Rocket Powered Sterling Engine-water cooled, effluent to thermal mass

This one is a little complicated. It will make sense to those familiar with sterling engines. Check out YouTube. Sterling Engines Don't Explode. Regular steam engines sometimes do.

Wood powered sterling engines are a proven reliable means of powering generators. They were used estensively in the past. Unfortunately they are not very fuel efficient and that is a big part of why they are seldom used today.

But they can be highly efficient if powered in conjunction with a rocket mass heater and hot water system. That is because the sterling would simply intercept the rocket effluent at the top of the heat riser where temperatures are highest. Power is generated within the home. All energy remains within the home wether it be in the form of electricity, hot water, heat stored within the thermal mass or heat radiated to the room from the riser and engine.

The engine is more efficient when water cooled. During a firing, water would cool the engine and the heated water would flow to storage for domestic use.

Sterling Engines normally have a built in firebox with the smokey incomplete combustion that comes with drawing off heat too soon and from restricted airflow. They are generally operated outside and all of the effluent gasses and cooling heat are wasted.

In a system incorporating an engine as part of a RMH , it would take longer than usual to bring the thermal mass to a given temperature because the engine would draw off quite a bit of heat. This would allow for long firings during which time, operations requiring electricity could be scheduled. It would make sense to do it in the evening when lights, the TV, washing machine,well pump etc. experience peak usage. This is the natural time to fire a RMH in preparation for cold nights. A battery bank would be charged as well. This would provide power after the firing is complete.

This converts our RMH into a complete home energy system providing electricity, hot water and space heating.

YOU'RE WELCOME

A few points

1. I am going to immediately advertise for a functional old unit.

2. The RMH should draw well since heat is drawn off the top of the riser.

3. The engine and generator may need to have it's own little room made of cob to cut down on noise.

4. I'm not going to entertain EMF concerns.

5. Some operations such as water pumping and clothes washing could be belt powered directly off the flywheel.

6. It's 2 AM. It took 30 seconds for me to conceptualize this and 2 hours to write it all down.

I am very interested in this. Just a question, perhaps gasification would be simpler and be just as efficient? I have on my drawing board to build a system with gasification where the heat is drawn off to dry wood in a kiln.

Tomorrow Fred-- Must sleep

Good morning------- Wood gas is used to power internal combustion engines among other uses. For our purposes that would seem to be the most practical. I like gassifiers but would never use one inside a home as they have a history of explosion. They also produce volatile gasses which must be contained. They are complicated systems requiring constant management.

The number of moving and non-moving parts is many times higher than with a Sterling. Corrosion has plagued many systems.Poisonous gasses are piped from place to place. Engines wear out faster than when they are on gasoline with crankcase oil contamination and piston scoring being two of the many possible issues. The amount of space required is greater.

Sterling engines simply require heat so I suppose wood gas could be burned to provide that but a J-tube with an insulated riser is vastly simpler. The moving parts of the Sterling are exposed only to clean steam.

Start up time and shut down is much longer with a gassifier. They are better used in large systems and used continuously. That's why they have been most successful in industrial applications such as sawmills where they are fueled by sawdust and other waste.

When the Sterling engine runs out of fuel , no management is required. It just stops until the next fire. Historically, many were used on farms to pump water to an elevated water tank large enough to supply the house and barn with a few days worth of water. Owners would load up just enough wood so that the fire would burn out as the resevoir filled up. Light it and walk away.

Sterling engines are a great idea. I haven't built one myself yet. I know you can out of a soup can if you want. I've thought about the many uses would could get out of them while multitasking other chores with the fire or heat. I'm sure there is a way to integrate a sterling into a gasifier if you keep the gasifiers heat contained within and the sterling. You would get thermal power plus the gas from gasifier. After that you would have even heat use plus the biochar after the process is done. Would could be using sterlings combined with solar for power when there is sun out and heat difference for sterling. I think it would take a long time to recover the cost of building it plus maintenance of posible bearing failure or some other failure. I just try to think of stuff to use if some reason oil just stopped for awhile or became unaffordable. I'd rather be independent
before then not after.

As I've been considering the ramifications of utilizing water as the primary thermal mass for a rocket mass heater I have come to the same conclusion. There are situations where electricity or a mechanical force is needed and a stirling engine or steam engine coupled with a rocket mass heater could provide those. I was up way late the night before last researching both.

