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

超燃冲压发动机是下一代空天飞机和超音速民用运输机的有力推进器。超声速混合是实现超燃冲压发动机的一个关键挑战。关于这一点，本研究的主要目的是开发一种简单的方法来评估在超音速混合层中的氢浓度，而不需要昂贵的设备。研究人员提出了一种利用铂丝表面催化反应的氢浓度探针。为了使用这种探头来检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。采用恒温式热线风速仪和激波管测量了非稳态铂丝表面的催化放热速率，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取决于铂丝温度。然而，当丝温度超过约680 K时，这种依赖性非常弱。这表明，当铂丝温度足够高时，控制步骤不是催化反应，而是从流体到铂丝表面的分子转移。结果表明，铂丝上的催化反应速率与温度超过680 K时的分子转移速率相比，具有较高的响应频率（超过100 kHz）。

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).