超声速燃烧与高超声速推进

Supersonic combustion and hypersonic propulsion

50多年的努力和曲折经历证明了超声速燃烧冲压发动机概念的可行性．本文对影响超燃冲压发动机技术成熟的主要因素作了扼要的分析．高超声速推进的首要问题是净推力，利用超声速燃烧获得推力遇到各种实际问题的制约，它们往往互相牵制．几次飞行试验表明高超声速飞行需要的发动机净推力仍差强人意，液体碳氢燃料（煤油）超燃冲压发动机在飞行马赫数5上下的加速和模态转换过程，成为高超声速吸气式推进继续发展的瓶颈．研究表明，利用吸热碳氢燃料不仅是发动机冷却的需要也是提高发动机推力和性能的关键举措，燃料吸热后物性改变对燃烧性能的附加贡献对超燃冲压发动机的净推力至关重要．当前，实验模拟技术和测量技术相对地落后，无法对环境、尺寸和试验时间做到完全的模拟．计算流体动力学（ComputationalFluidDynamics，CFD）逐渐成为除实验以外唯一可用的工具，然而，超声速燃烧的数值模拟遇到湍流和化学反应动力学的双重困难．影响对发动机的性能作正确可靠的评估．提出双模态超燃冲压发动机模态转换、吸热碳氢燃料主动冷却燃料催化裂解与超声速燃烧耦合、燃烧稳定性、实验模拟技术与装置、内流场特性和发动机性能测量、数值模拟中的湍流模型、煤油替代燃料及简化机理等研究前沿课题，和未来5。10年重点发展方向的建议．

After the long and strenuous efforts covering more than 50 years and the tortuous ex- periences, feasibility of the scramjet concept has finally been proven. In this paper, the main factors influencing the technical maturity of the scramjet engine are briefly analysed. A matter of utmost con- cern for this new type of air-breathing engine is the net thrust. The production of engine thrust using supersonic combustion encountered a number of practical requirements which were often found to contra- dict each other. Several flight tests showed that the net engine thrust was still not as good as expected. The acceleration capability and mode transition of scramjet with liquid hydrocarbon fuels （kerosene） operating at flight Mach numbers about 5 has become the bottleneck preventing scramjet engine from continuing development. Research showed that the use of endothermic hydrocarbon fuels is not only necessary for engine cooling but also a critical measure for improving engine thrust and performance. Changes of thermo-physical-chemical characteristics of endothermic fuels during heat absorption make additional contributions to the combustion performance which is essential to the scramjet net thrust. Currently, the technology of experimental simulation and measurement is still lagging behind the needs. The complete duplication or true similarity of atmospheric flight environment, engine size and test du- ration remains impossible. Therefore, computational fluid dynamics （CFD） has become an important tool besides experiment. However, numerical simulation of supersonic combustion encountered challenges which come from both turbulence and chemical kinetics as well as their interaction. It will inevitably af- fect the proper assessment of the engine performance. Several frontiers of research in this developing field are pointed out： mode transition in the dual-mode scramjet, active cooling by endothermic hydrocarbon fuel with catalytic cracking coupled with supersonic combustion, combustion stability, experimental sim- ulation and development of test facilities, measurements of the inner flow-field characteristics and engine performance, turbulence modeling, kerosene surrogate fuels and reduced chemical kinetic mechanisms, and so on. Also, directions for future research efforts are proposed and suggestions for the next 5-10 years are given.