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this presentation tells about the variable geometry turbocharger, their design and comparison with simple turbocharger
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Variable Geometry Turbocharger
MALAVIYA NATIONAL INSTITUTE OF
TECHNOLOGY , JAIPUR
Submitted by
RISHABH MISHRA
2011UME1540
M3
Content
Introduction
Turbocharging
History
Problems with simple turbocharging
Working of VGT
Benefits
Designing of VGT
Summary and Conclusion
References
Common questions
Introduction
Variable-geometry turbochargers (VGTs) also known as variable nozzle turbines/VNTs), are a family of turbochargers
Designed to allow the effective aspect ratio (A:R) of the turbo to be altered as conditions change
It produces variations in the flow of inlet air mass by geometry change of inlet conditions of turbine blades according to requirement.
Turbocharger
A turbocharger consist of four parts:
a) Turbine
b) Compressor
c) Common axle
d) Sub assemblies
e) Air cooler
WORKING
The turbine inlet receives exhaust gases from the engine exhaust manifold causing the turbine wheel to rotate This rotation drives the compressor, compressing ambient air After it delivers it to the air intake manifold of the engine at higher pressure, resulting in a greater amount of the air and fuel entering the cylinder
History 1927: Swiss engineer Alfred Buchi is granted the first Patent for exhaust driven
Turbo-Supercharging or Turbocharger. 1952: Garrett (Honeywell) & Schwitzer (BorgWarner) begin Turbocharger production
for Caterpillar & Mack Truck. 1962: First Passenger Car Turbo application, General Motors Corvair is introduced,
followed by 1963 Oldsmobile Jetfire Turbo-Rocket V8. 1979: Beginning of Downsized Turbo Era with Ford Mustang 2.3-liter, 4 cylinder engine,
Chrysler & GM also Compete with Turbo Models. 1980: BorgWarner and IHI Japan form 50/50 Joint Venture, Warner-Ishi.
MHI of Japan begins development for US. 1997: BorgWarner purchases majority shares of AG Kühnle, Kopp &
Kausch from Penske Corporation. 1999: Kuhlman Corporation, parent of Schwitzer is purchasedby BorgWarner and
becomes part of BorgWarner Turbo Systems. 2008: Bosch-Mahle & Continental Turbo Systems Begin Development.
Problems with simple Turbochargers
Difference in the optimum aspect ratio of nozzle at different running conditions
Low boost at slow running conditions
Choking at high speed
Variation in the inlet air mass according to engine performance
Starting lag
Turbocharger configuration
Turbocharger integration
Linking of engine performance with turbocharger performance
Variable geometry turbocharger
In variable geometry turbocharger the variation in inlet air mass is brought by compressor speed
Changes is done on the turbine
Nozzle angle is changed by stator vane, operated by ECU unit of vehicle
For low speed, the vane is brought in closed position so that boosting can be done by compressor
At high speed ,the vane comes at open condition allowing most of the exhaust to impact on the blades ,and the pressure decreases of exhaust gases and choking is avoided
Working of VGT Low speed run condition
Engine running parameters is taken by
ECU as input and send direction to vane
to close
High speed run condition
Benefits
No throttling loss of the waste gate 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 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
Designing of the VGT
Three parts
a) Electronic control unit
b) Compressor designing
c) Turbine designing
Electronic control unit The opening of the guide vanes is commanded by the electronic
control unit (ECU) of the car
Aspects of engine performance that ECU consider for the varying the nozzle angle
1) the instant and quantity of injected fuel
2) the opening and closing of the intake and exhaust valves
3) pressures, temperatures, flow rates
Mass flow rate is given by
Compressor design
Flow coefficient Circumferential Mach number Isentropic work coefficient
Turbine design
Parameters:
Pressure ratio
Corrected mass flow rate
Isentropic efficiency
Corrected speed
VNT positions
Conclusion
An VGT is designed to position the nozzle to attain the optimum air mass flow inside the engine and improving the break specific fuel consumption.
An VGT, under low running speed, provides closing of vane blades to allow more impact of exhaust gases on it improving intake air mass..
Designing of the compressor and turbine include the study of there design parameter
on the maps which allow us to decide standards for the components.
Pumping losses , pressure energy loss, engine noise and heat energy loss is recovered
by VGT. These problems commonly occur on vehicle with conventional turbocharging
system or in case of no turbocharging.
If there occurs VGT failure, the system will revert to normal turbocharging operation.
Normally the ECU unit will turn on the light in case of any fault.
References
K. Segawa, A. Iwakami, S. Yamaguchi, H. Tange, K. Kimachi, Improvement of turbine performance for small size variable geometry system Turbo charger, IHI Corporation, Japan,2010.
Rabih Omran, Rafic Younes, and Jean-Claude Champoussin, Optimal Control of a Variable Geometry Turbocharged Diesel Engine Using Neural Networks: Applications on the ETC Test Cycle, Lebanese University. Nov. 27, 2008.
Daniel Cristian Dinescu, Mohand Tazerout, mean value modelling of a variable nozzle turbocharger (VNT), U.P.B. Sci. Bull., 2010.
Zhang Yang Jun, Chen Tao, Zhuge Weil, Zhang Shu Yong & XU Jian Zhong, An integrated turbocharger design approach to improve engine Performance, Technological Sciences, January 2010
Tao Chen, Weilin Zhuge, Xinqian Zheng, Yangjun Zhang, turbocharger design for a 1.8 litre turbocharged gasoline Engine using an integrated method, ASME, June 2009