SHOCK-TUNNEL EXPERIMENTAL STUDY OF COMBUSTION ENHANCEMENT METHODS FOR A HIGH-MACH-NUMBER SCRAMJET
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摘要: 基于中国科学院力学研究所的JF-24激波风洞, 通过开展高马赫数超燃冲压发动机的直连试验, 研究了高马赫数燃烧的强化方法以及燃料类型对燃烧的影响. 试验段是采用凹腔结构的圆截面燃烧室, 喷孔布置在隔离段, 燃料分别是氢气和乙烯, 当量比均为0.7. 燃料喷注分别采用无支板和小支板两种构型, 后者部分喷孔位于小支板顶部. 两种构型均设置了流向近距双排喷孔, 可分别进行单环和双环喷注. 试验结果论证了飞行马赫数10.0条件下氢气和乙烯在超高速气流中的稳定燃烧性能. 并且, 相比于单环喷注, 双环喷注以及补充小支板可以强化燃烧. 推测其原因是双环射流和激波/分离结构的近距离交互作用很可能改善掺混, 而补充小支板顶部喷注还能利用更多空气组织掺混. 在同样采用双环耦合小支板顶部喷注的强化措施下, 氢气与乙烯燃烧效率接近, 但氢推力性能更优. 这是因为较高热值氢的释热更多. 此外, 试验还证明了在当前来流条件下, 释热受控于掺混, 且高温离解效应限制释热上限. 这是由于释热降低流速且提高静温, 使高温离解的吸热效应更加显著.Abstract: Based on the JF-24 high-enthalpy shock tunnel in Institute of Mechanics, Chinese Academy of Sciences, the current paper performed direct-connect combustion tests of a high-Mach-number scramjet engine to study high-Mach-number combustion enhancement methods and fuel types’ effects. The test-section was a circular cross-section scramjet combustor with cavity structures, and fuel injectors were arranged in the isolator. Hydrogen and ethylene fuels were severally used in current tests at the same equivalence ratio of 0.7. Fuel injection utilized two different test-section configurations without and with small struts, respectively. Some injection holes of the latter configuration were located on the strut tops. For each configuration, two adjacent rings of injecting holes were arranged for single-ring and dual-rings injections, respectively. Test results demonstrated that stabilized combustion performances of hydrogen and ethylene fuels in hypersonic flows under a Mach number
$ M{a_{\text{f}}}{\text{ = }}10 $ flight condition. Meanwhile, compared to the single-ring fuel injection method, dual-rings fuel injections and adding injections on small-strut tops were beneficial for combustion enhancements. The reason was speculated that interactions of adjacent fuel jets and shock/separation structures probably could improve fuel-air mixing, and additional fuel injection on small-strut tops meant more available air for mixing. Under the same combustion enhancement methods of dual-ring injections and additional small-strut top injections, hydrogen fuel generated better thrust performance than ethylene fuel, while their combustion efficiencies were similar. This was possibly because that the hydrogen fuel had a higher caloricity, and thus it could generate more heat release. Besides, test also verified that under the current high-enthalpy high-speed inflow condition, combustion heat release was controlled by fuel-air mixing processes, and meanwhile the upper limits of heat release was limited by high-temperature dissociation effects. This was because that heat release led to decreases of local flow speeds and increase flow temperatures. Consequently, high-temperature dissociation endothermic reactions would be more remarkable, resulting in decrease of heat release.-
Key words:
- high Mach number /
- supersonic combustion /
- combustion enhancement /
- small strut /
- JF-24 shock tunnel
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图 1 JF-24爆轰驱动激波风洞示意图
Figure 1. Schematic diagram of JF-24 detonation driven shock tunnel
图 4 试验段燃烧室模型简图 (单位: mm)
Figure 4. Schematic diagram of the test-section combustor (unit: mm)
图 8 不同温度条件
$T$ 下的点火延迟时间${\tau _{{\text{ign}}}}$ Figure 8. Ignition delay times
${\tau _{{\text{ign}}}}$ under different temperatures$T$ 
图 9 工况A沿程壁面压力分布随时间的变化云图
Figure 9. Streamwise wall-pressure distribution time history contour of Case A
图 11 无支板单环工况A和双环工况B的时均沿程压力分布
Figure 11. Time-averaged pressure distributions of single-ring Case A and dual-rings Case B without strut
图 12 小支板单环工况C和双环工况D的时均沿程压力分布
Figure 12. Time-averaged pressure distributions of single-ring Case C and dual-rings Case D with strut
图 13 单环无支板工况A和小支板工况C的时均沿程压力分布
Figure 13. Time-averaged pressure distributions of single-ring Case A without and Case C with strut
图 14 双环喷注无支板构型B和小支板构型D的时均沿程压力分布
Figure 14. Time-averaged pressure distributions of dual-rings Case B without and Case D with strut
图 15 氢燃料工况D和乙烯燃料工况E的一维压力
$p$ 和马赫数$Ma$ 分布Figure 15. 1-D pressure and Mach number distributions of H2-fueled Case D and C2H4-fueled Case E
图 16 不同初始温度
${T_{{\text{initial}}}}$ 下等压理论燃烧效率${\eta _{\max }}$ Figure 16. Theoretical constant-pressure combustion efficiency
${\eta _{\max }}$ vs. initial temperature${T_{{\text{initial}}}}$ 
图 18 一维流动分析典型的沿程燃烧效率
Figure 18. Streamwise combustion efficiency variations by 1-D flow estimations
表 1 激波管与真空舱的尺寸
Table 1. Sizes of the shock tube and vacuum chamber
Shock tube Vacuum cabin damping section driver section driven section legth/m 2.5 13 7.5 5.5 inner diameter/m 0.26 0.13 0.13 1.4 
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表 2 试验段来流条件
Table 2. Test-section inflow condition
$M{a_{{\text{in}}}}$ $T_{{\text{in}}}^*$/K $p_{{\text{in}}}^*$/kPa 4.3 3800 12000
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表 3 试验工况条件
Table 3. Test case conditions
Case Configuration Fuel Injection A no strut H2 ring 1 B no strut H2 rings 1 and 2 C small struts H2 ring 1 D small struts H2 rings 1 and 2 E small struts C2H4 rings 1 and 2
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表 4 各工况燃烧效率
$\eta $ 和推力系数${F_{{\text{tn}}}}$ Table 4. Combustion efficiency
$\eta $ and thrust coefficient${F_{{\text{tn}}}}$ of each caseCase $\eta $/% ${F_{{\text{tn}}}}$ A 50.3 0.061 B 53.4 0.066 C 49.4 0.054 D 54.9 0.069 E 56.0 0.056
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