Time for an update on the OSE Steam Engine project.
In the past month, I’ve pretty much finished up the technical aspects of what I am now calling the “Arrowhead Bump Valve” design, to distinguish it from the ball valve approach, which might be making a come back. At Marcin’s urging, I encouraged several people to review the design. Unfortunately, the current design suffers from several problems:
- Horizontal layout of the engine will lead to uneven wear on the moving parts
- Using high pressure steam at fast speeds is quite dangerous and includes the possibility of explosive failure
- Operating at low pressure and speed seriously reduces the power output.
- A fixed exhaust port in the cylinder means that air is compressed on the up-stroke, which is wasted work.
- The arrowhead valve design may have trouble maintaining a seal and operate under full speed.
- Bump valves will taking a beating and may fail.
While this is discouraging, it’s not the end of the project. Still, Marcin has experssed some concerns:
“Unless we have a proven design … I don’t feel comfortable on going forward, as that means years of development before product release. The key to success of our development method is its reliance on proven techniques. In their absence, we’re adding unnecessary risk.“
Those who have been with the project a while know that the steam engine has already been years in development, so I can understand why he’d want to avoid more years. Let’s take a closer look at some of those issues.
If you think about it, most internal combustion engines have a vertical orientation: the crank shaft is often at the bottom of the engine (thought not always), pistons in a straight six are set up vertically (vee engines are off of vertical, I would note). Back in the days of steam, engines were commonly laid out horizontally, but this started to change when people understood how the parts wear.
Since the piston is in fixed position with respect to the cylinder, if it moves in a horizontal plane, wear on the piston rings and any bearings will be on once side. In a vertical orientation, the piston is essentially balanced with respect to gravity (assuming the engine base is level). Wear is then distributed more evenly. Furthermore, if the control valves are located at the top of engine, gravity works in our favor to keep the seal on the cylinder while steam is not being admitted. Gravity also helps us to eliminate any water that may have condensed in the cylinder chamber.
I’ve gotten a healthy respect for high pressure steam (especially superheated steam – so called dry steam) as I’ve done my research. This is a highly regulated technology governed by federal laws that determine how steam fittings are made, how boilers operate, what safety precautions are required, etc. Escaping steam can cut through exposed flesh and leave very nasty burns. It can also corrode and erode metal if care is not taken on the quality of water used.
Given the dangers of high pressure steam, I started turning my attention to lower pressures (under 100 psi). Steam engines can work effectively with lower pressures, but put out less power (simple physics). This leads to ganging cylinders for more output, but also increases the overall cost of the engine. To some extent, it depends on what you want to use the engine for. If you’ve got a small solar concentrator that puts out a steady supply of steam and you want to generate electricity for storage in OSE batteries (which are coming along, I note), then you might get by with a low power engine, perhaps geared up for higher generator speeds. If, on the other hand, you want to generate a lot of power and use it directly – for an aluminum smelter, for example – a different engine design is likely called for, especially if you use correspondingly larger solar concentrators.
Valve design turns out to be it’s own sub-discipline in steam engineering. In many ways, it is the heart of any steam engine design. I’ve collected notes on valve designs. The bump valve approach in the current design was strongly influenced by the White Cliffs Solar Power Station project conducted in Australia in the 1980’s. The solar concentrator and steam engine developed for this project operated for years at high efficiency, low mainenance, and high power output. Besides resident housing, it powered a nearby opal processing factory, similar in some ways to the manufacturing capabilities describe in OSE Global Village Construction Set.
Unfortuately, some of the key technical details were left out of the White Cliffs Report including what materials were used. For these and other reasons, the design sifted from a ball shaped valve to an arrowhead shaped one. We were also planning on making the engine from scratch, rather than converting an exising engine (a GM Lister Diesel in the White Cliffs case).
Recently, Marcin and I have been in communication with Mr. Ron Whaley, who was an engineer at Power Kinetics, Inc. and worked on the White Cliffs project. Mr. Whaley has filled us in on some of the missing details left out of the report and has indicated a willingness to help us design a functional steam engine that will meet our needs. Marcin plans to visit him at his home shop in the next couple of weeks. This new information is likely to lead to some major design changes. Until then, things are on hold. We are not planning on prototyping the current steam engine design, as documented.
