Is the Stirling Engine Just Hot Air?

[snowgoose]

More than 180 years ago Robert Stirling, a Scottish clergyman found a way to make an engine work literally on thin air with no fumes or toxic gasses. The Stirling Engine is claimed to be a 'free energy' generator that uses the principle of dilation and contraction of a fluid when exposed to different temperatures to rotate the engine and the bigger this difference the faster it rotates.

But is the Stirling Engine a true revolution in technology as a hot-air engine for generating free energy, has anyone built or used one or is it like so many other free energy devices just hot air?

[mbrownn]

Stirling engines are excellent and although it is simple to make one that will run off a cup of coffee, it is not so easy to make one big enough to generate significant amounts of power. With modern manufacturing techniques and materials it would be possible to make these engines at a cost effective price but there is not enough demand at this time to make a manufacturer invest what would be required to do this.

[wonza]

Sounds like this: Heatmobile (from the latest energy times newsletter)

[EnergyExpert]

Stirling engine represents more than hot air..

In this world we have become slaves to fossil fuels and electricity. The Stirling engine is an example of the usage of more natural forms of energy to do work. Companies, especially industrial companies, use and deliver compressed air throughout their facilities for use in pneumatic tools. This engine can provide rotational power where it is needed without the cost or dangers of electrical or fossil based energy especially in sensitive environments, such as those with dust problems.

Another device that seems to deliver the same sort of natural energy utility is the gravitational systems engineering, which is selling pumps and stuff which generate compressed air from moving traffic.

[realmikel]

heatmobile is not similiar that uses memory wire. The stirling engines were actually built as large as 140 hp during the civil war and the rider version was used by many farmers to pump water. More recently Philips in holland built an engine for a car the size of ford pinto and chose to drop it rather than rebuild the factory to build a different style engine. In sweden they power submarines with this style engine. Munson changed up the design a little in the 50"s and you may find his design very interesting. Some people are even patenting variations on munsons design recently. It works , even the solar versions, It has been made by many modelers because it is a multifuel device, I have no idea why we stopped production of them in the 1800's unless it was the fuel wars that have gripped our country for some time.

[realmikel]

Munson

opps " Manson"

[Mad Scientist]

The Stirling engine is a unique engine but it is not a free energy device. It does require heat to run however that heat can come from any source, such as solar to burning yak dung. These engines have been built in various size and shapes. Their biggest problem is typically they have a poor power to weight ratio.

The typical working fluid in these engines is air, although other gases can be used. This air is in a closed system and is heated to produce pressure for the power stroke of the piston. The air is then cooled reducing its pressure and allowing the piston to return to its starting point. When watching one of these engines run it is kind of amazing to realize just how quickly this air is repeatedly being heated and cooled.

Due to the metals that were used and the high temperatures required to produce usable amounts of power the very early engines did not have a long life. That along with their size forced people to look for other type of engines.

By pressurizing the air inside the engine is simple way to effectively “supercharge” it. I’ve been temped to build a opposed two cylinder engine using this type of supercharging but have never quite gotten around to it.

[mbrownn]

I agree with all the failings of the early devices but with modern techniques these could be mostly overcome. The efficiency is similar to an internal combustion engine so if we are supplying the heat there is no great advantage. It makes sense that we use natural sources of heat that come for free then we can claim a COP of infinity. Another and probably more practical method would be to use exhaust heat from conventional equipment such as air conditioning units and power stations to provide an improved efficiency of these devices.

Just think about it, 60 to 75% of the energy produced in our power stations goes up the smoke stacks and into the cooling towers so we could theoretically recover 30% of that with no problem. Using staged engines that work on a lower heat differential at each stage we could recover almost all that energy but there comes a point where it becomes impractical as low temperature differential engines are large and expensive for the amount of power that they produce.

It would be cost effective using this technique to recover at least 50% of the losses if these engines were in mass production. They would be as expensive as internal combustion engines but cost nothing to run other than routine maintenance so after installation so its money in the bank for the power generators. We have to persuade the power companies to investigate this further. Nothing will come of it if we do not do this.

There is no increase in pollution caused by using sterling engines and it would create jobs in proportion to its implementation.

We just have to persuade a company to produce the the right size of engines for this purpose and they would get rich. We would benefit from reduced power costs but of course you know that will never happen.

It is not a final solution to power generation but is a cost effective solution to the mid term problem until we have a better alternative developed. We have all the engineering skills required, we just need the will to do it.

[snowgoose]

The Stirling engine is a unique engine but it is not a free energy device. It does require heat to run however that heat can come from any source, such as solar to burning yak dung. These engines have been built in various size and shapes. Their biggest problem is typically they have a poor power to weight ratio.

Thanks Mad Scientist, great explination. Stirling Engines seem to be making a comeback using the sun's thermal energy as their "free" heat energy source to generate electricity or heat water, I guess making it a free energy device. Don't understand the connection with the heatmobile though?.

Typical applications of Stirling engines seem to be mounted onto solar collectors and solar towers to concentrate the suns energy onto the engine. This site has some information about using Stirling engines as solar collectors.

It would be a nice little project to buy or construct a Stirling engine and put it on the end of a satellite dish and see if it works, if they are not too expensive, are there any suppliers?

[sykavy]

In 1986, when gas was selling at the pump for a dollar, NASA decided it would begin a project to improve the fuel efficiency of the automobile. This project was known as the "Stirling Automotive Engine Development Program."

Here is a promotional video of the experiments
https://www.youtube.com/watch?v=H_Vnxapd5fs

If you were observant (in the video) there was no concrete facts given on mpg; I mean miles per gallon efficiencies. They said it was more efficient and seemed to replace the internal combustion (IC) engine in the vehicle, with 10 less horse power Sterling. So they took out a 95 horse power engine and replaced it with a Sterling 75 horse power engine, but didn't explain why.

With a little research I found out that NASA was able to achieve 58 MPG by replacing the IC engine in the Chevy Celebrity with a Stirling engine with a 38% overall maximum efficiency (IC has only 15%); more than twice that of an IC engine. Although this project had impressive results, it fell short of the Holy Grail of 100 MPG. As an example of typical government behavior, the successful program was therefore shelved with no further development. Lack of interest by automakers ended possible commercialization of the Automotive Stirling Engine Program.

[Peter Kiproff]

Hi Snowgoose
There are differant types, I'd like to build one with Rotary Displacer
seems easiest to build & since it doesn't Recipricate the displacer acts more like a flywheel.