Exploration of Turbocharger Module in GT-Power

OBJECTIVES

• To list down different TurboChargers and locate examples from GT-Power
• Explore the tutorial no. 6 and 7 present in GT-Power
• To plot operating points on the compressor and turbine maps
• To find the applications where Variable Geometric Turbine is beneficial
• To explore the example file of Diesel VGT EGR and understand the modeling part

Different TurboChargers and their examples from GT-Power

The below images shows us the up-gradation trend of TurboCharger Technology implemented in practicality as we have moved from Euro1 to Euro6. The application of these different turbochargers varies according to the requirement and superiority of model as the cost increases and we use the latest technology.

List:

1. Waste Gate Turbocharger

2. Variable Geometry Turbine

3. Two-stage Turbocharger

4. Variable Geometry Compressor

5. e-Turbo

1. Waste Gate Turbocharger

In fixed turbo geometry, we cannot control the kinetic energy of the exhaust gas and everything that comes out of the exhaust port is been used for the expansion of the turbine which is undesirable for some cases and situations.

In Waste Gate Geometry, there's a pneumatic PID controller whose one end is connected with the compressor outlet through sensors which senses the compressor output pressure and then adjust the pneumatic pumps stiffness to the desired pressure and the remaining exhaust gas energy is bypassed. The need for Wastegate comes with high speed and torque applications.

Below is an example case for Waste Gate Controller from GT-Power.

2. Variable Geometry Turbine

In case of the turbocharger, the exhaust gas energy comes into the turbine radially and is been thrown outwards axially towards the compressor. Variable Geometry Turbocharger includes a ring of aerodynamically shaped vanes in the housing of the turbine inlet which are also known as guiding vanes. These vanes can be rotated to vary the gas swirl angle and the cross-sectional area as seen in the 3rd image. These internal vanes alter the area - to - radius (A/F) ratio to match the engine RPM, and so gives peak performance. As seen in the 1st image, we see the arrangement that turbine blades are placed inside the variable nozzle. For low rotation speed i.e. a small amount of exhaust gas the A/F ratio is narrowed whereas for high RPM the nozzle expands to match with the exhaust flow rate to work at an optimum level. This way, this technique reduces turbo lag and provides a wide and smooth torque band.

Below is an example case for Variable Geometry Turbo from GT-Power.

3. Two-stage Turbocharger

In case of V6 or V8 engines, the two-stage turbocharger can be implemented by assigning a single turbocharger to work with each cylinder or bank. It can also be used as Twin Sequential Turbocharging where one smaller turbo can be used at low RPM and larger turbo for higher RPM's giving us freedom for a wider operating RPM range. These turbochargers are generally used in higher-end premium cars, which generally used 3 or 4 turbos because of lot of power requirement. This is used in series and parallel, depending upon the application and configuration.

Below is an example case for 2 stages Turbo Charger from GT-Power.

4. e-Turbo

Electric Turbocharger is used to assist a normal turbocharger to eliminate turbo lag at a lower engine speed where a conventional turbo does not work efficiently. This is achieved by adding an electric motor which is connected with the compressor from the start and through the lower revolutions until the power from the exhaust volume is high enough to work the turbocharger efficiently. This significantly eliminated the turbo lag and increases the PRM band. Some of the disadvantages are the cost and the complexity along with the thermal management of the battery pack.

Exploration the tutorial no. 6 and 7 present in GT-Power

1. 6 cylinder Diesel Turbocharger (Tutorial no.6)

Geometry Model

This model consists of 6 cylinders with the implementation of Turbo Charger i.e. 2 inlets to the turbo as we see in the form of two end environments and compressor outlet at the bottom in the form of end environment. Generally, Twin Turbine inlets are used with more than 3 cylinders. In this case, we have 6 cylinders where 3 outlets of cylinders share on the turbine inlet. We were able to combine the outlets of different cylinders with the help of FlowSplit Template. Here, as there is no physical shaft connecting the turbine and compressor, we directly input the outlet pressure (Absolute) values for the turbine as well as compressor. Here the inputs for the turbine and compressor are absolute pressure, temperature and composition of air.

2. TurboCharger (Tutorial no.7)

Geometry Model

In this model again we have 6 cylinder diesel engine with the two inlets to the turbocharger which is a collection from 6 cylinders splitting into 2 inlets. This model is conceptually same as the above model in tutorial no. 6 with actual turbocharger setup implemented here, where the turbine is connected with the compressor impeller with the rotating shaft as seen in the image below. Here for the turbine and compressor inputs, we have a turbine map and compressor map which is a contour plot of Pressure ratio v/s Mass flow rate. This turbine and compressor map data consists of parameters like Rotational speed, Mass flow rate, Pressure Ratio and efficiency.

Plotting of operating points on the compressor and turbine maps

These Compressor maps and the turbine maps are generally provided by the manufacturers in a standard SAE format which has an extension of .cmp and .trp respectively. An alternative option for these files is the direct input of attributes like speed, mass flow rate, pressure ratio and efficiency.

