Steam Engine Reviews/Arrowhead Bump Valve
Steam Engine Reviews
The following reviews apply to the Bump Valve Design.
Tom Kimmel of SACA
Some observations and recommendations from Tom:
- Do more research.
- Come to my shop and look at real steam engines.
- Add teeth to the flywheel to allow an electric starter motor.
- Cylinder liners (sleeve) should be cast iron. Look into motor rebuild kits.
- Valves are not "chinese hat". Talk to Jay Carr about his design.
- Open or closed crank is a choice. Not critical.
- Lubrication is important, but had no specific recommendations.
- Start with conservative materials (like iron) and consider advanced materials later (like nitride coatings).
- Consider designing an exhaust manifold from the start.
- Visit Bill Ryan north of Chicago who has experience with making bash valves.
- Don't use stainless steel as a cylinder line.
- Consider 12v electric system for fans, solenoids, relays, water level sensors, and starter motor.
Ken Helmick of SACA
Some observations and recommendations from Ken:
- Initial decisions having huge influence on final design.
- Higher operating pressures and temperatures lead to potentially higher efficiency.
- A uniflow engine has the potential of higher efficiency.
- A counterflow engine has the relative advantage of being more easily operated.
- Wrapping a sleeve and welding is not likely to yield a satisfactory engine
- To make a sleeve, consider:
- Cast it using a sand mold.
- Use off-the-shelf sleeves.
- Purchase already honed hydraulic cylinder tubes.
- Convert an existing IC engine or extensively utilize IC engine components.
- If welding is employed, stress-relieve the assembly and then re-hone lightly in case of any slight thermal induced distortion to the bore.
- Valve springs must be wound from superalloys and heat treated. Conventional springs will fail from the heat of the steam.
- Bump valve engines probably are more efficient at some moderate rpm.
- An alternative to bump valves is a smaller piston valve mounted coaxially with, and upon, the engine piston.
- Always enclose the crankcase of any higher rpm engine.
- There is an incredible variety of piston rings available in almost any size, configuration and material imaginable and this is about the last reason I would select a given engine diameter.
- Electric starter motors are simple. Older General Motors alternators are widely available and they have an integral voltage regulator.
- A uniflow exhaust manifold could be very, very simple, depending on the cylinder.
- The crankshaft is the heart of the engine.
- The average home machinist is typically not equipped for (nor capable of) building a multiple throw, one piece crankshaft.
- One route to consider is the built-up crank.
- 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.
- The home machinist can balance a crank with a single throw but multiple pin cranks can only be balanced in a shop with a dynamic balancing machine.
Jonathan Herz -
Jonathan short | firstname.lastname@example.org | IP: 126.96.36.199
I read what you wrote about your engine ideas with interest. I agree with you that the possibility for integrating electronic valve timing with a traditional steam engine. When I looked into the most obvious solution, solenoid valves such as you suggested, I found that the requirements for the solenoid are not trivial. If you pursue this, you will want to look closely at the performance of the solenoid, both in terms of duty cycle and actuation time. The results suggest that you need a very powerful, very fast solenoid with nearly 100% duty cycle. This is not inexpensive. I tried reducing the weight of the valve to improve response time by actuating a very light pilot valve, but the problem is that the iron in the solenoid plunger has a lot of mass. You can increase the power of the solenoid by increasing the magnetic field, but greater the magnetic field, the longer you need to apply a given current to generate the field, thus the slower the response time.
The problem is not insoluble. I know that the automotive industry is looking at solenoid valving, which is an even more demanding application. But they are looking at a highly engineered solution. I do seem to spend a lot of time dishing out bad news in alternative energy circles, but I also wanted to let you know that if you wish to pursue your steam engine (and I hope you do), you will need greatly reduce your efficiency expectation below the 19% you quoted. I think you are about four times too optimistic. The sort of engine that you sketched can be expected to produce about 5% efficiency assuming a reasonably efficient boiler. You quoted the Skinner unaflow engine at 19% peak efficiency. Taking that as a benchmark, here are the ways in which an engine such as yours falls short. Ignoring boiler efficiency as outside the scope of this discussion:
- The Skinner used pressures around 800 psi, much higher than the 100-200 that is common for most smaller setups.
- It operated at several hundred degrees of superheat, which would be difficult to achieve without expensive controls and high alloy superheater tubes.
- It was Unaflow and condensing. Unaflow is a great way to go, but if you are not operating condensing at a low condenser pressure, unaflow operation requires complex auxiliary exhaust valve which opens only after the unaflow ports are opened. In any case, a non-condensing engine will be less efficient than a condensing engine. One advantage that marine engines had is that they were sitting in a body of water and could thus easily cool their condensers and keep them very low pressure. If you don’t use unaflow valving then compounding becomes VERY important for efficiency.
