"Ansys Fluent helps us to optimize catalyst structures (pipe, cone and mixer), and significantly shorten the product development life cycle. SCR simulations using DPM modeling can correctly simulate AdBlue dosing and wall deposition phenomena."
— Ecocat India
The catalytic converter converts the toxic gases and pollutants in exhaust gases into harmless compounds like CO2 and H2O. In India, due to increasing air pollution, the introduction of BS-VI emission norms has led to the development of selective catalytic reduction (SCR) technology as well as diesel particulate filters (DPF) and gasoline particulate filters (GPF) for the trapping of particulate matter. The BS-VI emission limits are shown in Figure 2 and 3.
The catalytic converter consists mainly of a diesel oxidation catalyst (DOC), DPF and SCR for a diesel vehicle as well as a three way catalytic converter (TWC) for gasoline and compressed natural gas (CNG) applications. The main purpose of the DOC is to oxidize the CO and HC into CO2 and H2O as well convert NOx into NO2 (this helps in passive regeneration). SCR tends to reduce NOx with AdBlue dosing, an aqueous solution of Urea (NH2)2CO (aq.) that undergoes thermolysis and hydrolysis reactions for ammonia NH3 formation, which reduces the NOx into N2. DPFs are filters that physically captures particulates (carbonaceous soot) and prevents their release in the atmosphere.
We simulated SCR to optimize the injector configuration, ascertain the AdBlue dosing required per the exhaust gas flow rate and temperature, determine the injection angle, optimize the mixer design with respect to the back pressure limitation, calculate the mixing length required and optimize the heat shield to maintain the desire temperature to prevent wall film thickness formation, and achieve a higher ammonia uniformity index at the substrate wall. We were also challenged to optimize the pipe/cone/diffuser for minimum back pressure and maximum flow distribution.
Constraints for exhaust flow through catalyst: