The Stirling Engine is one of those endlessly fascinating technologies. Though it can exactly approximate the Carnot Cycle – the King of heat cycle efficiency – it deviates rather substantially from the ideal in practical applications. So it's no surprise that while the technology has been around for a couple hundred years, and currently under study in some novel applications like powering a cooling fan, it's never really caught on in the mainstream.
Which makes it just the sort of intriguing design challenge Engineer Doug Connor was looking to take on in his spare time. He's learning more about the technology by building a working prototype of a small (desktop) engine powered by sunlight, taking measurements and figuring out how to improve the performance.
"A Stirling Engine is very simple in construction – you've basically got two pistons and a piston and a displacer," he says. "But the simplicity in the way it functions notwithstanding, the simulation and analysis of one can be quite difficult."
He's capturing the diabolical, nature of the task on his website, www.solarheatengines.com, where he has been documenting the steps he's taken to simulate, analyze, design, build and test a small solar-powered engine. See photos and watch a video of his most recent design.
Though Connor says he started the website mainly as a way to organize his own content, it's a treasure trove of information for anyone interested in building a solar-powered Stirling Engine of their own, including 3D CAD drawings, a parts list, and test results. Readers following his progress have the option to post comments on the site.
Even if you have no plans to build a Stirling Engine, it's a fun site to troll and get a behind-the-scenes peek at real-world design under development.
Connor's ultimate goal is to build something practical, and what that ultimately comes down to is figuring out a way to scale his model and deliver more power without driving costs up. "I showed a development engine with a power output of about 0.1 Watt," he says, describing his experience at the Maker Faire in Northern California in May 2008. "If I can increase the output to 1,000 times that, I think the interest is out there."
YouTube has some great videos of small Stirling Engines in action, like this coke can model. Type in "Stirling Engine" on YouTube to see more fun stuff.