Recent Developments in

Automotive Turbochargers

History

INTRODUCTION:

The power output of a naturally aspirated internal combustion engine can be

increased either by enlarging the swept volume or by increasing the rotational

speed. An increase in swept volume results in an engine which is larger and

heavier and thereby more expensive. There are several limitations and

disadvantages in increasing the engine speed, particularly on larger engines.

An elegant solution is to increase the engine output by pressure charging,

usually using an exhaust gas driven turbocharger. Use of exhaust gas

turbochargers is increasing very rapidly to achieve not only fuel economy but

also to control exhaust emissions.

EXHAUST GAS TURBOCHARGER :

Turbocharger normally comprises of a centrifugal compressor and a single

stage gas turbine mounted on a common shaft. The turbine recovers part of the

exhaust gas energy, thus driving the compressor. The compressor draws fresh

air and delivers it under pressure to the engine. This results in a greater mass

of air being delivered to the engine which allows more fuel to be burnt and the

engine develops more power. A schematic diagram of a 4 cylinder

turbocharged engine is shown in Fig 1.

Exhaust gas Turbocharging

Figure 1

ADVANTAGES OF THE EXHAUST GAS TURBOCHARGER :

• The turbocharged engine has a number of advantages over naturally aspirated

engine.

• Power – to - weight ratio of the turbocharged engine is higher than with a

naturally aspirated engine.

• The size of the turbocharged engine is smaller than that of naturally aspirated

engine of equal output.

• The application range of an existing series of naturally aspirated engine can be

extended to various power ranges with flexible matching of the turbocharger.

• The high altitude power loss of turbocharged engine is significantly less than

that of naturally aspirated engine.

• The turbocharged engine has a reduced specific fuel consumption since part of

the exhaust gas energy is utilized in the turbocharger.

• The turbocharged engine can be well adapted for control of exhaust emissions.

• The turbocharged engine is quieter than a naturally aspirated engine for the

same power.

ENGINE MATCHING OF EXHAUST GAS TURBOCHARGER

Although the installation of a turbocharger on the engine is quite simple, the engine must

fulfill certain pre-requisites. These are:

Thermodynamic compatibility of the engine and the turbocharger over the the complete

operational range of the engine. Based on the application of the engine the majority of the

operating points (load – speed characteristics) should lie in the efficient operating range of

compressor and turbine characteristics.

Mechanical integrity of the engine:

The engine components must be able to withstand the thermal and mechanical stresses

which are likely to be higher than the naturally aspirated engine.

The objective in matching the turbocharger to an engine is to find the right combination of

turbocharger compressor and turbine to suit the engine and its application. The pre-

requisite for a successful matching needs development of a number of compressor &

turbine modules to cover all intended applications. This matching requires very close co-

operation between the engine and turbocharger manufacturers.

A view of the turbocharger for truck diesel engine and the characteristics of the engine

super-imposed on the turbocharger compressor map are shown in Fig.1.

Types of Turbocharging

Constant Pressure Turbocharging

Pulse Turbocharging

Pulse Turbocharging

The kinetic energy of the exhaust gas exiting from the cylinders is

mostly recovered.

The exhaust manifold will be bifurcated to join the cylinders, which

do not interfere during gas exchange process.

Turbine housing is divided to accept the exhaust pulse from each

branch of the exhaust manifold.

Better low speed engine performance

Constant Pressure Turbocharging

The pressure pulsation is smoothened out by relatively large exhaust manifold.

Large marine engines, Gensets and Industrial engines use this type.

Construction and function of a Turbocharger

A Turbocharger consists of a compressor and a turbine connected by

a common shaft. Centrifugal compressors and centripetal turbines

are most popular types used in automotive applications and form the

basis for most turbochargers today.

Compressor

The turbocharger centrifugal compressor has three essential

components. Compressor wheel, diffuser and housing. With the

rotational speed of the wheel, air is drawn in axially, accelerated

to high velocity and then expelled in a radial direction. The

diffuser slows down the high velocity air, so that both pressure

and temperature rise. The housing collects the air and slows it

down further before it reaches the compressor exit.

Compressor Map:

Turbine

The turbocharger turbine, which consists of a turbine wheel and turbine

housing, converts the engine exhaust gas into mechanical energy to

drive the compressor. The gas, which is restricted by turbine housing

cross sectional area, results in a pressure and temperature drop between

the inlet and the outlet. This pressure drop is converted by the turbine

into kinetic energy to drive the turbine wheel.

Single entry turbine housing

Twin entry turbine housing

Variable turbine geometry

Turbine Map

Turbocharger Control Systems

Control system

To meet the demands of the engine at low speeds, full boost

pressure should be available. At the same time, at high speeds,

this boost pressure needs to be controlled to achieve the required

engine performance.

Control by turbine side bypass

The turbine size is chosen to meet the low speed airflow

requirements. Beyond certain speed, to control the boost

pressure, part of the exhaust is bypassed. The waste gate opens

or closes the bypass in response to the boost pressure, thus

maintaining the boost pressure.

Variable turbine geometryVTG allows the turbine flow cross section to be varied in accordance with the engine

operating point. VTG has variable guide vanes. As a result of continuous turbine

cross section adjustment to the engine airflow requirements, SFC and emissions are

reduced. High engine torque at low speeds and with adequate control strategy

ensures a significant improvement of dynamic performance.

Guide vane control is mostly electronic through a vacuum regulated actuator and a

proportional valve. Electric actuators with position feed back are also used for vane

control.

Torque-motor DC motor

Two Stage turbocharging

1 2 3

Conclusions

The application of Turbocharged engines –diesel as well as petrol is on the increaseworld wide due to stringent emissionnorms and need for more efficientengines.

This has been facilitated by thedevelopment of extremely smallturbochargers as well as various controlsystems.

This has led to better emission control andfuel economy

Turbocharger Test Rig

COMPRESSOR PERFORMANCE

TURBINE PERFORMANCE

Oil Free Rotary Screw Compressor for Turbocharger Test Rig

Type : Atlas Copco make

Model : ZE4 VSD

Flow Range : 0.218 to 0.812 m3 /s

Maximum Delivery Pressure : 3.5 bar (g)

Engine Test Dynamometer

I. Dynamometer Type : AVL Make

Model : Alpha 350

Maximum Power : 350 kW

Maximum Torque : 1500 N-m

Maximum Speed : 7000 rpm

II. Intercooler provision

III. Flow Meter for Fuel flow measurement

IV. Smoke Meter –AVL make

For matching

turbochargers

NVH Facilities for Noise and Vibration Analysis of

Turbocharger and parts.

1. LMS - SCADAS System for Data acquisition

2. Ultra low weight Accelerometer Sensors

3. High Temperature Microphone

4. High Frequency Shaker

Natural Frequency Measurement