Stirling engines for the third world

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cchagnot
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Response to Stirling engines for the third world

Post by cchagnot »

There's nothing wrong with the Diesel engine as evidenced by their domination of the
markets in most developing areas of the world. But I think it unfair to declare that Stirling
engines are a failed technology that can not and will not be able to compete in segments
of the market where either the unavailability or the cost of diesel fuel make them viable.

The ST-5 is not now nor has in the past been funded by development agencies. We're
working in a strictly commercial market focusing on competing on the basis of the
numbers alone against other technologies.
The high price of oil is currently helping that effort. Whereas in the past we found it
difficult to compete against $20/barrel oil, at near $100/barrel it makes a lot more sense.

Also, there are many places in the world where diesel is simply unavailable or too costly
for many to afford. It's these areas where the Stirling makes sense. Stirling engines are not
an overall remedy for every energy conversion application, just one of many.
To quote Dr Chopra of IIT India in a paper he presented last week at the 4th Renewable
Energy conference held in Chonju, Korea... "Let all flowers bloom".

Catherine
bptdude___2569
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Response to Stirling engines for the third world

Post by bptdude___2569 »

My apologies for improperly using American Stirling's name. I was confused with some other company. I'm sure all who use this board appreciate it as a topic to discuss the events of Stirling engine development.

This particular thread, Stirling engines for the third world has some of the most dedicated people who travel the world attempting to provide humanitarian assistance with special technology restrictions.

As one who has taken greater liberty perhaps than most with fielding thoughts on how to help, the patience is appreciated.

This board has also inspired me, by providing feedback from some of these experts with real world experience. Today I believe I have had the epiphany of a solution that could help. It consists of off the shelf components pieced together in a new way, some old school technology reworked by enthusiasts and some very new ideas used for other things. It is low cost, mere thousands I estimate, uses sunshine at New England average levels, and produces electricity into the several kilowatt range and could be scaled up easy. It would be small enough to be transported by a small truck. It would be simple to maintain and fix.

I need to work at obtaining my first patent and finding people to help me. It is so simple, it is one of those things that you would smack your head and go "DOAH!". Hence, I am sorry I can not reveal more.

When it becomes a real product, I promise I will do what I can to get it distributed to places in the world that need it most.

- Joe McLean
hislop
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Response to Stirling engines for the third world

Post by hislop »


Another old saying is: "When stuck in a hole, don't dig any deeper"! Having been there myself, I have great respect for those who innovate against all odds, and if there is a commercial market in the developing countries, fair enough, provided what is being sold is actually capable of delivering what is promised. But where is diesel not available under conditions that will encourage people to put scarce financial, time and technical resources into buying another engine that is more expensive than a diesel, and, in turn, requires them to grow/manufacture/organise their own fuel supplies and spend further scarce time, land and raw material resources? If you want to go down that route, what about biofuels, gasification of biomass and anaerobic digestion, all for existing diesel engines? I'm well aware of the technical problems, but the Indians (IIT) and others have been working on them for years.

What about the existing markets in the US (all the enthusiastic correspondents on this blog), UK (crying out for it) and other developed or at least relatively wealthy countries? Why not prove its commercial viability there, and then go to the much more difficult markets of developing countries? If we cannot manage a commercial product running on a simple fuel like natural gas, any claim to be able to do it with much more difficult biomass must be regarded with scepticism.

I'm not sure I'd call the Stirling a failed technology - it served its purpose in 19th century Europe and the US, and as a cooler has commercial markets now. However, the past 70 years have seen several billions of dollars/pounds/yen etc spent on trying to develop a commercial engine for a range of different markets, each engine going through several generations of minor development, each promising that each step will solve the problem and bring us the holy grail – that is a form of failure. Contrast that with, say, the PV industry, where efficiency has increased and prices have fallen significantly. The Stirling industry has continued on this path for so long because there has been nothing that could do the same job any better. My own (biased) view is that this is now changing.

tmckissick
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Response to Stirling engines for the third world

Post by tmckissick »

Mr. Hislop,

While I recognize your years of experience and effort in this area, I think you 'have lost that lovin feelin', so to speak. The heart of the US is innovation and it doesn't happen in the big corporations. Been there, walked away from that. Here's a short story to make my point.

