Alpha-type Stirling engine

[kilocharlie]

I'm considering an Alpha-type Stirling engine build for use with a "surrey" (4-wheeled "bicycle") - firewood powered engine + legs & pedals powered. I will very likely use the Stirling engine, belts & pulleys, to drive an alternator for recharging a battery and go with an electric motor + battery + pedals on the surrey.

Anyone built an Alpha-type? I'm looking for blueprints, suggestions, do's & dont's, suggestions on size and power. I can handle the final strengths analysis, sizing from strength required & materials, etc., but would like to hear more practical discussion on features to include (or exclude), heat shielding, heat exchangers, websites to check out, books on the topic. Thank you.

 

[Longboy]

Stirlings make excellent models but I see your application as impossible. There would be no power to overcome drag from an alternator with Stirling. Your fuel supply and firebox would weigh too much for mobility. Better use a lawn mower engine for your pedal car. Take a look at Stirling powered boats and the home made Stirling car on Youtube. How large the engines are and how fast they drive a boat.

 

[vederstein]

The following links are to the only commercially useful stirling engine that I know was sold in the past 60-70 years - the Philips MP1002CA Stirling.

http://youtu.be/M9UKu-AP02k

http://www.oldengine.org/members/croft/images/MP1002CA.pdf

...Ved.

 

[kilocharlie]

Thank you for the links.

The Beta-type and Gamma-type Stirlings I see on the internet are either slugs or extremely low power designs. I have seen an Alpha-type that was less that one cubic foot volume of the crankcase + cylinders + heads that put out about 3 horsepower, sufficient for a surrey. It appeared to be made of machined aluminum, though I would opt for something more heat tolerant. It made lots of noise under power.

 

[Longboy]

Thank you for the links.

The Beta-type and Gamma-type Stirlings I see on the internet are either slugs or extremely low power designs. I have seen an Alpha-type that was less that one cubic foot volume of the crankcase + cylinders + heads that put out about 3 horsepower, sufficient for a surrey. It appeared to be made of machined aluminum, though I would opt for something more heat tolerant. It made lots of noise under power.

Make your reference here....I'd like to see a 3 HP Stirling.

 

[purpleknif]

I saw at one time on one of those History or discovery channel shows about steam engines that the Norwegians had built a Stirling powered submarine that was so quiet no one could find it. Just sayin'.

 

[Mechanicboy]

the Norwegians had built a Stirling powered submarine that was so quiet no one could find it. Just sayin'.

Wrong answer, it was swedish Gotland class submarine who had the stirling engine.

 

[kilocharlie]

Actually, I'm here asking for links and references. Yes, there are quiet Stirlings, many with low power. There are some with considerable torque. The one I saw was not quiet. The main problem with automotive application is the Stirling's tendency to be difficult to accelerate quickly - it is far better suited to steady power use. To make a battery charger with one seems reasonable.
I have been on projects involving low-power-requirement, high-efficiency vehicles. I can tweak the power requirement to suit a practical engine. The limitations could be the weight of the battery pack and the recharging time, so I'll have some balancing acts to do.
My hope is to find a design that is relatively compact, has a fair to very good power-to-weight ratio, is durable, and has known characteristics that I can deal with.
The Stirling, the alternator, the firebox, and the firewood could go on a trailer for longer trips.

Thank you guys for the lead on the Swedish Gotland-class submarine. I have run a few searches, and apparently Saab has taken over from Thyssen Krupp in Germany with surprise raid on the shipyard by the Swedish FMV back in April, perhaps in order to keep some of the propulsion system a secret. I assume there will not be any "free" info floating around about the AIP Stirling propulsion system, apparently heated by diesel & liquid oxygen.

The submarine can stay submerged for weeks without surfacing, and has an extremely low signature for sound and sonar, making it very difficult to detect.

 

[Mechanicboy]

The main problem in the stirling engine powered car (Ford Torino Stirling) was sealing and leakage of hydrogen. Hydrogen was used to control of power and revolution by hydrogen valve and hydrogen compressor operated by car driver. The sealing lasted not more than 23.5 hour. It was in 1977-1978 under testing of the stirling engine powered car. Driving the car was not problem (Instant trottle response and wide speed range), and fuel consumption was lower than ordinary car engine and low pollution. Today in modern stirling engine can last up to 80 000 hours between overhauling the engine and can be a good power source for the hybrid/electric car. Hybrid car is not new invention. See pic.

 

[kilocharlie]

Hydrogen gives a very small advantage over plain air, and sealing is just about impossible, as are Helium and Nitrogen. The danger of hydrogen far outweighs any benefits gained. Plain air works just fine.

