With the upgrading of emission regulations and fuel consumption regulations,the efficient SCR(Selective Catalyst Reduc-tion)aftertreatment technology route has gradually become the mainstream technology route for diesel vehicle aftertreatment in China VI and above.The increase in urea injection volume and the limited space layout of light vehicle aftertreatment processors have led to the increasingly prominent problem of urea crystallization.Mixer design has become a key and difficult point in the development of light vehicle aftertreatment processors.By using CFD simulation technology,an improved design of a mixer was proposed from the per-spectives of crystallization,emission and back pressure performance.A new type of mixer consisting of a vortex tube and fin structure was proposed.Numerical simulations were conducted on the internal flow field of the catalytic converter before and after the improve-ment.The results showed that optimizing the fin angle of the mixer can effectively reduce the wall area of urea liquid film and increase the probability of secondary fragmentation and vaporization of urea droplets,reducing the risk of urea crystallization;The increase in the opening area at the bottom of the front guide plate of the mixer can reduce throttling loss and improve the anti-crystallization effect at the bottom of the mixer;After optimization,the mixer has improved the uniformity of airflow velocity at the DOC inlet and the unifor-mity of ammonia mixing at the SCR inlet by 2.5％and 1.3％,respectively;The maximum thickness of the crystalline liquid film de-creased by 0.306 pm;Increase the minimum temperature of the crystallization liquid film by 51 ℃;The NOx emissions in the WHSC cycle are reduced by 26％,ammonia leakage is reduced by 40％,hot WHTC cycle NOx emissions are reduced by 15％,and ammonia leakage is reduced by 41％;The back pressure of the rear processor assembly has been reduced by 10.6％;The crystallization assess-ment standard is based on the pulse spectrum of the universal characteristics of urea injection volume,combined with the commonly used operating conditions of application vehicles,to select harsh steady-state operating points for crystallization assessment,which can effectively avoid insufficient development verification and crystallization risks in mass production applications.
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