1. Piston Engine Operations
PISTON ENGINES
Part 7
Piston Engine Operations
(Cooling and Thrust)

2. Introduction Air Cooling and Liquid Cooling.
Of the total heat produced in a piston engine,
about 50% is used as energy, 40% passes into the atmosphere,
and the remaining 10% is absorbed by
the pistons, cylinder heads, valves etc.
and by the lubricating oil that splashes against them.
Unless these components are cooled by some means,
they become over-heated,
causing distortion, increased wear, and a reduction in strength.
Excessive temperatures can also result in engine seizure.
Two methods of cooling are in common use;
Air Cooling and Liquid Cooling.

3. Air Cooling A prime example of Air Cooling Simply expose the cylinders
The advantages of Air Cooling include :-
Simple and less costly to produce.
Lighter engines.
But there are disadvantages :-
Difficult to cool all cylinders evenly, especially inline engines.
Difficult to get engine to run at most efficient temperature
on ground and at altitude.
Except for small amount of ‘prop-wash’,
early systems only effective when aircraft or vehicle
is moving forward.
Air cooled engines tend to be noisier than liquid cooled engines.
Not so easy to streamline.
A prime example of Air Cooling
Simply expose the cylinders
to the slipstream air !

4. Air Cooling Air Cooling Flows Air cooling is light,
relatively cheap and little or no maintenance is required
as there are few working parts.
Cylinders
In air-cooled engines
the outer surfaces of the cylinder head
is extensively finned
and a flow of air is directed over
the exposed surfaces.
The fins are kept thin
and close together
to obtain a maximum surface
in contact with the air.
Modern flat-four
air cooled engine

5. Air Cooling Air Cooling Flows Air cooling is light,
relatively cheap and little or no maintenance is required
as there are few working parts.
The aircraft cross section shows
a typical cooling airflow
through the forward facing intakes,
one each side of the spinner
directly in line with the cylinders.
An outlet at the bottom is provided
to allow the cooling flow to escape.
Airflow circulation in different aircraft
would follow similar principals.
Air Intake
Air Outlet
Cross section of
typical light aircraft

6. Air Cooling Forced Air Cooling Fan assisted and ducted airflow
can overcome some of the air cooling disadvantages.
Engines can be fitted with a fan driven by the crankshaft,
and a duct to direct the air flow over the cooling fins.
The downside is that the fan takes power from the engine.
The engine shown here
is fan assisted air cooled,
and is an engine for static
(or near static)
industrial use
where a cooling flow would be
difficult to achieve.
Cylinder
Cooling Air Duct
Fan
Crankcase
Typical single cylinder engine

7. Air Cooling Forced Air Cooling
The picture shows a typical light aircraft flat four installation,
viewed from above.
Cooling air flow ducts are fitted to channel the cooling air
directly over the cylinder cooling fins,
ensuring maximum cooling.
Most modern vehicles have
an electric fan instead of
a crankshaft driven type.
This puts less load on the engine
when forced cooling is not required.
The fan usually cuts in when in
slow moving traffic,
where forward speed is too low
to provide ram air cooling.
Light aircraft installation
with cooling air ducts
to improve airflow over cylinders
Cooling Air Ducts

8. Air Cooling Air cooling, however, cannot keep the engine
at a constant temperature under all conditions.
Consequently the engine components tend to have
a shorter life than those of a liquid-cooled motor.
Air Outlet
Air Intake
Cooling Air Ducts

9. Liquid Cooling The advantages to Liquid Cooling include :-
The engine temperature can be maintained more evenly.
The operating temperature of the engine
can be kept within a narrower range.
The more even temperature makes the engine more efficient.
The cooling ‘jacket’ makes the engine quieter.
The engine can be more easily streamlined
and thus produce less drag.
But there are also disadvantages :-
Tend to be heavier.
More complex, more weight, costlier to produce.
The system needs more maintenance compared to air cooling.

10. Liquid Cooling Coolant / Engine COLD:- Coolant / Engine HOT:-
Thermostatic Valve CLOSED
Thermostatic Valve OPEN
Pressure Relief Valve
Cooling Fan
Radiator
Coolant circulates around engine block and radiator
Coolant circulates around engine block only

11. Liquid Cooling We will now look at these three areas
Thermostatic Valve
Pressure Relief Valve
The temperature in the engine coolant
easily attains boiling point,
and could boil away.
Therefore boiling has to be avoided.
Radiator
This is achieved by pressurizing the cooling system.
If the system pressure rises above a design value,
the excess will bleed off through the relief valve.
Constant loss of fluid with no obvious leaks
probably means the relief valve needs replacing.
CAUTION: -
NEVER REMOVE THE PRESSURE OR FILLER CAP
OFF A HOT ENGINE COOLING SYSTEM.

12. Liquid Cooling The Radiator A radiator is a means to transfer heat
Expansion Chamber Connection
Hot Coolant In
Top Hose Connection
A radiator is a means to transfer heat
from one medium to another,
so they are more correctly entitled
Heat Exchangers.
The coolant flows along horizontal tubes,
above and below which are
corrugated thin metal cooling strips;
these tubes and cooling strips are called
the ‘Matrix’.
Radiator
Cooler Coolant Out
Bottom Hose Connection

13. Liquid Cooling The Radiator Hot coolant heats the metal strips,
which are cooled by the passing air;
exactly the same as the cooling fins on an air cooled engine!
In this example we have air and coolant as the two mediums,
other systems have the following: -
Fuel and Oil – unwanted heat in engine oil
is transferred to the fuel, to prevent fuel icing.
Fuel Cooled Oil Coolers (FCOC) or
Fuel Oil Heat Exchanger (FOHE).
Air and Oil – unwanted heat in the
engine oil is transferred to the air,
which like the air cooled engine,
is then dumped overboard.
Air Cooled Oil Cooler (ACOC).
Heated Coolant
Warm Air Flow Out
Cool Air Flow In
Cooled Coolant

