A Variable-nozzle Ejector for a 120kW PEMFC Stack: Design and Performance

Abstract:

The ejector acts as a critical component in the hydrogen recirculation system for proton exchange membrane fuel cells which realizes anode exhaust recirculation via a supersonic jet. Traditional fixed-geometry ejectors are commonly designed according to the stack’s rated condition and achieve poor performance in off-design conditions. In contrast， variable-nozzle ejectors can adjust the throat’s opening dynamically and enlarge the operating range. Based on Sokolov’s theory， a one-dimensional model for the ejector was built to study its working characteristics， and a design methodology for the variable-nozzle ejector was later proposed. The results show that the ejector’s performance is mainly affected by its operating pressure， the throat diameter， and the mixing chamber’s diameter. By shrinking the throat and raising primary pressure， the working nozzle can be kept critical， which has little effect on entraining performance under high stack load. However， under low stack load， the entrainment ratio can be significantly improved， and the operating range expands toward low stack load.