In the times just prior to the Wright Brothers' success in flying a plane, there was another team with nearly unlimited support (money) behind them. Langley and his group launched countless steam planes into the Potomic River. You see, the engineers of the day had concluded that steam was the most powerful prime mover for the buck so that discussion was not even addressed. The wright brothers, on the other hand, had no money to spare so they were forced to rely on innovation to the full completion. They didn't have the luxury of making any more prototypes than absolutely mandatory. Obviously, everyone here knows the result, but it was because they were forced to break the rules and not just throw money at the problem that they even considered alternatives. I get almost hysterical hearing about engineering teams that spent millions on a design to get another 1-5%.

Just as in that scenerio, there are many today that have come down the 'Wright' path. I am aware of some other proprietary development in addition to mine and I would simply suggest that some technical statements you make as fact should be reconsidered. For example, the regenerator is nothing more than a bandaid for inefficient design. It costs on the design compromize side, on the manufacture side, on the heat receiving side, on the heat giving side and does nothing that a perfected cycle shouldn't already be doing. Another great example are the Exhaust Gas Recirculation valves that cars had in the last few decades. They cut NOx by detuning engine performance. Later, the engine makers figured out how to just make the engines reduce NOx by better tuning and the result was more performance. Amazing.

I can also suggest one point of view as to why these recent breakthroughs are not hitting the market by storm. In today's business world, it is virtually impossible to begin manufacture on a Holy Grail style breakthrough engine without first creating the market. This means that you have to apply it in a full 'off the shelf' solution and polish it to perfection before you can pitch it to investors. This is where the lion's share of time is spent. In my case, we're proposing an offering of a solar dish that resembles the old satellite dishes, which will produce up to about 2 kw peak from stored heat. Total kw out depends on total collected that day, but we're projecting over the '65% of Carnot' mentioned above.

The main reason we chose this application versus a US marketable whole house energy system with full out CHP and natural gas backup is the requirements for grid interconnect. In stand alone applications of the underdeveloped countries and remote regions of the US, we can delay the dozens of certifications that a grid tie US market would require until we can afford them. As Mr. Vanicek commented in this thread on May '06, even a 30 Tonne / 2 HP engine that ran on cheap/available/free fuel would be welcomed in his region.

I commend Catherine on her comments regarding the real roadblocks to past systems. I see quite a bit of interest in the contributors of this thread for solving the remaining problems. I would like to say question everything and look outside the box for K.I.S.S solutions. We're shooting for CHP on a solar thermal, Stirling based electrical grid tied generator requiring energy storage and critical backup. How many of those functions could be shared by less equipment? It's probably more than one would guess.
hislop
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Response to Stirling engines for the third world

Post by hislop »

Todd,

On innovation, I take your point about the Wright brothers and US positive attitudes - but it is 70 years since Philips set out on the path, followed by so many others, to modernisation and commercialisation of the Stirling. That tells us something about the combination of the technology, the market and the competition!

On the regenerator, let's be absolutely clear. If we are discussing the Stirling cycle as opposed to any other cycle, the regenerator is not a band aid for inefficient design - it is essential for an engine that is to do anything useful. The hot air engine, which is a Stirling engine without the regenerator, was well-known in the 18th century, but it never did anything useful until Robert Stirling invented the regenerator in 1816 and located it between the hot expansion end of the engine and the cold compression end. That very clever piece of thinking and design was what turned the hot air engine into something that could actually compete with the steam engine. Remember, because of the phase angle between the two pistons, the compression ratio in a Stirling engine is about 1.5:1 or at the most 2:1, so there is a huge amount of heat energy left in the hot gas after expansion (compare that with the compression ratios of petrol and diesel engines). If that all heat had to be disposed of through the cooler, the engine would run but produce virtually no power – which is how most of the many model Stirlings on the market operate. The invention of the regenerator allows the post-expansion heat to be stored, and then transferred back to the cooler gas after compression. That is what makes the Stirling potentially so attractive – its cycle is theoretically the equivalent of the Carnot cycle. Take away the regenerator and you have nothing.