While Marcin explores new options with Mr. Whaley, I’ve been giving some thought to experimenting with steam engine design. In software, when a new design concepts comes up, some one will often code up a prototype to see if it works. It usually doesn’t take all that long – a few hours at most. This is not the case with open source hardware. The materials used in prototyping can be expensive and it can take a long time to fabricate (or buy) the parts needed to create one. These are some of the reasons why we are holding off building the current design – too much time and too much money to spend on something that likely won’t work, in spite of what we might learn from doing it.
My thinking has led to the initial development of an experimental platform that’s designed to be less expensive, faster, and safer than building steam prototypes. First off, I’m using compressed air instead of steam. It’s easy to obtain from a commercial air compressor (I have one). It’s simple to regulate the pressure (up to 200 psi) and it is much, much safer. Secondly, I’m building a basic cylinder/piston system out of PCV pipe. It turns out that the end caps for 3″ pipes fits almost exactly inside of a 4″ pipe. It’s so close, I don’t think I’ll need piston rings or a seal of some kind – thought that remains to be seen.
I’m calling this an “air engine” and you can see more details of it at on the project page. Marcin has indicated that the OSE process is not an experimental one, so I have moved this work to my own open source hardware site at the Phase 3 Project. I’ve started blogging some of that work as well (see home page). The first set of experiments with this platform will be the development and testing of a rotating valve concept. Rotating valves are not a new idea, they were used in Corliss steam engines 110 years ago. Rather that used a fixed timing mechanism, like an eccentric crank, my plan is to control the rotating valve using a stepper motor and a computer, such as an Arduino board. If I can get a good seal and program it for rapid switching, I think we’ll be able to migrate this into the design of a truly Modern Steam Engine – one that uses a computer for timing. This will enable, among other things, dynamic control over shut-off (the point when steam is shut off from entering the cylinder). This degree of control allows for variable speed engines and simpler start up. Adding a similar valve to the exhaust port and you can have dynamic engine braking.
This work is still in it’s very early stages. If you are interested in supporting this work, let me know. I have some very early experiments in mind before tackling the fabrication of the rotating valves. There are also some intersting relationships to explore between the size of the steam flow channel and the diameter of the vavle.
Meanwhile, some good news. My submission to the Open Source Hardware Summit to take place on Sept. 15, 2011 in New York City has been accepted. While it won’t be a long presentation (ten minutes), it is an opportunity to make our work known to east cost hardware hackers. The proposal reviewers seemed quite interested in the project:
“The idea of an open source steam engine seems a bit inefficient at the surface but the logic behind it is actually quite intriguing especially when thought about it the solar heating context. I think this talk would a good shift in examples often cited in open source projects from the virtual to the real world. I would like to see more of the actual build process and the openness of the fabrication process rather than emphasis on the openness of the idea. Also the project has numerous CAD / specification type input while showing knowhow through videos / illustrations etc of the actual process would go a long way. Also the talk could touch up the idea of the Open Source ecology to make the steam engine part of it more relevant.“
“Open Source Ecology’s steam engine project would be an incredible addition to the Open Hardware Summit. Among many reasons, the project is very unique in the particular kind of ‘hardware’ it focuses on: a mechanical steam engine. Most submissions will probably focus on electronics, so the presenter’s focus on mechanics will undoubtedly stand out. If that weren’t enough, the mission of this project is of tremendous value to humanity. There are many important lessons that can be learned from the approach taken by the presenter and his colleagues at Open Source Ecology. The technology to end global hunger and poverty has existed for centuries, but this knowledge has not been effectively transferred to the developing world. Open Source Ecology has really nailed ‘appropriate technology'(E.F. Schumacher, et. al) and have seamlessly connected it to the open hardware movement. The Open Steam Engine appears to be a great representation of OSE’s work, and I highly recommend this presentation be included in the Open Hardware Summit.“
Hopefully my presentation will be received in the same sense of enthusiasm. My main message to this audience is that OSE has put a lot of effort into the development of a steam engine and though the current design has problems, we are continuing to work towards the creation of the worlds first open source steam engine.
– Mark Norton