Turbochargers in GT-SUITE

TURBOCHARGERS IN GT-SUITE

There are different varieties of turbochargers such as:

• Fixed Turbo charger model
• Waste gate Turbo charger model
• Variable Geometry Turbine (VGT) model
• 2 Stage Turbo charger model
• E-Turbo model

Fixed Turbocharger model:

In this model, the geometry of both the compressor and the turbine is fixed and cannot be altered after installation for performance purposes. This is the most basic type of turbocharger.

Waste gate Turbocharger model:

In this model, the geometry of the turbine or compressor can be manipulated as that when the air flow is beyond a certain limit or more than necessary, we could redirect the exhaust kinetic energy to the exhaust itself and not overload the turbocharger. This is done by ways of pneumatic actuators or mechanical connections which could handle the variations.

Variable Geometry turbine model (VGT):

In this model, the geometry of the compressor remains constant but the turbine geometry can be manipulated using outer fans and other flow altering blades that can contract or expand the air flow with respect to the demand for performance of the engine. This is a very famous and common model for Turbocharger design for its advantage to control air flow in a very easy yet controlled manner.

2 Stage Turbo charger model:

These kind of models utilize a low pressure and a high pressure turbine or a dual stage turbo that is required to pump in more air into the engine and subsequently increase the performance of the engine. These are only utilized in high end performance vehicles and are very costly and powerful.

E-turbo model:

In this model, the turbine is given a direct boost using an electric motor apart from the exhaust kinetic energy of the turbocharger to reduce the turbo lag of the engine and improve performance. These are also used only in performance vehicles due to their complexity and cost.

GT-Suite Examples:

Normal Turbocharger model:

VGT model:

Twin Turbo model:

Waste gate model:

Other than this, there are some tutorials too in GT-POWER that handle turbocharger modeling. We can explore those tutorials now.

Tutorials:

As we can see, both the 6cylDI final and the turbo step 1 begin models are the same. It is about a basic non predictive engine model where the initial conditions of even the compressor and turbine are provided for direct simulation of only the engine parameters.

As we can see, the initial conditions just provide the pressure and wall temperature boundary conditions which will then be used for the engine simulation.

But for the final model in tutorial 7, the complete assembly of turbine and compressor with the interconnecting shaft is included. By this way, we are also including the simulation of conditions in the turbocharger and hence, we include parameters like the compressor and turbine maps for the working of the turbocharger.

If you look closely, the turbine has two inlets which are from separate channel flows of the exhaust from 4 cylinders. This kind of configuration is called the twin scroll turbine.

The inlet to the turbine consists of two separate flows from the engines. These kind of setups are used in bigger cylinder engines, to not create turbulence in the machinery by mixing all the exhaust kinetic energy at once, but combining, say, 3 cylinder gases at once and feeding them in each module.

For the compressor map and turbine map, if we double click the respective parts, we can see how they have calibrated them.

Now, for a fixed turbocharger, we only have 1 rack position which explains the geometry configuration of the turbocharger as only one and not including variable geometry. When we select the compressor or turbine map object file, we fill get a list of functional data that is used to map the working of the turbocharger components.

For example, these are the values entered for configuring of a VGT turbine map. It is in terms of RPM and the corresponding data points related to it for the functioning of the turbine are given. These are industry and engine specific data and is given by the manufacturer of the turbocharger as to predict the possible ranges of efficiency values using the working conditions of the turbine and compressor.

We see that the compressor map also is similar to the turbine map and is taken from company specifications.

Now, we can turn on the speed and efficiency monitor map from the dialog box of the compressor from our final tutorial 7. We can also add some cases regarding the change of altitude and mass of fuel injected to analyze the change in performance of the turbocharger.

When we run the simulation, we can now get live feed of the data points in the speed and efficiency map of the turbocharger. For the compressor, we always look at the efficiency map and make sure that the target values are close to the heart of the map in the efficiency. The X and Y axes consists of mass flow rate and pressure ratio respectively.

As we can see, the default simulation runs and the operating point is determined by the small black outline circle in between the efficiency map. Since the default map consists of only one case, we can see only one outline circle to define its operating point. It has good efficiency but the RPM values are high for the compressor and needs to be designed for better rigidity.

Now when we add our own altitude and fuel consumption parameters to the case setup, the revised setup would be:

Operating points and efficiency plots:

Compressor:

Turbine:

In which application Variable Geometry Turbine is beneficial?

VGTs tend to be much more common on diesel engines, as lower exhaust temperatures mean they are less prone to failure. Early gasoline-engine VGTs required significant pre-charge cooling to extend the turbocharger life to reasonable levels, but advances in technology have improved their resistance to high-temperature gasoline exhaust, and they have started to appear increasingly in gasoline-engined cars. Typically, VGTs are only found in OEM applications due to the level of coordination required to keep the vanes in the most optimal position for whatever state the engine is in. In trucks, VGTs are also used to control the ratio of exhaust recirculated back to the engine inlet.

There is a separate model just to demonstrate the use of VGT in GT-SUITE for diesel engines.

If we explore this model, we can see that it has a semi predictive intercooler and a predictive EGR and VGT where the turbine is alone variable with different racks and consists of a separate rack controller.

Rack controller is nothing but the bandwidth of variations that can be incorporated into the geometry of the turbine from 0.1, i.e, 10% of opening for exhaust flow to 100%. Each of the percentage case of rack control consists of a separate compressor and turbine map data sheet that is pre-determined using experiments from the company itself.

The turbine maps are alone modified coz they contain different rack positions and hence it is a variable geometry turbine turbocharger. The compressor data contains only 1 rack, i.e, there is a constant fixed geometry profile for the compressor.