Building a Fast Running Engine Model
Building a Fast Running Engine Model (FRM)
9.1 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 (Hardwarein-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.
9.2 Building a Fast Running Engine Model (FRM) Launch GT-ISE and open the file SI_4cyl_GDI_Turbo-WOT.gtm from 'File' -> 'Examples' -> 'Engine_1D_Gas_Exchange_Combustion' -> 'Gasoline' -> 'SI_4cyl_GDI_Turbo'. This is the starting model for this tutorial. Before making any changes to the model, save the model to a local directory and run the solver to generate results that will be used for calibration and comparison of the FRM.
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.
Timestep Restricting Parts, Number of Subvolumes
To get an overview of parts that potentially limit the timestep open the SI_4cyl_GDI_Turbo.gdx result file in GT-POST. The file should be in the same directory as the model. Select RLT Contour Map -> Pipes/FlowSplits -> Flow Control -> "Minimum Courant Time Step (Explicit Circuits Only)". This will give an overview of all parts and the associated courant number. The lower the value, the more likely the part will limit the timestep. This enables the user to determine multiple parts that will limit the timestep.
Another option to determine timestep limiting parts is to select "Fraction of Timesteps Limited by Part" directly above "Minimum Courant Time Step (Explicit Circuits Only)". In contrast to the courant number only parts that limit the time step will be displayed.
Figure 1: RLT Contour Map Minimum Courant Time Step The RLT Contour map can also be used to check the number of subvolumes for each pipe modeled. The more subvolumes are used the slower the execution time will be. The Number of Subvolumes can be selected under Pipes/FlowSplits > Flow Control > Number of Subvolumes.
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. The process information is stored in a *.frm file which can be saved and reloaded at any time to review the process or to continue where you left off.
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.
The open model will be reloaded in order to assure no changes were made before starting the conversion; click "OK". If the results are ready, you will get a message indicating the results file has been detected; click "Next". If the results are not yet ready and a message indicates this, click "Back", wait for the simulation to finish, then click "Next" and "Next" again once the results file is properly identified.
In the "Accuracy Checking" dialog, select key RLTs to track the accuracy of the model as the conversion progresses. Optional Tolerances may be specified for which additional comparison plots will be generated, and the user will be warned if a particular RLT becomes outside of a given tolerance. See Figure 2 below where these RLTs and some tolerances have been filled out. These can optionally be copied in from Excel using the KeyRLTs.xlsx file located in %GTIHOME%\v2018\tutorials\Modeling_Applications\Engine_Performance\09-FastRunningModel.
Once the Accuracy RLTs and tolerances have been defined, click "Next (Begin First Step)" to begin the conversion process.
Step 1: Exhaust Manifold
The FRM Converter should now be at the Model Reduction page, as shown below. 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.
Before we apply simplifications to the exhaust manifold, the Maximum Time Step limit of 1 crank angle degree will be removed. This is a default limit that is imposed when an EngCylinder component is in the model. If the Courant Condition allows for a larger time step (by monitoring gas velocity and subvolume length in all flow components), removing this limit will allow the time step to increase in size. Click "Collapse" at the top-left of the FRM Converter to collapse it into a smaller, more manageable dialog. Then, from the "Home" tab, click on "Run Setup" and go into the "FlowControl" folder, then double-click on the "ExplicitControl" green text within the "Time Step and Solution Control Object" attribute to edit the ExplicitControl reference object. Set "Maximum Time Step" to 720, then click "OK", and "OK" again to close Run Setup.
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. This setting prefills the attributes for the design optimizer used later for model calibration steps. If accuracy is of higher importance than run-time, choose the "Simplify for Accuracy" option. This will combine the Exhaust Ports/Runners together, and left separate from the manifold volumes. If a real-time capable model is required choose "Simplify for Speed". In this case the Ports, Runners, and Manifold volumes will be combined together at once. This will be performed in a later step, whereas accuracy will be the focus for now, so proceed by clicking on the “Simplify for Accuracy” button. 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 Discretization Length in the pipe parts will be overwritten with an automatically created parameter called [dxe_FRM]. Its value will be set to 300mm. Port Heat Transfer dominates vs. Runner Heat Transfer, therefore a parameter for the heat transfer multiplier called [HTM_Exhaust_Manifold_1_Step_1] will be automatically created in all port/runner pipes Thermal tab. This parameter will be used to calibrate heat transfer in the combined volume to assure the Turbine Inlet Temperature is maintained.
