Study On Expansion Optimization Of High Efficiency Zone Of Vehicle-borne Fuel Cell Centrifugal Air Compressor

Studies have shown that the performance of fuel cell stacks improves with increasing input air pressure.Air compressors play a key role in this process.The most promising development in the field of automotive fuel cells is the centrifugal air compressor.Improving the isentropic efficiency of centrifugal air compressors and expanding the range of high efficiency zones of air compressors can effectively improve the performance of on-board fuel cell stacks.At present,the efficiency of industrial low-flow centrifugal compressors is low and cannot fully meet the requirements of on-board fuel cells,and there is little research on centrifugal compressors for on-board fuel cells.This paper therefore investigates the efficiency improvement of centrifugal air compressors for vehicle-mounted fuel cells and optimizes their design in order to improve their rated efficiency and expand the range of high efficiency zones with certain economic and social benefits.The main research work of this paper is as follows.(1)A prototype of vehicle fuel cell centrifugal air compressor with high speed and low flow and high pressure ratio is developed.The numerical calculation model of air compressor is established.The performance and flow characteristics of the centrifugal air compressor are analyzed by numerical simulation.The performance variation law of centrifugal air compressor is revealed.The formation mechanism and characteristics of internal flow defects of centrifugal air compressor are discussed.(2)The influence of different impeller structure parameters on the performance of centrifugal air compressor was studied by numerical simulation.The performance curves and flow conditions at design points of air compressor under different impeller structure parameters are analyzed.The influence of different impeller parameters on the flow field in centrifugal impeller and the causes of the influence are discussed.The influence law of different impeller structure parameters on pressure ratio and isentropic efficiency of centrifugal air compressor is revealed.(3)To improve the rated pressure ratio and rated efficiency of air compressor and expand the range of high efficiency as the goal.Combined with the influence of impeller structure parameters on the pressure ratio and isentropic efficiency of centrifugal air compressor.The prototype air compressor was modified and optimized on the premise that the volute size of the prototype was unchanged.The optimized system characteristic curve of centrifugal air compressor is obtained through numerical simulation.The system characteristic diagram of the prototype before and after optimization is compared and analyzed.It is found that the flow range of centrifugal air compressor decreases after optimization.The isentropic efficiency decreases under the condition of large flow.But the pressure ratio goes up.The isentropic efficiency of the design point is increased and the high efficiency area is enlarged.The system characteristic curve moves in the direction of low flow.Comprehensive performance has been improved.(4)Participated in the design and construction of the centrifugal air compressor pneumatic test bench.The performance test of air compressor pneumatic system was carried out.The system characteristic curve which is close to the real situation of the centrifugal air compressor prototype is analyzed.It was found that the actual pressure ratio and rated efficiency could not meet the design index and the high efficiency area was narrow.The air compressor needs further optimization.The error analysis is carried out by comparing with the simulation results.It is found that the error of the two is within a reasonable range in the whole basin.The effectiveness and accuracy of the research on efficiency improvement of vehicle fuel cell centrifugal air compressor using the numerical simulation method in this paper are verified.