Various Turbocharger application in GT Power

1. Different types of Turbocharger 

  • Fixed Geometry turbocharger - The amount of exhaust gas into the turbocharger cannot be varied, the turbocharger is optimized for the particular operating condition & the turbine size and/or A/R ratio tend to be relatively large for a given application because of the need to size the turbocharger so that at the highest flow conditions, the turbocharger does not Overspeed or provide excessive boost pressure.
  • Wastegate turbocharger - It consists of the bypass gate so at high power output the bypass value gets open & exhaust gas is directly let out. The main advantage is that the size of the turbocharger is reduced due to the gate.
  • 2 stage turbocharger - Twin-turbo designs have two separate turbochargers operating in either a sequence or in parallel. In a parallel configuration, both turbochargers are fed one-half of the engine's exhaust. In a sequential setup, one turbocharger runs at low speeds and the second turns on at predetermined engine speed or load. Sequential turbochargers further reduce turbo lag but require an intricate set of pipes to properly feed both turbochargers.
  • Variable geometry compressor turbocharger - Variable-geometry turbochargers use moveable vanes to adjust the air-flow to the turbine, imitating a turbocharger of the optimal size throughout the power curve. The vanes are placed just in front of the turbine like a set of slightly overlapping walls. Their angle is adjusted by an actuator to block or increase airflow to the turbine. This variability maintains a comparable exhaust velocity and back pressure throughout the engine's rev range. The result is that the turbocharger improves fuel efficiency without a noticeable level of turbocharger lag.
  • E turbo - A hybrid turbocharger is an electric turbocharger consisting of a high-speed turbine generator and a high-speed electric air compressor. The turbine and compressor are high-speed aero machines, as in a conventional turbocharger. The electrical motors run at speeds more than 120,000 rpm and when used as generators generate electricity at up to 98.5% electrical efficiency. High electrical efficiency is paramount because there is no mechanical link between the turbine and the compressor. This design flexibility leads to further improvements in turbine and compressor efficiency, beyond a conventional turbocharger.

Example from GT Power 

  • FRM_Diesel_VGT_EGR - This example demonstrates the capabilities for models to run near real-time with simplified flow paths. The model is the result of converting the example model "Diesel_VGT_EGR".
  • xRT-3pt4L-V6-TwinTurbo-GDI - GT-POWER-xRT example model of a 3.4L twin/parallel turbo V6 direct-injected (GDI) gasoline engine.
  • Diesel_6cyl_TC - This example is a basic model of a diesel engine. It demonstrates many of the objects which can be used to model a turbocharged, compression ignition engine.
  • Diesel_VGT_EGR - Diesel VGT EGR model using charge air cooler. This intercooler is an air-to-air intercooler that is modeled using a "semi-predictive" method based on heat exchanger effectiveness.
  • Diesel_WGController - This example demonstrates how to control the boost pressure of a turbocharged engine using a model-based 'ContTurboWG1Stage' wastegate controller.
  • 3pt4L-V6-TwinTurbo - Example model of a 3.4L twin/parallel turbo V6 direct-injected (GDI) gasoline engine.

2. Tutorial 6:

The six-cylinder engine was built using from the basic model of a single-cylinder engine where the inlet & outlet end environment are been deleted.

The intercooler for the intake is been assembled, the template library is used to import the parts to the model.

The inlet condition is set to the compressor outlet condition and intercooler is mainly used to reduce the temperature of the intake air as at high temperature the density reduces which will reduce the volume of the air intake. The intercooler model is run to check for the pressure drop of 0.2 bar across the cooler to check whether all conditions are set properly. After the verification, the model is then attached six-cylinder model.

The intercooler effective is added to the model that actuates the intercooler outlet gas temperature based on intercooler effectiveness data.

Tout = Tin - (Intercooler effectiveness) * (Tin - Tcoolant).

Where:

Tin = Temperature of intercooler inlet gas

Tout = Temperature of the intercooler outlet gas

Tcoolant = Temperature of intercooler coolant

The next process is the addition of pipes depending on the flow of the gases and the conditions are set to default. 

Tutorial 7 

The four different models were set with the same environment conditions only the parts used are different and the output of each model is compared.

i) Without Turbocharger

The compressor outlet and the turbine inlet conditions have already been set through EndEnvironment boundaries. In this way, the base engine performance can be tested for errors. This would indicate if the base engine model (manifolds, valves, cylinders, etc.) is properly modeled before we start complicating the system with the turbocharger.

