Fast Running Model FRM - Understanding and utilization of FRM converter and FRM builder tools in GT suite

Tutorial - 9 (Building a fast running model)

Introduction
Fast Running Engine Models are dynamic, fully-physical engine models that are designed specifically to run fast. While high-fidelity engine models are commonplace in the engine performance department, they are often too slow running to incorporate into system-level models where long transient events may be simulated, or where the simulation model must respond faster than real-time, such as for HiL (Hardware-in-the-Loop) simulations. When simulation speed is of priority, high-fidelity GT-POWER engine models can be simplified into FRMs using a standard conversion process. It is up to the user how far to simplify the model, depending on the accuracy-vs.-runtime requirement.

FRMs are able to achieve such fast run times by two means: (1) increasing the simulation time step size, and (2) decreasing the number of calculations per time step. These two means are often accomplished at the same time by lumping various flow volumes together which will reduce the total number of subvolumes and also allow for a larger time step size by increasing the effective subvolume length (which is responsible for the time step size). In addition to simplifying and combining flow volumes, there are additional solver options that can reduce the number of calculations per time step and, thus, further decrease the run time without changing the time step size.

This tutorial covers the process of creating a Real-Time capable Fast Running Engine Model from a detailed, high-fidelity engine model. While this tutorial shows a specific set of steps, note that each engine model is unique and so the steps required to convert a detailed model will depend on the complexity of the model, as well as on the goals of the end-user. For certain applications, such as Vehicle Thermal Management where engine coolant heat rejection must be maintained, the procedure may differ slightly in order to maintain certain key results. While this FRM process will focus on preserving general engine performance results, special considerations will be noted along the way.

This tutorial provides a step by step process of understanding how to convert a detailed engine model into an FRM model, Following detailed engine model is chosen:

4-cylinder Turbocharged Gasoline Direct Injection engine with turbocharger wastegate controller and semi-predictive intercooler.:

This model is a 4-cylinder 2.0-liter turbocharged Gasoline Direct Injection (GDI) engine. The turbine wastegate is being dynamically controlled in order to target BMEP. A full-load speed sweep is being simulated, from 5000 RPM down to 1000 RPM. A semi-predictive charge air cooler is included such that the outlet temperature is predicted as a function of inlet gas temperature and mass flow rate, coolant temperature, and charge air cooler effectiveness.

Launch FRM Tags
With the high-fidelity engine model open in GT-ISE, go to the Tools tab and click on \'FRM Tags\'. The model has already been tagged. You can select the individual subsystem and the parts are getting highlighted on the map.

Launch the FRM Converter
The GT-SUITE FRM Converter is a tool that will track the FRM Conversion process, organize all model files automatically within subdirectories, and provide result comparisons of key RLTs throughout the conversion process. 
With the high-fidelity engine model open in GT-ISE, go to the Tools tab and click on \'FRM Converter\'. This will prompt you to create an FRM Conversion Project. It will validate the tagged subsystems and report if the validation is successful. Confirm that the correct model is specified in \"Select the Baseline Detailed Model\" per below, then click Next.

Step 1: Exhaust Manifold
It is now time to start simplifying the first subsystem of the model. It is most efficient to start by simplifying the subsystem that is currently restricting the time step. For high-fidelity models, this is almost always the exhaust manifold where the highest gas velocities occur, which in turn restricts the time step. For Step Name, type \"Exhaust Manifold\". Select Exhaust Manifold 1 from the Tagged Subsystems list.

Click \"Expand\" on the FRM Converter to expand the Model Reduction page. The Exhaust Manifold will now be simplified. Make sure that the \"Apply Smart Calibration Settings\" check box is selected. This option can be found below the simplify buttons.

Clicking on the \"Simplify Manually” tab will allow to manually simplify geometry for parts that were not tagged or where a different combination of volumes is desired.

The above manifold is converted into a single volume using FRM converter.

