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NOx emissions i.e., nitric oxide (NO) and nitrogen dioxide (NO2) contribute to the formation of smog and acid rain and affect the tropospheric ozone. NOx gases are usually produced during the combustion of fuels in the air, especially at high temperatures. Automotive emission remains one of the highest contributors of NOx emissions.

NOx emission can be controlled by two methods: precombustion technologies (use of ULNB, flue gas recirculation, etc.) and post-combustion technologies. Selective catalytic reduction (SCR) is a post-combustion NOx reduction technology.

With SCR, aqueous ammonia (NH3 ) is injected into the flue gas. The injected ammonia mixes with the flue gas containing NOx in the flue gas duct. The mixed stream is then sent to the SCR unit, which contains a catalyst bed. Ammonia then reacts with the NOx in the catalyst bed to form nitrogen and water. This technology requires an effective injection system and an optimized duct design for better emission reduction. Mixing is usually challenging because the amount of injected ammonia (ppm) is very small compared to the flue gas volume.

The video showcases how a basic automotive SCR setup can be developed in Ansys Fluent. The setup does not discuss the details of the catalytic reactions. The reactions are assumed to be gas phase only.  



Somenath Chatterjee, Ph.D.  

Senior Application Engineer  

Ozen Engineering, Inc. - Ansys Elite Channel Partner    

America’s Channel Partner of the Year: 2015, 2018, 2021      

Phone: 408-416-3240  Email:   

1210 E Arques Ave., #207, Sunnyvale, CA 94085    

Post by Somenath Chatterjee
June 27, 2023