Michel Clement

Hydrogen leak detection using an optical fibre sensor for aerospace applications

Abstract An optical fibre sensor has been developed for the detection of hydrogen leakages on the cryotechnic engine of the European rocket ARIANE V. The principle of this sensor is based on the variation of reflectivity of a palladium micromirror deposited at the output end face of a multimode optical fibre. An experimental set-up using a monitored high power laser diode provides an optical heating of the palladium layer, which allows to keep up the performances in the wide range of temperatures between −196°C and +23°C. Depending on both the concentration and the temperature, detection responses between 1% and 17% with response times shorter than 5 s have been demonstrated. Fast and accurate detection of hydrogen concentrations inferior to the explosive limit has been performed.

Surface plasmon resonance hydrogen sensor using an optical fibre

An optical fibre surface plasmon resonance (SPR) sensor has been developed for the detection of hydrogen leakages. A thin palladium layer deposited on the bare core of a multimode fibre was used as the transducer. In this device, modification of the SPR is due to variation in the complex permittivity of palladium in contact with gaseous hydrogen. This effect is enhanced by using selective injection of high-order modes in the fibre via a collimated beam with non-normal incidence on the input end of the fibre. Measurements of concentrations as low as 0.8% of hydrogen in pure nitrogen have been found to be possible. The response time varies between 3 s for pure hydrogen and 300 s for the lowest concentrations. Such a large range can be explained by the two different crystallographic phases of the palladium-hydrogen system. Moreover, the response of the sensor is dependent on the length of the sensing area. In preliminary experiments, it has been possible to split the sensing area in order to achieve a two-point detection device.

TEMPERATURE MEASUREMENTS BY CARS AND INTRUSIVE PROBE IN AN AIR-HYDROGEN SUPERSONIC COMBUSTION

Static and stagnation temperature measurements are performed by CARS and by an intrusive probe in a Mach 2 cylindrical jet of hydrogen, injected into a Mach 2 coflow of air. The single-shot CARS static temperature measurements are based on nitrogen. A stagnation temperature probe has been developed and tested. This method consists in identifying the transient regime of a thermocouple probe with a numerical prediction modeling the high speed effects on the probe recovery factor. The paper presents and discusses the comparison between the temperature measurements performed by the intrusive probe and the CARS non-intrusive techniques (1) at the inlet of the combustion chamber; (2) in the ignition zone of the hydrogen jet; (3) in the burnt gases.

Gaseous hydrogen leakage optical fibre detection system

Liquid hydrogen has been intensively used in aerospace applications during the past forty years and is of great interest for fuel cells technologies and future automotive applications. Following upon major explosive risks due to the use of hydrogen in air, previous studies were carried out in our laboratory in order to develop optical fiber sensors for the detection of hydrogen leakage. This communication is aimed towards a prototype optical fiber system designed for the detection of gaseous hydrogen leakage near the conecting flanges of the liquid hydrogen pipes on the test bench of the engine Vulcain of the rocket ARIANE V. Depending on the configuration, the prototype sensor provides a two-level alarm signal and the detection of gaseous hydrogen leakage is possible for concentrations lower than the lower explosive limit in air (between 0.1 and 4%) with alarm response times lower than 10 seconds in a wide range of temperatures between -35°C and 300°C. The sensing principle based on palladium-hydrogen interaction is presented as well as the detection system composed of an optical fiber probe and an optoelectronic device.