Steam Engine/Correspondence
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Steam Review
Erik Rossen, Documenter of White Cliffs Solar Steam Project
On Sun, May 08, 2011 at 08:40:06PM +0000, nick raaum wrote: > > Mr. Rossen, > > I am contacting you on behalf of an open source project, openfarmtech.org in > hopes that you may be interested in helping answer some questions concerning > the construction of your lift ball valve design on your converted lister > diesel engine.
Hello,
This is the second time that someone from openfarmtech.org has contacted me about the solar steam engine. The first time was an inquiry in September 2008 from someone in your group named "Elliot", <offonoffoffonoff@gmail.com>.
You seem to have mistaken me for the creator of this system. In fact, it was a team of people at the Australian National University who put the solar steam engine together in the mid-1980s. I merely visited one of the project participants, Dr. Ken Inall, back in 1998 and documented my visit with him (http://www.rossen.ch/solar/anu.html). When I got back to Canada, I bought a copy of the White Cliffs report from the NSW DOE and asked them for permission to publish the main chapter concerning the solar steam engine at http://www.rossen.ch/solar/wcengine.html.
> In particular I would like to know how you achieved acceptable life span on > such a valve, what sort of metals were used on seat plate and ball valve, how ...snip...
I am afraid that I am the wrong person to ask for these sorts of details and I believe that you are going to have a difficult time trying to find someone to answer your questions - the team has mostly dispersed over the years.
But there is good news: the entire overview report of the early White Cliffs project (before is was converted to concentrating PVs) has been digitised by the New South Wales government and it is available online for free! You can get the PDF at
or
http://www.rossen.ch/solar/sustain_renew_solar_white_cliffs_project_report.pdf.
There is even a Wikipedia page about White Cliffs at http://en.wikipedia.org/wiki/White_Cliffs_Solar_Power_Station.
Good luck in your project,
-- Erik Rossen rossen@rossen.ch http://www.rtfm-sarl.ch OpenPGP key: 2935D0B9
Tom Kimmel
May 2, 2011 to Tom Kimmel of SACA
I have been working with Marcin Jakubowski of the Open Source Ecology project lately to update a design for a steam engine. Marcin tells me that he had some discussion with you back in 2009 on an earlier version of this engine.
To refresh your memory, OSE is trying to develop a prototype steam engine that is:
- Easy to fabricate from stock materials (steel, cast iron, perhaps brass, etc).
- Modular such that it can easily be broken down for maintenance and repair
- Stackable so that multiple cylinders can be ganged to a common crankshaft for more power
The current design is similar to the older one (single action, uniflow), with the following improvements:
- Piston activated bump valve
- Steam entry at end of the cylinder, rather than the side
- An oil sprayer for lubrication
- A water drain to remove condensed water
We would welcome any comments you might have about these updates to the design. Several drawings can be viewed at http://openfarmtech.org/wiki/Steam_Engine_Design and I am included the mid-cycle drawing as an attachment. The design of the bump valve was influenced by comments on the SACA forums - the "chinese hat" shape that is self centering and less likely to be damaged by the bump pin.
Some questions to consider:
- How likely is this bump valve to work? What improvements could be made?
- We at thinking of making the bore 4" in diameter, in part so that we can use off-the-shelf piston rings. What impact does this have on the performance/function of the engine.
- Will the oil sprayer shown be sufficient to lubricate the engine?
- Should we leave the crankshaft end of the cylinder open or close to to keep dirt out?
- If we put a hand crank on the flywheel, would that be sufficient to start the engine?
- There is a cylinder liner shown in blue, what material would you suggest for it?
- What are we missing or should consider?
Tom replied on May 3, 2011
May 3, 2011 Dear Mark,
I am sending this message on to another club member who may reply with some comments. If anyone other than me responds they will know more than I do, so listen to them. Secondly, you are invited to come to my shop and look at steam engines and take them apart and look at my extensive blueprint collection. I suggest that a little research will go a long ways when designing steam engines. Thirdly, there is a great need for a manufactured steam engine. For stationary purposes it does not have to be light or small, just cheap and reliable, which makes the design and manufacture much easier.
And to answer some of your questions:
A hand crank will get the engine started rotating the right direction. Off the shelf re-built starters should be available that are cheap and reliable so making provision for a flywheel with teeth on the outer edge, in other words, using a used IC engine flywheel may be the better way to go. You will want a pretty good sized flywheel for this anyhow because of the high recompression on the up-stroke.
