State of the Art - EEECS

Source

Engineering - Electrical Engineering and Computer Sciences, University of California, Berkeley
2007

Characteristics

Type:    gamma, free piston
Theoretical power:  26.9W (Schmidt analysis) with Th=175°C and Tc=25°C and air at ambiant pressure
Measured power:    9.3 W delivered to electric load
Beale:   0.0039
Heater:    210 cm3 * 27,5%, wetted area = 0.35m2
Cooler: 210 cm3 * 23%, wetted area = 0.37m2
Regenerator: 260 cm3 * 63,4%, wetted area = 1.9m2

Illustrations

1) End cap
2) Cold end plate
3) Hot end plate
4) Power piston assembly
5) Precision Shaft
6) Peek cylinder
7) Socket cap screw
8) Socket cap screw
9) Coil windings
10) Heat exchanger frame
11) Cooler fin assembly
12) Heater fin assembly
13) Wooven Screen
14) O-ring
15) Displacer piston assembly
16) Magnetic spring assembly
17) SwageLok
18) PVC Pipe
19) Plug

Details

www.eecs.berkeley.edu -  [ pdf ]

This Gamma-type free piston engine is controlled mainly with magnetic forces. The engine has been tested at 3 Hz with air at ambient pressure as working fluid.

The piston weight is 6.4 kg, it is made of low-carbon steel and located at the cold side of the engine.

Displacer and power pistons have the same dimensions, the displacer stroke is 15cm. The displacer is made of PEEK (polyetheretherketone) that endures temperatures up to 250°C. It is designed to resonate with linear magnetic spring at the frequency of 3 Hz. Permanent magnets (Sm-Co) are incorporated in the displacer to enable the magnetic spring and also to act as linear motion actuators.

Piston and displacer slide along a central shaft. Linear ball bearings enable smooth and low friction motion of the piston and displacer. Ceramic ball have been chosen to avoid any interaction with the magnetic field.

Heater and cooler are base on fin-tube structures.

The regenerator is a stack of woven wire screens with circular cross-section wire.