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screw expander?

Posted by HYDRAGON 
Re: screw expander?
April 11, 2015 05:18PM
> "The rotary motion is transferred to the drive
> shaft by an eccentric (illustrated in blue)
> that rides in a matching bearing in the rotor. The
> drive shaft rotates once during every power stroke
> instead of twice as in the Otto cycle.

Right three operating voids or chambers and the eccentric shaft rotates three times per one rotor revolution. Thus three compression events. You don't know the Wankel.

> I do know what im talking about you are just an old coot. smiling smiley

Right, one with a hell of a lot of experience. And,there was a steam Wankel demonstrated at an old SACA meet, nothing new.

Try Museum of Retro Technology then go to rotary engines.
Re: screw expander?
April 11, 2015 06:21PM
Jim I still like you smiling smiley

forgive me for poking you a little.
Re: screw expander?
April 12, 2015 06:13PM
Rotary Steam Engine

The original 4 cycle porting has been modified on this engine

If this guy had a bigger boiler capacity and addressed thermal losses there is something there..
Re: screw expander?
April 13, 2015 08:16PM
Looks like what you said Jeremy and he could go either Rankine or Brayton as well....with the right compressor(eats about half the Wankel hp. re-compressing if he did).

At the same time, I think we all had the first attempt at an idea go like his, instead of a perfect system totally lined out....
Re: screw expander?
April 13, 2015 08:28PM
I think the expander the guy built would fall under a rankine cycle and uses tons of steam. when you see the water coming from the tail pipe there's lots of thermal loss.

Im going to post to that youtube video and say "I like what I see". Sure there's lots to nitpick but he built the thing.
Re: screw expander?
April 15, 2015 07:45PM
Why is it that the Wankel is so difficult to understand.

The crank rotates 3 times to the rotor pistons one. The rotor piston has 3 crowns. If we start with the crank throw aligned with a crown. That crowns chamber is at min desplacement. Rotate the crank 90 degrees and the throw will be pointing at an apex. The crown opsite the apex is at max displacement.

A min to max volume change takes 270 degrees of crank rotation . We have a chamber at min volume every 180 degrees of crank rotation.

A power stroke takes 270 degrees of crank rotation. Exhaust takes another 270 degrees of rotation . A complete power exhaust takes 540 degrees. In that crank rotation of 540 degrees the rotor has only rotated 180 degrees.

This gives you two overlapping power strokes per revolution of the piston. You have a power stroke starting ever 180 degrees of the crank rotation. Or could have if smart.enough to figure it out.

This requires two sets of inlet and exhaust valves.

Take the Wankel chamber looking at it with the nerrow vertical and wide horizontal. When the crank throw is horizontal it points at an apex. The chamber opsite the throw direction is at max displacement. When the crank throw is vertical it points away from an apex at a chamber at min displacement. At 90 degrees through a power stroke you have a chamber at max displacement ready to start an exhaust.

The rotor has 3 crowns. The crank makes 3 rotations to the rotors one. Below is a state map of crank rotation to rotor function.

I = Start of power stroke. Or Inlet start.
P = Power stroke or continued inlet.
X = Exhaust or compression stroke.
I and P = volume increases with crank rotation.
X = volume decreasing.
Crank  Crown
angle  1 2 3
000    I X P
090    P X X
180    P I X
270    X P X
360    X P I
450    X X P
540    I X P
630    P X X
720    P I X
810    X P X
900    X P I
990    X X P
1080 crank and rotor at initial position.

The above is for a single rotor. A two rotor rotor engine with the chambers at 90 degrees could have a power stroke starting every 90 degrees of crank rotation and further would have its inlet coensiding with the exhaust of the other roter. You could have a steeple compound with HP exhaust going to LP rotor.

The steam Wankel I designed was quite different then an IC design. I figured on using a cerved apex seal. In effect the roter had a varing k factor across the apex seal. The rotor sealing apex edge was a half circle. The k factor had to be right or the seal would be changing direction. That is the point of transition of the apex to the edge seal would be doing figure eights at some points. The design allowed a continuous ring (sort of) type seal eliminating the joint between apex and side seals. It also like a normal IC piston ring provided sealing pressure fource.

