| The global energy crisis and environmental problems are becoming more and more serious,and the development and research of new energy technologies are imminent.Proton Exchange Membrane Fuel Cell(PEMFC),as a kind of hydrogen fuel cell,has a new development opportunity.If the temperature is too low,the catalyst within the PEMFC will not reach the optimal activity point;if the temperature is too high,the proton exchange membrane will be dehydrated and the proton conductivity will decrease,leading to the degradation of the PEMFC performance.Uneven temperature distribution will cause single-cell performance degradation,and the temperature difference between single cells within the stack is too large,making the membrane electrode unevenly heated and reducing the PEMFC lifetime.In this thesis,we focus on the internal temperature characteristics of PEMFC stack,and investigate four aspects of temperature monitoring,temperature distribution,steady-state characteristics and dynamic characteristics.The main contents are as follows.(1)Firstly,the sensing principle of Fiber Bragg Grating(FBG)sensor and the wavelength division multiplexing technology of fiber optic sensing are analyzed,fiber grating string and PEMFC cathode flow field plate are designed and FBG sensor is embedded into the cathode flow field plate,and the online temperature monitoring platform of PEMFC internal temperature based on FBG temperature sensor is built.The performance of the PEMFC stack before and after embedding the FBG sensor was tested.The results show that the embedded FBG sensor has no significant impact on the performance of the PEMFC stack and can be used for online monitoring of the internal temperature of the PEMFC stack.(2)In order to select the temperature characteristic points,the temperature distribution law inside the stack under different operating parameters and current conditions is studied.The experimental results show that the temperature of each single cell of the PEMFC stack shows a trend of gradually decreasing from the middle to the surrounding area,and the highest temperature point of each single cell is located in the middle area,and the lowest temperature point is located at the cathode gas inlet position.Based on the experimental results,the temperature characteristic points were selected and the cathode flow field plate was redesigned for the subsequent experiments.(3)A proton exchange membrane fuel cell electrochemical model was developed to analyze the heat source of the proton exchange membrane fuel cell stack.Experiments were designed and monitored online for the variation of the internal temperature of the PEMFC stack under different current conditions and operating parameters,and the steady-state characteristics of the temperature were analyzed in terms of the maximum temperature,the temperature difference within the membrane electrode and the temperature uniformity.(4)The temperature variation process of the PEMFC stack after variable load is analyzed and divided into dynamic and steady-state processes,and the temperature response time,initial temperature rise rate and temperature rise amplitude are defined,and the temperature versus time after variable load is established using logarithmic fitting.The effects of different operating currents and operating parameters on the temperature dynamic characteristics of the PEMFC stack are experimentally investigated. |