I agree that existing regenerators are not perfect - they often have high pressure drops - but modern ones are over 95% effective in the transfer and storage of energy. We can improve them with a manufacturing technology that can vary the geometry of the regenerator over its length, which helps with the pressure drop.

Drummond
tmckissick
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Response to Stirling engines for the third world

Post by tmckissick »

Drummond,

There you go again, letting yourself get confined by that box. 70 years of development has zero to do with future development. Statistically, yes, but technically zilch. How long before the problem gets solved? 17, 71 or 171 years? Try not to quote past experience in explaining future decisions. They didn't work then so what's going to be different this time? You're right, though. That development does tell us something. It says what didn't work. The ONLY thing that should be referred to is the laws of physics/thermo etc.

I'll try to give a good example of a good example of blinders without giving away any details. I completely agree with your rationale for why a regenerator is needed, but only if I have to agree with your boundries. I never mentioned pistons, a hot or cold end, 90 degrees of phase shift or a low compression ratio because those boundries influence the design. I did, however, refer to a perfected Stirling cycle and for that cycle, a regenerator IS a bandaid. Stating that a regenerator is anywhere near 95% efficient is neglecting the total effect on the engine. How does that dead space affect the cycle?

Yes, I know your next reply will say you can't get the C/R higher because of other problems and I say just keep going down those paths. Spending money on better and better regenerators to go from 94% to 95% efficienct is such a waste. In other words, stop tossing steam powered planes in the water.

Best of luck tho,
Todd
hislop
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Response to Stirling engines for the third world

Post by hislop »

Todd,

It’s not that Stirling engines don’t work; there are hundreds, possibly thousands, that do work, and some of them work quite well. The point is that none of them has, in 70 years of intensive development, been cost effective enough – in terms of cost, efficiency, size, weight, reliability – to reach its potential mass markets. Now alternatives to the Stirling are at last emerging, it is becoming increasingly clear that one of the main reasons for the lack of cost effectiveness is a fundamental problem with the Stirling cycle.

I’m intrigued by your view on the boundaries – fair enough. But: the Stirling cycle is a reciprocating, non-valved cycle that involves pistons, cylinders etc, and, especially, depends on a regenerator between the hot expansion end of the engine and the cold compression end to produce any significant power. That is what Robert Stirling developed, and that is why it is called a Stirling cycle (initially by Philips in the 1930s). If your cycle is different, it is not a Stirling cycle as commonly understood by the Stirling industry and discussed in many years of academic, industrial and modelling publications in the ISEC, ESF, and IECEC. Your cycle/engine may be more or less cost effective than the Stirling, but if it does not conform to the above there is little point in calling it a Stirling engine. It might be Brayton, Ericsson (add some valves) or one of several others, it might be rotary, it might be a version of the Wankel engine, it might be completely original; it might be the answer to all our prayers - fine, and good luck, but it is not a Stirling engine! To repeat: if, in your cycle the regenerator is a band aid for poor design, then the cycle is not a Stirling cycle, perfected or otherwise.

Drummond
tmckissick
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Response to Stirling engines for the third world

Post by tmckissick »

Drummond,

Good discussion. I enjoy it and hope that the other members do as well.

However, I still must stand my ground. The Stirling Cycle is nothing more and nothing less than heating a gas to get it to expand and perform work followed by the reverse. The equipment to accomplish this is not specified. This is proven by the many types of Stirlings out there. There are Alphas, Betas, Gammas, rotaries, lanimas, acoustics, crazy phase change or gravity driven ones and a couple other proprietary ones. They all satisfy the above. In addition to those types, there are LTD (Low Temp Differential), MTD and HTD versions. The equipment used in these varies substantially but they still qualify as Stirlings. The issue here as I see it is whether we can make economic, usable power with one of these and not need a regenerator. If that's correct, then I submit the following.

