P12472: Solar Stirling Generator
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Background Research

Stirling Engine Type Research

Engine Configuration/Description Pros Cons

Alpha

  • conceptually simple design
  • high power to volume ratio
  • allows simple use of regenerator
  • hot side piston sealing issues

Beta

  • one power piston
  • one cylinder housing
  • seal is on cold side
  • less power output than the alpha configuration

Gamma

  • mechanically simple
  • separate cylinder for the power piston
  • lower compression ratio

Free Piston-

same as other configurations except uses a diaphragm instead of a piston. Also includes the fluidyne configuration.

  • reduces moving parts
  • no need for linkage
  • can nearly eliminate friction
  • short life span
  • poor response to load change

Rotary

  • No pistons
  • No seals
  • many moving parts (more than the Wankel)
  • has not been proven to work

Fluidyne

  • no seal
  • inexpensive
  • only efficient at a large scale

Ringbom

  • very few moving parts
  • indirect control of engine
  • energy wasted with loud thumping sound during operation

Franchot

  • more efficient than single alpha
  • connecting rod on hot side has sliding seal

Engine Selection:

We selected the Beta type configuration because...

Materials Research

Engine Body - bulk of the material used in the engine, weight is a big issue

Body Material Pros Cons

Steel

  • Strong
  • Durable
  • Low cost
  • Easily obtained
  • Heavy
  • Corrodes

Aluminum

  • Light
  • Relatively corrosion resistant
  • Expensive
  • Weaker than steal

Brass

  • Aesthetically pleasing
  • Expensive

Pistons - must provide a good seal but must also be very low friction

Piston Material Pros Cons

Graphite

  • Low friction
  • Brittle
  • Difficult to machine

Cast Iron

  • Low friction
  • Corrosive
  • Heavy

Heat Sink - must be a highly heat conductive material

Piston Material Pros Cons

Copper

  • great conductor
  • Expensive

Aluminum

  • Easy to machine
  • relatively inexpensive
  • not as conductive as copper

Electric Motor Research

Motor Type Pros Cons

Stepper Motor

  • Are brushless (don't wear out as fast)
  • Produce more voltage at lower speeds
  • Drive electronics are complex (for self start)

DC Motor

  • Drive electronics are simple
  • Need to be operated faster than a servo for comparable voltage
Sources: http://hibp.ecse.rpi.edu/~connor/education/IEE/lectures/Lecture_8_Stepper_motors.pdf

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