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