A turbocharger or turbo is a forced
induction device used to allow more power to be produced for an engine of a
given size. A turbocharged engine can be more powerful and efficient than a
naturally aspirated engine because the turbine forces more intake air,
proportionately more fuel, into the combustion chamber than if atmospheric
pressure alone is used. Turbo are commonly used on truck, car, train, and
construction equipment engines. Turbo are popularly used with Otto cycle and
Diesel cycle internal combustion engines.
There
are two ways of increasing the power of an engine. One of them would be to make
the fuel-air mixture richer by adding more fuel. This will increase the power
but at the cost of fuel efficiency and increase in pollution levels… prohibitive!
The other would be to somehow increase the volume of air entering into the
cylinder and increasing the fuel intake proportionately, increasing power and
fuel efficiency without hurting the environment or efficiency. This is exactly
what Turbochargers do, increasing the volumetric efficiency of an engine.
In a
naturally aspirated engine, the downward stroke of the piston creates an area
of low pressure in order to draw more air into the cylinder through the intake
valves. Now because of the pressure in
the cylinder cannot go below 0 (zero) psi (vacuum) and relatively constant
atmospheric pressure (about 15 psi) there will be a limit to the pressure
difference across the intake valves and hence the amount of air entering the
combustion chamber or the cylinder. The ability to fill the cylinder with air
is its volumetric efficiency. Now if we can increase the pressure difference
across the intake valves by some way we can make more air enter into the
cylinder and hence increasing the volumetric efficiency of the engine. It
increases the pressure at the point where air is entering the cylinder, thereby
increasing the pressure difference across the intake valves and thus more air
enters into the combustion chamber. The additional air makes it possible to add
more fuel, increasing the power and torque output of the engine, particularly
at higher engine speeds.
Turbochargers were originally known as Turbo superchargers when all
forced induction devices were classified as superchargers; nowadays the term
"supercharger" is usually applied to only mechanically-driven forced
induction devices. The key difference between a turbocharger and a conventional
supercharger is that the latter is mechanically driven from the engine, often
from a belt connected to the crankshaft, whereas a turbocharger is driven by
the engine's exhaust gas turbine. Compared to a mechanically-driven
supercharger, turbochargers tend to be more efficient but less responsive.
HISTORICAL PERSPECTIVE
AVIATION:
During the First World War French engineer Auguste Rateau fitted turbochargers to Renault engines powering various French fighters with some success. In1918, General Electric engineer Sanford Moss attached a turbo to a V12 Liberty aircraft engine. The engine was tested at Pikes Peak in Colorado at 4,300 m to demonstrate that it could eliminate the power losses usually experienced in internal combustion engines as a result of reduced air pressure and density at high altitude.
Turbochargers were first used in production aircraft engines in the 1920s, although they were less common than engine-driven centrifugal superchargers. The primary purpose behind most aircraft-based applications was to increase the altitude at which the airplane could fly, by compensating for the lower atmospheric pressure present at high altitude.
PRODUCTION AUTOMOBILES:
The first turbocharged diesel truck was produced by Schweizer Maschinenfabrik Saurer (Swiss Machine Works Saurer) in 1938 .The first production turbocharged automobile engines came from General Motors in 1962. At the Paris auto show in1974, during the height of the oil crisis, Porsche introduced the 911 Turbo – the world’s first production sports car with an exhaust turbocharger and pressure regulator. This was made possible by the introduction of a waste gate to direct excess exhaust gasses away from the exhaust turbine. The world's first production turbo diesel automobiles were the Garrett-turbocharged Mercedes 300SD and the Peugeot 604, both introduced in 1978. Today, most automotive diesels are turbocharged.
