Steam Engine Correspondence/Kennedy
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Max Kennedy
Blog Comments - July 5, 2011
Max K says: July 5th, 2011 at 7:46 pm e
Just looked at the diagrams. Why is a horizontal design which introduces gravity induced side forces the primary consideration? Vertical cylinders are much more common (for good reason) and reduce wear due to not having side forces, Also reduce bump valve complexity due to vertical travel.
Mark J Norton says: July 5th, 2011 at 8:17 pm e
A reasonable suggestion, Max. I will make a note of it to consider this in future design modifications.
Matt says: July 6th, 2011 at 6:56 am e
Is there a requirement on the volume of steam needed to run this at max efficiency or at minimum of load?
Mark J Norton says: July 6th, 2011 at 7:24 am e
The engine is designed to run across a range of steam pressures. Likely there will be optimal operating conditions and some of them will need to be determined experimentally. Power and efficiency suggest high pressures and speeds. Wear and breakage call for low pressures and speeds. High pressure steam is dangerous. As you can see, there are trade offs.
Max K says: July 5th, 2011 at 7:25 pm e
Though bump valves are simple and easy to build my research online for a DIY steam engine indicates they are not reliable long term, indeed they wear out quite quickly both the valve and seat. How will this be overcome?
Mark J Norton says: July 5th, 2011 at 8:16 pm e
Bump valve designs have been proven in designs such as the White Cliffs Solar Power Station project. A decent steel valve should handle wear at reasonable speeds. However, other designs are being considered as well.
Max K says: July 6th, 2011 at 8:36 am e
I am familiar with the white cliffs design but have never found details regarding what they meant by “satisfactory materials and hardness matching”. Have you determined the materials and hardness criteria? If so please share the info.
Mark J Norton says: July 6th, 2011 at 8:50 am e
Sadly, these details were deliberately removed from the White Cliffs report. Intellectual property associated with the solar concentrator and steam engine were sold to Power Kinentics, Inc. of Troy, NY. The current thinking is that low speed will limit damaged cause by impact. However, the bump valve design has other problems, chief of which is the compression of air after steam has vented. This was handled by the White Cliffs folks by putting a vacuum on the exhaust vent. For this, the reasons you brought up and others, we are investigating an alternative design that uses rotating valves. See http://opensourceecology.org/wiki/Steam_Engine_Design/Rotating_Valve. This eliminates all of the bump valve design problems but does complicate things by requiring stepper motors and computer control.
Max K says: July 6th, 2011 at 4:17 pm e
For a bootstrap technology why is added electronic technology being considered? Finding the technology in sub saharan Africa, for example, is unlikely, repairing it virtually impossible. A similar effort with water pumps left thousands unusable when a part broke and couldn’t be repaired locally. Let’s learn from that and KISS this project. Every part should be readily available and manufacturable locally.
Max K says: July 6th, 2011 at 4:23 pm e
Don’t get me wrong, I’m all for the steam engine idea, but I’ve done a lot of research on DIY Steam and the sicking point has been a robust valve design thats readily available and long lasting. I haven’t found one yet but have looked intensely at the options so know most of the pitfalls.
Mark J Norton says: July 6th, 2011 at 4:28 pm e
Well, simple is better. I can’t argue with that. Certainly there are other designs possible. Slide valves on a continuous flow engine is a classic approach dating back well over a hundred years. To be honest, I was asked to flesh out the bump valve design. It was Marcin’s choice and I followed that direction. Now that we have a better understanding of steam engines (though no build experience yet), other ideas are starting to suggest themselves. Personally, I think that an electronically controlled engine would be a great experimental platform that would allow us to tinker with timing, sizing parameters, cut-off, etc. It might not be the best model for Sub-Saharan Africa, but it could teach us a lot. I view this as a process, Max.
Mark J Norton says: July 6th, 2011 at 4:31 pm e
Perhaps the rotating valve could be operated by a linkage off of a shaft eccentric? I believe the Corliss valve engine uses a rotating valve, though I could be wrong.
Max K says: July 6th, 2011 at 4:31 pm e
For mechanical rotary valves look at the Corliss Steam Engine.
Max K says: July 6th, 2011 at 4:34 pm e
The timing of the Corliss also has the advantage of being variable.
July 6, 2011
Max:
Thank you for your comments in blog. I appreciate your thoughtful replies and suggestions. You seem to have some grasp of the subject matter. Do you have any experience building or designing them? Do you have any interest in participating in the project?
- Mark Norton
Interested, yes. have built one out of an old lawnmower but it was activated by a reed switch controlling a solenoid valve. Another valve option that wasn't reliable. Ran about 5 hours then quit. After 3 valves gave up the ghost forgot about that option. My target is a 10kWe system to take advantage of the Ontario microfit program, solar with a biomass backup option. Have also built 2 axial flux PMG's similar to
http://www.ijme.us/cd_08/PDF/190%20ENT%20202.pdf
Love to combine all 3.
MK
It has been suggested that we consider creating steam engines out of ICE's, like the lawn mower you mention. The White Cliff's engine was built on a modified diesel engine. Air compressor's have also been suggested.
Marcin and I have considered solenoid activated valves, but there seemed to be a lot of problems with them. What failed in your design, if I may ask?
Frankly, Max, if I had my druthers, I'd conduct a series of experiments on control valves themselves. Forget about powering anything, just work on the operating characteristics of the valves, as I think they are the critical element in the steam engine design. This is why I think a computer controlled valve test board would a useful thing to build. If software controls both steam and exhaust and has sensors that allow piston position and pressure to be measured, many aspects of the steam engine could be examined empirically.
However, Marcin is hell bent on building an engine in the next few months. I have warned him about the flaws in the existing design, but he hasn't said anything that would lead me to believe that he's not going to move ahead with it. Meanwhile, I've started to explore other options.
I'm very interested in hearing your suggestions and perhaps learn from your experience, if you are willing to share.
- Mark
In all 3 valves the wire enamel on the actuator burnt through. The combination of heat conducted from the steam passing through the valve and the heat induced by running current through the wire non-stop was too much for it. I agree that the engine itself is relatively easy compared to the valving so a reliable valve should be investigated 1st. As for the piston position/pressure/ideal inlet timing that was all worked out a hundred years ago. Don't have one but have seen several old steam engineer's handbooks with that data already tabulated. Have thought something like this might be a starting point.
http://www.youtube.com/watch?v=WmjRTU2Brdg&feature=related
http://www.youtube.com/watch?v=nWhintxC5JQ&feature=related
Those valves probably not good for steam but there may be something similar that could take the heat. Haven't had the opportunity to investigate this though as moved last fall and have major house projects.
Max
July 7, 2011
Thank you for verifying my suspicions about solenoid problems. I had suspected that heat would be the problem. Solenoids will generate their own heat if a lot of current is passed through them, which is needed if they are to have sufficient force to keep the valve closed (or open against a spring). Add the head from the nearby engine and you've got a problem.
Using stepper motors instead of a solenoid is likely to be better in this regard. Force needed to rotate a valve open/closed is much less that push/pull it open. Also, the motors can be mounted a bit further away from the engine and perhaps shielded from the heat.
Regarding old books, you might want to look at http://opensourceecology.org/wiki/Steam_Engine_Research/Books. I have collected links to several Google books on steam engines and steam engineering. Some of these are quite good.
As for major house projects, I am in the middle of building my own house this year. It is a major time sink.
I'm going to be gone the next few days, but I'd like to continue this conversation when I return.
- Mark
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