Alpha motor with 180 degree crank phase?

[justincorhad]

Hey Matt, can’t find the PM for some reason. Essentially you are correct in how I’m imagining it to operate. The heating and cooling wouldn’t be turned on and off so much as the pistons would move the working fluid in and out of the cylinders. Exactly the same way a conventional alpha type Stirling engine would do it, the hot side is always hot and the cold side always cooling, just a matter of moving all or most of the working fluid in or out of them. My whole thinking is essentially is this not what most Stirling engines do? They expand their working fluid with heat, push the power piston (thereby gaining volume) and then cool that same fluid to then contract it (decrease volume)?

When you’re speaking of the Ericsson engine, are you talking about his caloric engine? That one is definitely fascinating. I guess if I had to thinking of some difference to what I’m thinking and Ericsson’s engine it would be that the larger end of his cylinder is the hot and the smaller (the rod side) is his cold. Also this would be a closed cycle like a conventional Stirling.

[justincorhad]

Here’s a few crappy pictures to try and explain better, sorry for the bad art.


https://ibb.co/jThQNx8
https://ibb.co/NsjMMNk

[Bumpkin]

Hey Justin,
Think of it this way: When your engine is at maximum displacement, more of the air is at the cool end. When your engine is at minimum displacement, more of the air is at the hot end. That’s the same in principle as the thermal lag engine except you’ve complicated it and you still need to add a timing component to delay heating until after compression and cooling until after expansion. (Or as close as you can come to that in a practical world.) — But two separate piston/cylinder sets with cooling and heating fins unshrouding at the bottom of their strokes, or some other magic dedicated to just that purpose might indeed open up new possibilities, so who knows?

Bumpkin

[justincorhad]

Oh okay I see, so in otherwards in this fashion maybe it would move a tiny bit when heated but at some point it will most likely reach a stage where it would “stall” correct? It would be trying to heat and cool at the same time.

Now correct me if I’m wrong, but if I took what I drew and connected it to a crankshaft like a conventional reciprocating Stirling engine, would it not achieve those delays while both pistons are at TDC and BDC respectively? At both TDC and BDC all reciprocating pistons have a “dwell time”, the pistons will stay put for several degrees of flywheel revolution before moving back up or down. Or would that dwell time most likely just be too insufficient for the task of hearing and cooling?

[justincorhad]

Slight correct on my above reply. What I meant to say was if you took what I drew, got rid of the lever and connected the pistons to a crankshaft and flywheel 180 degrees apart, would that then give enough dwell time to heat/cool the gases?

[matt brown]

Justin - yes, it would stall, despite 'changing' volumes. In a roundabout way, that's why I used the previous fixed volume pipe 'engine' example to demonstrate cold gas 'pools'. Heat eng is really a fuzzy term, since they're really driven by pressure. It's always best to scheme engs from low energy part of cycle, and_most_PV start with 'state 1' at low(est) energy point and progress thru cycle. Another fuzzy issue with scheming engs is very subtle, but rears its head in hindsight...when "heat" is construed interchangeably (at convenience) as energy AND temperature. As you probably figured, I'm with Bumpkin here as to thermal lag, but he also points out that 2 such 'double diameter' mechs appear valid, but I've never seen this simple (obvious) solution (maybe why the Canadian guy with the complex multi-cyl eng is chasing patents).

[matt brown]

Can someone tell me how to post pics ??? Obviously, waaaay different than 4 yrs ago (total BS)

Justin - adding dwell at TDC & BDC is the same as my turning 'on & off' heating & cooling...

[justincorhad]

Matt I had trouble with it earlier as well, just go to https://imgbb.com/ upload your photo and it will give you the option to copy the link it creates for your photo.

[justincorhad]

Matt I just looked up some brief tutorials on how to read PV graphs and I completely understand what you were talking about now. Basically if you try to implement my idea into a PV graph it would simply be a straight line that goes back and forth with no curves, no pressure changes. I think possibly the only way to get some arch in those curves with my idea would be to add such an enormous amount of heat that the volume change between the cylinders may not be quick enough to change linearly with the expanding gas, so you may be able to gain a small amount of pressure that way, but even if that were so, yes technically it would be an engine, yes technically it would run, but it would be the most inefficient and underpowered engine in the world haha wow, I’m glad you mentioned the PV graphs because it got me to wrap my head around it a little better, thank you!

[matt brown]

Thanks Justin, I'll give it a try. Hopefully, here's the classic Ericsson eng...

https://ibb.co/vYngxNJ

edit - well, that was painless, but what happened to the pic option above message box ???

[justincorhad]

I’ve often wondered with the Ericsson, what is the point of the large reservoir?? Would it not achieve the same thing using a simple tube in place? Maybe for extra cooling I’d imagine.

[matt brown]

Check out this little PV modeling app which has options for showing isobars & adiabats, and calcs energy of cycle. The bummer is that the rubber band cursor is lame, so requires patience to manipulate. I've been trying to find a simple app like this for many yrs, but to no avail. However, I want something slightly more upscale (and rock solid with cursor action) which tracks PVTQW per process and cycle.

https://www.geogebra.org/m/KAZHEN8c

Another thermo issue is Cv & Pv, where Cv is the heat capacity at constant volome, and Cp is the heat capacity at constant pressure. We can't just fantasize how much heat we put in & out...

[matt brown]

This is the classic Ericsson 'scheme' which never seemed to work, and Brayton tried similar res with his early piston engs. The idea was to create a slight compression cycle which would have 4 points on PV plot, thus achieving work vs 2 point plot where W=0. This is the value of PV plots, they're hard to cheat. Ericsson tried several such schemes before being laughed out of England, whereupon he settled here in USA. He was originally from Sweden, and his earliest Pat. is 1933 I think, so he goes back to the age of Carnot when energy was thought to be a mysterious force in the ether by many.

If you really what to go nuts (from our modern view) try to grasp the caloric 'theory' from period texts. Circa 1800, science was still heavily religious, and this contaminated many guys. Benjamin Thompson (aka Count Rumford 1753-1814) was convinced that there was a relationship between heat & motion due to cannon boring, but could never grasp it. It was Joules ~1850 that finally established the mechanical equivalent of heat by carefully measuring the rise in water temp while stirring water and carefully measuring the energy input of stirring via dropping weights and E=mv^2. This trashed the caloric theory and brought us the kinetic theory (what a ride).

This Ericsson scheme seems simple enough, and dreamy eyed isothermal compression & expansion are not the main issues (tho mega issues on their own). Nope, the killer here is 'mass flow' where his single valve can't regulated the same molecular gas mass per cycle within several variables. His regen idea is good, but in reality the regen would have to be far larger than depicted. It's not enough to simply pop a regen in scheme to 'save' heat when...in reality...the regen would_ideally_be recycling more heat than (ideally) added from heater. Again, this is where PV plots are handy, and some basic thermo. It's interesting that the later Ericsson-Rider is more like a low pressure open cycle Stirling than an 'Ericsson".

[justincorhad]

Oh wow, I was under the impression that Ericsson had built and sold many caloric engines, one even powering a ship, is this not true?

[matt brown]

The ship was named the Ericsson, and was quickly refitted with steam engines. Ericsson was a bright guy, just too close to the cutting edge of a fledgling science. BTW it was Rankine (1820-1872) that coined the term thermodynamics to unify heat with motion.

IIRC no 1833 pat caloric eng was ever built, and unsure if the full pat. still exists (just some figs.). If you really want a trip thru thermo history, hunt down how Nicholas Otto 'discovered' his compression cycle (while messing with an Otto-Langen eng). This will really show you where stuff was in the late 1870s.