Week-6 : Turbocharger Modelling

ASSIGNEMNT 6- TURBOCHARGER MODELLING

Aim:

To perform various activities to understand turbocharger modelling using GT-Suite.

Introduction:

For this particular assignment, we would be performing different activities to understand turbocharger modelling in GT-Suite. To do this, we would solve different questions. Thus this assignment has been divided into different sections, based on the questions.

Question_1:

Turbocharger is an add-on device used primarily in diesel engines to provide intake air boosting. The various types are:

• Fixed geometry:
  Single turbo

2. Twin turbo
3. Twin Scroll Turbo

• Variable Geometry:

1. Variable Geometry Turbo
2. Variable Geometry Twin Scroll

As a high boost prevention device, these turbos can be fitted with a ‘WasteGate’ which can regulate the exhaust flow to the turbine in case too high a boost is being provided.

Some of the tutorials that have been located are from the GT Suite software are:

• Xrt-3pt4L-V6-Twin-Turbo-GDI
• CompressorTurbine-Flow
• CompressorTurbine-Maps
• SimpleTurbineCompressorTwoStageMeanValue
• SI_4cyl_GDI_TurboThermal
• DI_VGT_EGR
• 6cylDI-final
• Turbo_Step_1/2/3/4/5
• Diesel_VGT_EGR
  

Question_2:

In this question we will be exploring the tutorials:

• 6cylDI-final
• Turbo_Step_1/2/3/4/5

First we will be looking into the 6cylDI-final tutorials. This is a typical 6-cylinder direct injection diesel 4.7 litre engine which is turbo charged as well. As we have seen in multiple assignments till now, certain components such as EngCylinder, EngineCrankTrain, PipeRound, etc have been used to model the entire system. Refer Fig_1 for the model.

Also, this system is turbocharged as well, with the only difference that there is no turbocharged modelled. Instead, the BoundaryPressure component has been given a pressure of 2.4 bar instead. After this turbocharging, the compressed charged is cooled using intercooler.

Now we will look into the Turbo_Step_1/2/3/4/5 model, in total 5 models. So, in 5 steps, the previous model that we used has been modified to include a turbocharger in 5 steps. Refer Figs_1/2/3/4/5 for the same. The steps are:

1. The first step is the same as that of the model we have previously discussed, no changes
2. In the second step, a compressor and a speed defining module has been added
3. In the 3^rd step, instead of exhausting the gasses to the environment, a turbocharger module has been added with its speed defining component
4. In this step, there is no difference component wise, only a few settings have been changed
5. Finally, a mechanical connection between the turbocharger and the compressor has been established using a shaft component.

Question_3:

Please refer Fig_6 and Fig_7 where both the maps an the respective operating points have been plotted.

Question_4:

The Variable Geometry turbocharger is a turbine which can change its geometrical characteristics to change the boost level that can be provided by the turbine. Its main application is in High end cars, given the cost barriers. But the detailed technical advantages of using this turbine are:

• Improving low speed torque characteristics by increasing boost. Thus gives a much higher and flatter torque output from the engine.
• Reduce turbocharger lag by improving boost
• Prevent over boosting at higher engine speeds
• Improving engine emissions
• Reduce fuel consumption
• Give the engine a higher flexibility in terms of boost required.

Question_5:

This model displays a 4-cylinder 2 litre direct injection diesel engine. Also, a VGT (Variable geometry turbine) has been modelled, which is one of the main differences as compared to the previous model. Refer Fig_8 for the same.

As we had seen in the previous 6-cylinder example, there is not much difference as how the components like the turbine and compressor are modelled. The main difference wrt VGT lies in the use of a VGT Rack control which controls the VGT settings of the turbocharger turbine portion. This is the component that defines that this particular turbine is a VGT one. Also modelled is the muffler circuit after the turbine which is used to supress any unwanted NVH violations.

Alongside the VGT, other components which have been modelled to the component level like Airbox, Intercooler, EGR cooler also add on to the complexity of the model.