1. Mike Weaver, CD-adapco Seattle
2008 CLEERS Workshop, May 14
STAR-CD Shared Library Interface
for
Third Party, 1-D Models in es-aftertreatment
Mike Weaver, CD-adapco Seattle

2. Outline
Overview of es-aftertreatment - Analysis methodology and physics - Modeling abilities and examples
1-D Model Interface - Physics - Modeling and Use

3. AFTERTREATMENT MODELING GOALS
Physical Mechanisms Included:
Flow characteristics in individual monolith channels
Global flow characteristics upstream/downstream of monolith (eg. expansion/contraction of exhaust tube)
Chemical Kinetics: Catalytic surface reactions and gas phase chemistry using DARS
Solid/Fluid heat transfer of the entire system
Soot Filtration Model for DPF
Temporal and 3D spatial variation upstream due to the Aftertreatment Device

4. Representative Channel Coupling
Velocity, pressure, and all other flow variables are continuously coupled with a coupling algorithm in STAR-CD (connect average)
Coupling insures average flux continuity across discrete pairs of boundary regions
In this example, each channel is associated with a different radial zone of the inlet and outlet manifold

5. REPRESENTATIVE CHANNEL COUPLING
Cartesian Based Subdivision
Automatic subdivision/coupling from user supplied model

6. REPRESENTATIVE CHANNEL COUPLING
User Supplied Subdivision

7. Conjugate Heat Transfer Couplingz
T = T (z)
q = q (z)

8. SIMPLE Transient Solver for Multiple Time Scale Physics
Conduction heat redistribution time on order 10’s minutes
Catalyst adsorption/desorption time on order of minutes
Thermal warm-up/light-off time on order of minutes
Fluid channel resident time on order of ms
Chemical equilibrium time on order of 1ms
Fluid & chemistry is in a quasi-steady state relative to the warm-up, adsorption, and heat diffusion time scale
SIMPLE transient with DARS Coupling
Completely implicit, stable at any time step size
Stable for time steps on the thermal time scale and yet accurate representation of the fluid and chemistry quasi-steady states
>1000 fold increase in performance over PISO

9. Example: SELECTIVE CATALYTIC REDUCTION (SCR)
AMMONIA MASS PERCENT
Injection captured with STAR-CD’S Lagrangian spray model
Composition modeled with STAR-CD’s multi-component spray feature
Thermolysis and hydrolysis of urea can also be treated:
WATER MASS PERCENT
CO(NH2)2  NH3 + HNCO
HNCO + H2O  NH3 + CO2
WATER SPRAY TRAJECTORIES

10. SELECTIVE CATALYTIC REDUCTION (SCR)
WITH SOME MECHANISM MODIFICATIONS, NO2 CONVERSION CAN ALSO BE PREDICTED...
NH3 MASS FRACTION
NO MASS FRACTION
NO2 MASS FRACTION
NOTE: IMAGES ARE SHOWN GREATLY FORESHORTENED ACTUAL L/D OF TUBE IS ~100:1.

11. Surface Methane OxiCatalyst Mechanism in an Aftertreatment Device
Device light-off near centerline
Device warm-up
Heat radial conduction redistribution
Mid-channel light-off
Continued heat redistribution
OD channel light-off
Approach steady-state
Temperature contours (°C)

12. Loaded filter soot mass density
uneven distribution of the collected soot within the DPF
strong lateral variations
somewhat weaker axial variations with more soot downstream

13. Complete Systems with Multiple Devices
Loading
Thermal warm-up, light-off and regeneration
Heat losses on piping
SiC DPF, Corderite DOC each with 30 representative channels
Non-catalyzed soot filter
Model compared to well instrumented experiments
Exit from Turbine
90° bend
DOC
DPF
Flexible Coupling

14. Warm-up and Regeneration - Temperature
DPF
t=25s
t=300s
DOC
t=75s
t=500s
t=150s
t=1000s

15. Complete Systems with Multiple Devices
Exhaust manifold + Turbo charger
Catalyst 1
Catalyst 2
Diesel-particulate filter
Pipes
Pipes + Absorbing ducts

16. 1-D Model Physics

17. 1-D Model Physics STAR-CD Solid Temperature Solution
STAR-CD applies Porous Coefficients to
match pressure drop returned by 1-D
Model (each channel)
1-D Model to STAR-CD
Channel Outlet Boundary (each channel):
Temperature
Pressure
Transported Scalar Concentrations !
Solid Enthalpy Solution Along Channel
(z position) each channel
From 1-D Model to STAR-CD
Wall Heat transfer to solid, Q(z)
Heat Capacity and enthalpy
Cp(z) and h(z)
Thermal Conductivities:
K_axial(z), K_radial(z)
STAR-CD to 1-D Model
Channel Inlet Boundary (each channel):
Mass Flow Rate
Temperature
Pressure
Transported Scalar Concentrations !
Solid Temperature Solution Along Channel Axis,
(z position) each channel
From STAR-CD to 1-D Model
Solid temperature, T(z)
STAR-CD Solid Temperature
Solution

18. es-aftertreatment Modeling for 1-D Models: Scalars and Storage
Transported Scalars: All reactants and products that are transported in the flow are defined as transported scalars in Prostar and given inlet boundary concentrations for the model.
Post processing: of transported scalar concentrations is available over the flow and over the device volume.
Non-transported Scalars: 1-D models additionally may define any number of non-transported scalars, independent of Prostar, through the esafter1d interface. STAR-CD provides and efficiently manages cell storage for this data for restarts as well as distribution in parallel processing. These are also available for post processing over the volume of the device they apply to.
Arbitrary Device and Channel Memory Storage: In addition to cell-wise storage, STAR-CD provides and manages additional memory per device and per channel.

19. es-aftertreatment Modeling for 1-D Models: Prostar Definition

20. es-aftertreatment Interface for Third Party 1-D Models: Concluding Points
Benefit from established, advanced, calibrated reaction models developed at universities and research laboratories with a specific focus on aftertreatment
Couples Star flow and thermal solution with 1-D kinetics
Can use multiple vendor 1-D models in a single simulation with multiple devices.
Interface accommodates either cell discretization or vertex discretization in the 1-D model.
Present Vendors Providing libraries for STAR-CD 1-D interface: - axi-suite, Exothermia (Affiliated with Aristotle University, Thessaloniki) - XMR (Affiliated with the Institute of Chemical Technology, Prague)