To check the created parameters, launch Case Setup from the toolbar. Note that this Heat Transfer Multiplier parameter will be calibrated to match the Turbine Inlet Temperature, and so a value of 1 is simply used as an initial guess.
Click "Next (Calibration)". Note that by default, the simplified model will be preprocessed in order to assure it is ready to run before setting up calibration. Once preprocessing is complete, close the preprocessing window to progress to the Calibration page. - - - Special Considerations for Studying Coolant Heat Rejection: If Coolant Heat Rejection must be maintained (for example, if this FRM is to be coupled with a cooling system model), then the individual Valves and Port Pipes need to remain in the model. In this case, the user would simply set the discretization length of the port pipes to [DXE_FRM] and combine the Runners and other manifold volumes into a single FlowSplit using the Combine Flow Volumes wizard (Simplify Manually tab). For the Ports, the Heat Transfer Multiplier would be used to calibrate coolant heat rejection, while the remaining FlowSplit would use a unique and separate Heat Transfer Multiplier parameter to further calibrate the Turbine Inlet Temperature. Note that leaving the original port pipes, even with the increased discretization length, may result in a significant time step restriction due to how short port pipes generally are. Therefore, their length could be artificially increased (and that additional volume taken away from the downstream flowsplit) in order to allow for a significantly larger time step. Even with the increased length (and thus increased surface area), the Heat Transfer Multiplier will still be calibrated to match coolant heat rejection. - - - In the Calibration page, click "Select Case(s) for Calibration / Open Case Setup". For this conversion, we will only calibrate for the highest speed case. So, turn Off all cases except Case 1, then click OK. If additional accuracy is desired, and if the extra computational time of calibrating additional cases is acceptable, the calibration could be performed across all cases.
Click "Configure Calibration" to open up the Design Optimizer settings. Make sure "Target" is selected for "Objective". Use the value selector for Response RLT and browse to and select "MassflowAveraged Inlet Temperature" from the Turbine part, as shown below:
Notice how the Target Value for the calibration is pre-defined as a parameter. The values for this parameter are taken automatically from the results of the baseline, high-fidelity model. This will assure that the calibration will try to match the results from baseline model.
Go into the "Factors " tab to define the factor along with the Lower and Upper values for the Range, and finally the Resolution. See the screenshot below for the appropriate values. Note that the [HTM_Exhaust_Manifold_1_Step_1] parameter is automatically placed into the first column. A different parameter can be selected if desired using the value selector. Click OK in the Design Optimizer dialog, then finally click "Run calibration…" from within the FRM Converter and run the simulation. Once the optimization run is completed, close the simulation window and then click "Next" to go to the Results page. Note that the optimized parameter value has been automatically placed back in the model, and all of the original cases turned back On. Therefore, from the Results page, click "Run Model" to run the complete set of cases using the optimized value. Once the Step 1 results model has finished running, close the simulation window and click "Populate Accuracy RLT Table Below" to see a comparison of results for the RLTs which includes specified tolerances. If any tolerance is outside of the specified range, the tab will show a "!" indicator, and the text of the cell which contains an error outside of the specified tolerance will show up as red.
Click "Open Key RLT Plots in GT-POST" to launch an automatically-generated Report File (*.gu file) containing plots of (1) "Accuracy Requirements Check" for each RLT with a specified tolerance, (2) "Calibration Check" showing results for the calibration performed, (3) "Full Results" showing a comparison of all of the Key RLTs, and (4) "Simulation Run Time" showing a comparison of the Factor of Real-Time and average time step sizes. After checking model results and assuring that they are satisfactory, click "Next (Begin New Step)" to move on to Step 2.
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.
Since the pipe at the outlet of the Turbine is rather short (70mm), this pipe will be combined with the Catalyst volumes into a single FlowSplit part, see the "Simplify Manual" tab for instructions. Select the EP1_Pipe1-1 pipe along with the EP1_PDrop1-1 FlowSplit and the OrificeConn between them, then rightclick on the selection and launch the Combine Flow Volumes Wizard.
