Water And Thermal Management For Automotive Proton Exchange Membrane Fuel Cell

Hydrogen fuel cell electric vehicle(FCEV)has been considered as one of the most promising new energy vehicles due to its advantages of low-emission and high efficiency.Proton exchange membrane fuel cell(PEMFC)serves as the main driving component of the current FCEV because of its fast development in recent years.At normal temperature,the water and heat transfer behaviors are different under different current loadings.Cathode flooding and anode drying have been recognized as the key issues that need to be addressed during the engineering development.At subfreezing temperature,the strong heat loss and water freezing and blockage will surely lead to serious degradation of fuel cell output performance and self-starting up capability.Therefore,water and thermal management in wide-range temperatures is an important engineering issue to be solved in the commercialization of FCEV,which is also beneficial for its high-performance operation,good durability,high environmental adaptability and low-cost development.In this study,the issue of water and thermal management of full-power PEMFC is studied.The water and thermal managing strategy for PEMFC under various conditions are analyzed in detail.A comfort index is proposed to evaluate the water and thermal state inside the cell.The application of cold start theory and researches on the PEMFC into engineering development are also achieved based on the newly established lumped parameter model.The results are carefully discussed based on the numerical simulation,engineering experimental tests and theoretical analysis.The main work in this study includes:(1)Establishment of quasi-2D multi-phase numerical model for PEMFC.A quasi-2D numerical model has been established in this study in order to predict the cell output performance and the inherent water and heat transfer behavior.Note that various-humidification strategies,coolant flow and correction of the effective catalyst utilization rate are all taken into consideration.This study aims to provide theoretical basis for the water and thermal management in the engineering work.(2)Proposal of the comfort index of water and heat behavior under high-load conditions.Comfort index is firstly proposed in this study according to the similar method used in meteorology science.The water accumulation in cathode and anode hydration state are all taken into consideration to comprehensively evaluate the comfort level.Simulations are carried out to obtain the specific analytical formula of comfort evaluation index for representation of water and thermal characteristics.The model is also dimension-reduced,which is accounted more convenient for the fuel cell engineers to implement online water and thermal management on PEMFC.(3)Analysis of water and thermal management of PEMFC during low load and high efficiency operation.Simulation and experimental tests based on the electrochemical impedance spectroscopy(EIS)are conducted under the low catalyst loading and anode circulation.Under cathode humidification,the humidity in catalyst layer(CL)is found higher than that of the anode humidification and anode circulation.Under anode humidification,the operating temperature and the operating pressure are full-sensitivity parameters,and the anode circulation ratio and the cathode stoichiometric ratio are interval-sensitivity parameters.Under low current loading conditions,the recommended hydrothermal management strategy is to appropriately reduce the operating temperature,increase the operating pressure,increase the anode circulation ratio,and reduce the cathode stoichiometry.This study aims to provide theoretical foundation for the high efficiency operation of PEMFC with anode circulation.(4)The establishment of lumped parameter model and engineering analysis for the cold start of PEMFC.The current 1-D transient cold start model of PEMFC is further developed into a lumped parameter model which is considered more convenient for the engineering development of PEMFC.This model is also carefully validated based on the engineering tests.The effects of several key parameters on the cold start behavior are then investigated.The results show that proper upper current and current loading rates are critical for a successful cold start.The initial temperature determines the success or failure of the cold start process mainly through electrochemical reaction kinetics and electrolyte water absorption capacity.The cold start capability could be greatly improved by replacing the conventional graphite bipolar plate with the thinner stainless-steel one.In addition,a cold start capability index is defined in this study to represent and capture the operational state of PEMFC during starting up process.