Thermodynamic work vs. real work

[Tom Booth]

To make this clear, view the engine as a "fire piston" with a sliding regenerator in the bottom of the chamber.

Have the piston driven by a heavy flywheel.

Now imagine whenever the piston passes the halfway point a solenoid is tripped that switches from the hot to the cold regenerator on the way up and back again on the way down.

Something like this:

Compress_20240908_231001_1637.jpg (22.19 KiB) Viewed 1585 times

You can have heat going in from the candle on the right to compensate for friction or crank/drive power output. But in the way up, once all the heat is exhausted the piston is carried up further cooling the gas while the cold regenerator moves into position.

The cylinder walls, of course, should be non-heat conducting and inert, not absorbing or releasing any heat.

As hopefully can be seen or imagined, there is no transfer of heat between the hot and cold regenerator/heat exchangers. At least not through the working fluid. In this arrangement heat could conduct directly through the divider, but let's just say the divider is a perfect insulator.

[VincentG]

Tom give me some time to respond, specifically to the vacuum engine comment.

[Tom Booth]

Tom give me some time to respond, specifically to the vacuum engine comment.

OK,

But that wasn't really my question.

viewtopic.php?p=24772#p24772

[Fool]

I can't find any PV or indicator diagrams for a flame licker engine.

[Tom Booth]

I can't find any PV or indicator diagrams for a flame licker engine.

Senft, "Mechanical Efficiency of Heat Engines"

The text reads

Figure 1.8(c) is the imagined cycle of a vacuum engine in which the hot gas is drawn into a cylinder at atmospheric pressure and then captured by closing valve and cooled; the pressure drops and a compression follows in which energy is transfered to the engine shaft.

Compress_20240911_094505_5744.jpg (25.46 KiB) Viewed 1472 times

[Fool]

Thanks.

[Tom Booth]

Also: on the previous page it reads:

A plus sign along a segment of the cycle indicates efficacious piston work, i.e. where positive work is done on the mechanism by the piston.,

[Fool]

It would be helpful to see how that ideal compares to a measured indicator diagram.

[Tom Booth]

Note (d) is the Ideal Stirling Cycle, comparable to VincentG's opening diagram.

According to Senft, + "positive work" on both expansion and compression or "contraction".

[VincentG]

The vacuum engine is a great example. It is different in that it really has no compression work until very near tdc, ideally, while the ideal Stirling cycle is compressing its internal volume all the way from bdc to tdc using the buffer pressure to do real work and thermodynamic work.

So what is the maximum efficiency of the vacuum engine?

[Tom Booth]

The vacuum engine is a great example. It is different in that it really has no compression work until very near tdc, ideally, while the ideal Stirling cycle is compressing its internal volume all the way from bdc to tdc using the buffer pressure to do real work and thermodynamic work.

So what is the maximum efficiency of the vacuum engine?

I disagree.

When the valve in the vacuum engine closes at BDC the situation from there to TDC is identical in both.

The hot gas cools and "contracts" or the pressure reduces and atmospheric pressure does POSITIVE (mechanical) work.

This is not "different" at all

In both, from BDC to TDC the gas is trapped, enclosed, contained and the volume decreases due to "compression" by atmospheric pressure.

[VincentG]

Ideally there is no gas in the vacuum engine once the valve closes. Or at least you are gaming the curve where any significant compression occurs only very near TDC.

The Stirling cycle as defined by Fool and Senft above has a fixed mass of gas that is fighting the piston all the way from BDC to TDC.

[Tom Booth]

Ideally there is no gas in the vacuum engine once the valve closes. Or at least you are gaming the curve where any significant compression occurs only very near TDC.

The Stirling cycle as defined by Fool and Senft above has a fixed mass of gas that is fighting the piston all the way from BDC to TDC.

The gas at BDC is at approximately atmospheric pressure. So how can there possibly be "no gas" ? The partial "vacuum" occurs after the valve closes and the existing gas in the chamber "contracts".

You bunch of idiots can believe whatever you want to make up I suppose. Have fun deluding yourselves

Even if it's imagined the flame burns up ALL the oxygen after the valve closes, that only amounts to 20% but atmospheric pressure would push in more gas to replace whatever oxygen gets burned on the way in.

[Tom Booth]

You guys, all three, have to be paid shills. No normal person could possibly be so irrational as to ignore all common sense and just keep spewing the same crap over and over.

I had a friend who did what you do and he told me all about it and he got paid very well for his constant lies, but eventually he got a conscience and quit the oil company.

[VincentG]

You guys, all three, have to be paid shills. No normal person could possibly be so irrational as to ignore all common sense and just keep spewing the same crap over and over.

I had a friend who did what you do and he told me all about it and he got paid very well for his constant lies, but eventually he got a conscience and quit the oil company.

O boy you're right, just ran the numbers on a 100cc vacuum engine with a full gulp of 3000 degree F gas at BDC and already hits 1 bar at 20cc and 80 degrees F. I figured an ideal cycle like that would be much more impressive. Seems to me the vacuum engine is uninspiring after all.

Those big wigs at my oil company should have fed me a better line of BS that was harder to unravel. I'll have a word with them at our next meeting. In the meantime I'll continue to try and break the atmospheric Watt/cc power record for hot air engines all while keeping it open source and hiding it from my big oil overlords who pay me to troll this forum.