1962 Oldsmobile Cutlass Jet fire
1962 Chevrolet Corvair Monza Spyder
1973 BMW 2002 Turbo
1974 Porsche 911 Turbo
1978 Saab 99
1978 Peugeot 604 turbo diesel
1978 Mercedes-Benz 300SD turbo diesel (United States/Canada)
1979 Alfa Romeo Alfetta GTV 2000 Turbo delta
1980 Mitsubishi Lancer GT Turbo
1980 Pontiac Firebird
1980 Renault 5 Turbo
1981 Volvo 240-series Turbo
OPERATING PRINCIPLE
COMPONENTS
OF A TURBOCHARGER
The turbocharger has four main components. The turbine (almost always a radial turbine) and impeller/compressor wheels are each contained within their own folded conical housing on opposite sides of the third component, the center housing/hub rotating assembly. The housings fitted around the compressor impeller and turbine collect and direct the gas flow through the wheels as they spin. The size and shape can dictate some performance characteristics of the overall turbocharger. The turbine and impeller wheel sizes dictate the amount of air or exhaust that can be flowed through the system, and the relative efficiency at which they operate. Generally, the larger the turbine wheel and compressor wheel, the larger the flow capacity. The center hub rotating assembly houses the shaft which connects the compressor impeller and turbine. It also must contain a bearing system to suspend the shaft, allowing it to rotate at very high speed with minimal friction. Waste gates for the exhaust flow.
TURBINE WHEEL:
The Turbine Wheel is housed in the
turbine casing and is connected to a shaft that in turn rotates the compressor
wheel.
COMPRESSOR WHEEL (IMPELLER)
Compressor
impellers are produced using a variant of the aluminum investment casting process.
A rubber former is made to replicate the impeller around which a casting mould
is created. The rubber former can then be extracted from the mould into which
the metal is poured. Accurate blade sections and profiles are important in
achieving compressor performance. Back face profile machining optimizes
impeller stress conditions. Boring to tight tolerance and burnishing assist
balancing and fatigue resistance. The impeller is located on the shaft assembly
using a threaded nut.
WASTE GATES:
On the
exhaust side, a Waste gate provides us a means to control the boost pressure of
the engine. Some commercial diesel applications do not use a Waste gate at all.
This type of system is called a free-floating turbocharger. However, the vast majority
of gasoline performance applications require Waste gates. Waste gates provide a
means to bypass exhaust flow from the turbine wheel. Bypassing this energy
(e.g. exhaust flow) reduces the power driving the turbine wheel to match the
power required for a given boost level.
ADVANTAGES
1. More specific power over naturally
aspirated engine. This means a turbocharged engine can achieve more power from
same engine volume.
2. Better thermal efficiency over both
naturally aspirated and supercharged engine when under full load (i.e. on
boost). This is because the excess exhaust heat and pressure, which would
normally be wasted, contributes some of the work required to compress the air.
3. Weight/Packaging. Smaller and
lighter than alternative forced induction systems and may be more easily fitted
in an engine bay.
4. Fuel Economy. Although adding a
turbocharger itself does not save fuel, it will allow a vehicle to use a
smaller engine while achieving power levels of a much larger engine, while attaining
near normal fuel economy while off boost/cruising. This is because without
boost, less fuel is used to create a proper air/fuel ratio.
DISADVANTAGES
1. Lack of responsiveness if an
incorrectly sized turbocharger is used. If a turbocharger that is too large is
used it reduces throttle response as it builds up boost slowly otherwise known as
"lag". However, doing this may result in more peak power.
2. Boost threshold- A turbocharger
starts producing boost only above a certain rpm due to a lack of exhaust gas
volume to overcome inertia of rest of the turbo propeller. This results in a
rapid and nonlinear rise in torque, and will reduce the usable power band of
the engine. The sudden surge of power could overwhelm the tires and result in
loss of grip, which could lead to under steer/over steer, depending on the
drive train and suspension setup of the vehicle. Lag can be disadvantageous in
racing, if throttle is applied in a turn, power may unexpectedly increase when
the turbo spools up, which can cause excessive wheel spin.