Similarly, the following steps are done in order to completely convert a detailed model into an FRM model.

Step 2: Exhaust Pipes
For the second step of model simplification, the exhaust pipes downstream of the turbine will be simplified. Name the step \"Exhaust Pipes\". Select Exhaust Pipes 1 from the Tagged Subsystems list. Click on \"Simplify for Accuracy\" and click \"Yes\" for the \"Delete Part\" dialog.

Run the calibration, and once it is finished, click \"Next\". In the Results page, click the \"Run Model\" to rerun the full set of Cases. After checking model results and assuring that they are satisfactory, click \"Next (Begin Next Step)\".

Step 3: Intake Manifold

The steps followed for exhaust manifold are repeated for the intake manifold.

Step 4: Compressor Outlet Pipes
Name the step \"Compressor Outlet Pipes\". Select Boost Pipes 1 from the Tagged Subsystems list. Click on \"Simplify for Accuracy\". Collapse the FRM Converter to provide space to work in the model map.

the compressor is similarly calibrated as shown in the previous steps.

Step 5: Intake Pipes
Name the step \"Intake Pipes\". Select Intake Pipes 1 from the Tagged Subsystems list. Click on \"Simplify for Accuracy\". Collapse the FRM Converter to provide space to work in the model map.

the Intake pipes are similarly calibrated as shown in the previous steps.

Step 6: Additional Changes
Name the step \"Additional Changes\". Select Exhaust Manifold 1 from the Tagged Subsystems list. Click on \"Simplify for Speed\".

The exhaust manifold are made further changes in order for achieving more speed and is also finally calibrated.

Step 7: Cylinder Slaving
The final simplification to the model will utilize the Cylinder Slaving capability of the EngCylinder component. Name the new step \"Cylinder Slaving\", then collapse the FRM Converter to provide space to work in the model map.
Right-click on any of the EngCylinder parts on the map and choose \"Edit Parent Object\". Go to the \"Advanced\" tab and for \"Cylinder Slaving Option\", select \"slave-RT-full-v2018\", then click OK. Now double-click on Cylinder-01, go to the \"Advanced\" tab, and set the Cylinder-01 override value of \"Cylinder Slaving Option\" to \"master\".

Selecting Valve Type for Cylinder Slaving

Advanced Setup Improved Solution for Large Flow Through Cylinders

Output Setup Storage Suppression

Step 8: Real-Time Solver (requires GT-RT license)

adding real-time solver in an FRM model allows us to operate the GT suite with hardware in loop with real-time responses from the virtual engine. It requires the GT-RT license to run the real-time solver.

The simplified FRM model is shown below:

Thus any detailed model can be converted into an FRM model using the above mentioned FRM converter tool by following the steps.

Now to build a new FRM model the FRM builder tool is used. FRM builder is a tool provided by GT suite to build our own fast running engine model. A 6 cylinder CI engine model was built using FRM builder with following specifications

• Bore 102 mm stroke 115 mm CR 17
• No of cylinder 6
• CI engine
• Twin Scroll Turbine
• GT Controller

The generated engine model is shown below:

25 cases were set up and five cases were run individually:

Case 1-5:

a. Case setup:

b. Results:

Averaged compressor and turbine speed maps:

Case 6-10:

a. Case setup

b. Results:

Averaged compressor and turbine speed maps:

Case 11-15:

Results:

Averaged compressor and turbine speed maps:

Case 16-20:

a. Case setup:

Results:

Averaged compressor and turbine speed maps:

Case 20-25:

a. Case setup

Results:

Averaged compressor and turbine speed maps:

Conclusions:

1. All cases were able to produce target BMEP.
2. High-speed cases(4000 RPM) have higher BSFC values compared to low-speed cases with a disadvantage of producing less power and torque.
3. compressors and turbines operate at critical speeds in full load condition, some cases produce operating points outside the compressor maps.
4. FRM models operated in real-time speeds.