This paper examines the scram/dual-mode combustion limits of hydrocabon fuels within a Mach 8, scramjet combustor. Flight-equivalent flows were delivered to the axisymmetric, cavity combustor via a reflected shock tunnel. Two scramjet fuels were examined: ethylene and a surrogate mixture representing endothermically cracked n-dodecane. Combustion modes were examined via static pressure sensors and through both chemiluminescence imaging, and planar laser induced fluorescence (PLIF) of the OH combustion radical in the combustor exhaust plume. Ethylene-fuelled experiments developed scram-mode combustion under reduced fuelling conditions, experiencing shock wave dominated flowfields. OH PLIF diagnostics indicated such combustion modes developed a ring-like structure of combustion products, primarily axisymmetrically adjacent to the combustor wall. Increased fuelling anchored combustion downstream of the fuel injector, while further increases instigated dual-mode combustion. In this mode, subsonic combustion regions combine with the supersonic coreflow to permit the transfer of information upstream with substantially increased pressure encountered. Optical diagnostics indicate broadly asymmetric, unsteady combustion features. The surrogate mixture representing endothermically cracked n-dodecane experienced rapid onset from no-combustion (optically confirmed) to fully developed dual-mode combustion at critical fuelling rates. OH PLIF signals and chemiluminescence of this fuel were weaker than comparable ethylene cases, indicating potential differences in combustion pathways.

本文研究了8赫兹超燃冲压燃烧器内氢碳燃料的超燃/双模燃烧极限。等效飞行流量通过反射激波隧道输送到轴对称腔燃烧室。检查了两种超燃冲压燃料：乙烯和代表吸热裂解的正十二烷的替代混合物。燃烧模式通过静压传感器，化学发光成像以及燃烧器排气羽流中OH燃烧基的平面激光诱导荧光（PLIF）进行了检查。以乙烯为燃料的实验在减少燃料的条件下开发了以加速模式燃烧，并经历了以冲击波为主的流场。OH PLIF诊断表明，这种燃烧模式形成了燃烧产物的环状结构，基本上与燃烧室壁呈轴对称。增加燃料喷射器下游的锚固燃烧，同时进一步促进双模式燃烧。在这种模式下，亚音速燃烧区域与超音速核心流相结合，可以在压力显着增加的情况下向上游传输信息。光学诊断表明大致不对称，不稳定的燃烧特征。代表吸热裂化正十二烷的替代混合物经历了从无燃烧（光学确认）到以临界加油速率完全发展为双模式燃烧的快速发作。该燃料的OH PLIF信号和化学发光比可比的乙烯情况弱，表明燃烧途径存在潜在差异。同时进一步促进了双模燃烧。在这种模式下，亚音速燃烧区域与超音速核心流相结合，可以在压力显着增加的情况下向上游传输信息。光学诊断表明大致不对称，不稳定的燃烧特征。代表吸热裂化正十二烷的替代混合物经历了从无燃烧（光学确认）到以临界加油速率完全发展为双模式燃烧的快速发作。该燃料的OH PLIF信号和化学发光比可比的乙烯情况弱，表明燃烧途径存在潜在差异。同时进一步促进了双模燃烧。在这种模式下，亚音速燃烧区域与超音速核心流相结合，可以在压力显着增加的情况下向上游传输信息。光学诊断表明大致不对称，不稳定的燃烧特征。代表吸热裂化正十二烷的替代混合物经历了从无燃烧（光学确认）到以临界加油速率完全发展为双模式燃烧的快速发作。该燃料的OH PLIF信号和化学发光比可比的乙烯情况弱，表明燃烧途径存在潜在差异。光学诊断表明大致不对称，不稳定的燃烧特征。代表吸热裂化正十二烷的替代混合物经历了从无燃烧（光学确认）到以临界加油速率完全发展为双模式燃烧的快速发作。该燃料的OH PLIF信号和化学发光比可比的乙烯情况弱，表明燃烧途径存在潜在差异。光学诊断表明大致不对称，不稳定的燃烧特征。代表吸热裂化正十二烷的替代混合物经历了从无燃烧（光学确认）到以临界加油速率完全发展为双模式燃烧的快速发作。该燃料的OH PLIF信号和化学发光比可比的乙烯情况弱，表明燃烧途径存在潜在差异。