Ansys Fluent: Automotive Selective Catalytic Reduction

Hello everyone, in this tutorial we will explore droplet evaporation and volumetric reaction setup using an application example similar to selective catalytic reduction of NOx for emission control. Geometry is a 2D pipe system.

The spray inlet is on the left-hand side, the highlighted portion of the walls, and the outlet on the other side. Transfer the geometry and mesh. The mesh is generated using a face size of 5 x 10^-4 meters. The name sections are carried forward from the geometry.

As we look at the cell zones, we can see that the SCR is marked as green. There are three more cell zones. Once the mesh is generated, the mesh will be transferred to Fluent. Set up a steady-state case. A turbulence model, which is the default model, will be used for this case.

Activate the species transport model and activate volumetric reactions. Select the appropriate mixture. In this case, we have selected the urea-water-air default mixture. It contains urea, ammonia, carbon dioxide, NOx, and nitrogen in the mixture.

We have added the reactions in the finite rate section. The first reaction is urea breaking down into ammonia and isocyanic acid. The second reaction is isocyanic acid reacting with water vapor to give ammonia and carbon dioxide.

The third reaction is ammonia reacting with NOx and oxygen to give nitrogen and water vapor. The fourth reaction is ammonia reacting with NO2 to give N2 and H2O. The fifth reaction is ammonia reacting with NO2 and O to give out N2 and H2O. The reaction mechanism tab now shows the reactions listed.

We have created two mechanisms with reaction 1 and 2 in one and the rest of the reactions in mechanism 2. In this case, we will be using the finite rate options with no turbulence chemistry. To set up the urea injection, we will go into the discrete phase model.

We will activate the interaction with the continuous phase. Keep the other values default. Now setting up the injection. We will set it up as a group injection as droplets and with 25 streams. We will set it up as a group injection as droplets and with 25 streams.

Now add the position, velocity, diameter, temperature, and the flow rate for the injection. And the injector will be displayed in the GUI. In the geometry, we have 2D baffle plates in order to improve the mixing. And the particles will interact with the incoming flow and mix with the system.

As it moves downstream, it will be mixed with the incoming flow. As it moves downstream, it will be mixed with the incoming flow. We have the porous media in this region where the SCR reaction will take place, moving out to the exhaust.

The drag law is spherical, and the turbulent dispersion model will be active. The drag law is spherical, and the turbulent dispersion model will be active. When you activate the droplet injection, you will also get a new material, which is called the urea liquid droplet.

And you should change the material properties based on your requirement. And you should change the material properties based on your requirement. And you should change the material properties based on your requirement. Update the gas inlet with an appropriate velocity.

Thermal property, what kind of species are incoming. In this case, we have a higher quantity of CO2 and NOx coming in. In this case, we have a higher quantity of CO2 and NOx coming in. Present a gas exhaust coming out of the combustion chamber of an engine.

The outlet is set up as open to atmosphere. The species reverse flow will be water vapor and oxygen, and the DPM condition is set to escape. The reverse flow temperature condition is 300 Kelvin. All the walls are set up as insulated. Now we take a look at the cell zones.

The SCR reaction takes place in this specific cell zone, and we have to activate the porous zone and the reactions for this cell zone. For the porous resistance, we can add a porous resistance in a specific direction.

In this case, the porous resistance is lowest in the X direction and highest in the Y direction, and the porosity is set to 0. 7. In the SCR region, we select mechanism 2, which contains three reactions taking place in the XCR catalyst region.

The cell zone just downstream of the SCR has no reaction in it. The cell zone upstream of the SCR region has two reactions in them, which are the urea to ammonia conversion and the urea to carbon dioxide conversion.

Now create report definitions such as what is the relative humidity at the inlet region? What is the parts per million value of the NOx at the outlet?

To compute the species values in terms of ppm, we create a custom field function, which is essentially taking the mass fraction of the species multiplied by a million. Create report definitions for NO and NO2 at the inlet and at the outlet. Initialize the problem.

Set up the time step size for the pseudo-transient solver and run the calculation. We can see from the report that the result is very good. We can see from the report that the result is very good. We can see from the report that the result is very good.

Note that the inlet concentration of NOx was 1000, and as it reaches the outlet, the NOx concentration has dropped down. At the end of the calculation, we check for mass imbalance. In this case, it is within the acceptable limits. Also, the energy imbalance is within the acceptable limit.

Now create a contour for temperature. We can see how at the DPM injection point, because of the evaporation physics, the temperature has dropped. We can see how the particles move through the system and interact.

We can see how the reaction changes the temperature internally within the SCR and finally it moves out of the domain. Similarly, when you look at the velocity contours, you can see how the temperature changes. We can see how the velocity changes. We can see how the velocity changes.

Similarly, when you look at the velocity contours, you can see how the baffles interact with the incoming flow. We can see how the flow becomes uniform in the porous region. We can see how the flow becomes uniform in the porous region.

Looking at the isocyanic acid concentration, which is mainly located close to the DPM injection. The urea concentration, which is highest close to the DPM injection point. As we look at the NO2 concentration, we can see as it reaches the SCR region, it is converted.

Similarly, the NO concentration drastically drops as soon as it reaches the SCR region. We can use the DPM track to see how the particles are moving in the domain. We can use the DPM track to see how the particles are moving in the domain.

The contour of urea shows us how the droplet evaporates and moves into the gaseous phase. And we can bring them together in a scene. And we can bring them together in a scene. And this is how we can set up a basic automotive SCR using DPM droplet injection and volumetric reactions in Ansys Fluent.

Thank you for watching.