明，五喷嘴结构的进气道燃料喷注可以实现4倍喷注压力下的激波封口和快速完全掺混，而三喷嘴、后移五喷嘴和单喷嘴结构分别需要5倍、5倍、6.6倍来流静压实现进气道马赫6的激波贴口。

Abstract:

Pre-injection of cracked hydrocarbon fuel in hypersonic inlets can increase the mixing length of the fuel significantly， and can also be utilized for inlet shock and flow control. In the present work， an alternative cracked fuel C12H24 is applied for the pre-injection. Numerical simulations were undertaken to investigate the performance of a two-dimensional hypersonic inlet designed at flight altitude 26km. The inlet flow feature at Mach 5 without fuel pre-injection， and at Mach 6 with fuel pre-injection were both analyzed. Emphasis was focused on the shock control effect and the fuel mixing efficiency. The results indicated that shock-on-lip at Mach 6 for the inlet (which was designed at Mach 5) can be obtained by adjusting the injection pressure. Fully-mixing of the fuel was also achieved through multiple-interaction of oblique shocks inside the inlet. With cooled surface， only small amount of pre-combustion was observed. The mass fraction of the generated CO₂ was only on the order of 10-7. The average total pressure recovery of the inlet decreased 2.5%， but still remained around 0.5. Compared to the flow field and the mixing efficiency of three parallel injectors， five downstream injectors and a single 90 degree injector， five parallel injectors can achieve shock-on-lip and fast fully-mixing with an injection pressure at 4 times the inflow pressure， whereas it was 5 times， 5 times， and 6.6 times of the inflow pressure for three parallel injectors， five downstream injectors and a single 90 degree injector， respectively.