Once in the Combine Flow Volumes wizard, keep "Combine flow volumes to Flowsplit" selected and click "Next" through the wizard until the last page, "Object Attribute Definition and Object Naming". Select "EP1_PDrop1-1" at the top of the dialog, then set the object name to "CAT". The Thermal tab shows that inputs are missing. We are dealing with it later, click "Finish". Hit Close in the "Combine Volume Wizard Report".
Open up the "CAT-1" part and go to the Thermal tab. Select the radio button for "Imposed Wall Temperature". Edit (double Click) the "GasT" Reference Object. Use the value selector for the "Wireless Signal or RLT (X)" object value and replace "tav:catconn1" with "tav0:CAT-1” and click "OK". Close the object dialog for the "CAT-1" part as well.
Lastly, we need to Open Case Setup and set the value of [DIA_Exhaust_Pipes_1_Step_2] to 40 mm. This is only an initial guess, and will be used to calibrate the Turbine Outlet Pressure. In the FRM Converter, click "Next (Set Calibration)".
In the Calibration page, select Case 1 for calibration. Under "Configure calibration…", set the Response RLT to the Turbine Massflow-Averaged Outlet Pressure (trb-poa:Turbine), and set the lower and upper values of the range of DIA_Exhaust_Pipes_1_Step_2 at 35 and 45 mm, respectively.
Run the calibration, and once it is finished, click "Next". In the Results page, click "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
Name the step "Intake Manifold". Select Intake Manifold 1 from the Tagged Subsystems list. Click on "Simplify for Accuracy". Click "Yes" on the Delete Part dialog; this will be handled later. Collapse the FRM Converter to provide space to work in the model map.
Minor modifications need to be made to the Characteristic Length and Expansion Diameter attribute values for the combined volume. Open the new IM1_Plenum1-1 part and define the Boundary Data folder as shown below, with the values better representing the complete combined geometry.The characteristic length is defined as the distance that the flow entering the boundary will travel before crossing another boundary or impacting a surface. Boundary #1 represents the boundary between the flowsplit and IM1_Pipe1-1. The fluid entering the flowsplit in this direction can travel all the way across the plenum before impacting a surface, so the characteristic length is equal to the length of the plenum. The other boundaries are adjacent to the runners, where backflow from the cylinder would travel across the diameter of the plenum before impacting the plenum wall, which is why they are given a characteristic length of 70mm. The expansion diameter defines the maximum diameter that the flow may expand to after entering a boundary (or contract from when leaving a boundary). For Boundary #1, it is simply the diameter of the plenum because the fluid expands from IM1_Pipe1-1 into the plenum in a straight direction. The expansion diameters for the other boundaries are equal to the plenum diameter multiplied by 1.4. This is because as the fluid backflows into the plenum, it encounters a wider cross section than the plenum diameter to expand into. For more information on Characteristic Length and Expansion Diameter, please see the Flow manual under Modeling_Theory.
To resolve the "Delete Part" warning that was previously displayed, double-click on the EngineCrankTrain, go to the "RLT Norms" folder, and change the value of the attribute "Part Name for Manifold Volumetric Eff. Reference" to "IM1_Plenum1-1". Then, go into "Run Setup" -> "ConvergenceRLT" folder and change the first RLT Variable to "pav:IM1_Plenum1-1".
Finally, open Case Setup and check [DXI_FRM] is 200 mm, and [HTM_Intake_Manifold_1_Step_3] is 1 (this is an initial guess and will be calibrated). Expand the FRM Converter and click "Next (Calibration)" to preprocess the model and continue to the Calibration page. Note the additional dialog indicating certain Accuracy RLTs that were removed in this most recent simplification step. Select replacement RLTs associated with the new combined intake manifold so that the pressure and temperature can continue to be monitored and compared.
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.
Since the intercooler core (previously a bundle of pipes) has been replaced with a FlowSplit and "HeatExchangerConn" part. The "BP1_CAC1-2 HeatExchangerConn" part will be used to assure the intercooler outlet temperature is maintained. Double-click on the "BP1_CAC1-2 HeatExchangerConn" part and set the Imposed Fluid Temperature to 300 (this will be overridden), then click OK. Open the "BP1_CAC1-1" Flowsplit part, go to the Thermal tab and select Imposed Wall Temperature. Set the temperature to 300 (this will be overridden), then click OK. Finally, reconnect the Control links, sensing Upstream Temperature from "BP1_Pipe1-1" Pipe and Upstream Mass Flow Rate from the "6” OrificeConn upstream of the "BP1_CAC1-1" Flowsplit, and sending the actuator output to both "BP1_CAC1-1" Flowsplit (actuating Wall Temperature) and to the HeatExchangerConn (actuating Imposed Fluid Temperature).
