Pressurization

Discussion on Stirling or "hot air" engines (all types)
PetePeterson
Posts: 10
Joined: Wed Feb 08, 2017 12:33 pm

Re: Pressurization

Postby PetePeterson » Mon Feb 20, 2017 8:07 am

Aviator168,
"But not all stirling engines are one cylinder. For a double acting four cylinder stirling, there is no crankcase pressure to speak of."

With a double acting power cylinder the other side of the piston is Not at atmosphere. When it is compressing on one side, the other side is expanding thus helping the flywheel.

"The true reason for a higher power output is the increase the amount of work fluid in the engine. Not the increase in pressure of the crankcase.
"
As to the last statement: my intent (I don't always say it right) was if the internal pressure of the engine stayed the same, and you then pressurize the crankcase, you would get more power. The amount of work fluid was still the same.

Another way to look at it: if you add pressure to just one side of a double acting cylinder if gets hard to compress that side, if you add the same pressure to the other side you can move the piston by hand more than before.

Bumpkin
Posts: 121
Joined: Fri Mar 02, 2012 1:42 pm

Re: Pressurization

Postby Bumpkin » Mon Feb 20, 2017 10:41 am

Aviator, I forgot to mention another problem with a pressure imbalance above and below the piston. (beyond the normal power pulses) There is a greatly increased rod and main bearing load. I bumped into that while trying to think up a pressurized diaphragm type engine. A set of two opposed and linked solidly together in a push-me pull-you fashion might have worked, but it would have been a mess for what I wanted to do.

Bumpkin

Aviator168
Posts: 308
Joined: Tue Feb 08, 2011 2:29 pm
Location: Brokeville, NY. USA

Re: Pressurization

Postby Aviator168 » Mon Feb 20, 2017 11:34 pm

I worked out all the numbers. Pressurizing the crank case would not increase the power of the engine. However, it does lighten up the loads of the bearings, cranks, and the connecting rods. It also reduce torsional vibrations greatly.

Ian S C
Posts: 1970
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Pressurization

Postby Ian S C » Wed Feb 22, 2017 2:40 am

If you only pressurise one side, the power piston will be at bottom dead center, if you have 200 psi/15 bar, and try and turn the motor you just aint gonna do it.
Ian S C

spinningmagnets
Posts: 17
Joined: Sat Aug 02, 2008 7:34 pm
Location: SouthWest Utah, USA

Re: Pressurization

Postby spinningmagnets » Sat Nov 11, 2017 7:34 pm

I studied the Rider-Ericsson engine a while back. It is an alpha with two vertical / parallel cylinders, and the crankshaft is at the top of the engine. The crank side of the pistons are open to the ambient air.

It had an integral air-pump which could be adjusted to compress air at any degree of the flywheel position. If it was adjusted to add air to the interior at the moment of lowest pressure, it would be drawing the least amount of power away from the engines output. I am not aware of any other benefits that might occur if the air-pump was activated at a different position, but it is interesting that the designers felt that it was a useful option (would it run smoother at a different position?).

I seem to remember that the interior pressure at its lowest point was two atmospheres? (don't take my word for it), which was regulated by a relief valve on the air-pump. The air-pump also had an adjustable stroke, so when the leather seals on cylinders became worn (and thus leaked more) then the stroke could be increased to maintain the desired pressure.

I found it interesting that the leather seals were stationary on the tops of the cylinders, and the long "pipe-like" pistons entire length was a smooth surface. This meant that the cylinders could be simple pipe with no need to machine or hone the ID. Machining only the OD of the piston "pipe" was much easier.

Ian S C
Posts: 1970
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Pressurization

Postby Ian S C » Mon Nov 13, 2017 2:00 am

With the early "pressurized" engines the basic idea of the pump was to replace lost air. to keep the internal pressure at, or just above atmospheric pressure.
Ian S C


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