Assignment 6

A. List down different TC and locate examples from GT Power

Turbocharging:-

1. In turbocharging, the supercharger is being driven by a gas turbine which use the energy in the exhaust gases. There is no mechanical linkage between the engine and the supercharger. The major parts of a turbocharger are turbine wheel, turbine housing, turboshaft, compressor wheel, compressor housing and bearing housing.
2. During engine operation, hot exhaust gases blowout through the exhaust valve opening into the exhaust manifold. The exhaust manifold and the connecting tubing route these gases into the turbine housing, they strike on the fins or blades on the turbine wheel.
3. When the engine load is high enough, there is enough gas flow and this makes the turbine wheel to spin rapidly. The turbine wheel is connected to the compressor wheel by the turboshaft. As such, the compressor wheel rotates with the turbine which sucks air into the compressor housing. Centrifugal force throws the air outward.
4. This cause the air to flow out of the turbocharger and into the engine cylinder under pressure. In the case of turbochargine, there is a phenomena called turbolag. It refers to the short delay period before the boost or manifold pressure increase. This is due to the time the turbocharger assembly takes the exhaust gases to accelerate the turbine and compressor wheel to up.

Type of Turbocharger are as follows:-

1. Single Turbo:-

• Single turbocharger are what most people think of as turbo. By differing the size of the element within the turbo, completely different torque characteristic can be achieved. Large turbo provide higher level of top end power, while list smaller turbo can spools faster and provide better low end power. They are cost effective way of increasing engine power and efficiency and such have become increasingly popular, allowing smaller engine to increase efficiency by producing the same power as larger naturally aspirated engines, but with a lower weight. They do however tend to work best within a narrow RPM range and driver will often experience 'turbolag' until the turbo start to operate within its peak rev band.

2. Twin turbo:-

• As the name implies twin-turbo means adding a second turbosupercharger to an engine. In the case of V6 or V8 engine, this can be done by assigning a single turbo to work with each cylinder bank. Alternatively one smaller turbo could be used at low RPM with a larger turbo for higher RPMs. This second configuration known as twin sequential turbocharging allows for a wider operating RPM range and provides better torque at low revs, reducing turbo lag, but also gives power at high RPM. Unsurprisingly having two turbo, significantly increase the complexity and associated costs.

3. Twin Scroll turbo:-

• Twin Scroll turbocharger require a divided inlet turbine housing and exhaust manifold that pair the correct engine cylinder with each scroll, independently. For egs, in a four cylinder engine with a firing order 1-3-4-2 cylinder 1 and 4 might feed to one scroll of the turbo while cylinder 2 and 3 free to separate scroll. This layout provides more efficiently delievery of exhaust gas energy to the turbo and result and help provide denser purer air into each cylinder. More energy is sent to the exhaust turbine meaning more power. Again there is a cost penalty for addressing the complexity of a system requiring complicated turbine housing, exhaust manifold and turbos.

4. Variable Geometry Turbocharger (VGT):-

• Typically, VGT include a ring of aerodynamically shaped vanes in the turbine housing at the turbine inlet. In turbo for passenger car and light comerical vehicles, these vanes rotate to vary the gas swirl angle and the ds area. These interval vanes alter the turbo area to radius ratio allows the turbo to quickly speed up by increasing exhaust gas velocity and at higher revs the AIR ratio increase, there by allowing increased air flow. This result in a low therehold reducing turbolag, and provide a wide and smooth torque band.
• While list VGT are more typically used in diseal engine where exhuast gases are lower temperature, until now VGT have been limited in petrol engine application due to their cost and the requirement for component to be made from exotic heat resistant material to prevent damage. This has restricted their use to application within luxury high performance engine.

5. Variable Twin Scroll Turbocharger (VTS):-

• A VTS turbocharger combine the advantage of a twin scroll turbo and a variable geometry turbo. It does this by use of valve open can allow for the exhuast gases to split to both scrolls. The VTS turbocharger design procedure a cheaper and more robust alternative to VGT turbo, meaning it is value able option for petrol engine application.

6. Electric Turbocharger:-

• An electric turbocharger is used to eliminate turbo lag and assist a normal turbocharger at lower engine speed where a conventional turbo is not most efficient. This is achieved by adding an electric motor that spin up the turbo compressor from start and through the lower rev until the power from the exhuast volume is high enough to work the turbocharger. This approach makes turbo lag a thing of the past and significantly increase the RPM band within which the turbo will efficiently operate. It appear that electronic turbo are the answer to all the negative characteristic of convential turbocharger, however there are some disadvantage. Most are around cost and complexity as the electric motor be accomdate and power plus also cooled to prevent reliability issue.

