Assignment 7

OBJECTIVE:

• Explore tutorial number 9 and write a detailed report 
• Build FRM Model for following configuration using FRM builder approach
• Bore 102 mm stroke 115 mm CR 17
• No of cylinder 6
• CI engine
• Twin Scroll Turbine
• GT Controller
• Run all cases

FRM Modelling :
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. (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.

1. Converting a 4- cylinder GDI turbocharged model in a FRM model.

In this model a 4-cylinder 2.0 liter turbocharged Gasoline Direct Injection (GDI) engine is used. 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. Following is the original model of the engine.

1. Exhaust System :
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.
Following is the tab, which pops up when FRM convertor option is used, and accordingly we need to convert the systems in FRM.

GT-Power automatically calibrates the exhaust manifold and creates a single volume for the complete system.
After the calibration the model needs to be post-processed and RLT plot accuracy table is shown in GT-suite which has to be checked as follows.

Following is the converted model for exhaust manifold

After running the simulation we can move to the next step to convert another system in FRM.
Same procedure is used to convert the sub-systems into FRM models. The subsystem model are as follows.

2. Exhaust pipes:

3. Intake manifold:

4. Compressor outlet pipes:

5. Intake pipes:

6. Cylinder slaving:

FRM builder approach:

The modelling is done by choosing the option called FRM builder.

First we choose the architecture type

Next we input the cylinder dimensions

Then the turbocharger type is selected

we choose the engine type

Then the control logic

GT-suite Controller consists of 3 controller configurations :
1. Waste Gate controller : It takes input in the form of boost pressure of exhaust gases and gives signal to the turbocharger by controlling the Waste gate diameter. Hence by controlling the diameter the pressure inside the turbocharger is controlled and optimised acccording to the requirement.
2. EGR Controller : It gains input signal in form of air mass flow rate, and it controls the EGR gas by controlling two components. One, EGR valve diameter which determines the amount of gas to be flowed in the intake side, and two, The throttle Angle, controlled by a throttle body. A throttle body is incorporated inorder to control the intake pressure, if the intake pressure is more than the exhaust pressure, gasses won't flow from exhaust to intake. Hence intake pressure is kept lower than the exhaust pressure using throttle body.
3. Controller for Direct Injection : It receives the input signal from three measurements, BMEP, Engine speed and average air flow, it calibrates the fuel injection rate based on these 3 quantities and sends signal to the injector.

Final FRM model:

Results:

• From the above results it is observed that FRM model solves the model in very less time.
• The BSFC increases for high speed values as seen in FRM builder approach.