Stirling Engine Demonstration Model. It is a do-it-yourself construction out of simple materials like test tubes, Lego pneumatic cylinders and marbles.
The starting position of the engine is tipped to the left. The alcohol burner heats the air in the right area of the test tube; the air expands and pushes the pneumatic cylinder and thus the test tube upwards. The marbles roll to the right. The hot air is then forced to the left, where it gets cooled. The cool air shrinks, the pneumatic cylinder moves downwards and the test tube tips counter clockwise. The marbles roll left and the air is pushed right, to the hot side. The air expands and moves the piston again. And so on and so forth.
There’s a piece of steel wool in the bottom of the test tube (hot side). It’s both, heat exchanger and cushion (to avoid the test tube to break). In the test tube are placed five marbles that act as displacer piston as they move the air from the hot side to the cold side and backwards. As friction is a common problem in building Stirling engines, I decided to use a low-friction “LEGO” pneumatic cylinder as working piston. Furthermore the whole system has to be 100 % leak-proof; I used an original Edradour Scotch Whisky cork to close the test tube and finally silicon to seal all crucial parts. To make the engine finally run some fine tuning in terms of balancing the test tube and positioning the pneumatic cylinder and the heat source is necessary.
The Stirling cycle machine, which can operate as either an engine or a heat pump, has aroused much interest because of its many favorable characteristics. These include:
Minimal pollution. In the case of an engine, the exhaust gases are comparatively clean and cool.
Silent and practically vibrationless operation in some configurations.
Potential for low fuel or energy consumption. The maximum attainable efficiency or COP for any heat engine operating between the same temperature differential.
Multi-fuel capability. The energy source may be almost of any form whatever, so long as it is available at a sufficiently high temperature. Stirling engines have been run on solar energy and a variety of liquid and solid fuels. This applies to heat pumping as well by the use of the duplex configuration.
In many instances, it is possible to hermetically seal the machine thus eliminating problems arising from dirt ingress. Some of these configurations have demonstrated operating lives exceeding 10 years.
Reversible operation allowing the same device to be used as an environmentally friendly wide temperature range refrigerator or heat pump. This feature also introduces the possibilities of regenerative braking.
Reasonable specific power (currently between 0.067 kW(e)/kg for higher power engines down to 0.033 kW(e)/kg for lower power engines). As a low capacity heat pump (up to a few hundred Watts), the specific lift is considerably better than other heat pump technologies (30 to 40 W/kg).
Favorable torque characteristics for transportation applications. This leads to simpler transmission designs.
Mechanical simplicity. In some configurations gas bearings are easily implemented thus avoiding the need for oil lubrication.