Converting 2-stroke motors to steam

[DetroiTug]

At some point, a simple overhung crankshaft running in pillow blocks is easier than a conversion....

- Bart

Agreed. Tiny power has that 2.5" X 3.5" steam cylinder group of castings for $125. That is a really good deal. The rest of the engine can be made with simple plate and barstock. Without machining i.e. lathe and mill, the only alternative is an I/C conversion. The issues: Stroke is typically too short for the bore, steam cylinders are usually configured whereas the bore is about 75% of the stroke. Not exactly sure why that is, but it has been repeated in many engine designs. I/C conversions usually wind up single acting. With leakage around the rings and if there is a crankcase, condensate/water winds up in the crankcase. My experience with Uniflows, while very efficient, if one is after the traditional sound of a steam engine, they aren't going to get it, rather an engine that sounds like a flathead four gasoline engine. The valve arrangement in many of them are of the "bash" design, where the rising piston bashes in to a plunger- opens a valve and admits steam. Noisy and no way to control cutoff. The main issue: While not a huge effort, it takes time to perfect and convert an engine to steam. The end result, although it may work just fine, if it is to be sold, it is simply not going to go for a very high price.

If I was in the position of needing an engine and no access to machine tools, I would just buy an existing steam engine at a fair price, use it, if and when it is sold, the entire investment can be recovered, and probably more as steam stuff is increasing in value.

-Ron

[ccdewitt]

I built one of those engines with a stem on the piston that lifted a disc valve and exhausted through ports at the bottom of the stroke, a uni-flow if you will, single acting. It was difficult to start, had to spin it pretty quick to take off and it ran very fast, rpm wise. It had a 3/4" bore so not really suitable for boat application. I became disillusioned with it because of the high rpm's. I very much prefer ponderous machinery moving slowly. Also it was very noisy. It was however an interesting exercise in machine work.

[hartleymartin]

Like I said, it could make a nice little auxiliary engine running off the exhaust steam to power other things.

It just seems like an interesting project. Whilst, of course, I would always want to have a proper marine steam engine, it would be something interesting to muck around with.

[Mike Rometer]

If nothing else it's proved an interesting discussion point. Stirred the grey matter a little!

[DetroiTug]

it could make a nice little auxiliary engine running off the exhaust steam to power other things.

Any restriction/pressure induced on the steam exhaust of an engine, sufficient enough to run another engine is going to limit the performance. Ref "exhaust throttle".

Not much is really free available extra energy in a steam plant. Everything costs something. Even a superheater as a performance enhancement costs something by cooling the combustion gases to some degree, and even degradation of the engine and throttle if piped in that manner. Economizers above the steam generation section are probably the most advantageous.

-Ron

[cyberbadger]

Note that most of those 2-stoke conversions are fun little projects, but not really practical to do work long term with much efficiency.

Most of the videos online aren't even using steam, just compressed air.

The silliest ones in my mind still leave the cooling fins on. Internal combustion engines want to get rid of heat. External combustion steam engines want to keep as much of the heat in the cylinders as possible to avoid condensation.

It can be done, and if that's your cup of tea then go for it.

Is it practical or efficient, not so much.

-CB

[hartleymartin]

If you wanted "practical" and "efficient" I don't think you'd be getting a steam-boat in the first place.