Piston Engines: Thrust Augmentation

1. Piston Engine Propulsion
Thrust Augmentation

2. • Air enters the carburettor at atmospheric
pressure and is mixed in the carburettor with
the fuel.
• The fuel/air mixture leaves the carburettor at
near-atmospheric pressure, is compressed in
the supercharger to a pressure greater than
atmospheric, and then enters the engine
cylinders..

3. • The power required to drive the supercharger
impeller is transmitted from the engine
crankshaft by means of a gear train.
• Because of the high gear ratio, the impeller
rotates much faster than the crankshaft

4. • The higher an aircraft climbs, the less oxygen
is available to the engine for combustion.
Therefore, as a reciprocating engine powered
aircraft climbs, the power output of the
engine decreases.
• To help prevent this loss of engine power,
more oxygen must be forced into an engine.
One method of getting more air into the
engine is with a supercharger.

5. Supercharging
The main purpose of supercharging an aircraft engine is
to increase the manifold pressure above the pressure of
the atmosphere in order to provide high power output
for take-off and to sustain the maximum power at high
altitudes.
Increased manifold pressure increases the power output
in two ways:
• It increases the weight of the fuel/air charge delivered
to the cylinders of the engine.
• It increases the compression pressure. The
compression ratio for any given engine is constant;
hence, the greater the pressure of the fuel/air mixture
at the beginning of the compression stroke, the greater
will be the compression pressure

6. • Most superchargers used on conventional
aircraft are alike in that an impeller rotating at
high speed is used to compress either the air
before it is mixed with the fuel in the
carburettor or the fuel/air mixture, which
leaves the carburettor.

8. • Air enters the carburettor at atmospheric
pressure and is mixed in the carburettor with
the fuel.
• The fuel/air mixture leaves the carburettor at
near-atmospheric pressure, is compressed in
the supercharger to a pressure greater than
atmospheric, and then enters the engine
cylinders.

9. • The power required to drive the supercharger
impeller is transmitted from the engine
crankshaft by means of a gear train.
• Because of the high gear ratio, the impeller
rotates much faster than the crankshaft.

10. AIR COMPRESSORSUPERCHARGER – DRIVEN BY THE ENGINE
GEAR OR BELT DRIVE
SIMPLIFIED PISTON ENGINE FUEL SYSTEM

11. Turbocharger
• A drawback of gear driven superchargers is
that they use a large amount of the engines
power output for the amount of power
increase they produce.
• This problem is avoided with a turbo
supercharger, or turbocharger, because an
engine’s exhaust gases power turbochargers.
• In other words, a turbocharger recovers
energy from hot exhaust gases that would
otherwise be lost.

12. • Another advantage of turbochargers is that
they can be controlled to maintain an engine’s
rated sea- level horsepower from sea level up
to the engine’s critical altitude.
• Critical altitude is defined as the maximum
altitude under standard atmospheric
conditions that a turbocharged engine can
produce its rated horsepower.
• In other words, when a turbocharged engine
reaches its critical altitude its power starts to
decrease just like a normally aspirated engine

14. COMPRESSED
AIR TO ENGINE
TURBOCHARGER – DRIVEN BY THE ENGINE EXHAUST GASES
EXHAUST GASES
FROM ENGINE
THROUGH
EXHAUST PIPE
TURBINE BLADES
SIMPLIFIED PISTON ENGINE FUEL SYSTEM

15. CARB.
AIR
FILTER
ENGINE
THE PARTIAL VACUUM TENDS TO WORK AGAINST THE PISTON MOVEMENT MAKING
IT HARDER FOR THEM TO PULL AIR IN
INLET
MANIFOLD
AND FLOW RESTRICTION THROUGH THROTTLE VALVE CAUSED BY SUCTION
FROM ENGINE
BETWEEN THROTTLE VALVE AND ENGINE IS A PARTIAL VACUUM
EXHAUST
MANIFOLD
INLET MANIFOLD VACUUM
AND THEREFORE, THE CYLINDER MAY NOT BE FULLY CHARGED 100% WITH
AIR/FUEL MIXTURE
IF AIR COULD BE FORCED INTO THE ENGINE, THERE WOULD BE A GREATER
VOLUME OF AIR/FUEL IN THE CYLINDER
THEREFORE MORE POWER WOULD BE PRODUCED
SO HOW COULD THIS BE ACHIEVED?
BY USING AN AIR COMPRESSOR
LET’S SEE HOW
SIMPLIFIED PISTON ENGINE FUEL SYSTEM

16. AIR COMPRESSOR
AIR
COMPRESSOR
TAKE THE LID OFF
AND LOOK INSIDE
SIMPLIFIED PISTON ENGINE FUEL SYSTEM

17. CUT IN HALF AND LOOK AT CROSS SECTION
CROSS
SECTION
ROTOR
ROTOR
ROTOR
VANES
STATOR
VANES
OUTLET
DUCT
TAKE LID OFF AND LOOK INSIDE
SIMPLIFIED PISTON ENGINE FUEL SYSTEM
AIR COMPRESSOR
TYPICAL
ROTOR

18. AIR ENTERS
THE ‘EYE’ OF
THE ROTOR
SIMPLIFIED PISTON ENGINE FUEL SYSTEM
AIR COMPRESSOR