Open Case Setup and set the value of [DIA_Boost_Pipes_1_Step_4] to 35 mm as an initial guess. Finally, Expand the FRM Converter and click "Next (Calibration)" to preprocess the model and continue to Calibration.
In the Calibration page, select Case 1 for calibration. Under "Configure calibration…", leave the Response RLT as the Compressor Massflow-Averaged Outlet Pressure (cmp-poa:Compressor). Since the wastegate controller is maintaining engine BMEP, engine air flow is also effectively maintained since the Air-to-Fuel ratio is fixed. Therefore, as the effective diameter of the Intercooler changes, the resulting compressor outlet pressure will change so that engine air flow is maintained (via the wastegate controller). Therefore, the Intercooler Diameter will be adjusted in order to maintain compressor outlet pressure. Set the lower and upper values of the range for DIA_Boost_Pipes_1_Step_4 at 30 and 40 mm, respectively.
Run the calibration, and once it is finished, click "Next". In the Results page, click "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 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.
Go into Case Setup and set the value of [DIA_Intake_Pipes_1_Step_5] to 45 mm (this is just an initial guess).
Since every subsystem has now been simplified, we will assure that there are no remaining pipes with short discretization lengths. Go to the Data tab in the GT-ISE toolbar and click "Delete Unused Objects". Then, in the Model Tree to the left, right-click on the PipeRound template and choose "Edit Parts in Spreadsheet". View the Discretization Length column to assure that only [DXI_FRM] and [DXE_FRM] are used. Click "Return to Map View". The pipes can be sorted by increasing length clicking on the "Length" column.Finally, Expand the FRM Converter and click "Next (Set Calibration)" to preprocess the model and continue to Calibration.
In the Calibration page, select Case 1 for calibration. Under "Configure calibration…", change the Response RLT to the Compressor Massflow-Averaged Inlet Pressure (cmp-pia:Compressor). . Set the lower and upper values of the range for DIA_Intake_Pipes_1_Step_5 at 40 and 50 mm, respectively.Run the calibration, and once it is finished, click "Next". In the Results page, click "Run Model" to rerun the full set of Cases. Check the model results and assure that they are satisfactory. At this point, we should have a Fast Running Engine Model running at a Factor of Real-Time of around 5 xRT and with very high accuracy. The Simulation Run Time can be checked clicking on the "Open Key RLT Plots in GT-POST" and plotting the Simulation Run Time data. The RT factor can be accessed as well by opening the model result file -> Case RLT tab -> Global -> Special -> "Factor of Real-Time". If this runtime is satisfactory for a given application, the user may click "Finish" to exit out of the FRM Converter, where the final FRM will be saved. However, if additional run simulation speed is desired, further changes can be made to the model. Since each subsystem of the model has already been simplified, we will open the latest set of results in GT-POST to identify how additional simulation speed could be achieved.
With the Results page of Step 5 still open, click on "View Results" in the Home tab of the GT-ISE toolbar. This will launch the results file (*.gdx) of Step 5 in GT-POST. In the GT-POST toolbar -> Home, click the "No Map" button . Then click on the "Report Tables" tab, expand the group "Flow Solution Numerics", and view the table "Time Step Restriction (1)" (either with a double-clicking or by highlighting and pressing F4). Notice how the part EM1_Collector1-1 is restricting the time step 96% of the time. Therefore, the Exhaust Manifold will be simplified further in order to achieve larger time steps and, thus, a faster runtime.
Go back to GT-ISE and click "Next (Begin New Step)" in the FRM Converter.
Step 6: Additional Changes
Name the step "Additional Changes". Select Exhaust Manifold 1 from the Tagged Subsystems list. Click on "Simplify for Speed".
Click "Next (Calibration)" to preprocess the model and continue to Calibration. In the Calibration page, leave all cases enabled for calibration. This may take some additional time to calibrate vs. only calibrating for Case 1, but it will result in better accuracy across all operating conditions. Under "Configure calibration…", change the Response RLT to the Turbine Massflow-Averaged Inlet Temperature (trb-tia:Turbine). Set the lower and upper values for HTM_Exhaust_Manifold_1_Step_6 of the range at 0 and 2, respectively. Set the Resolution (% of Range) to 1.
