Experimental study on stability enhancement of a novel centrifugal compressor for hydrogen recirculation in aviation proton exchange membrane fuel cell (PEMFC) systems

Conventional hydrogen recirculation in automotive PEMFCs typically relies on positive displacement compressors or ejectors. However, in high‑specific‑power applications such as aviation, where liquid hydrogen storage is preferred, displacement machines tend to be bulky and heavy, and ejectors lose effectiveness without a high‑pressure hydrogen source. In previous work, a magnetically levitated centrifugal compressor was therefore introduced as a lightweight, efficient and pulsation‑free alternative. Nevertheless, the operating range of centrifugal compressors is inherently constrained by the surge limit to protect themselves and PEMFCs. Moreover, acute variations in water‑vapor and nitrogen content significantly broaden the required operating envelope compared to fixed‑composition systems. Reconciling these conflicts forces an overly conservative surge margin to safeguard against rare extremes, yet shifts normal operation away from its peak‑efficiency sweet spot. To overcome these limitations, this study proposes a novel flow-control strategy based on blade-integrated recirculation jets to extend the surge limit of the prototype. High-frequency dynamic pressure measurements are conducted to locate critical flow regions of surge inception. Informed by these flow-physics insights, targeted structural modifications are developed and comparatively tested in helium and air. These modifications consistently improve surge margin and pressure ratio across varying gas properties and rotational speeds, with negligible impact on efficiency. The optimized configuration achieves a 40 % increase in surge margin over the baseline and enhances pressure ratio throughout the operating range. These benefits are attributed to momentum addition from steady recirculation jets, which counteract the strong streamwise adverse pressure gradient upstream of the volute tongue—the identified trigger for surge.