Study On Anode Emission Characteristics Of PEMFC Based On Hydrogen Recirculation

Affected by the deterioration of the global climate,the formulation of emission regulations is becoming more and more stringent in various countries.The application of proton exchange membrane fuel cells in the automotive field has gradually attracted attention.The hydrogen system is an important part of the fuel cell vehicle power system.The hydrogen system based on the recirculation mode can effectively improve the hydrogen utilization rate and cell performance,but it is accompanied by the accumulation of nitrogen and liquid water.Therefore,periodic anode emission is required to avoid deterioration of PEMFC performance and durability.In this paper,the anode emission characteristics of PEMFC based on hydrogen recirculation have been investigated.First,a lumped parameter model of the hydrogen system based on ejection was established by the MATLAB/Simulink with combining the intrinsic mechanism and empirical formula.Component transport,electrochemical reaction consumption and nitrogen crossover were considered in the model.Based on the hydrogen system model,the effect of emissions on the operating state of the hydrogen system was studied.The results showed that the important operating parameters such as anode inlet flow,inlet pressure,injection ratio of ejector and opening of proportional valve fluctuated during the anode purge process.The magnitude of the fluctuation is directly related to the duration of the emission.The anode nitrogen concentration is controlled within a certain range by the periodic emission of the anode,and the emission strategy determines the nitrogen concentration level in the hydrogen loop.Finally,the anode emission strategy is formulated by analyzing the average nitrogen concentration of the anode inlet and the hydrogen utilization rate of the system under different emission strategies.Next,a two-dimensional CFD transient model with multi-physics field of the PEMFC stack was established.The model combined physics fields such as electrochemical reaction,component transfer and fluid flow.The reliability of the model was verified by comparing with the experimental results of the bench.The results of the hydrogen system model were coupled with the PEMFC stack model to study the effect of anode emissions on the operating characteristics of the PEMFC stack.The results showed that the performance of the stack decreases due to the accumulation of nitrogen in the hydrogen loop during the emission interval.The stack performance fluctuated during the emission process,and returns to the initial state quickly after the emission.The performance of each single cell was affected differently.The decline of single cell performance decreased gradually toward the outlet of stack.The strategy of short emission period-short emission duration is not only conducive to the stable and efficient operation of the PEMFC system,but also improves the uniformity of cell performance and component distribution inside the stack.Finally,the emission characteristics of liquid water in the anode channel were studied based on the VOF method.The effects of different emission strategies on liquid water were compared,and the effects of different factors on the emission of liquid water were comprehensively analyzed.The results show that the increase of the emission duration is beneficial to the emission of liquid water.However,due to the higher stoichiometric ratio of andoe inlet on the hydrogen recirculation mode,the anode emission has little effect on the transport of liquid water in the flow channel.Factors such as flow velocity,contact angle of GDL,gravitational environment and droplet size all affect the emission of liquid water.In addition,the corners of the U-shaped flow channel are designed to be rounded transitions,which is beneficial to the emission of liquid water.