The cylinder liners should be cast iron and they should be an easily available one. There are custom made ones from India available from a company in Texas and on a good day I can find that address. The ones that the people who know what they are doing use are from a re-build kit for a small International four cylinder tractor. For a couple of hundred dollars you get four sleeves and four pistons. This is what Jim Tangeman used and what Art Gardiner used. They are the two smartest people I know. Jim took a six cylinder in-line Ford engine and cut the block off sideways from the crankcase and then turned it upside down and cut it in half. This left him with a 3 cylinder engine and a store bought crank and connecting rods. He then bolted these cylinder liners onto some type of a frame and had a very good and reliable boat engine that is still running. Art used the liners in a 3 cylinder Outboard motor and made a 100 hp engine for the dragster that Chuk drives. This way you have a cylinder liner and a piston and rings that all fit.
With regards to the bump valves that you are using, these are the same design more or less as the MSS people used on the Hirth snowmobile engine that is in the VW they made. The difference is that the sealing surface was machined spherical instead of conical. The advantage of that design, yours and the MSS one, are that the pin bashes against the part of the valve that is not part of the sealing surface, because the bashing deforms it. You can go with a round sphere if it is silica nitride from McMaster Carr. The true Chinese hat design done by Jay Carter, the next smartest person I know, is no where like the design you have. Therefore I suggest a little more research there.
An open or enclosed crank case is not a serious issue if we are talking stationary power. You do not want to get caught in the mechanism on the one hand and you want to watch it go around on the other hand, so it is a toss-up. Jim went with an open crank.
Lubrication is a serious issue and I suggest that smarter people than myself be asked that question.
The answer to your first question is that the bash valve design is a pretty good one and it will work as long as you have enough area for the steam to flow through. As for going with a 4” bore in order to get rings, I suggest that rings are available for every sized bore there is in the world, so the precise diameter is not an issue as far as rings go. What you will want is a good piston and connecting rod and the issue is how to get lubrication to the bearing at the little end. This is why most people go with a two cycle engine because there are needle bearings there. I would ask Jim T. what he used for lubrication at the little end.
People are working on all kinds of exotic materials, such as nitride coating of the cylinder as they do in drag racing to minimize friction and wear and others are going with carbon pistons in order to get around the lubrication issue, but the long term reliability of the carbon piston is unknown. Therefore I suggest that this engine start with conservative materials.
I suggest that you take a long look at the way the MSS people made the exhaust manifold for the uniflow engine. Theirs’ was the most clever and easiest and smartest of all the designs I have seen and it needs to be designed into the engine from the beginning. And finally I suggest a long day visiting Bill Ryan up north of Chicago who has years of experience making bash valve engines that go like the wind for at least short periods of time. I am going to be looking at a well-developed two cylinder double acting uniflow using poppet valves and a sliding cam shaft with castings made by a fellow over north of Detroit. I find it easier to use other people’s work than it is to do my own.
Sincerely, Tom Kimmel
Mark responded on May 3, 2011
Thank you for your prompt reply, Tom
I'd love to come and visit your shop some time. Where are you located?
I agree that more research is needed and perhaps some experimentation as well.
We certain agree that a manufactured steam engine would be a wonderful thing. Even better, perhaps, is a steam engine that one could build yourself give metal working tools like a lathe, mill, drill, etc.
With regards to starting the engine, having a toothed flywheel is a good idea. Starter motors can be had cheap or for free, so why not support that in the design? However, having an electric starter motor does require an electric power supply to run the motor, which adds a require that should be optional, if possible.
Concerning the cylinder liner, would it be possible to use a sheet of flexible stainless steel, curl it into a cylinder, and insert it into the cylinder chamber with out welding the seam? I understand that any gap would cause a steam blow-out, but purchasing cast iron liners adds to the cost of the engine, in addition to purchased pistons.
You make mention of the MSS people and the Hirth snowmobile engine. Can you tell me who the MSS people are? Perhaps a web link?
Could you provide an email address for Jay Carr? I'd like to ask him questions, if he can spare the time. Any links to bash valves that you have on hand would be quite useful.
I will look into exhaust manifold design. I've been considering that, but haven't included it in the design yet.
Who is Bill Ryan? I get out to Chicago occasionally and it would be nice to meet him.
Thank you again for your time, insight, and willingness to contribute, Tom. It is my belief that not only OSE will benefit from this, but many people across the world.
