Multi-channel Optical Fiber Thermometer for PEM Fuel-Cell Applications

Miniature, durable, and fast-responding temperature sensors are needed for proton exchange membrane fuel cells (PEMFCs). When embedded in a single cell or in a cell stack, they can provide useful information both at the design stage for optimizing the cell efficiency and during operation for monitoring the working conditions and thus preventing failures. Optical fiber sensors are especially promis- ing in this field because they are small, rugged, and inexpensive. In addition, they can provide safe temperature measurements in an electrically hostile environment. A four-channel optical fiber thermometer, based on intensity-independent fluorescence lifetime thermometry was developed at INRIM. It consists of a photonic unit for the excitation/detection of the fluorescence signals and a set of custom optical fiber probes based on a temperature-sensitive fluorescent material attached to the distal end of an optical fiber. The system was characterized in the range from room temperature to about 100 ◦C in order to point out its metrological features. A temperature repeatabil- ity to within 0.06 ◦ C with a response time lower than 1 s to a step temperature change was obtained. A preliminary investigation inside a PEMFC stack using the optical fiber fluorescence thermometer was also performed. In order to check the tempera- ture uniformity along the stack, temperatures within an adjacent membrane electrode assembly (MEA) of a six-fuel-cell stack were measured during the unit operation. The system design, the probe construction, and its laboratory testing are presented in this article together with an assessment of the overall system performance. The application of such a system in a fuel-cell test rig is also described. The experimental results demonstrate the suitability of the system in real-time temperature mapping in operating fuel cells.