5-turbocharger ganesh 2011
TRANSCRIPT
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