Development Study of High-response Hydrogen Concentration Probe for Supersonic Flows

超燃冲压发动机是下一代空间飞机推进器和超音速民用运输机的有力候选者。超音速混合是实现超燃冲压发动机的一个关键挑战。对此，本研究的主要目的是开发一种在不需要昂贵设备的情况下评估超音速混合层中氢浓度的简单方法。研究人员提出了一种在铂丝表面进行催化反应的氢浓度探针。为了用这种探头探测超音速混合层中的浓度变化，催化放热速率的响应必须仅取决于探头周围的浓度变化。利用恒温式热线风速仪和激波管测量了铂丝表面非稳态催化放热速率，研究了催化放热速率响应与铂丝温度的关系。当铂丝温度较低时，催化放热的增加速率依赖于铂丝温度。然而，当铂丝温度超过680K时，这种依赖性很弱，这表明当铂丝温度足够高时，控制步骤不是催化反应，而是分子从流动到铂丝表面的转移。结果表明，在680K以上的温度下，铂丝上的催化反应速率比分子转移速率高，具有与热线风速计相同的高响应频率(100 kHz以上)。

Scramjet engine is a strong candidate for use as thrusters for space planes and supersonic civil transporter in the next generation. Supersonic mixing is a key challenge to in realizing scramjet engines. Regarding this, the main purpose of this research is to develop a simple method to evaluate hydrogen concentration in a supersonic mixing layer without the need for costly apparatus. The investigators have proposed a hydrogen concentration probe using catalytic reaction on Pt wire surface. To use this probe to detect a concentration change in a supersonic mixing layer, the response of the catalytic heat release rate must depend only on concentration change around the probe. Catalytic heat release rate on the Pt wire surface in unsteady state is measured using a constant temperature type hotwire anemometer technique and a shock tube to investigate the relation of the response of the catalytic heat release rate and Pt wire temperature. The increasing rate of the catalytic heat release depends on the Pt wire temperature when the wire temperature is low. However, the dependence is very weak when the wire temperature is over about 680 K. This shows that not the catalytic reaction but moleculartransfer from the flow to the Pt wire surface is the controlling step when Pt wire temperature is high enough. As a conclusion, catalytic reaction rate on the Pt wire is high enough comparing with the molecular transfer rate with the temperature over about 680 K, yielding high response frequency as hotwire anemometers(over a hundred kHz).