A Study on Flame-Holding and Ignition of Hydrocarbon Fuel in Supersonic Flow

烃类燃料以其高能量密度对超燃冲压发动机具有很大的吸引力。然而，它的反应性低是一个很大的缺点。为了在超燃冲压发动机燃烧室中使用烃类燃料，保证超声速气流中的点火和保焰是非常重要的。在本研究中，我们使用煤油作为燃料，将其注入一个长度为L，深度为D的腔体的超燃冲压发动机燃烧室。马赫数为2，总温度为1800K-2400K。我们还进行了数值模拟和风洞实验。从实验结果来看，L和D有一定的组合可以最大程度地提高保火性能。数值结果表明，在这种情况下，在腔内产生了大而复杂的涡结构，延长了燃料在燃烧室中的停留时间。另一方面，预测由于来流的减少，腔内温度升高。然而，用热电偶等侵入式方法测量温度是困难的。因此，我们以H2O为目标粒子，采用双波段发射方法。我们可以在不干扰流场的情况下测量腔内温度。将实测温度与预测温度进行了比较，两者吻合较好。研究发现，设计合理的空腔通过延长停留时间和提高温度，在超声速流动中对烃类燃料具有良好的保燃性能。

Hydrocarbon fuel is attractive for scramjet engine because of its high energy density. However, its low reactivity is pointed out as a large demerit. In order to use hydrocarbon fuel for a scramjet combustor, it is important to ensure ignition and flame-holding in a supersonic airflow. In this research, we use kerosene as a fuel and inject it into a scramjet combustor with a cavity, which is L in length and D in depth. The Mach number is 2 and the total temperature is 1800K-2400K. We also conduct numerical simulations as well as wind tunnel experiments. From the experimental result, it is found that there is a certain combination of L and D that leads to the maximum improvement of flame-holding performance. The numerical result shows that in a such case, large and complex vortex structure is generated in the cavity and prolong the residence time of the fuel in the combustor. On the other hand, it is predicted that the temperature in the cavity increases due to the decrease of the incoming flow. However, it is difficult to measure the temperature with intrusive method, such as a thermocouple. Hence, we adopt the two-band emission method instead with H2O as a target particle. We can measure the temperature in the cavity without disturbing the flow filed. The measured temperature was compared with the predicted one and they agree well. It is found that the well-designed cavity has good performance for flame-holding of hydrocarbon fuel in supersonic flow by prolonging the residence time and increasing the temperature.