The rocket mass heater has a great ability to heat water but getting that water to move to precisely where you need it is a problem. A pump powered by a Stirling engine or steam engine would be very useful and waste heat becomes a non-issue as it is captured somewhere. I think this is a perfect example of using technology to empower the individual.

C. J. Murray. -------------- I was mulling over what we talked about in the thread entitled Exploring Water as the Primary Thermal Battery for Rocket Mass Heaters when I decided that I would use the storage water idea for cooling a Sterling. The beauty of this is that it shouldn't consume much more wood than the RMH would consume as heat storage alone. The only energy leaving the system is electricity which will heat the home as it is consumed.

actually the other reason for the lack of stirling engines is he sheer size needed to give a relatively high power. those engines where extensively used at sea and worked well for low speed high power applications like ships screws. Cooling is not a real problem in many applications and can be used to heat domestic water I dont see why one couldn't couple an engine to a rocket stove. I do see a problem if you cant get the speed up to where it can spin a generator. I dont have any experience with modern stirlings and would like to find out more in time. not gonna replace my electrical system with one but i might have some ides if the modern ones run faster.

Because Sterling Engines don't care, where the heat comes from, it should generally work. To get the hot end of the machine directly on the heat riser, the stove needs some redesign, but why not?

Your plans to charge a battery bank suggests, that you plan an off-grid solution. This is hard to accomplish with a Sterling-Engine and one- or three-phased AC with tinkering means. You need an exact rpm-control, because most of your machines expect a certain grid-frequency (50Hz or 60Hz). Sterling engines react very slow on regulations, so you need a synchronous generator with a seperatly controlled excitement. Quite a challenge, I think!

The cheapest method in my mind to get usable electricity out of a sterling engine off the grid would be an off-the-shelf car-alternator/charge-controller-combination. This is fed directly to your battery. From there on, you can feed every DC-capable device directly and use an invertor for your AC-needs. You dont need to care for rpms or any home built control.

The efficiency is quite low, though... lets assume 10% of the heat, transferred to the engine is electricity afterwards.

/edit: found some interesting source of information for a Stirling motor, but its a little too small for a car alternator.
http://ve-ingenieure.de/projekt_st05g_cnc_engl.html

The proper spelling is Stirling ---Oooops I've written it al least 10 times.I'm only considering a DC system, similar to what is found on an R.V. with alternator and battery bank. Those systems can charge whether the vehicle is idling or travelling at highway speed.

The public grid is at least $30,000 away from my site and it comes with a monthly bill and lots of poles, so that's the motivation for going off grid. Items requiring AC power can be run off an inverter. So lights, TV, computer can all run off relitively small system. DC well pumps are more efficient than AC. Refrigerators can do the same or be run from a belt.

Compressors aren't at all picky about speed so the Sterling could run a compressor for shop tools.

I assume that speed issues can be delt with with a gearbox or with belts and pulleys. What about an automotive transmission? A giant pulley followed by a little one would be simplest. Sometimes belts hum.

As for the space issue, I don't mind using 100 sq ft. for energy independance. Some of the Stirling engines are just as attractive to me as any other work of art so neither space nor asthetics figure hugely. Costs do matter. For a start I'm shopping for something under $2000 but I will go up to $5000 for a large perfectly maintained antique. Anything between 1/2 hp. to 20 hp. will be considered. And I suppose 5 tons as a weight limit.

I saw one on a boat and it had sea water pumping to cool it. That's what got me thinking about the hot water.

I've lived in relative comfort while only occasionally having electricity or heat for the past 13 years so this won't be terribly rustic for me. I welcome a step up to 19th century technology.

In the long run this may be back up power since I hope to tap a huge hydro resource on the property. The hydro power is only available October through June. Local runoff--- 120 ft. of head. 200 gallons per second during peak flow. Totally dry in the summer. No resivoir would make sence since it would flood the neighbors and the gravelly ground percolates quickly.

These things don't grow on trees. So far I haven't found anything for sale except for thousands of models ranging from tea cup to shoe box size. And that's without any geographical limitations on the search.

Something the size of a garbage can produces only about 500 watts so this will take some time. If I do find a suitable unit it should be reasonably theft proof due to size and weight. Turns out I'm competing with collectors rather than with homesteaders. Most units seem to belong to old guys who show them at fairs. They don't seem to be a bone yard item. On the bright side I was able to reach a collector who assures me that maintainance is minimal and that any big antique machine that I find is likely to last centuries.

