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A wood fired stirling engine to make heat and electricity and boil water
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A wood fired stirling engine to make heat and electricity and boil water

This post is about creating a household-scale stirling engine that runs on wood or dried plant material as part of a distributed biomass energy economy. This is a viable energy option for much of the central and midwestern United States where sunshine is spotty but plant growth is fervent.
I plan to develop this project into a working engine and to publish a well written fully-enabling book on how to build it. For now, I'm just sharing the plans for free. Sharing the technical plans but selling the full book is in keeping with my ongoing attempts to balance pursuits in open source vs. intellectual property.
Anyway, download the plans for yourself. They're free, and you never know when you might need some reliable energy independence. (;->)

Open source engine plans: I designed the Apocalypse Engine (snappy name?) to meet the energy needs of a single household, provided you have access to flammable biomass. This can include firewood, straw, leaves, or pretty much anything organic put through a chipper-shredder. (Dried zombies included... in keeping with the theme.... ) You have my permission to build and use this engine for your home, business, or weekend getaway.

Requirements to build: metal fabrication skills Making this engine is not exactly a DIY project, unless you are a skilled metal fabricator. There is some machining involved, but most of the project involves cutting, rolling, fitting, and welding sheet metal. You won't need a CNC lathe, nor a foundry. If you want one of these engines, take the plans to a fabricator near you. The parts list totals around $1500 in parts and metal supplies. Disclaimer: unbuilt, untested - for now. I have designed this project to the best of my abilities, but have neither built nor tested it. Available numerical simulation tools suggest a nominal mechanical output of around 1.5 kw. By the time you are driving an electrical generator, this equates to right around 1 hp (746 Watts) of electrical power output.

Description of the engine: The base is essentially a wood stove, which provides around 100kbtu/ hour of heat. The top is a 20 gallon water tank, providing boiling temperature water that can be used for bathing is also rendered safe for drinking. The chamber in the middle is the expansion chamber of the stirling engine. There is a flywheel at the top with cranks on either side that are driven-by and drive a piston and an internal displacer respectively. When the whole thing is running, a belt wrapped around the flywheel drives an electrical generator. Available numerical simulators suggest a nominal mechanical output of around 1.5 kw. Accounting for frictional and electrical losses of driving a generator, the final electrical output scales to right around 1 horsepower.

Tech Specs:

Hot water tank: 20 Gallons

Burner heating power: 100,000 BTU/hr

Stirling engine power: 1.5 kw mechanical

Generated electrical power: 750W max at 24VDC

Engine speed: 100-150rpm

Swept engine volume: 3777 cubic inches (61893 cc)

Hot side Temp: 1200˚F (649˚C)

Cold side Temp: 212˚F (100˚C)

Working fluid: Air

Estimated median operating pressure: 25psi (172kPa)

Piston diameter: 8 inches (20.3 cm)

Piston travel: 4.75 inches (12 cm

Generator speed: 1000-1500rpm

System total weight, minus water: 220 lb (100 kg)

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