Turbocharger modelling
Q.1. List down different TC and locate examples from GT Power.
Ans. There are mainly 3 types of turbocharger that are commonly used in practice:
1. Fixed geometry Turbocharger: This is the simplest form of turbocharger whose geometry is fixed.We cannot control the geometry and speed of the turbine or compressor of thiss turbocharger which makes it prone to the mechanical failure at very higher speed.
We can locate this turbocharger in GT power as shown in figure 1.
Figure 1
2. Wastegate turbocharger: In this type of turbocharger the amount of exhaust gas going to the turbine can be controlled by a small opening called wastegate.Due to this mechanism the speed of the turbine can be controlled and hence can be prevented to mechanical failure.
Figure 2 shows the wastegate turbocharger in a diesel engine in GT power.
Figure 2
3.Variable Geometry Turbocharger or VGT: In this type of turbocharger there are vanes around the turbine entry which controls the amount of exhaust gases entering into the turbine inlet.So in that way we can control thee rpm of the turbine and hence the compressor.This is the most advanced version of the turbocharger and hence most costly.
Figure 3 shows the example of the diesel engine model with VGT turbocharger in GT power.
Figure 3
Q.2. Explore tutorial number 6 and 7.
Ans: Figure 4 will show the tutorial 6 which is 6 cylinder diesel engine.
Figure 4
This is a diesel engine with a square cylinder configuration.The cylinder geometry are as follows:
Bore = 100mm.
Stroke = 100mm.
Connecting rod length = 220mm.
Compression ratio = 16.5.
Lets run the simulation and see the results.Results will be shown in figure 5.
Figure 5
Now let us see the tutorial 7 which is nothing but the same engine with a turbocharger,see figure 6.
Figure 6
We can clearly see from the figure 6 is that the turbine is connected to the exhaust port whereas the compressor is connected to the inlet port.The turbine and the compressor is coupled by the shaft whose moment of inertia is 0.0005kg-m^2.
Now run the simulation and see the results and also compare it with figure 5.See figure 7 for the results.
Figure 7
Now compare these results and see what happens to the performance of the engine when a turbocharger is connnected to it.
See table 1.
Table 1
From this table we can clearly see that the overall engine performance is improved by adding the turbocharger to the engine system.
Q.3. Plot operating points on compressor and turbine maps.
Ans: Figure 8 and 9 will show the operating points on compressor and turbine maps respectively.
Figure 8 Figure 9
Q.4. In which application Variable Geometry Turbine is beneficial?
Ans: VGT devices are designed to increase boost pressure at low speeds, reduce response times, increase available torque, decrease the boost at high engine speeds to prevent over-boosting, reduce engine emissions, improve fuel economy and increase the overall turbocharger operating range.
Q.5. Explore example- Diesel VGT EGR and understand the modeling part.
Ans: Figure 10 will show the example file of Diesel VGT EGR.
Figure 10
In this model we can see that the exhaust exit is divided into 3 parts.One part of the exhaust gas goes through the EGR system,one part goes through the aftertreatment system and the last part of the exhaust gas goes through the VGT turbocharger system.
The turbine part of the turbochrger is controlled by the VGT rack control module which controls the position of guide vanes of the turbo housing.
The rec boost tempelate is connected to the vgt rack control .It receives the signals from the ECU wirelessly to tell the VGT rack controller about the boost pressure at a particular RPM.If the boost pressure is going high which needs to be lower the VGT rack controller changes the position of the guide vanes that permits only required amount of the exhaust gases so that the mechanical failure of the turbo can be prevented.
This technology helps to reduce the turbolag,and allow the engine to perform more better at every operating ranges.