Model

ii) With Compressor only

Start by deleting the EndEnvironment part that represents the compressor outlet conditions. Next, open the template library and copy the 'Compressor' template from the Flow                -->Turbines, Pumps and Compressors folder and 'SpeedBoundaryRot' template from the Mechanical --> 1-D Rotational Mechanics folder into the project library. Double-click on the 'Compressor' template and start filling in the object values below as the values provided for our conditions. The data related to the compressor were explained in detail by the Compressor-turbine model below.

Model

Compressor Map data

Output

iii) With turbine only

The inlet conditions of the engine are provided from the compressor outlet condition which is obtained from the previous model are set. 

Copy the 'Turbine' template from the template library into the project library. Double-click on the 'Turbine' template and create an object with the following values. Note that the inlet and outlet pressure flag attributes should be set according to how the turbine performance data was measured. For turbines, turbocharger suppliers commonly measure total inlet pressure and static outlet pressure.

iv) With turbine and compressor

The combination of both the compressor and turbine have attached to the model but these model are not coupled and 

v) With turbine and compressor coupled

Now we can connect the compressor and turbine using a part created from the 'ShaftTurbo' template. Copy the 'ShaftTurbo' template from the Mechanical --> Engine Mechanics folder of the template library into the project library and delete the 'SpeedBoundaryRot' parts and their connections from the project map. Create an object from the 'ShaftTurbo' template called "Shaft" and fill in the attributes with the values shown in the figure below. The initial shaft speed is important for making the model converge in a reasonable number of cycles.

The model is run for the 4 different cases and the plot of these done

Turbine plot

i) 3600 rpm

ii) 3000 rpm

iii) 2400 rpm

iv) 1800 rpm

The fixed geometry is set to obtain maximum efficiency for the single rpm so the efficiency decreases with the rpm variation. The value at 3600 rpm is obtained as 80% efficiency and so in order to have constant efficiency the variable geometry turbocharger is used. 

The benefits of variable geometry turbines over wastegate turbines include :

  • no throttling loss of the wastegate valve
  • higher air-fuel ratio and higher peak torque at low engine speeds
  • improved vehicle accelerations without the need to resort to turbines with high pumping loss at high engine speeds
  • potential for lower engine ΔP (the difference between the exhaust manifold and intake manifold pressures)
  • control over engine ΔP that can be used to drive EGR flow in diesel engines with High-Pressure Loop (HPL) EGR systems
  • a better ability to cover a wider region of low BSFC in the engine speed–load domain;
  • ability to provide engine braking
  • ability to raise exhaust temperature for after-treatment system management.

Diesel VGT EGR

The engine is a 4-cylinder, four-stroke, direct injection, 2L diesel engine. The intake system consists of the air piping upstream of the compressor inlet and contains a simple model of an airbox. The airbox is modeled as a group of interconnected flow splits that represent the total volume of the airbox. At the inlet and outlet of the air box, "bellmouth" orifice connections are used to model smooth transitions. The intercooler is found downstream of the compressor outlet. This intercooler is an air-to-air intercooler that is modeled using a "semi-predictive" method based on heat exchanger effectiveness.

The intake manifold is modeled as aluminum using heat conduction objects to calculate the wall temperatures. The fuel is injected directly into the cylinders. Both the injection timing and the injection profile are looked up using an 'RLTDependence' as a function of engine speed and injection rate. The exhaust manifold is modeled as cast iron using heat conduction objects to calculate the wall temperatures. The model includes an exhaust gas recirculation (EGR) system to transport exhaust gases from the exhaust manifold back to the intake manifold. The turbocharger in this model contains a fixed geometry compressor and a variable geometry turbine (VGT). For the VGT, there are 5 different sets of turbine map data entered at each of 5 VGT rack positions. A full vehicle exhaust system is modeled downstream of the turbine outlet. The geometry of a Diesel Oxidation Catalyst (DOC) is modeled using a 'CatalystBrick' part.

The model is run for the 5 different cases

The turbine is set for the 6 different rack array & for each case map data are set.

Compressor data 

Output data

The pressure rise decrease in the turbine and the compressor pressure rise increases pressure ratio must be always greater than 1 so the turbine & compressor is working & the efficiency of the compressor is high but the turbine efficiency is less this due to variation of the vanes depending on the power output so there is more loss.

 

 

 

 


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First Assignment
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