Selective catalytic reduction(SCR)system is the core of diesel engine to remove NOx from exhaust gas.The atomization performance of urea nozzle directly affects the NOx conversion rate and crystallization of urea.The pressure swirl nozzle has more performance advantages than the simplex nozzle.Taking a newly designed pressure swirl nozzle as the research object,combined with the experimental data and the volume of fluid(VOF)method,a three-dimensional numerical simulation was carried out by coupling the swirl inside the nozzle and the near-field spray outside the nozzle.The thickness and cone angle of the liquid film were accurately obtained.Based on the mathematical model of the flow field inside the orifice and Sauter mean diameter(SMD),the coupling study of the nozzle structure on the atomization performance of the spray was realized.The influence of key structural parame-ters of the pressure swirl nozzle,such as the length of the swirl chamber,the diameter of the swirl chamber,the length of the orifice and the diameter of the orifice,on the spray performance were analyzed.The results show that the geometrical parameters of the nozzle should be adjusted according to the growth of the gas core.When the inter-face between the gas phase and the liquid phase presents a multi-stage staircase pattern,reducing the ratio of length to diameter of the swirl chamber and orifice can effectively reduce the particle size and enhance the atomization ef-fect.The newly designed pressure swirl nozzle has the potential of SMD less than 30µm.
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