- your engine is smaller and therefore you will have less mechanical and thermal efficiency.
- You do not jacket the cylinder and head with high pressure steam. Again, more condensation losses.
- Unless you have a very constant load, you cannot obtain good efficiencies without variable cutoff (varying the expansion ratio to accommodate different loads). One of the advantages of electronic valving is that you can more easily implement variable cutoff, but your electronics would be more complex and you would need some form of sensing for the electronics to determine the right cutoff.
Those are the major efficiency factors that you would want to consider if you want to achieve better than 5% efficiency. As you can see, there is, as always, a tradeoff between efficiency and manufacturability.
Good luck with your work. I look forward to hearing more about it in the future.
P.S. This comment has been floating around my hard drive for a long time. I first started writing it when I read your initial posting. I see that my comments about the performance requirements of solenoid valves have already been discussed. Have you found something satisfactory?
May 1, 2011 7:45 PM — [ Edit | Delete | Unapprove | Approve | Spam ] — Steam Age meets the Digital Age: Open Source Steam Engine
My vision is to just be a part of the project. I'm sure I can be useful to you. However, I also know very little about steam driven engines. Ideally, someone more experienced in this arena would be guiding us. The likelihood of us coming up with something great in a short period of time is slim to non....:) You must know this already....no? But, we will learn about each other and develop a process that will be useful in the future I'm sure. So here comes some ramblings.
The design as it stands has many shortcomings. On one hand it is relatively simple which certainly needs to be, but at the same time is not likely to produce much power or be very durable. Eventually, after many prototypes, there will need to be some sort of happy point between efficiency and complexity.
Andrew makes some good points regarding the valving. I can add a few more. One problem with this sort of arrangement is the valve opens before TDC (top dead center). This may be fine at high RPM but really bad at relatively low RPM. The piston is on it's way up and suddenly the steam starts to enter before it's ready to go down again. So for part of the stroke, you're fighting against high pressure steam. Combine that with the fact that the exhaust port does not fully evacuate the "spent" steam and you have a problem.
I would avoid the double pin design either way. It would be very hard to insure an even amount of pressure from both sides. This would lead to piston rocking and premature failures. A single centered valve is better. Also, put the pin in the valve not the piston. I would just have a hardened contact point on the piston.
I suspect that this general design would only be good for very short stroked, very high RPM applications. The higher the RPM the tighter the tolerances need to be to get any useful life out of the engine. Also, in the steam world, short stroke means very low HP. Not a direction we want to go in I suspect.
Some general goals might be:
- Low RPM - Long life, design less critical
- Large diameter piston - more torque, need less stroke for same amount of work being done
- Adjustable valving - need to be able to move the valve timing where we need it to be
- Simple construction - it will be nearly impossible for "the Farm" to build it otherwise
I would seriously look at trying to use off the shelf components as much as possible. What about converting a small compressor instead of making it all from scratch? This would get us up and running relatively quickly and give us the opportunity to learn about all aspects of steam without reinventing the wheel. We could then take this knowledge and start looking at scratch build ideas as time permits.
The techie in me says yes to electronic valving. The practical side says hell no. "We" are undecided....:)
> How easy is this design to fabricate?
Compared to other designs, much easier. Can a guy off the street walk into a fully outfitted shop and build this. Not likely.
> Will steam leak out of seams or joints? Does it need seals of some kind? If so, what?
High pressure steam needs to be used very carefully. It is very dangerous. A leak can easily cut the flesh off a finger in seconds never mind the associated burns. Pipe fittings must be used at all the joints and gaskets between mating surfaces.
> Are the parts over-engineered? > Are they too heavy? > How could things be made lighter?
If we keep the RPM down the weight is much less critical. I haven't seen any dimensions yet so can not comment much more.
> Will the crankshaft assembly work as designed? How much vibration is likely based on this design?
Again, low RPM is your friend here. But a counterweight will likely be needed
> Where are the wear and failure points in the design? > How long will the engine last?
Low RPM good again. Engine like this will need constant attention compared to what we are used to with a Honda gas engine. Rather than trying to make it last forever make it easy to repair maybe. The basic parts of any steam engine can last a very long time. Keep in mind, the early locomotives spent more time in the shop than running. It was normal back then.
> Can the engine handle high pressure, super heated steam? 500+ PSI, 500+ degrees.
Probably not that high no. You would need a very small valve at those pressures. The piston would never get the valve open with that kind of back pressure. The higher the numbers here the better efficiency we will see from the system as a whole.
> What safety considerations should we be making?
That kind of pressure can kill. I would avoid it.
To conclude, hobby engineers with years of steam experience take months to build their engines. This is with a shop full of proper machining equipment at their side and the knowledge to use them. Even if I were to build this, which I haven't decided on yet, it would take me months in my spare time.
I hope you find my comments useful.