Tom Kimmel replied on May 3, 2011
May 3, 2011 Dear Mark, My shop is in Southwestern Michigan, a two hour drive from the Loop of Chicago. I suggest that your time would be better spent looking at the 100 or so steam engines in my collection than in trying to design one yourself. However, a person needs to think about them a lot and to try to design a few of them to begin to appreciate what one is looking at.
Secondly, as for a cylinder liner, one never wants to use stainless steel in any form because of the large grain size in the material that leads to spalling and galling when it is used for any sliding surface. This is why it helps to build on other people’s wisdom and experience. That mistake has been made a few times already.
Secondly, a standard automobile electrical system, 12 volts, is quite useful around a steam power plant. There is always a use for a few fans or solenoids or relays or water level sensors or even a little light so that gauges can be checked in the dark. It is possible to design a control system around a completely analog system, and that is the ideal toward which we aim, but in the meantime using a little electricity makes things go a lot faster.
As for contacting Jay Carter, he is pretty old now and busy and so I am hesitant to have some new steam person contact him and take up his time. He did the experimentation and had quart jars of bash valves that he had tried and that did not work.
Tom Kimmel
Mark responded on May 3, 2011
I've always enjoyed Chicago as a place to visit. Now there is another reason to go there. :)
Point taken about stainless steel. Thank you for sharing your knowledge. Sharing knowledge is part our mission at OSE, which is why I and others are taking the time to collect information and put it on our web site (wiki). With your permission, I will include our discussion as well.
Concerning Jay Carr, I understand what you are saying. I have no desire to impose on him or be a bother. Still, it seems a shame that so much acquired knowledge should fade away with time. Did he happen to write down his observations, experiments, etc? A web site would be perfect, but if it was ever published as a book, I'd be willing to purchase it. Did he happen to train an apprentice or some such who might be willing to talk with me?
'Tom Kimmel replied on May 3, 2011
May 3, 2011 Dear Mark,
Jay Carter has several patents, long since expired, and I have copies of them. You might inquire as to whether or not Marcin acquired the CD from Ken Helmick that has over 5,000 patents on it all classified and in a searchable form, which would make it easier to find and look at these steam patents.
Secondly there is an SAE paper on Carter’s work, but it does not have the good details in it. Jay has been coming to the steam meets for years and telling everyone about his work, but no it is not written down. I have interviewed him and have notes. And he did not have an apprentice. His son worked with him but they are on to other things these days.
Tom Kimmel
Ken Helmick of SACA
May 3, 2011 reply to copy of Ken's messages
We haven't been introduced, so allow me to take some liberties. My name is Ken Helmick and I'm a resident of southeast Michigan. I am a recipient of e-mails to and from SACA President Tom Kimmel and am therefore assuming he'd like me to add my thoughts. Please excuse any abruptness that may occur in this mail, I'm in a lull between assignments (which may end any moment) and therefore may unintentionally come off as brusque in my hurry to finish before that occurs. For much the same reasons, this message may tend to be a bit unorganized.
The problem of designing and building a steam engine involves many parameters with initial decisions having huge influence on final design. Higher operating pressures and temperatures lead to potentially higher efficiency, but the design must be optimized to realize this potential else the energy and initial cost expended to generate this highly energetic steam is wasted.
Generally speaking, a uniflow engine has the potential of higher efficiency, but in order to achieve this the clearance and cutoff are necessarily tightly controlled and (preferably) the exhaust is sub-atmospheric. A counter flow engine has the relative advantage of being more easily operated across a wider variety of steam inlet conditions at the cost of higher engine complexity and potentially lower efficiency.
The issue of cylinder liners was bought up. Wrapping a sleeve and welding is not likely to yield a satisfactory engine for a whole variety of reasons I won't attempt to describe in detail. The methods I would employ would include:
- Fabricate wooden pattern and core box, sand cast iron cylinder, machine. I actually have such a pattern, core box and cast cylinder in my basement.
- Purchase engine sleeves off the shelf--one example of a manufacturer capable of supplying both finished and 'raw' centrifugally cast sleeves is LA Sleeve Co. http://www.lasleeve.com/master.html
- Purchase already honed hydraulic cylinder tubes and fabricate the engine around those. One of many suppliers is http://www.nationaltubesupply.com/stocklist/NTSC_Honed_Metal_Catalog.pdf
- Convert an existing IC engine or extensively utilize IC engine components. Some motorcycle engines have replacable cylinders (notably V twins) and could be readily modified, as can the original VW Beetle Boxer engine which can be purchased in any variety of original or aftermarket configurations and level of assembly.
