My final project for an Alternative Energy's class at Sierra Nevada College, is a stirling engine. Which is a catchall term for any heat engine that uses the expansion and contraction of air under the influence of a temperature change to convert thermal energy into mechanical work.
A stirling engine uses air, which is repeated heated and cooled. To allow the air to be heated and cooled the can contains a displacer which is like a loose piston that can move up and down forcing the air around the engine. When the air is heated it expands pushing the diaphragm or in my case a cork- outward, which turns the cranks. When the cranks turn they move the displacer down so that the air is near the top where it is cooled causing it to shrink and pull the cranks back, which moves the displacer upwards allowing the air to be heated at the bottom, this repeats over and over.
This type of engine can run off of various heat sources such as solar, a candle, biomass, coffee steam, the heat from decomposition and more. For the sake of simplicity and budget I built my engine to generate electricity using an alcohol based candle.
Materials[edit | edit source]
- Tin can
- Smaller tin can (diced tomatoes)
- Balsa/scrap wood
- Coat hangers
- Plastic fittings
- Alcohol based candle
I had fooled around with a couple of designs, all using a tin can as the container to store the pressurized air. Inside the can is the smaller can that is the main displacer forcing the air upward and downward to heat and cool, expand and contract. This can is attached to a rod (coat hanger), which penetrates the wood above to create a seal with the larger can and wood, and then hitched with copper to the crankshaft.
My first trial the diaphragm rubber was too stiff to expand and push the crankshaft what so ever. Most designs use regular balloon, but I found a different design I thought would be “simpler”. Which is the current design, rather than having a diaphragm, has a separate displacer inside a copper chimney that forces the crank upward. I had the most difficult time bending the right measurements of the crankshaft so that it wasn’t thrown to far out to not function. I have FINALY achieved the rhythm and coordination it requires and led myself to believe it was ready to function. Yet, my engine is still not harnessing any energy… At this point I am led to believe it the containment of the air and pressure and still plan to continue tinkering to make it work.
Further reading[edit | edit source]
Here is a link to more about a stirling motor: Stirling_engine