Example in GT:-

FIXED TURBOCHARGER:-

2. WASTEGATE TURBOCHARGER:-

3. VGT TURBHOCHARGER:-

B. Explore tutorial number 6 and 7

Tutorial 6:-

In this model the inlet condition to the manifold as like the compressor input to the manifold, without using the compressor template and similar to the exhaust also, instead of using turbine at the end of the model, the ambient condition is modified accordingly.

The pressure and the temperature is defined as like the compressor output.

Tutorial 7:-

In this tutorial the compressor and the turbine is modelling using the data and also the map files can be used *cmp format and *trb format for turbine.

Compressor Map Data

Compressor map data, typically supplied by the compressor's manufacturer, and creates a version of the map that is interpolated between the given data points and extrapolated to a pressure ratio of 1.0 and speed of 0.0 RPM. The data must be corrected before it is entered, so that the 'Compressor' component can calculate accurately the performance of the compressor. There is an option to extrapolate data to higher speeds. It is possible to enter data for which the pressure ratio is less than 1.0, to model an "overblown" condition.

If this object is called directly from a 'Compressor' component, the map is read directly (i.e. the map is stored in memory), but there in an option to save the interpolated and extrapolated map into an external file, which the 'Compressor' may subsequently use independently of this reference object.

Turbine Map Data

Turbine map data, typically supplied by the turbine's manufacturer, fits it to equations that have been shown to represent the data well and extrapolates the map to a wider range of pressure ratio and reduced speed, so it may be used in a simulation. Fitting will remove irregularities in the data caused by the measurements and extrapolation is always needed to fill the edges of the map down to low speeds and low pressure ratios. Extrapolation to speeds and pressure ratios above that in the raw data is also possible.

If it differs from 'TurbineMap' in that the data specified here is reduced, thus eliminating the need for a reference temperature or reference pressure (see mass flow rate and speed units specified below). 'TurbineMapGrid' must be used when the input data is to be used without interpolation.

C. Plot operating points on compressor and turbine maps

1. Compressor Map:-

• The compressor operating behaviour is generally defined by map showing the relationship between pressure ratio and volume or mass flow rate. The useable section of the map relating to centrifugal compressor is limited by the surge and choke line and the maximum permissible compressor speed.

• Pressure Ratio - 3.654 Pa
• Reduced Mass Flow rate - 0.076635 kg/s

2. Turbine Map:-

• Turbine map is oriented differently than the compressor map with the pressure/expansion ratio on the horizontal axis and the corrected flow on the vertical axis, turbine are also known as expanders as the gas start off at high pressure entering the turbine and expand to a lower pressure as its exist the turbine. Therefore, when speaking specifically about turbine, the pressure ratio is also known as expanison ratio. Turbine efficiency also Hooks different as compared to the compressor map, there a efficiency line which correspond to each compressor speed line with the efficiency values also plotted on the vertical axis. The turbine map also has corrected mass flow rate and corrected speed just like the compressor map. However, one different is how the turbine pressure ratio is calculated. The pressure ratio on the turbine sides uses total pressure at the turbine inlet and statics pressure at the turbine outlet.

• Pressure Ratio - 3.043 Pa
• Reduced Mass Flow rate - 0.045252 kg/s

D. In which application Variable Geometry Turbine is beneficial?

• Application in which VGT is beneficial are as follows:-

1. No throttling loss of the wastegate valve;
2. Higher air–fuel ratio and higher peak torque at low engine speeds;
3. Improved vehicle accelerations without the need to resort to turbines with high pumping loss at high engine speeds;
4. Potential for lower engine ΔP (the difference between exhaust manifold and intake manifold pressures);
5. Control over engine ΔP that can be used to drive EGR flow in diesel engines with High Pressure Loop (HPL) EGR systems;
6. A better ability to cover a wider region of low BSFC in the engine speed–load domain;
7. Ability to provide engine braking;
8. Ability to raise exhaust temperature for aftertreatment system management.

E. Explore example- Diesel VGT EGR and understand the modeling part

Diseal VGT EGR Model:-

The VGT is highly beneficial for the commerical vehicle like automobile and also in some high end cars, because the VGT cause the change in blade geometry when the there is any requirement. In commerical cars, based on the condition the exhaust kinectic energy can be altered, hence VGT play a major role in the commerical cars.

CONCLUSION:-

Thus different turbocharger can be modelled in GT using the map, and it can also be calibrated and optimized to make the working range of turbocharger in the heart region of the maps GT plats a vital role in the operation.