Water cooling increases power output. None of the antique units have been exposed to the temperatures possible when heated by a rocket.

Investigation led me to learn that there are stirling powered subs. Those are slightly out of my price range. The world record for efficiency of sunlight to electricity is held by a stirling. When operated in reverse stirlings can make things very cold, down to 10 Kelvin. Used in microchip manufacture. There are weirdos who make up all sorts of unsubstantiated efficiency claims. Possibly Tessla defectors.

its not to complicated to make one yourself that is in the large range. however you are very correct in that its not homesteaders you are competing with. kinda the same problem with large pelton wheels. Collectors want them and that drives the cost up till no homesteader can afford them as they where made. but you can sometimes find them in old scrap yards. the modern version should actually be able to be more efficient. possibly approaching 20 percent. not to bad i think.

I've done very little metal work but I know some people. One guy owns a large foundry and he's always keen on new things. He has made a few tools for me and I've supplied him with lots of metal.

that would be the ticket. the plans for larger engines are not that costly and you could most likely get one made for a couple thousand. the thing is even the machining was not that precise on the old ones. so with the new levels of machining i would assume things would work better than when they where invented. I am not sure but i would suspect at this moment in history that it may be cheaper to get one built than to buy one.

another potential option

my understanding is that these folks are converting diesel motors into steam engines. I don't think they've got anything in production yet, though. I also don't know how their efficiency would stack up to a well-built Stirling. and there is the potential risk involved with high-pressure steam. at least something else to consider.

I want to put this in the livingroom so a stirling is much safer. Even little steam plants are noisy affairs. There are a multitude of components to maintain.

If converting an internal combustion engine, I would go with wood gas. But it would need to have its own blast resistant room. Far more complicated than a stirling.

If it came down to building a unit, efficiently could be enhanced by using an alternative material for the "bell" which is the part exposed to the fire. Heat transfer is altered by the metal chosen. A ceramic bell is possiblebut might come in at the same price as those space shuttle tiles.

Nothing I could have built will be as attractive as an old cast iron unit embossed with the company logo and stylized flywheel spokes.

Hey Dale,
Sterling cycles are nice (I'd love to have one (or more) to tinker with), and I know that they are relatively simple but they do have moving parts. That and the mods you'll need to make to the stove, dealing with hot water systems and all that makes for a project chock-a-block with complexities. Complexities mean higher maintenance and increasing likelihood of breakdown.

Have you seen Seebeck Generators, also called TEG (Thermo-Electric Generator)? No moving bits (maybe a cooling fan, run off the generator itself), makes electricity directly from heat.
Check it out.

http://www.tegpower.com/products.html
http://www.customthermoelectric.com/powergen.html

Regarding the concept of Sterling engines being "low power", this company would beg to differ.

http://cyclonepower.com/whe.html

They apparently have models capable of running on temperatures as low as 500°F. Their aim is more toward industrial / military applications, but they do have a modest 10 kWh model.

I've never used, nor seen one in action myself, but considering the topic at hand, I thought this might be interesting food for thought.

Dale,
A couple of thoughts......

1. Your idea about the air compressor might be the whole answer. The Amish use all kinds of air powered tools and equipment, from power saws to sewing machines and blenders. Less worry about the output RPM that way.
Google "Amish electricity"

2. I manage the machine shop for a fairly large industrial repair company. We have a servo motor repair shop and I know they "back drive" the DC servos to test them (turn the output shaft with another electric motor). This produces DC power @ about 90 volts & could probably be driven by the air above. Used servos are cheap and might be a good way to get the generator your looking. Someone with more electronics than me will have to say for sure.

A couple months of advertizing has not produced any useful leads on a used unit. But, I did learn a few things.

1. The shipyard sometimes gets aprentices to build Stirlings as part of the training.

2. Ads for this sort of thing are answered by those who don't know a thing about them or where one might be obtained.

3. There's a lot of kooks out there! They are a harmless bunch who call on the ad so they can pitch all sorts of alternative information, products and fraudulent malarkey. If you're bored and have some free time, run one of these ads. Be sure to record the kookiest replies. Great fun.

Andrew Vliet wrote:Regarding the concept of Sterling engines being "low power", this company would beg to differ.

http://cyclonepower.com/whe.html

Andrew, this is not a stirling but an organic rankine cycle, in other words a steam engine using refrigerants instead of water. Nice prototypes but haven't seen production models as yet.