Use of the centrifugally cast sleeve would require an external retaining cylinder which could be either cast or machined from stock metals. Honed hydraulic cylinders could be used the same way or, in the case of cylinders with heavier side walls, it may be possible to join upper and lower flanges as well as exhaust manifolds directly to the cylinder. If welding is employed, I'd likely stress-relieve the assembly and then re-hone lightly, just in case there is any slight thermal induced distortion to the bore.
One problem with bump valves is that of valve springs. If higher temperatures are contemplated, special springs must be wound from superalloys and correctly heat treated. This is well beyond the home machinist and probably some more pedestrian heat treat vendors. Conventional springs will rapidly fail under higher steam conditions. Another problem with bump valves is mass, the heavier they are, the more potential damage due to impact, this is why Jay Carter invented the light weight valve. Too many bump valve engines had very short life between failures.
At first blush, bump valves shouldn't work. The valve is open just as long before TDC as after and the combined effects of compression and steam pressure admission just before TDC should rob as almost as much power as steam admission and expansion after TDC. This would tend to imply that steam inertia advantageously provides for asymmetrical flow around TDC. The corollary is that the acceleration effects are tied to the amount of time the valve is open and, therefore, RPM must come into play very significantly. I'd postulate that depending on size, inlet geometry and pressure differential the engine rpm has an effect on how well the bump valve engine performs with performance and efficiency degrading both above and below some particular rpm 'sweet spot'.
Asymmetrical valve events for bump valves can be achieved by either staggering the cylinder according to the DeSaxe principle so that the cylinder axis does not intercept the crank axis or by offsetting the piston wrist pin. The second method is very common in modern IC engines although the wrist pin offset is done primarily to help the piston distribute the peak cylinder pressure against the side wall over a longer time period and thus reduce wear. In any case, offset should improve the bump valve engine operation but will lead to deteriorated performance (or even non operation) in reverse.
Besides the thought that bump valve engines probably are more efficient at some moderate rpm, there are other reasons for operating at higher speeds than traditional steam engines. Blowby around the piston rings is a significant loss of power and efficiency. This is proportional to both the mean effective pressure and the residence time in the cylinder. For high steam pressures, a very short cutoff lowers MEP to a point where blowby is less of a problem. Higher rpm provides less time for the blowby to occur. In addition, the short cutoff (high expansion) of most uniflow engines and associated low MEP reduces the amount of power generated per unit of cylinder volume. All things being equal, power goes up wirh rpm, so this is a way to gain back power lost by pursuing more efficient expansion. Fluid lubricated bearings employ hydrodynamic suspension (Langmuir theory of lubrication) to reduce friction and wear. The strength of the suspension film rises with shaft velocity, and so does the load the shaft can bear without bearing failure. Typically, lugging wears out more car engines than racing.
There is a potential alternative to the bump valve that is otherwise pretty similar in overall operating characteristics. Basically, this is a smaller piston valve mounted coaxially with, and upon, the engine piston. This piston valve opens to admit steam only around TDC and is otherwise closed...the same condition a bump valve attains. The disadvantage is more friction, extra rings or seals and the need for more precision in manufacture. The advantages are no springs to weaken from temperature and no hard impact leading to valve failure.
I would always enclose the crankcase of any higher rpm engine, smaller such engines are traditionally referred to as 'splash lubricated' for very good reasons.
I agree with Tom concerning piston rings, there is an incredible variety available in almost any size, configuration and material imaginable and this is about the last reason I would select a given engine diameter. I have chosen a 4 inch bore because it is about the largest diameter used in modern passenger automobile practice, not because of the rings. Possibly the supplier with the best selection is a local company, check their pdf download for diametric applications: http://www.hastingsmfg.com/
I don't know that I see an issue with an electric starter. The electric power supply can be incredibly simple. Older General Motors alternators are widely available and they have an integral voltage regulator. Simply connect the alternator to a 12 battery with standard automotive cables and a self regulating system is in place, explaining why these units are often seen in hotrods built up from other makes of cars. This also allows for niceties like electrical steam plant controls and a light to see what is going on in the dark.
A uniflow exhaust manifold could be very, very simple, depending on the cylinder. If using something like a honed heavy wall hydraulic tube or a cylinder with a liner, I'd consider haunting the steel supply houses and finding a piece of larger rectangular tube, say maybe something like 2 x 6 inches. Weld a cap on one open end of the tube and a flange on the other, bore a hole in the face equal to the cylinder OD, slide over the cylinder and lightly weld.
