Function Principle of the Stirling Motor

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Function principle of the Stirling motor

T

he principle of the Stirling motor is very oldand very simple! Over 2000 years ago in ancient Egypt, the

expansion of heated air was used to set temple doors in motion. The hot air engine patented in 1816 by

Robert Stirling is based on a similar principle: A burner filled with fuel heats the air inside a cylinder and

thereby purveys energy to the motor that activates through piecing of the flywheels.

Stirling motors are impressive machines despite their simple design!

The air in the closed operating cylinder is heated by the flame, expands, and flows past the expulsion

piston to the other side of the cylinder, where it pushes the working piston towards the outside. Since

the expulsion piston is now connected to the rotating flywheel it now moves back, letting the air behind

the expulsion piston cool to create a vacuum. This vacuum ensures that the working piston gets sucked

back. The process then repeats from the beginning and the machine works.

Function principle of the vacuum motor

T

he vacuum motor patented by Henry Wood in 1758 is also commonly referred to as flame eater and is

part of the hot air engine family along with the Stirling motor. Similarly to the first Otto-motor, the

atmospheric pressure performs the major part of the work.

The piston sucks the frontally positioned flame into the cylinder through a valve (the characteristic

operating noise this makes is reminiscent of a Lanz tractor). The flame heats the air in the cylinder,

pushing the piston back.



Thereupon the valve connected to the flywheel shuts, letting the air in the cylinder cool. Because of the

atmospheric pressure, the piston moves back to its starting position. When the piston reaches its top

dead center the valve opens again and the process begins anew. The flywheel supports the overcoming

of both dead centers.

Functional models of vacuum motors are often constructed as stationary motors with a horizontal or

standing design and one or many cylinders. One can also find vacuum motors in historical models of

tractors and railcars.

Help for problems with your Stirling motor

What can I do if my motor doesnt run?

Dismantle the operating cylinder and clean the piston and working cylinder with a dry cloth. Clean out

the brass cylinder down to the bottom. Reassemble the motor and check proper functioning.

The connection rods have to be slightly laterally moveable and should not jam. Do not pull the screw too

tight since the connection rod can jam if you do.

Make sure that the rocker arm can swing freely (Remove the connection rods to test this). Any friction

can bring the model to a halt.

Make sure that the gap between flywheels and ball bearings is approximately 0,2mm wide so as toprevent braking of the bearings.



How should I glue the bearings?

Degrease the ball bearings and bore holes with ethyl alcohol and a cloth before setting the bearing

aside. Dip a needle in superglue (wear protective goggles and gloves to prevent injuries) and guide the

needle tip along the bore holes so as to apply only a thin coat of glue. Put the side frame over the

bearing with the countersink facing downward. The spacing is correct if the side frame rests directly onthe table. After a short time the bearing is attached.

Does the motor need to be lubricated?

Too much oil will bring he motor to a halt, forcing you to disassemble and completely clean it again. Oil

must only be applied to the displacement axis after the first test run. Greasing can bring the motor to a

halt!

Ceramic past should only be applied wafer-thin after the first test run. Too much ceramic paste leads to

the motor not starting up (see 1.).

Use of other lubricants voids the guarantee!



How do I regulate the rotation speed?

The rotational frequency depends on the packing length and the vertical and horizontal distance to the

heating cylinder. The engine should only be operated with ethyl alcohol (94%). Use of other fuels voids

the guarantee. Tea candles are not appropriate since they soot the motor.

For your safety

Never leave an open ethyl alcohol bottle near fire. There is an explosion hazard.

Only fill the burner up to the lower mark!

Legal regulations for naked flames apply. The device is not appropriate for children! It should only be

operated by adults and under constant supervision.

No flammable objects should be placed near the burner.



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Function Principle of the Stirling Motor