Here is an ORC: http://www.infinityturbine.com/ORC/ITmini_ORC_System.html

They run about $20K. I'd be interested to know if they actually worked well.

The ST05G Stirling Engine Project
http://www.ve-ingenieure.de/stirlingshop.html

karol kerl wrote:The ST05G Stirling Engine Project
http://www.ve-ingenieure.de/stirlingshop.html

Yep, completed engine only E14,000! Plans might be interesting. Couldn't see the power rating.

In the UK a large utility gas supplier started offering the whispagen unit to it's customers for about £2000. not ideal for your purposes as it's a sealed unit with a gas burner tip, but it is compact and has appropriate power output for a small household. they were temporarily withdrawn from distribution because of reliability issues though.
I am surprised to hear people saying that you can 'easily' make a stirling engine! They look super-complicated to me. I did a bit of a lightweight university project about the theory and feasibility of using one for something like this, but I wouldn't dream of building one- surely the gas-tightness, heat-handling and fine tolerances put it well beyond the reach of anyone less than a very accomplished amateur engineer with a fully equipped toolshop and lots of spare time.

Well stirlings are fascinating.
May i share a few of my favorite youtube stuff with you?

This one was designed to be built locally it seems: sunpulse sunpulse water
This 2 is designed and built in a DIY manner: 6 waterbottle stirling water bottle 10W check out the other vids of the guy!

But if you are more interested in the electricity rather than the building of a stirling engine i would advise to get a TEG instead. Its not that cool, but it works. It will be more useful than most DIY stirling, and will be cheaper than most bought stirling.
However do note that thermo electric generators are sensitive to high temperature. (i know of max 250 C) Go over the limit, and you have scrap!

I have been lost on this topic for weeks including borrowing some very expensive books from an inter-library program and the few things I have concluded are that to build for yourself (no matter how talented and capable a machinist) a stirling engine capable of running extended cycle times and generating a worthwhile amount of power would be unfeasible. Not impossible but very very very unlikely. What looks like the simplest of contraptions lies a pandora's box of complication and for even the most advanced do-it yourselfer it just wouldn't be worthwhile. I was wondering why this isn't mainstream yet as it holds so many attractive features and it took awhile and now I can see the difficulties the engineers have faced bringing this to mass market. The rocket stove is a great source of heat but to couple the two and get barely enough to power a few lightbulbs (and for who knows how long) isn't worth the chase to me.

I would like to add my 2 cents here. I am under non-disclosure and confidentiality agreements, so I can't speak on or share specific technical data. Stirling engines are a potential technology to use in conjunction with rocket stove technology. My research and design with Stirling engines is what led me to rocket stove technology. I am working on my own design, and have been on the inside track of some other viable designs.

Here are some of the current downsides that are preventing main stream usage;

1) 3kw to 10kw engines must either be very large, or use very high temps (1200°+ F). A well designed rocket stove can overcome the latter issue.

2) Materials to build an efficient engine are very expensive, and the tolerances are very, very tight. This equals expensive manufacturing. Current engines capable of meaningful power generation are in the $50k to $150K range.

3) The Stirling engines that are being developed for home power usage are for supplemental power, not whole house power.

That being said, I have seen engines that can convert roughly 10kw of energy to 3kw of output power. That is an impressive 30% efficiency, far better than a gasoline or diesel powered generator, but you can buy the gas generator and many years worth of fuel for the same price. The long and short of this is economics. It would take over 20 - 30 years to get to a break even point with a Stiriling. The current market is very narrow, mostly government and military projects.

Still, we plug along, working on improvements and experimenting with new materials. It is my dream to someday build a cost effective Stirling engine capable of significant power that will run on either solar and/or a variety of combustible fuels. A lofty goal, to be sure, but one I ponder on everyday. I hope to have a working proof of concept this spring for one of my engine innovations. As always, the problem is funding. It is hard to get funding for development, when cheap alternatives exist.

Shane McKenna wrote:
Here are some of the current downsides that are preventing main stream usage;

1) 3kw to 10kw engines must either be very large, or use very high temps (1200°+ F). A well designed rocket stove can overcome the latter issue.

2) Materials to build an efficient engine are very expensive, and the tolerances are very, very tight. This equals expensive manufacturing. Current engines capable of meaningful power generation are in the $50k to $150K range.

3) The Stirling engines that are being developed for home power usage are for supplemental power, not whole house power.

Hi Shane!
It is great having a pro on this rare filed among us!