Below is the standard compressor map where thick blue lines indicate the speed in RPM, and the thin vertical rail lines indicate the efficiency of the compressor. The x-axis represents the Mass flow rate and Y-axis represents the Pressure Ratio. In the middle of the map, we where Heart is written suggests the highest efficiency of the compressor and as we move outwards, the efficiency decreases. Also, we see other zones named Choke zone, Surge zone and Excess Rotor Speed which our operating points should avoid.

We tried to plot the compressor and turbine map with 6 cylinders turbocharged diesel engine constant 3600 rpm for 3 cases changing its altitude and the amount of fuel to achieve maximum compressor efficiency as we see in the below plot, the operating points are highlighted with the blue circle and we see a downward trend. For 1st case, fuel kept is 80mg at sea level i.e. 0m altitude, for 2nd case, fuel kept 60mg with 2000m altitude and for 3rd case, fuel kept is 40mg with 5000m altitude. From these plots, we are trying to see at what mass flow rate what pressure ratio we are able to obtain and decide how good and compatible is our engine. Along with these changes we have tried to maintain the Air to Fuel Ratio.

Below is the efficiency Map with the corrected mass flow rate for the compressor. For the 1st case, we get a pressure ratio of 3.654 for the mass flow rate of 0.4469kg/s. For 2nd case, we get a pressure ratio of 3.46 for the mass flow rate of 0.4265kg/s and for the 3rd case, we get a pressure ratio of 3.3 for the mass flow rate of 0.4kg/s. For the contour plot we may conclude that the compression efficiency is predicted to be around 70 to 72%.

Below is the Efficiency map for a turbine with Mass flow rate v/s pressure ratio. For the 1st case, we get a pressure ratio of 3.04 for the mass flow rate of 0.045kg/s. For 2nd case, we get a pressure ratio of 2.9 for the mass flow rate of 0.045kg/s and for the 3rd case, we get a pressure ratio of 2.78 for the mass flow rate of 0.045kg/s. Here the mass flow rate remains the same but the pressure ratio decreases for 3600 RPM. From the contour plot, we may conclude that the turbine efficiency achieved falls in the maximum zone i.e. 80.55%.

As we are increasing the altitude, we see a decreasing trend in Brake Power, Torque and increase in Brake Specific Fuel Consumption at 3600 RPM.

The applications where Variable Geometric Turbine is beneficial

Implementation for Variable Geometric Turbine demands to add the 'electronic controller' as different speed and load conditions we have different possibilities to achieve the target boost pressure. Boost input the electronic controller can be done with 'Receive Signal' template wireless signal.

The VGT is beneficial when used in high-end passenger car we have a wide range of RPM to operate along with the high torque. A turbocharger can be employed in huge range fo applications like a commercial on and off highways, marine as well as rail internal engine applications.

To exploration of the example file of Diesel VGT EGR and understand the modeling part

Below is the detailed model for Diesel Variable Geometry Turbine along with the EGR system implemented.

Ambient air is been sucked into the Airbox at environmental pressure and temperature along with the density of 1.1kg/m^3. As variable geometry turbocharger is implemented in the model to force more air inside the cylinder, the ambient air from the airbox is compressed increasing its pressure, temperature and density significantly. Followed by the compressor, an intercooler is attached lowering down the air temperature and hence making it denser which increases the amount of air to be supplied to the intake manifold. This intercooler is an air to air intercooler that is modeled using a semi-predictive method based on heat exchanger effectiveness

Along with the turbocharger, an EGR system is also integrated with the model which adds up the air coming from the intercooler which further goes to the intake manifold. This EGR flow is driven by a positive pressure difference between the exhaust manifold and the intake manifold is controlled by an orifice connection. This EGR system consists of EGR-Cooler as well as EGR-Controller which is controlled by PID controller and which operates the throttle and becomes active when enough pressure drop within the EGR system is not enough to achieve the target EGR rate. Now, EGR cooler works on the concept of the heat exchanger and is the best choice when high amount of EGR is used.

Once EGR mixes with the mainstream, it gets supplied to 4 manifolds of the 4 cylinders. These cylinders are 4 valve cylinders with 2 intake and 2 exhaust valves. The combustion model used here is a DI Pulsed and the firing order kept is 1 -3 - 4 - 2. A controller is been used for Diesel Injection to achieve and maintain the targeted BMEP by controlling the amount of fuel to be injected. This template can be used to target various engine performance parameters at part-load operation. A single scroll turbine is used with the shaft connected with the compressor. For both Compressor and the turbine, the compressor and turbine map files are used as an input. After the turbine expansion, the exhaust gas with emissions flows through after-treatment devices like DOC and DPF.

Intercooler

EGR Cooler

EGR Controller

After Treatment Model