Theoretical studies on wide-operating-range ejector based on operating conditions and multi-parameter coupling effect in proton exchange membrane fuel cell system

When the ejector in a fuel cell system operates under off-design conditions, its performance will significantly decrease. To improve the performance of the ejector under all operating conditions, this paper proposes a theoretical model for predicting performance and optimizing the structure of the ejector that has not been studied before. Based on the jet theory, a two-dimensional three-segment velocity distribution is established, and the exponent of the velocity function is modified by simulation and experimental data, reducing the model's calculation error from 15% to 6.5%. By combining the Lagrange algorithm, we investigate the influence of operating conditions and multi-parameter coupling effects on ejector performance, obtaining optimal values for structural parameters under different load conditions. The results show that the optimal value of main nozzle exit position (Lx) increases with increasing current and the optimal value ranges from 0.5 to 6 mm. The influence of dimensionless parameter (lambda c), dimensionless parameter (lambda d) and diffusion angle (alpha d) on ejector performance is significant and optimal values exist. Reducing the nozzle throat diameter (dnt) can effectively promote the entrainment performance at low power, and four adjustment conditions are proposed. When dnt decreases from 3.2 to 2.0 mm, the operating range of the current is increased by 38.42%, the power range is increased by 42.12%, and the pressure drop of the ejector (pd) decreased by 9.66 bar. The theoretical model not only improves the accuracy of predicting the entrainment ratio, but also realizes the study of the influence of multi-structural parameter coupling effect on the performance of the ejector, which leads to a significant improvement in the optimization accuracy and efficiency, and extends the applicable power range of the ejector. This provides a new direction for the future performance optimization of wide operating range ejectors considering multi-parameter coupling effects.