Tverskoy-Pasechnik Rotary Steam Engine

[russkey]

Please forgive the possible blasphemy, but has anybody tried using a electronic valve timing mechanism? Something based on solenoid valves would be quite quick. A simple microcontroller would handle the input from a rotary encoder of some sort and the output to the valves. You could even use some of the power coming out of the engine to recharge the battery for such a system. I got to thinking about this because the current design has a particularly wooly flaw. The steam distribution and timing system is built in as part of the cylinder and drum. As such, there is always a force on one side of the drum when steam is not being passed through it. This would cause the other side of the drum to be pressed against the cylinder wall, increasing the friction. There is also a fairly significant amount of dead space in the distribution system. If I put simple on/off valves right at the inputs, I could cut this dead space down to practically nil.

[SL Ethel]

I have seen a couple of videos on youtube showing a solenoid valve uniflow steam/air engine. It was very crude, but made an effective demonstration that it worked. The builder just had a magnet on the flywheel and little reed switch. The magnet closed the switch when it came around near it. The reed switch controlled a normally closed solenoid valve. It was so basic that he just held the reed switch near the flywheel. No control over length of admission, but he could change the timing just by moving the switch with relation to the flywheel. I'm sure that a more carefully engineered system could work very well.

You mentioned before the issue of early machining before <50 micron machining would have been possible. Piston rings have long been the way this clearance issue is dealt with. Even today, full sized steam engines (or IC engines, for that matter) can't be fit too closely between piston and cylinder simply due to thermal expansion considerations. As I think Wes suggested, you might look at just using seals from a wankel engine. Just trying for close tolerances without some sort of seal system will inevitably lead to huge blow-by and attendant loss of power and efficiency, having the engine seize, or both.

Cheers,
Scott

[RogerV]

As far as I can recall, I've only heard of two applications where rotary steam engines saw much use. The first was the type of engine being discussed here mounted on steam locomotives to power the generator for the locomotive's lights. The second is a considerably different design which used what I can only describe as two rotors with what look like gear teeth engaged with each other for about half of each revolution. I know that's kind of a vague description, but I really can't think of anything to compare it to. This engine was used on Silsby steam fire engines, where it drove a rotary pump that was very much like the engine. In fact, when looking at a diagram of the two, it's difficult which is the engine, and which is the pump. The pump could handle water with all kinds of debris that would jam a piston pump, and I suspect that is one reason Silsbys were popular in the western parts of North America. The engine was simple and easy to repair, and used in a situation where fuel efficiency was not an issue. Also the combination of rotary engine and pump produced a steady stream of water without the "pulsing" sensation that some piston pumps produced.

[russkey]

RogerV, the interlocking rotary engine you are referring to is indeed in interesting design. The original Tverskoy documentation actually states that it can also double as a pump. He designed it for battleship use. His thought was that you could have a set of these engines all attached to a single axle. They could be thrown into forward or reverse at a moment's notice by simply redirecting steam (presumably losing some of the expansion efficiency in the reverse direction?). In case of an emergency, one of a hypothetical pair could be switched to take in water instead of steam, acting as a high speed pump. There's even reports that during a test, they got a rock into the engine while pumping, quickly threw it into reverse for a bit to dislodge the rock, and then continued as before. If I recall correctly, the twin rotor interlocking engine was claimed to be a bit inefficient because some of the steam pressure goes into a radial force, instead of creating all torque. Other than that, it seems like a nifty design! It would use fewer gears than mine.

Incidentally, I've basically finished the various calculations I was interested in for this design. I've got a rough estimates spreadsheet (adjustable to various engine parameters) and I'm pretty happy with what I'm seeing. Going back to the Solidworks CAD this week, and then hopefully some real machining before the year's end!

[RogerV]

Russkey,
I along with everyone else, will watch for reports on your progress. After I made my last post, I came home and looked at my copy of The New Catechism of the Steam Engine (originally published by Audel's in 1904) and was reminded that Silsby was at some point absorbed by the American Fire Engine Company, which continued to use the rotary engine and pumps in some models. I believe in most rotary models, the hoses connected under the driver's seat, rather than in the more usual location at the sides.

PS: If it isn't obvious already, steam fire engines are another interest of mine.