Abstract
A new mixer for a diesel engine after-treatment system is developed to meet the requirements of China VI emission regulation. As for the structure of the mixer, it is surrounded by spiral blades, and the center is staggered with small blades, which is conducive to the crushing of urea droplets and can make the droplets fully mixed with air, improve the conversion efficiency of nitrogen oxides (NOx) and reduce ammonia leakage. The numerical analysis, engine bench test, and vehicle road test were carried out on the after-treatment system equipped with the new mixer. The numerical calculation results show that the velocity uniformity index of the selective catalytic reduction (SCR) carrier can reach 0.98, as well as the ammonia uniformity can reach 0.95, meanwhile, the low wall film height shows excellent anti-crystallization properties. engine bench test results are consistent with numerical results. The crystallization status of the mixer after the vehicle durability test is acceptable and well performed.
Highlights
The new schemeThe new mixer can improve the ammonia uniformity coefficient and overall mixing effect
From July 2021, China VI emission regulation will be implemented widely, and the emission of nitrogen oxides (NOx) requires to be less than 0.4 g/(kWh)
Zhang et al combined with diesel oxidation catalyst (DOC), catalytic diesel particulate filter (CDPF) and selective catalytic reduction (SCR) technologies to modify pollutant emissions of heavy diesel engines, including NOx conversion efficiency and ammonia leakage, upstream DOC and diesel particulate filter (DPF) reduced particle number (PN) and particulate matter (PM) by an average of 91.6% and 90.9% respectively, while downstream SCR reduced NOx by 85% [5]
Summary
The new mixer can improve the ammonia uniformity coefficient and overall mixing effect. The center of the mixer is staggered blades, which are conducive to urea crushing and surrounded by swirling blades, which can make the airflow rotate, enhance the mixing degree of urea and air, reduce the crystallization risk of mixer and the surrounding area, extend the evaporation path and residence time of urea droplets, and improve the evaporation efficiency
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