Development Of Coaxial Two-nozzle Ejector For Hydrogen Recycle In PEMFC

The hydrogen recirculation system is an important part of the fuel cell.As the core component of the jet hydrogen cycle system,the ejector has the advantages of no parasitic power consumption,no rotating parts,simple structure,low noise,and low cost,and has become one of the research hotspots of PEMFC.However,the contradiction between the performance of the traditional fixed-geometry ejector and the variable operating conditions needs to be resolved urgently:when the ejector works under non-design conditions,its performance is greatly reduced,which cannot meet the wide-power operation requirements of the PEMFC system,Therefore,it is of great theoretical significance and application value to promote the development of fuel cells to develop an ejector with a simple structure that can meet the hydrogen cycle requirements of fuel cells under variable working conditions.In view of the above problems,this thesis proposes a coaxial two-nozzle ejector with two nozzles which improves the hydrogen recirculation performance under variable operating conditions.The main work includes:(1)A nozzle design method for the coaxial two-nozzle ejector is proposed,a numerical simulation model of the ejector is established,and the key geometrical parameters of the ejector are determined.(2)The internal flow mechanism of the coaxial two-nozzle ejector is revealed,the influence of different working parameters on the performance of the coaxial two-nozzle ejector is studied,and the influence of different hydrogen supply strategies on the performance of the ejector under the same primary flow rate is analyzed.(3)According to the different power parameters of the fuel cell,a combined logic control strategy of the coaxial two-nozzle ejector suitable for the wide output power range of the fuel cell is proposed,and the recirculation performance of the traditional ejector and the coaxial two-nozzle ejector under variable working conditions of the fuel cell are compared.(4)The influence of anode exhaust humidity on the performance of the fuel cell cycle system is analyzed.(5)The coaxial two-nozzle ejector is manufactured by high-precision machining technology,the experimental test platform for the coaxial two-nozzle ejector is established,and a systematic experimental study is carried out.The results show that:(1)Through the combination of the three working modes of the coaxial two nozzles,the problem of poor recirculation performance in the low operating condition area of the ejector is solved,and the performance is excellent under variable working conditions,which effectively widens the working range of the ejector.(2)When used in an 80KW fuel cell system,the coaxial two-nozzle ejector not only has excellent recycle performance with a recirculation ratio above 0.9 at high power output but also can maintain a high recirculation ratio above 2.0 at low power output,which meets the hydrogen cycle requirements in the range of 17.9-84.0 kW of the fuel cell.