The crankshaft is the heart of the engine. All the loads focus on the crank and it is subject to compression, torsion, tension and shear loads as well as cyclic fatigue and potential damage from localized heating; proper design and fabrication is necessary to minimize destructive inertial unbalance loads, misalignment and bending. People have been making cranks for a long time, and almost anyone can do so, building a crank capable of trouble-free operation at high speed and power for long periods of time is another matter.
The average home machinist is typically not equipped for (nor capable of) building a multiple throw, one piece crankshaft capable of turning high rpm and decent torque for extended periods; this isn't an insult but reflects the high degree of specialization needed to produce such an item. The most certain and economical means of obtaining such an item are to buy a crank used in a mass produced engine.
If that isn't feasible, one route to consider is the built-up crank. These are found in many smaller engines such as those used in ATVs and snowmobiles. Since the crank is assembled, it is possible to use ball bearings in the connecting rods.
If a one piece crank is desired, the best route to go would be to either cast a rough out of a high grade of iron (still used in some V-8 engines) and machine it leaving the pins and mains a bit over sized. Another option would be turning the crank a bit over-sized from billet steel. Many engine rebuild shops have the equipment to accurately grind mains and pins (the pins are the hard part) as well as micro size (polish) to final dimension. Manufactured cranks tend to be fillet rolled to increase toughness, but this won't be feasible, so filleted pins would be needed along with matching bearings. Such bearings are stocked by racing crankshaft builders. Before having a rebuild shop grind and polish the crank, it should ideally be stress relieved and possibly nitride hardened; something available from job shops. The home machinist can balance a crank with a single throw (assuming he remembered to add counterweights to the design and fully understands the issues involved) but multiple pin cranks can only be balanced in a shop with a dynamic balancing machine---many hot rod shops have such capability
Even production cranks will need to be rebalanced if changes are made to the pistons, connecting rods and so on UNLESS the crank is of a symmetrical design. Typically, this would be radials, inline and boxer 4 cylinders, inline 6s, inline 8s and V-12 engines.
Hope these initial thoughts are of some help.
Regards, Ken
May 5, 2011 from Ken Helmick
Steam engines can be classified in many ways:
- Simple or compound
- Single or Double acting
- By valve type (piston, slide, poppet, rotary, Corliss and so on)
- open or closed frame
- short or long cutoff
- And so on ad infinitum and ad tedium.
One of the critical classifications is Counterflow VS. Uniflow.
The engine you've designed, and any bump valve engine I've seen, is a uniflow.
The uniflow can be more simple and efficient than counterflow, but more careful design is also required. The definitive work on uniflow engines was performed by Prof Johann Stumpf around 100 years ago. He wrote a book on the subject that was reprinted in a second, later edition. The second edition is the more important work. If you can find an old copy, this book will run over $100. A good scanned image of both editions is available free, online. [1]
I'd recommend reading this work through a few times until the concepts really come home.
Stumpf writes of the benefits of higher temperature and pressure, of shorter steam cutoff and higher expansion, of minimum clearance volume to improve efficiency, of the benefits (and drawbacks) of recompression and how to achieve the correct recompression. Although written for uniflow engines, most of the principles outlined are equally valid for counterflow and compound engines, so this is a 'must' book for anyone contemplating design of a serious engine versus a hobbyist toy.
A few comments on your comments:
"As I think of it, this is probably one of the simpler castings to make, since there are no hidden surfaces. I was also thinking that the liner might be lathed out of cast iron stock. A bit wasteful, I suppose, since most of the inside of the rod stock must be removed. Still, it avoids the need to cast something. Casting is a technique that OSE is planning on support in the future, but we are not there yet." Even if you are determined to get into casting at a later date, that in no way invalidates having parts cast locally in the interim.
Unless casting is hobby you REALLY want to get into, I'd skip it. There are small to mid-sized mom and pop shops everywhere that cast components professionally and take in loose patterns. They have furnaces, crucibles, pyrometers, flasks, sprue and gate cutters, riddles, rammers, various grades of both naturally and synthetically bonded sands, core sands, parting agents and a good selection of industrial grade ingots from which to cast parts as well as equipment to test sand quality. More important, they know what they are doing, this is a very skilled discipline. These folks can turn out castings rougly equal to the best high end manufacturing plants in the world (those plants are expensive because they produce in quantity, rapidly and cheaply) whereas the novice attempting his own castings will be more likely to end up with a porous and rough component and quite a few extra gray hairs until having accumulated the requisite number of hard knocks. I have the porous parts and used to have the gray hair to prove it.
