Research On Cooling And Heating Characteristics Of Fuel Cell Thermal Management System For Bus

With the deepening application of hydrogen fuel cells in the field of commercial vehicles,hydrogen fuel cell buses are gradually becoming the mainstream of urban buses.In this paper,the cooling and heating characteristics of fuel cell thermal management systems(stack and stack auxiliary thermal management system)for city bus that driven by hydrogen fuel cell(80 k W)and power battery(105 k Wh)battery-powered were studied.Meanwhile,the heat dissipation characteristics of the stack roof radiator were analyzed,and the optimization study was carried out.Firstly,the composition and energy management strategy of the bus power system were clarified,the heat generation power of the main heat-generating components were obtained through theoretical analysis,and the structure of the fuel cell thermal management system was clarified according to the design requirements.These provides a basis for the establishment of thermal management system models and the study of characteristics.Secondly,the model of bus power system and fuel cell thermal management system were established based on the AMESim platform,and the validity of the models were verified.The influence of series-parallel scheme on the cooling performance of the thermal management system of stack accessories was studied,and the influence of the initial SOC(state of charge)of the power battery and vehicle load on the cooling performance and energy consumption of the fuel cell thermal management system were analyzed.It was found that when the series scheme is selected,the intercooler should be in the front of the air compressor,and when the parallel scheme is selected,the coolant flow of the intercooler should be controlled.Compared with the initial SOC of the power battery at 100%,the maximum temperature rise of the components reaches 10.3%,and the energy consumption of the thermal management system increases by 185.3% when the state of the initial SOC of the power battery is 20%.The effect of vehicle load on the temperature of components is not obvious,but it has a great impact on the energy consumption of the thermal management system,and the maximum gap reaches 30.6%.Thirdly,the external auxiliary heating and internal self-starting heating models of the stack were established based on the AMESim platform,and the heating performance of the stack from-30 °C to 10 °C was compared with different heating modes.It is found that for the external auxiliary heating mode,gas-liquid heating has the shortest heating time,and has the best temperature uniformity.For internal self-starting heating,compared with the constant pressure method,although the hydrogen consumption of the constant current method is slightly larger,the time required to complete the heating is shorter,so the constant current self-start has stronger practical application.When liquid heating and internal constant current self-start mixing heating is used,the lower the temperature of the stack corresponding to constant current self-start,the shorter the heating time.When liquid heating and constant current self-starting synchronous heating is adopted,the higher the liquid heating power,the shorter the heating time and the lower the energy consumption.Finally,based on the equivalent characteristics of porous media and densely fins,the roof radiator models of stack thermal management system were established by the Fluent platform.The effect of radiator and roof spacing on air mass flow and coolant temperature were studied.The experimental bench was independently designed and built to verify the effectiveness of the models.By adding a roof deflector,the performance of the radiator cannot be fully utilized at low spacing is improved,combined with the fuel cell thermal management system model in AMESim,the cooling effect of the optimized front and rear radiators was compared.It is found that with the reduction of the distance between the radiator and the roof,the airflow can be missing in the radiator fin channel,the air mass flow rate can gradually decrease,and the coolant temperature gradually increases,resulting in the heat transfer capacity of the radiator cannot be fully utilized.By adding the roof deflector,the spacing between the roof and the radiator can be reduced,and the heat exchange effect of the radiator can be guaranteed.