The IC Wankel doesn't lend itself to a two stroke cycle. But that is because it already operates simular to a two stroke piston engine. It already uses port timing instead of inlet and exhaust valves. The steam Wankel as I described would have twice the power strokes as it IC counter part. But it would have two sets of inlet and exhaust valves per rotor. Thing is that a reversing engine would have separate inlet and exhaust ports that would be offset from the center so power strokes and inlet could overlap. Reversing would require switching the offset ports function as well.

The Wankel design was before I got into cycle analysing. Before I wrote that first cycle analyzing program many years ago. Jerry's paper on the Williams engine got on that road. He was using exponent calculations. I decided to do the same using actual steam properties. The normal cycle calculations were static assuming 0 clearance. So wrote a calculator that included clearance and compression. That first cycle calculator program used the ASME steam formulations and figured the mix properties of the residual steam and it's compression and mix with inlet steam. It also figured the negative work expanding below external exhaust pressure.

Sorry for long off subject comment but some do not seam to understand the difference between strokes and cycles.

If you do a steam Wankel right would have a power stroke starting every 180 degrees of crank rotation For each crank throw. Or rotor.
Re: screw expander?
April 15, 2015 08:26PM
A 13b dual rotor Wankel will have one power stroke every 180 degrees of crankshaft rotation.
Re: screw expander?
April 16, 2015 02:11AM
Sorry you could not comprehend how the two rotor compound Wankel I designed started a power stroke every 90 degrees.

An IC Wankel is a 4 cycle engine. All IC piston engines are 4 cycle engines. Even two stroke engines. You have intake, compression, power, and exhaust. A two stroke simply combines exhaust and intake. Having pressurized the fuel air mix in the lower end. The exhaust aids in creating a draw on the intake which is compressed on the remaining up stroke, ignited and expands on the down stroke were the exhaust port is uncovered and the outflow exhaust create a low pressure and draws in a fresh fuel mix pressurized in the lower end.

There is a certified mechanic that rented from us. My wife paid him to change our breaks. He didn't know how to compress the hydraulic plungers to get the new ones to go in. I had to show him.

A steam engine is not equilivant to a two stroke IC engine. A steam piston engine simply has a power and exhaust stroke. Not all of the Ranking cycle is implemented in the engine. By the way there are engine ranking cycles and power plant cycles. The engine cycles are power stroke (admittance and expansion) and exhaust stroke (exhaust and compression). Compression and clearance are not part of the text book ranking cycle. The power plant Rankine cycle has admitance and expansion. Instead of exhaust we have condensation toboilerfeed. pumping to boiler pressure heating to inlet state.

Try another explanation of Wankel. Following a Roger face through 360 degrees or rotor rotation in 90 degree steps.

1. Rotor face down. Crank throw is pointing down. Down face
chamber is at min displacement. Rotor rotates 90.degrees. crank rotates 270.

IC engine ported inlet stroke Steam engine power stroke. Valved steam admittance.

2. Rotor as above at 90 degree point. Rotor face is at max displace position. Roter face rotates from 90 degree position to 180 degree position. Ending in a min volume state. The crank has now rotated 540 total degrees.

The IC engender has just completed its compression stroke. It's an exhaust stroke for the steam engine.

3. Another 90 degrees for the rotor to a max bounded volume point.

Finely the IC power stroke. It's also anote power stroke for the steam wankel.

4. Another 90 degree of rotor rotation. And we are back to were we started.

The IC engine completes it's exhaust stroke. Just another exhaust stroke for the steam Wankel.

The inlet and compression strokes of the Wankel are power and exhaust strokes for the steam engine.

To make more clear. Where the IC Wankel has an inlet port the steam Wankel has a inlet valve. And the exhaust port is.a steam exhaust valve. Were the IC wankel has a spark plug the steam Wanke has another set of inlet and exhaust valves. On the steam Wankel the inlet and exhaust valves are placed off center simular to the IC ports so as to be able to.atain self starting power strokes. But such placement is counter to self starting reverse. In order to have self starting forward and in reverse the inlet and exhaust valves need be switched. A third valve could switch the inlet and exhaust functions. It's a simple valve.


IC: inlet compression power exhaust
STEAM: power exhaust power exhaust

Edited 1 time(s). Last edit at 04/16/2015 09:58AM by steamerandy.
Re: screw expander?
April 16, 2015 04:31AM
Well expalined Randy. A lot of surface area, but a very workable solution. -Keith
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