A piece of rolled steel large enough from which to cut a cylinder out may well cost as much as purchasing a casting. It will take more time to make a wooden pattern than to bore out the stock, but, this rapidly shrinks to insignificance if you decide to build more engines, or whatever. Once a good set of patterns is made, it is now possible to cast parts and sell them to others wishing to build their own engines. This would be a huge labor savings and would promote uniformity in construction and thereby increase the likelihood of success if the patterns were used to generate parts in a sucessful machine
"The idea of re-purposing a hydraulic cylinder is interesting. I'll give that some thought."
I'd avoid using a hydraulic cylinder. A new one would cost too much considering how much of the cylinder you would be tossing out. A used cylinder would likely require reboring and honing, which would make standardizing components more difficult. I would look at buying prehoned cylinder tube from hydraulic equipment suppliers. This would allow fabricating an engine without the need for precision cylinder boring and honing; it might also be hard to guarantee exactly the desired sizes when using cylinders while honed tube can be ordered to spec. There are a few shops in my area carrying such tube and they purchase directly from the manufacturer, so it is not difficult to get exactly what you desire.
Automotive valve springs reside on top of the cylinder head and receive ample engine lubrication, which carries off heat, they are never exposed directly to combustion gasses. Their temperature rarely goes far above 200 F, so the use of a high quality spring alloy of moderate temperature resistance is perfectly fine. Steam may start at 450 and run up to about 1000, and hotter is better --- up until you start to run into limits imposed by lubrication and material strength. Jay Carter was running his engine somewhere around 800 to 1000 F. I can't remember what he used for springs, they were custom wound out of something like Hastelloy or Inconel and heat treated under very exacting conditions. The only way I know of to use off the shelf springs would be to run at non critical temperatures, this is easily done but at the cost of consuming far more fuel.
You pretty much have the idea of the piston valve. Only nit I'd pick is that you need to connect the top of the valve cylinder to the steam chest otherwise you will eventually get some ferocious compression in there and this will cause problems.
You can seal the piston valve off with standard piston rings just so long as the individual ports aren't too large. A number of circumferential holes would do fine. Some kind of lubricant will be needed to prevent galling.
You show a drain on the cylinder, which isn't a bad idea, but I think having a drain on the steam chest is just as important. When starting cold, the steam will condense in the chest, and you'd like to vent that out before it ever gets to the cylinder. The cylinder vent should be near the cylinder head You do not want the piston to ever block it, if possible. If there is a fair amount of water in the cylinder and the piston blacks the drain valve, the incompressible water may convert rotational energy into enough hydraulic pressure to destroy the engine. Actually, a relief valve (of minimum clearance) in the top of the head isn't a bad idea. The bump valve can dispense with this as the valve itself acts as a pressure relief back to the steam chest. Attached is an example of a valve for the cylinder head. It has a movable element, a seat, some ports along the bottom and is held in place by a snap ring. The larger diameter of the steam chest end provides greater down force than the cylinder pressure provides until the cylinder pressure exceeds the chest pressure, then the valve relieves back to the steam chest. It was designed this way to eliminate the need for a spring. Of course, this is just a very quick sketch and any variety of mechanisms could do much the same.
Before undertaking a built up crank, I'd spend some money on a couple of repair manuals just to familiarize myself with the crank design elements, assembly inspections and processes; then I'd tear apart a junk two stroke or three with built up cranks and get some hands on feel. Typically, the crankpin ends are ground tapers with keyways that fit into matching tapered holes in the crank disc or crank web. These fits have to be ACCURATE if longevity is an issue. Often the crank is assembled on a surface plate with a set of vee blocks and a dial indicator and stand is used to check and correct alignment until everything is within a tight tolerance. With all this effort, engines using these cranks rarely last the same number of hours as an automotive engine, let alone a diesel.
A single cylinder engine cannot achieve full balance without the use of balance shafts, dummy pistons or other added hardware; but they ARE balanced to the sum of the rotating masses plus half the reciprocating masses in order to minimize the unbalance forces. Without this degree of balance it would not be feasible to run at any significant speeds.