Run the calibration, and once it is finished, click "Next". In the Results page, click "Run Model" to rerun the full set of Cases. Check the model results and assure that they are satisfactory. The model should now be running around 1 xRT. In the FRM Converter, click "Next (Begin Next Step)".
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".
For the full cylinder slaving to function, each Valve must be specified as either an Intake or Exhaust valve. Find the ValveCamConn template in the model tree on the left and select "Edit Parts in Spreadsheet" view. The intake and exhaust valves are easy to distinguish. The intake ones start with "IM1_PortRun” and the exhaust ones start with "EM1_PostRun". Go to the Output folder and set "Valve Type for RLT Variable Calculations" to "intake", respectively "exhaust"Expand the FRM Converter and click "Next (Calibration)" to preprocess the model and continue to Calibration. Calibration will not be performed for this step, so simply click Next to get to the Results page without performing calibration, then click "Run Model" to run the full operating range with this latest modification.
With the final run complete, view the results and assure that the accuracy is acceptable. The runtime of the model should now be below 1 xRT for all operating conditions. Note that the runtime is affected by the CPU, stored data, monitors as well as any other processes that are running while the simulation is progressing, so it is possible this final model may not run below 1 xRT on a given machine. To achieve faster runtime suppress storage in Output Setup -> Data_Storage like Instantaneous Plots, Time RLTs and if run local turn off monitors.
Step 8: Real-Time Solver (optional)
Click "Next (Begin Next Step)" in the FRM Converter. Name this new step "Real-Time Solver", then collapse the FRM Converter. To run with the real-time solver, the license type of the model must be changed. However, certain templates are not allowed with the real-time solver, and so they must first be removed from the model.
In the Main assembly delete the Turbo_Speed-2 monitor part coming off of the turbocharger shaft. Next, right-click on one of the EngCylinder parts and choose "Edit Parent Object". Go to the Advanced folder and set "Evaporation Object" to "ign" and click OK. Next, open the WG_Controller, go to the Convergence folder, and set "Steady State Error Tolerance" to "ign". Lastly, in the GT-ISE toolbar, go to the Data tab and click the arrow next to "Delete Unused Objects" and choose "Objects and Templates". Expand the FRM Converter and click "Next (Calibration)" to preprocess the model and continue to Calibration. Calibration will not be performed for this step, so simply click Next to get to the Results page without performing calibration, then click "Run Model" to run the full operating range with the Real-Time Solver.
Note that most RLTs are ignored when running the RT solver in order to improve the simulation speed. Therefore, certain results will not be automatically compared using the "Populate Accuracy RLT Table Below" or "Open Key RLT Plots in GT-POST" buttons. However, they can still be used for certain results that are stored (e.g. Engine BMEP and flow component Temperatures and Pressures).
To complete the FRM Conversion process, click "Finish" in the FRM Converter. This will save the final model into the \SI_4cyl_GDI_Turbo-WOT_FRM_FINAL\ subdirectory. To continue working on the model, or to review the process, the *.frm file can be reloaded at any time into the FRM Converter to continue the process where it was left off.
If Real-Time cannot be achieved with an FRM, another method to reduce a detailed model is to build a Mean Value Engine Model. The process to build a Mean Value engine is more complex and time consuming and less physics are included in a mean value engine model, so the FRM is the preferred solution. However, if an FRM cannot meet the run-time requirements (for example, if trying to run a large number of cylinders on a HiL), then a Mean Value engine model may be required. The next tutorial will show the process of building such a model.
- Build FRM Model for following configuration using FRM builder approach (50 marks)
- Bore 102 mm stroke 115 mm CR 17
- No of cylinder 6
- CI engine
- Twin Scroll Turbine
- GT Controller
- Run all cases
The FRM model had been bulided by using FRM build tool and the simulation of the model hadd been done and result are as follows,
\
The engine model had been simulated for six different rpm's with various load types.
The can able to produce 990N-m torque at 2500rpm at full load condition and it can produce 329.9Kw power at 3500 rpm.
BSFC rangr of this model is 380-194g/Kw-hr for various rpm and load conditions.
A/F ratio range 17.45-52.5
CONCLUSION:
FRM model help us to increase the time step size and to decrease the simulation time. 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.