By Melanie_Groisil

To accurately assess the vehicle tail-pipe emissions, efficient modeling of exhaust systems is becoming a very important but also a very time-consuming task. The chemistry inside a catalyst is complex; that leads to many kinetic parameters to calibrate in order to obtain a predictive system simulation model.

The exhaust calibration tool has been greatly improved to Simcenter Amesim 17. It is designed to ease this calibration stage thanks to a detailed and user-friendly workflow as well as to go faster thanks to its adaptive optimization feature. Regardless of whether you work on a synthetic gas bench or driving cycle test data, the whole calibration process can be carried out through this Simcenter Amesim tool.

Let me showcase how this flexible integrated workflow helps you to deal with all kinds of test data.

Let’s take an example of a three-way catalytic converter. In an ideal calibration process, it will start with synthetic gas bench test data and a simple sketch:

Once you have built the sketch, the entire calibration process will be performed within the exhaust calibration tool, which contains 5 distinct stages and you can go back and forth within these stages as needed:

Sketch definition: this step allows you to specify the discretization of the same monolith. In the sketch above, the three-way catalytic converter is discretized into two elements to better capture the longitudinal temperature gradient.

Geometry definition: geometrical parameters for all the catalytic components can be edited at this stage and it gives an overview of the volumes and surfaces that characterize the monoliths.

Kinetic scheme definition: the flexibility of the monoliths in the Simcenter Amesim IFP-Exhaust library is characterized by the fact that any chemical reaction using the 12 standard gases of the library can be implemented in it. Therefore at this stage, it is possible to load a predefined kinetic scheme or to add user-defined reactions, and even both.

Test data import: a database of tests that will be the reference results for the calibration has to be created at this stage. The calibration of a classical three-way catalytic converter on SGB test data requires different light-off tests for different space velocities and probably OSC (Oxygen Storage Capacity) tests: the database can be constituted with all these tests and contains both inlet and outlet data:

Calibration: the final stage allows you to run simulations for every test from the database defined in the previous step. The kinetic parameters used for chemical reactions are editable, therefore it enables you to easily iterate on values.

Indeed, this tool has greatly facilitated the process, nevertheless it still takes a long time to calibrate the complete kinetic scheme by hand. That’s where the optimization feature can be of great help. You can launch it directly from this last step and a specific window allows you to set up the parameters and the objectives of the optimization, as well as the tolerance and the algorithm to use.

The next and often final step of an exhaust line calibration is the correction and validation of kinetic parameters on driving cycles. The exhaust calibration tool is also perfectly adapted for this task since you can add a new test for each driving cycle. In the same way, you can move until the calibration step and use concentration, mass flow rates or even cumulative masses to find how to fit your experimental data.

To sum up, the Simcenter Amesim exhaust calibration tool now enables accelerated test data import, batch processing and automated optimization of model calibration.