Nearly everyone knows of the toy/model LTD versions like the ones sold on this site. They very nicely display the Stirling Cycle. They generally have a Carnot limit of less than one percent, yet they overcome their friction and do run. Others with a little oomph have Carnot limits of around 10-20% yet they only produce maybe 2%. Why is that? You would say because of regenerator design limitations while I would say something else. It's dead space is too high of a percentage of working space. Remember that any space in it's power cylinder plus regenerator volume plus transport passages is removed from the heat transfer surfaces and counts as dead space.

Consider a hypothetical LTD with zero dead space and unlimited compression ratio and 50% full heating time and 50% fully cooling time and nearly instant heat transfer. I'll use an LTD because of the high surface area to volume ratio. That's the ideal situation, right? Wouldn't you match the compression ratio to volume increase (in this case theoretical = actual) resulting from the ideal heat transfer? Wouldn't that remove all the newly added heat energy from said gas as usable work and eliminate the need for a regenerator? Wouldn't that square off the corners on the PV diagram and approximate a perfect cycle? On top of that, with this 'ideal' thermal transfer, your power output (read that as kw/kg) is mostly only dependant on RPM.

You'll say that this cannot be done because it hasn't. Hasn't it? Then I would ask how many of these capabilities you need just to make our little engine 'viable' in all the ways you requested.

I've been studying Stirlings and the physics behind them since I found out I wasn't the first inventor of it in high school. I've simulated many existing ones with surprising accuracy. Over decades, I've learned a few things that are not mentioned anywhere in the Stirling world, but most of them are dismissed as only viable in the hypothetical without serious consideration. I used to listen to this which is why my first few dozen designs had traditional results. It took a year to convince my head engineer to think outside these boxes so I only offer you the advice that there are alternatives.
bptdude___2569
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Response to Stirling engines for the third world

Post by bptdude___2569 »

Dai -

While the debate goes about about the theoris of what is and isn't a Stirling engine, and as I had my brainstorm about something I will have to actually sit down and start to play with, I have not forgotten your problem.

The thread is really about affordable idea for the third world.

In other inquires on the Internet, people have been kind enough to suggest things and kick ideas around. So far, the best goes like this.

http://www.greensteamengine.com/

On this page are a couple of things. One is a picture of a steam engine tied to an electrical generator

More for your purpose of providing water without little deadly things in it, is a schematic of a "Green Water Distiller". This thing uses a normal kitchen pressure cooker to generate steam, and feed this guy's "Green Steam Engine".

The "steam engine" is really a tool driven by air pressure, and does in fact run off an air compressor also. The pressure required is between 4 and 20 psi. A standard pressure cooker you can get off ebay is rated at a cooking standard of 15 psi.

I considered your statement about your region of Nigeria not being as brightly lit as the more sub-sahara region. Many people confirm what I found with lots of number to back it up, that the very best way to produce usable steam heat in the less than 400 degree F range from difused and cloudy solar are evacuated tubes.

Evacuated tubes are glass tubes inside glass tubes with a vacuum between them for near perfect insulation, and a few extra parts that are very low tech. One company in India trying to ramp up production was concerned because the Chinese are about to mass produce these and undercut his costs, etc. The point being, they should soon be plentyfull and cheap enough, and are fairly rugged.

I also found a university in Nigeria starting research into low cost energy. I lost the link to which one.

So:

you get hold of some evacuated tubes, some pressure cookers, play with the "green steam engine", or just realize you can figure out for yourself how to make air tools into "steam engines", and you should be able to actually solve your problem on a really really cheap budget using only sunshine for power.

These things could be used in villages or on rooftops in the city.

I know Nigeria is poor and even these materials cost, but if you get some kids at the university to help you put together these things as projects, you would have something specifc, cheap, and practical to pitch for help.

Best wishes.

