Study On Efficiency Improvement Of Ultra-High-Speed Electric Air Compressor For Vehicle Fuel Cell

Fuel cell vehicle has the advantages of no pollution,high power performance,short hydrogenation time,long driving distance,etc.,and has become an ideal way for the development of new energy vehicles.The ultra-high-speed electric air compressor is used to deliver compressed air to the reactor,which is the key component to ensure the electrochemical reaction of fuel cell.In order to meet the requirements of wide power range in all working conditions of fuel cell vehicles,high power fuel cell must be adopted,which requires further improvement of air supply flow rate and pressure ratio of ultra-high-speed electric air compressor.Ultra-high-speed electric air compressor is mainly composed of compressor and drive motor.Compressor structure and drive motor speed affect air supply flow rate and pressure ratio.Under the current situation that the compressor structure design has not made a major breakthrough,the driving motor speed should develop to high speed and ultra-high speed,and ultra-high-speed electric air compressor has become the development trend.Ultra-high-speed electric air compressor produces great parasitic power to fuel cell,and its power consumption accounts for more than 80%of the entire parasitic power of fuel cell.In order to improve the efficiency of ultra-high-speed electric air compressor,this study started from the establishment of numerical equation of ultra-high-speed electric air compressor and studied its efficiency improvement.The main research contents are as follows:Firstly,the numerical equation of ultra-high-speed electric air compressor was established.The Naiver-Stokes equation in relative cylindrical coordinate system was used to describe the viscous gas flow in ultra-high-speed electric air compressor,and the standard K-Omega model was used to characterize the turbulence.The geometric model of ultra-high-speed electric air compressor was meshed and boundary conditions were set.The continuous computing domain was separated into finite grid nodes,and the boundary conditions were set according to the actual operation of ultra-high-speed electric air compressor.The experimental bench of external characteristics of ultra-high-speed electric air compressor was built,and the experimental results were compared with the simulation results to verify the accuracy of the numerical equation.Secondly,the temperature rise mechanism of ultra-high-speed electric air compressor is analyzed,and the influence of heat loss and pressure boost is considered to study the temperature rise of air in the impeller passage and flow parts,and the influence of different working conditions of ultra-high-speed electric air compressor on the air temperature rise is analyzed,and the temperature rise characteristics of different positions of ultra-high-speed electric air compressor are obtained.The results show that the air temperature rise of ultra-high-speed electric air compressor for fuel cell is 2-4 times higher than that of turbocharger for diesel engine,especially at high speed,the maximum temperature rise of air passing through impeller and diffuser is 33.97 K and 48.95 K respectively.Thirdly,the heat dissipation is introduced into the calculation of the compression work to analyze its influence on the inlet and outlet air temperature and pressure of the ultra-high-speed electric air compressor,and the relationship between the heat dissipation and the compression work under the cooling and compression process is obtained,which is verified by changing the thermal conductivity of the shell in the simulation.The results show that enhanced shell heat dissipation can improve the efficiency of ultra-high-speed electric air compressor,and the efficiency is more obvious under high speed and high pressure ratio conditions.When the thermal conductivity of ultra-high-speed electric air compressor shell is increased to 397 W/（m·K）and 524 W/（m·K）,the efficiency is increased by 1.3%and 2.4%,respectively,verifying the efficiency improvement effect.Finally,analysis of super high speed electric air compressor used the air flow state,under the condition of the field synergy theory is adopted to super high speed electric thermal air compressor’s inner structure is optimized,according to the working condition of fuel cells with super high speed electric air compressor,the design can effectively improve the efficiency of super high speed electric compressor slightly ribbed tube structure and is verified by simulation.The results show that the efficiency improvement is best when the ratio of micro rib height to laminar bottom thickness is ε/δ₀=1.6.Under the condition of rotational speed of 90000 r/min and flow rate of 68 g/s,the efficiency of the optimized ultra-high-speed electric air compressor is increased by 1.9%.