I wonder if this power ranges are a bit high for us? Most the times, with modern electronics and with a conscious power usage, 3kw looks a bit much. I mean stirlings are best used as continuous generators rather than on demand, right? I guess most permies don't want to heat water, or run AC or use electric ovens with the power the engine gives. I wonder if a big ,5 to 2 kw range engine would be more economically feasible?

The efficiency is, in some usages is not paramount. I'm thinking about that fuel flexibility and low maintenance would be enough for some markets, and a bit of efficiency could be sacrificed for a quicker return on investment.

Or the market is just too small for such a designs? I guess the 1-2 kw market probably got owned by solar already.
Anyway, i guess i just want to ask if such a design is possible and just has no market currently, or it simply does not make any sense to make a 1 kw engine, since it is not much easier (or cheaper) to do than a 3 or 5 kw one?

The rocket has the heat output potential but governing it poses another difficulty. If enough money and brains could be thrown at the problems that exist I am sure a solution could be created, here is a thread on a company that is trying to develop an affordable stirling generator. Curious to see what comes of it.

http://stirlingengineforum.com/viewtopic.php?f=1&t=1491

(Quote) "I wonder if this power ranges are a bit high for us? Most the times, with modern electronics and with a conscious power usage, 3kw looks a bit much. I mean stirlings are best used as continuous generators rather than on demand, right? I guess most permies don't want to heat water, or run AC or use electric ovens with the power the engine gives. I wonder if a big ,5 to 2 kw range engine would be more economically feasible?

The efficiency is, in some usages is not paramount. I'm thinking about that fuel flexibility and low maintenance would be enough for some markets, and a bit of efficiency could be sacrificed for a quicker return on investment.

Or the market is just too small for such a designs? I guess the 1-2 kw market probably got owned by solar already.
Anyway, i guess i just want to ask if such a design is possible and just has no market currently, or it simply does not make any sense to make a 1 kw engine, since it is not much easier (or cheaper) to do than a 3 or 5 kw one?"



I am a realist, and the reality is that an engine smaller than the needs of a well appointed home, or shop is not going to attract much in investment dollars, or in government funding. We just have too much conventional energy available for anybody to get excited about alternatives that cost significantly more. For example just under Utah, Colorado and Southern Wyoming is a 12 trillion barrel oil deposit, with 6 trillion viable for extraction. That is 822 years worth of oil at current US consumption in just one deposit. Weather you agree with using oil or not, that is simply too tempting an energy source to ignore, and when push comes to shove, it is going to be used, it would be naive to think otherwise. Now here is the good news about this oil and other fossil fuels. I consult regularly on a project that can sequester all of the combustion gasses into usable compounds. I have seen the technology at work, and it is cheap and efficient. This is coming, and we will have not only clean burning technology, but we will actually compound useful chemicals from combustion. We have also been using this technology in organic growing situations, but I can't talk more about that yet. Let me just say, that the future is bright, and potentially clean. As we work to make existing technologies more efficient, cleaner, cheaper, we are also developing new technologies everyday.

To bring this back around to RMH, imagine being able to sequester the CO2 out the exhaust, storing it, then delivering it to your plants in a controlled form at the most beneficial time for plant growth. This is exactly what some of our testing is proving can be done, and with very little energy input. Just as permaculture is driving a better understanding of natural plant systems and using human guidance to maximize the benefit, the same desire is driving energy systems to maximize energy usage and multiple benefits. I am extremely confident and optimistic about how much we are going to be able to clean up our current technologies, and provide benefit and opportunities. We are going to look back on this time in our history and see the changes with marvel, just as we look back on the early industrial revolution and see how far we have come from those antiquated realities of an emerging technology.

Also, when the gasses are sequestered, 100% of the thermal energy stays in the system (if we want it to). This means we will be able to create a system that extracts all of the thermal energy out of what ever fuel we burn. In addition, the exhaust would never become a factor in draft blockage. The only question that will remain is whether the return on investment of the added system components is worth the added BTUs and the carbon resource. The energy input required is about that of running a conventional furnace fan.

If you know anyone with deep pockets, and an interest in advancing these kinds of technologies, we would certainly be interested in more funding.

I love the concept of using small stirlings to recover waste heat, however I understand the challenges...
Y'all might enjoy this gentleman's work - open source stirling plans: http://www.solarheatengines.com/

Andor

p.s. @ Shane, I am very interested in the developments you allude to