- Joe
bptdude___2569
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Response to Stirling engines for the third world

Post by bptdude___2569 »

and now, back to the theorists.

lots of people call many variations Stirling engines. if a purist things the whole world has gone mad and they are all wrong and have strayed from the absolute pure and true, well, who knows. but the notions of a sealed fluid machine that works by having a hot end, a cold end, and a cycle of expansion and compression seems to unite people to at least have a common term for their favorite underdog technology.

Rev Stirling devised the regenerator, something that soaks up the heat when it is coming from the hot end to the cold side, and gives it back to the cold stuff on its way back to the hot side, for the purpose of saving fuel. Modern people have fancy names for why and efficiency numbers. Stirling was trying to save fuel, for reasons never known for sure.

Another way to improve the Stirling action is to either make the hot end hotter and the cold end colder. I see many power Stirling engine designs that seem to ignore the cold side. The st-5 is a notorious example. A few cooling fins exposed to the air doesn't seem to me to really be a strong effort. Also, burning husk in a piece of junk wood box really doesn't seem a serious attempt to fire up the hot end. If the ST-5 needs improvement, heating the hot and cooling the cold seems a lot more bang for the buck than reinventing the regenerator.

I was chatting with my teenage son about this stuff last night. We have a coffee cup Stirling engine. As I was trying to explain theory of regenerator, he wanted to show me something. He put the thing on an ice pack, then took the hair dryer and heated the top side. The thing went so fast, it flew apart, with the propeller flying across the kitchen. Everybody broke out laughing, except him, who thought he was in trouble. Naw, he wasn't, I laughed too, and we put the thing back together pretty easy. The point was made quite clear to me.

Lets say I have some Stirling engine and I want to use it for power production, for me, at my home, given my unique conditions. There are things that I can do to increase the effectiveness, hopefully to make it practical. The purist would say these things are very complicated and take from the efficiency. But that is really really true, or doesn't have to be.

Like, Rev Stirling, I want to get the most from my fuel, which we will say is firewood in my case. There are things I can do to make the hotter end hotter. Let's say I'm using a wood stove to burn the wood. If I put my wood stove inside a kiln, with the hot end of the Stirling coming right into the kiln and into the stove, this thing will heat up much more just from physical construction.

Now, let's say I take a separate little Stirling I buy, that runs off the stove heat to spin a fan, and use it to force air into the stove, turning it into a wood furnace. I have plenty of heat to spare, and I don't have to "rob" my main Stirling to do things to help it. This is also an example of feedback I was also trying to explain to my son. As the little Stirling fan force blows air into the furnace, the furnace gets even hotter, making the little Stirling spin even faster, making the furnace even hotter, up to the limit of the wood capacity or the stove goes meltdown on me.

Here is the link to the little stove fan for my theoretical example:
http://www.kk.org/cooltools/archives/001525.php

Also, we know at home, in my real wood furnace, that we don't want truly seasoned wood, and some wood burns hotter than others. If I use harder wood and let it dry completely and put that in my furnace, the heat becomes too much too easily. So, I could make my theoretical Stirling furnace use the hottest driest wood fuel. The would increase heat quite a bit.

Now, on the cold side, I buy a second little stove-top Stirling fan, and use it to slowly pump the very very cold water from the well under the house up to the bathtub-from-the-junkyard I am using for my water cooling tank on the cold end of the Stirling, instead of air cooled fins. The tub is allowed to drain out the drain hole, and back into the ground through the septic system, which will never affect the temperature in the well.

As you can see, what I am doing is "cheating" on the Stirling cycle, and trying to turbo charge the process.

None of this is my "big idea", that has to do with a regenerator. But, I think you can see where this is going.

A purist would cry foul, and throw me out of the Stirling engine genius contest.

But, if people in real need in parts of the world where unconventional energy sources would save the day, people who have real expertise in such machines should encourage them to do anything practical and some things even silly, if it would help them to help themselves. Solutions can be unique to situations to overcome the perceived doom-to-failure belief, when a little creative Yankee inspiration might just push the heat engine theory over the mark.

- Joe


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