3. Cost- Turbocharger parts are costly
to add to naturally aspirated engines. Heavily modifying OEM turbocharger
systems also require extensive upgrades that in most cases requires most (if
not all) of the original components to be replaced.
4. Complexity- Further to cost,
turbochargers require numerous additional systems if they are not to damage an
engine. Even an engine under only light boost requires a system for properly
routing (and sometimes cooling) the lubricating oil, turbo-specific exhaust
manifold, application specific downpipe, boosts regulation. In addition inter -cooled
turbo engines require additional plumbing, while highly tuned turbocharged
engines will require extensive upgrades to their lubrication, cooling, and
breathing systems; while reinforcing internal engine and transmission parts.
TURBO LAG AND BOOST
The time
required to bring the turbo up to a speed where it can function effectively is
called turbo lag. This is noticed as a hesitation in throttle response when coming
off idle. This is symptomatic of the time taken for the exhaust system driving
the turbine to come to high pressure and for the turbine rotor to overcome its
rotational inertia and reach the speed necessary to supply boost pressure. The
directly-driven compressor in a supercharger does not suffer from this problem.
Conversely on light loads or at low RPM a turbocharger supplies less boost and
the engine acts like a naturally aspirated engine. Turbochargers start
producing boost only above a certain exhaust mass flow rate (depending on the
size of the turbo). Without an appropriate exhaust gas flow, they logically
cannot force air into the engine. The point at full throttle in which the mass flow
in the exhaust is strong enough to force air into the engine is known as the
boost threshold rpm. Engineers have, in some cases, been able to reduce the
boost threshold rpm to idle speed to allow for instant response. Both Lag and
Threshold characteristics can be acquired through the use of a compressor map
and a mathematical equation.
APPLICATIONS
·
Gasoline-powered cars
Today, turbo charging is commonly used by many manufacturers
of both diesel and gasoline-powered cars. Turbo charging can be used to
increase power output for a given capacity or to increase fuel efficiency by
allowing a smaller displacement engine to be used. Low pressure turbo charging
is the optimum when driving in the city, whereas high pressure turbo charging
is more for racing and driving on highways/motorways/freeways.
·
Diesel-powered cars
Today, many automotive diesels are turbocharged, since the
use of turbocharging improved efficiency, driveability and performance of
diesel engines, greatly increasing their popularity.
·
Motorcycles
The first example of a turbocharged bike is the 1978 Kawasaki
Z1R TC. Several Japanese companies produced turbocharged high performance
motorcycles in the early 1980s. Since then, few turbocharged motorcycles have
been produced.
·
Trucks
The first turbocharged diesel truck was produced by Schweizer
Maschinenfabrik Saurer (Swiss Machine Works Saurer) in 1938.
·
Aircraft
A natural
use of the turbocharger is with aircraft engines. As an aircraft climbs to
higher altitudes the pressure of the surrounding air quickly falls off. At
5,486 m (18,000 ft), the air is at half the pressure of sea level and the
airframe experiences only half the aerodynamic drag. However, since the charge
in the cylinders is being pushed in by this air pressure, it means that the
engine will normally produce only half-power at full throttle at this altitude.
Pilots would like to take advantage of the low drag at high altitudes in order
to go faster, but a naturally aspirated engine will not produce enough power at
the same altitude to do so.
Here the main
aim is to effectively utilize the non renewable energy such as petrol and
diesel. Complete combustion of the fuels can be achieved. Power output can be
increased. Wind energy can be used for air compression. We conclude that the
power as well as the efficiency is increasing 10 to 15 % and pollution can also
decrease. From the observation we can conclude that when the full throttle
valve is open at that time the engine speed is 4000 rpm and by this the
turbocharger generate 1.60 bar pressurized air. Generally the naturally
aspirated engine takes atmospheric pressurized air to the carburetor for air
fuel mixture but we can add the high density air for the combustion so as the
result the power and the complete combustion take place so efficiency is
increasing.
