Analysis of improvement in entraining ability and control linearity in a 40 kW-grade variable-nozzle hydrogen recirculation ejector

• Published in: International journal of hydrogen energy 2024-12, Vol.93, p.1512-1523
• Main Authors: Lu, Yikang, Wang, Xuhui, Tang, Xingwang, Gong, Dapeng, Yang, Guang, Xu, Sichuan
• Format: Article
• Language: English
• Subjects: Hydrogen recirculation; Linearity; PEMFC; Variable-nozzle
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2024.11.078

Hydrogen recirculation ejectors are commonly used to achieve anode exhaust recirculation in proton exchange membrane fuel cell systems to obtain higher fuel efficiency. By adopting variable-nozzle designs in traditional fixed-nozzle ejectors, recirculation rates under low loads and the operating range of ejectors can both be improved. In this study, the design methods of different variable-nozzle structures for a 40 kW-grade ejector are proposed. A 2D numerical model is subsequently constructed and experimentally validated to investigate the influence of nozzle structures, needle profiles and needle protrusion length on entraining performance and control linearity. The results indicate that the variable-nozzle designs take greater effects at lower loads in increasing the entrainment ratio. Convergent nozzles with short throats are optimal for variable-nozzle ejectors due to their more significant and linear performance improvement. Adopting frustum needles or radical-function needles further enhances the linearity to over 0.96 across all power levels, but increasing needle diameters results in a reduction in the entrainment ratio. Additionally, the maximum needle insertion depth should be kept below 5.0 mm to minimize performance loss caused by excessive needle protrusion. •A convergent nozzle with a short throat is optimal for variable-nozzle designs.•Frustum needles and radical-function needles both significantly improves the control linearity.•Increasing needle diameters or protruding length leads to the reduction in entraining ability.•The needle insertion depth should be kept below 5.0 mm to minimize performance loss.