Symmetrical is a term of art in engine balance, and as such is tightly defined, I should have been more clear but used it out of habit. Generally speaking, a symmetrical crank is one in which the vector sum of the forces generated by the reciprocating masses in the cylinders is even on both sides of the crank center AND the angle of the crankpins is such that the forces work to cancel one another end to end. For example, an inline 4 cylinder automobile engine has two 4 crankpins, viewed from the end and in sequence these are at positions of 0 - 180 -180 - 0 degrees. There are two pistons going down while two go up, so these cancel out the primary shaking forces in the engine. At the same time, the two upwards pins are equidistant from center, as are the two downward, so they generate no primary rocking couples. No matter what the piston weights are (as long as they are all identical), the primary unbalance forces are cancelled (not the secondary, but that's another story). A two cylinder engine can't do that. If the crankpins are at 180 to one another, the shake is eliminated but there is a vertical rocking couple that can only be minimized by balancing the crank at rotating plus 1/2 reciprocating on each pin. If the pins are in unison, effectively the engine is a single cylinder with no rocking couple but a huge primary shake that must be minimized by balancing at rotating plus 1/2 reciprocating. A 90 degree V-2 would have no significant shake or rock, IF balanced to the same specifications as the previous two. The only 2 cylinder design I can think of that would more or less almost classify as symmetrical would be a boxer with two pins at 180 as it would have no primary shake and a reduced rocking couple.
The REALLY BIG question to ask yourself about all this is: "How many annual hours is this engine going to run?" The Ecotec in my Chevy S-10 lasted 250,000 miles with hit or miss maintenance before I broke it on the interstate at 80 mph. Assuming an average speed of 50 mph during the 9 years of operation, that translates out to about 5,000 hours of use. Aircraft engines used to be rated 2,000 hours TBO (Time Between Overhaul), so automotive technology is pretty darn good. There are 8,766 hours in a year including the allowance for Leap Year.
Hmmmmm.....this is why most of us buy electricity from the utility company, their steam turbines are virtually vibration free and built to hair raising (and expensive) specifications which means they can probably run 100,000 to 200,000 hours, or more, without risk of significant casualty. To get a reciprocating engine to do that would require either similar very expensive construction or require the engine be massively overbuilt or run at inefficient but forgiving settings.
I only mention this because the first oil embargo occurred when I was a teen, and we lived in a rural area. To save money, a large percentage of people in the area installed wood burning furnaces on the theory that firewood was free and forests plentiful. Turned out that calculation didn't account for the time and energy and expense needed to gather wood. After a few years most of those wood furnaces were out of action because the owners eventually realized, when factoring in their labor, fuel oil and natural gas were significantly cheaper. With a steam power plant, the overhaul cycles are going to be a prime limiting factor. Use of 'off the shelf' components and distributing construction among a wide group of enthusiasts will go a long way towards making the "in service hours" to "fabrication and maintenance hours" ratio favorable.
Ken
Nick Raaum
Msg from Nick on May 8, 2011
After a quick review of this design concept, my main questions revolve around the bump valve design. Two questions:
- How can the cutoff ratio be controlled?
- Durability?
Question number one may not be important in the first iterations, but I suspect if you want anything close to acceptable efficiencies you will have to be able to vary the cutoff ratio on the fly. One idea that pops to mind is to install the bump valve on a gear rack that can raise or lower the height of the bump valve on the fly, this coupled with a speed sensor and plc would give you a governor and some efficiency optimization.
As far as durability goes, if you are working with wet saturated <600F temps this may not be supercritical, however if you eventually want to achieve efficiencies I suspect the valve geometry, and valve materials will really have to be scrutinized if its going to last beyond a couple hundred hours. Overall the bump valve is simple, but in all my readings of the history of steam engines it does not seem to really be present, is there a reason for that, or is it just a good design that was overlooked?? I don't know, but that seems to me to be a good question worth discussion.
Otherwise good luck and please feel free to keep me in the loop of these discussions.
Best, Nick Raaum
White Cliffs Solar Thermal Power Station
May 2, 2011 to Mal Williams of Australia NSW DOE
I am involved with a project to build a small, scalable steam engine for farm use. I came across an article by Erik Rossen (http://www.rossen.ch/solar/wcengine.html) that commented favorably on the solar steam engine developed by NSW DOE back in the eighties. Mr. Rossen mentioned that you might have an electronic form of the report, "White Cliffs Solar Thermal Power Station", Design, operation, and results. 242 pages, 1991. If possible, could you send me a copy? I'm very interested in the diesel engine conversion and the use of bump valves.
I am doing this work for the Open Source Ecology project (http://openfarmtech.org/wiki/Main_Page). Our intention is to design and prototype a set of 50 tools (the Global Village Construction Set) that would enable the development of high standard of living and local economy at a village scale in virtually any setting globally.
