Supercharging : Supercharging Introduction:
The method of increasing the inlet air density is called Supercharging.
“More fuel + More air = Bigger explosion = Greater horsepower”.
Supercharging can be done both for SI engines as well as in CI engines
Supercharging of an engine can be done using either
one of the following components;
2) Turbochargers Why Supercharging ?? : Why Supercharging ?? Increases the power of an engine.
Increases the torque produced.
Necessary in aero-planes as they have less oxygen at high altitudes.
Ensures complete combustion of the fuel.
Reduces pollution to some extent. Supercharger : Supercharger A supercharger is an equipment that compresses the air being delivered to an engine, allowing the combustion chamber to be overfilled without enlarging
The higher concentration of
oxygen provided by a super-
charger is matched with a larger
amount of fuel from the fuel
injectors thus boosting the power
of the engine. Classification of Superchargers : Classification of Superchargers Based on method of compression, Superchargers can be classified as:-
1. Positive-displacement type, which deliver a nearly-fixed volume of air per revolution at all speeds and a fairly constant level of boost regardless of engine speed.
2. Dynamic compressors rely on accelerating the air to high speed and then exchanging that velocity for pressure by diffusing or slowing it down & deliver increasing boost with increasing engine speed. Commonly used Superchargers : Commonly used Superchargers Roots supercharger: : Roots supercharger: The Roots supercharger is the oldest design. Philander and Francis Roots patented the design in 1860. In 1900, Gottleib Daimler included a Roots supercharger in a car engine
As the meshing lobes spin, air trapped in the pockets between the lobes is carried between the fill side and the discharge side & Large quantities of air move into the intake manifold and "stack up" to create positive pressure.
Roots superchargers are usually large and
sit on top of the engine.
Roots superchargers are the least efficient
supercharger for two reasons:-
1.)They add more weight to the vehicle.
2.)They provide air in discrete bursts instead of
providing in a smooth and continuous manner. Twin-Screw Supercharger: : Twin-Screw Supercharger: A twin-screw supercharger operates by pulling air through a pair of meshing lobes that resemble a set of worm gears.
A twin-screw supercharger compresses the
air inside the rotor housing (That's because
the rotors have a conical taper, which
means the air pockets decrease in
size as air moves from the fill side
to the discharge side).
As the air pockets shrink,
the air is squeezed into a smaller space Slide 8: Comparison of Twin-screw Supercharger with Roots Supercharger:
Twin-screw superchargers are more efficient than Roots supercharger
They cost more because the screw-type rotors require more precision in the manufacturing process.
They also make a lot of noise.
The compressed air exiting the discharge outlet creates a whine or whistle that must be checked with noise suppression techniques Centrifugal Supercharger: : Centrifugal Supercharger: A centrifugal supercharger works by powering an impeller
(a device similar to a rotor) at very high speeds to quickly draw
air into a small compressor housing.
Impeller speeds can reach ‘50,000 to 60,000 RPM’.
Centrifugal superchargers are
the most efficient and the most
common induction systems.
They are small, lightweight and
attachable to the front of the
Engine. Slide 10: Working of Centrifugal supercharger:
As the air is drawn in the hub of the impeller,
centrifugal force causes it to radiate outward.
The air leaves the impeller at high speed,
but low pressure.
A diffuser converts the high-speed ,
low-pressure air to low-speed ,
Thus pressurized air is achieved. Drives Used in Supercharger:
Belt (V belt, Toothed belt & Flat belt).
Chain drive Slide 11: Advantages of Superchargers Over a Turbocharger:
Supercharger do not suffer lag which is a serious problem in Turbocharger .
Modification of the exhaust system:- Installing a turbocharger requires extensive modification of the exhaust system, but superchargers can be bolted to the top or side of the engine , that makes them cheaper to install and easier to service and maintain.
Shutdown procedure:-No special shutdown procedure is required with superchargers as they are not lubricated by engine oil . They can be shut down normally. Turbochargers must idle for about 30 seconds or so prior to shutdown so the lubricating oil has a chance to cool down.
Disadvantages of Superchargers:
It derives power from the engine itself: Crankshaft drives superchargers so they steal some of the engine's horsepower. A supercharger can consume as much as 20 percent of an engine's total power output
An added strain on the engine: Supercharging puts an added strain on the engine, which needs to be strong to handle the extra boost and bigger explosions
Since some of the superchargers are larger in size the efficiency of the engine decreases as it is the additional component bolted on to it.
Detonation is serious problem Turbochargers : Turbochargers Introduction:
Turbochargers are a type of forced induction system whose function is same as that of Supercharger.
In order to achieve the boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump.
The turbocharger is bolted to the exhaust manifold
of the engine. The exhaust from the cylinders
spins the turbine, which works like a
gas turbine engine. The turbine is
connected by a shaft to the compressor,
which is located between the air filter and
the intake manifold. The compressor
pressurizes the air going into the pistons. Slide 13: Important Parts of Turbocharger:
Ball bearings & Fluid Bearings
Intercooler: When air is compressed, it heats up; and when air heats up, it expands. So some of the pressure increase from a turbocharger is the result of heating the air before it goes into the engine. An intercooler or charge air cooler is an additional component that looks something like a radiator, except air passes through the
inside as well as the outside of the
intercooler. Methods of Turbocharging and their Advantages and Limits: : Methods of Turbocharging and their Advantages and Limits: Constant Pressure Turbocharging:
The exhaust from various cylinders discharge into a common manifold at pressures higher than the atmospheric pressure. The exhaust gasses from all the expanded in the exhaust valves to an approximately constant pressure in common manifold from here it passes to turbine. Thus the blow-down energy, in the form of internal energy, is converted into work in the turbine. The exhaust gases are maintained at constant pressure during the whole cycle so that a pure Reaction turbine can be used.
The exhaust piping is very simple for a multi-cylinder engine as well as single-cylinder, highly efficient turbine can be used.
Engine speed is not limited by the pressure waves in the exhaust pipes.
Scavenging is not efficient.
At part load the efficiency of turbine reduces due to partial admissions to the turbine Pulse Turbocharging:
Considerable part of the blow-down energy is converted into exhaust pulses as soon as
the exhaust valve opens. Towards the end of exhaust the pressure in the exhaust pipe drops below the scavenging and large air pressure making scavenging quite easy. The rate of the exhaust gas at the various turbine inlet is different and variable in time.
The space required is less due to short and smaller diameter pipes.
Comparatively better scavenging is obtained at low loads due to reduced pressure.
With large number of cylinders complicated inlet and exhaust pipe arrangements are needed.
The length of the pipe or engine speed is limited. Two Stage Turbocharging: : Two Stage Turbocharging: Two –stage turbocharging is defined as use of two turbochargers of different sizes In
series; for example a high-pressure
stage operating on pulse system
and a low-pressure stage on constant
Better matching of the turbochargers to engine operating conditions possible.
The efficiency of two-stage turbocharger is higher than that of a single stage turbocharger having a high boost ratio.
The space requirement is higher.
The total system is heavier. Slide 16: Limitations of Turbocharging:
The use of Turbochargers requires special exhaust manifolds.
Fuel injection has to be modified to inject more fuel per unit time.
The efficiency of the turbine is sensitive to gas velocity so difficult to obtain
good efficiency over a wide range of operations.
One of the main problem with turbochargers is that they do not provide an
immediate power boost. It takes a second for the turbine to get up to speed before
boost is produced. This results in a lag known as ‘Turbo Lag’ Advantages of Turbochargers over Superchargers:
Less weight and size.
No load on the engine.
Efficiency of the engine is increased. Slide 17: THANK YOU