14. Liquid Cooling Thermostatic Valve
The Thermostatic Valve is usually housed
in an easy to access bell housing
on the engine block,
generally where the top hose
is connected to the engine.
Consisting of
a temperature sensitive wax pellet,
within a rubber diaphragm,
it is no more than a heat switch.
Thermostatic Valve
Thermostatic Valve
Connection
Typical
Thermostatic
Valve
Rubber Diaphragm
Wax Pellet

15. Liquid Cooling Thermostatic Valve
With a cold engine, the valve is closed;
isolating the radiator flow,
and forcing coolant around the engine block only.
As the coolant heats up, it heats the wax pellet,
which expands against the diaphragm,
pushing the valve open.
When the valve opens,
coolant is directed to flow
through the radiator.
A ‘Jiggle-pin’ in the valve plate
allows air to escape,
and a small coolant flow to
the radiator so it starts to heat up
before the hot coolant
is allowed full flow.
OPEN
with Flow
CLOSED
No Flow
To Radiator
‘Jiggle’ pin
Rubber Diaphragm
Wax Pellet

16. Liquid Cooling Other Features
The expansion tank provides for the heated coolant to expand.
Most systems have the pressure relief valve on this tank,
and a simple gravity fill priming point on the radiator.
Hot coolant goes through a heater matrix, to heat the vehicle.
The air passes through the matrix via the control valves,
and a multi speed fan can be switched on
to increase the air flow into the vehicle.
Pressure Relief Valve
Air intake
duct
Fan
Feet
Screen Demist
Facia
Expansion Tank
Heater matrix
Control valves
Heating Unit

17. Thrust Augmentation What is it? Supercharging and Turbocharging
A method of extracting more power
from Internal Combustion Engines.
It’s a form of ‘Power Boosting’
There are two types of booster: -
Supercharging and Turbocharging
both working on air compressors

18. Thrust Augmentation The Air Compressor Let’s take a closer look here.
Between the Throttle Valve and the Engine is a partial vacuum.
This vacuum works against the piston movement,
and the cylinder may not be fully charged with Air/Fuel.
If Air was forced into the engine,
there would be a better Air/Fuel mix in the cylinder.
Because more air means
more fuel can be added.
More air and fuel means
more power is developed.
more THRUST !
CARBURETTOR
AIR FILTER
ENGINE
INLET MANIFOLD
EXHAUST
MANIFOLD
AIR COMPRESSOR
Let’s take a closer look here.

19. Thrust Augmentation The Air Compressor
The compressor works with a rotor, using centrifugal force.
The rotor spins the air between the rotor vanes,
forcing it from the centre out to the rim,
then pushing the air through the static fins or stator vanes.
This compressed air is then piped to the fuel controller,
and the engine, via the outlet ducts.
STATOR VANES
OUTLET DUCT
ROTOR VANES
ROTOR
CROSS SECTION
LET’S TAKE THE LID OFF
TAKE A CROSS SECTION

20. Thrust Augmentation The Air Compressor
The air enters the ‘eye’ of the rotor,
and is forces outwards.
It is then pushed into the stator vanes,
and forced through the outlet ducts.

21. The Super Charger The Air Compressor
Supercharging is an air compressor
driven by the engine
via a gear train or belt drive.
They can take some 20% of the engine power to drive,
but can increase overall engine power up to 50% or more,
giving a net gain of 30%+ power.
COMPRESSED AIR TO ENGINE
GEAR OR BELT DRIVE

22. The Turbo Charger Turbocharging is a similar air compressor,
but driven by the engine exhaust gases,
passing through a turbine.
Turbo’s take very little power from the engine to drive them,
therefore the net gain in power is relatively greater,
although they can suffer from what is called ‘turbo-lag’.
COMPRESSED AIR
TO ENGINE
TURBINE BLADES
THROUGH
EXHAUST PIPE

23. Check of Understanding
What is the main benefit of using liquid,
as opposed to air, to cool an engine?
The engine will be lighter
A steady temperature
is easier to maintain
The engine will be simpler
The engine will be less costly
to maintain

24. Check of Understanding
Of the total heat produced in a piston engine,
approximately how much is used as energy?
20%
40%
50%
60%

25. Check of Understanding
What is the purpose of the fins
arranged about the cylinder and cylinder head
of an air-cooled engine?
To reduce the engine weight
To allow air to move freely through
the engine compartment
To allow heat to dissipate rapidly
To prevent the engine coolant
from boiling

26. Check of Understanding
Fan assisted airflow can overcome
some of the air cooling disadvantages.
What is the major downside to this?
The fan takes power from the engine
The temperature of the coolant
easily attains boiling point
The fan makes the engine noisier
A partial vacuum forms between
the throttle valve and the engine

27. Check of Understanding
In a liquid cooled engine,
how is coolant boiling avoided?
By making the cylinder fins
thinner and closer together
By the use of heat exchangers
By forcing the coolant
through a heater matrix
By pressurizing the cooling system

28. Check of Understanding
What is the purpose of a thermostatic valve?
It isolates the radiator flow
It provides for the heated coolant
to expand
It maintains pressure
in the cooling system
To bleed off excessive coolant

29. Check of Understanding
Up to what increase in overall engine power
can supercharging produce in a piston engine?
20%
30%
50%
60%

30. PISTON ENGINES
End of Presentation