Old Messages, 2009
2000 to VK Desai of Tinytech Plants
Letter to VK Desai of Tinytech Plants (Tinytech are an Indian company that make steam engines)
Dear VK,
Can you share your knowledge of steam power with us?
In order to make our solar turbine a success, we need to build the steam engine at low cost - in house. If I do my own labor, use our machine shop, and use casting in house, then the price for the engine parts should be about $150 for a 3 hp engine. Do you think that is realistic?
Please share with me your basic design. Simple drawings on the back of an envelope would do. I am smart at studying design. Please just give me the essentials and material specifications.
Please respond, or put your notes up directly at:
http://openfarmtech.org/index.php?title=Steam_Engine_Construction_Set
If you have any pictures of steam engines in fabrication, please share.
Sincerely,
Marcin
2009, From nick to Mike Brown
Mr. Brown, I have been working lately on developing a simple horizontal uniflow steam of 3" x3.5" bore and stroke that is controlled by an electronic solenoid valve and a small programmabale logic controller. My full intention is to power this engine with a gasifier monotube style boiler and utilize the exhaust in a 750 gallon thermal storage tank for home heating purposes. In my research in this project I found reference to Skip Goebel's work through your site.
that Skip Goebel may already be building a boiler of similar design, if possible could you give me his contact info? I would also be interested to know if you have given any thought to developing an electronically valved steam engine? I intend to try an asco 1/2" direct acting steam valve that claims to cycle at 800cycles/min for a million plus cycles. I intend to run my engine at 100rpm which in theory may give my controll of the cutoff ratio in increments of .25. This obviously will not be efficient but I want to try the concept first. Perhaps you know more about what this actually would take? In any case I do appreciate your time to read this email and I hope you keep up the good work in small scale steam power development.
seek out mike brown steam engins on google
Response from Mike Brown Steam engines
Nick,
Skip Goebel is in Peru, do you have the DVD he did on building a prototype boiler?
I doubt if your solenoid valve will last six months on a steam engine.
Sorry, we don't get involved in other people's engineering projects (we average two emails like yours a day).
Best wishes, Mike
Skip Goebel Sensible Steam Peru s.a.c. Lima, Peru Lima 51 996 984 741 US· 559 922 2410 www.sensiblesteamperu.com
January 26, 2009, to Skip Goebel
To: info@sensiblesteamperu.com Sent: Monday, January 26, 2009 10:22:16 AM Subject: Wood Fired Monotube Boiler
I came across your site in studying the works of Skip Goebel in home powered steam systems. I intend to build a 3kW cogeneration DC system for home and experimental use. All my research leads me to conclude that Mr. Goebel may have pioneered this idea the furthest and I would be interested in purchasing any information that he has made available on the subject.
I'm not unfamilar with steam, I worked 2 years as Mechanical Engineer at a 400MW coal fired power plant, but am now envisioning working on something a little more decentralized. In any case I strongly feel the case for more self sufficient energy systems is here and given the fuel flexibility and reliability of the steam engine I wish to pursue this idea further. My plan is to construct a simple monotube fired 3kW mechanical valve steam engine to charge my DC battery bank and thermal storage tank. After I am comfortable with this design I would like to investigate the potential improvements of using a low cost programable logic controller for boiler control. Additonaly I am looking for a a high speed durable solenoid valve and the right steam valve to investigate the possibility of electronically conrtolling steam into the engine.
Right now I am thinking that I could use a control loop to continously vary the cutoff ratio of the steam engine for my governor. This would optimize efficiency by running with the lowest allowable cutoff ratio. In any case it seems at least feasible to think that in the future steam engines efficiencies can be improved by better steam control which is one more reason that this technology attracts me. So if Sensible Steam has any information avaialable by Skip Goebel on steam engine system construction and experiences with it I would be very eager to hear more about it how to get it.
January 31, 2009 to Alan Nelson
Sent: Saturday, January 31, 2009 12:30 PM To: Alan Nelson Subject: Atkomatic Solenoid Valve Response Times
Alan, I am looking at your atkomatic line of solenoid valves and would like to know if you offer anything suitable for the a 2-way continous duty pulse cycle valve for saturated steam up to 600 deg. The valve also needs to have a very fast response time of 75ms for open and 75 ms for close. Is there anything in the atkomatic line that might fulfill that response time requirement? If not do you know what other type of valve I might try looking at for that desired response time? Thank you for your time.
Regards, Marcin Jakubowski
Response from Alan Nelson
We do not have any valves capable of handling 600F steam.
Alan Nelson, Fluid Process Control Corporation