Gasses other than plain air are tried largely to increase heat exchanger efficiency. Better gains are made by improving flow past the heat exchanger - think much larger filter box, finer filter element = more flow + better heat exchange.

I helped build a hybrid car some years ago, GM's prototype for the EV-1, originally named the "Impact", a very very poor choice of names for a passenger car. It went off the market for 3 years while they lived that down, then leased the vehicles instead of selling them - multiple faux-pas syndrome.

On the positive side, the prototype got over 210 miles on a single charge. It out-accelerated a Miata and a 300 ZX from 0 to 60, after being substantially behind at 30 mph, then quietly slipped past both other cars in the test run. Quite sad that the state of California never supported the idea with the charging stations they promised. As battery technology gets better, performance improves.

 

[Longboy]

http://blog.hemmings.com/index.php/tag/stirling-engine/ http://www.farmshow.com/view_articles.php?a_id=1094

 

[RichD]

Try this site. Lot's of simple stuff but hey...they run
Tin Can Stirling Site

 

[Hopper]

The Gotland class subs use an engine that is a development of the Phillips stirling engine. They run them on diesel fuel and liquid oxygen. They are used to run generators to charge the sub's batteries, which run the main prop motors. They still have diesel engines for main charging duties at surface but the Stirlings extend underwater time greatly as they are silent and can run under water (the exhaust is mixed with sea water and pumped overboard silently.
Phillips also had a bus running around Holland with a Stirling engine at one stage.

The Japanese are also building a licensed version of the Gotland with a Kawasaki built Phillips stirling engine in it.

But a Phillips is a far cry from a simple home built single cylinder Alpha. You should probably build a model Alpha before you strike out on the big stuff and see how the power output goes.

 

[Mechanicboy]

Phillips also had a bus running around Holland with a Stirling engine at one stage.

The DAF bus with Philips Stirling engine in Holland is not in operative today, test run only for about 45 year since. The problem was roll sock sealing between piston rod and crankcase, it craked after some hours and power was reduced. The problem is not resolved in this engine in the bus.

 

[kilocharlie]

Rich D - The video that followed the walking-beam tin can Stirling website was from www.greenpowerscience.com, which turned out to be helpful in the right direction. A V-2 Compressor assembly just might work out, or get me close enough with some modifications for heat insulation and the addition of the gas transfer / heat exchanger tube. Another video on their site shows a beta-type Stirling working pretty good on a Fresnel lens in the sun. Big THANK YOU.

Jens - thank you for the heads up on failure mode for the bus.

Hopper - I don't know of a single cylinder Alpha-type, I've only seen the 90 degree V-2 with both rods on a single crankshaft throw journal. Run with additional cooling and heating, the Alpha-type does make a lot of power for its weight. The single-cylinder types are mostly slugs - Beta- and Gamma-type Stirlings are usually a lot of material used to make a little bit of power. Their design niche appears to be where a low- to medium temperature difference is being exploited for low ongoing cost, such as downstream heat leftover in an Organic Rankine Cycle turbine (medium temp. difference example) or passive solar heater (Low temp. diff. example), so excellent durability and low maintenance on a free heat / power source make them feasible in some cases.

I've worked in 4 engine machine shops, and have machined many custom rods, modified cranks, and balanced engines more complex than this. I could get a bit crazy and make a cylinder head with a compression-adjustment screw, and experiment with a single design. Long rods make a lot of sense - up to some limit, of course. A known, good rod ratio would be a big help. I do not need ideal, just close enough.

I was hoping for someone with some design answers /building experience before starting. I have scalable plans for a block, cylinders, and a crank. I know that heat isolation between the two cylinders is of great importance, so the block has an insulator material built in and the oil system is high-volume with a radiator downwind of the cold piston and blowing at the hot side because the rotating / reciprocating mass is the main thermal conductor and the oil system is a "good parasite" against this.

There are many areas where opportunities abound to improve the Alpha-type Stirling for performance - I only need enough to efficiently charge a few horsepower worth of batteries. I'll use what works out well in the cost-to-additional-torque column, if feasible.

 

[RichD]

I've only thought about this, but I think the ratio of surface area to volume is the key to success with external heat engines. For example...we always think pistons should be cylindrical, but maybe a corrugated/grooved or (your guess goes here...) piston and cylinder for the displacer end would increase the heat transfer rate from the flame to the gas inside the engine. One idea I've envisioned would look like a distributor cap on the hot and cold ends of the displacer cylinder and mating piston.

The beauty of the tin can stirling's is that you can try out oddball ideas and sizes without a lot of machining or expense. As long as it is "air tight", the only fits that matter are on the power cylinder, bearings, and such. The efficiency is really in the burner/heater/cooler and regenerator designs.
Rich