Long stroke

[dly31]

I have no idea what the rate of pressure drop would be or at what point the energy would be essentially dissipated. The drop due to increasing volume could be calculated but there is an additional drop due to cooling. I know that in 'normal' stroke engines the exhaust valve is commonly opened before BDC and have read that improved scavenging more than makes up for the little energy lost in the exhaust because the pressure has already dropped so much. So there would seem to be little or no advantage for extremely long strokes. I would consider a 1:2 ratio to be a really long stroke engine but I am sure there are people with better knowledge on the subject.

[camerart]

Don,

I hope to squeeze as much energy out of each combustion stroke before reversing, leaving just enough energy for good combustion of opposite cylinder.

In the experiment, I think this can be controlled 1/ by a compressor with outlet controlled. 2/ By amount of fuel intake.

Therefore I think it is better to move for the longest distance before reversing each time.

So at the moment your guess is 1:2. I will average out any other guesses before starting to machine. Feel free to amend your guess.

Thanks.

[GlennW]

I also wonder about what might be happening to the combustion between ignition and reversal of the piston, with no TDC.

Doe it not use a crankshaft or transmit linear motion into rotation?

Sounds like an opposed two cylinder "pile driver"!

[ronm]

"Linear engine"? No TDC? How about a sketch or something? You're losin' me here...I hate to throw cold water, but the internal combustion engine has been experimented with for over 100 years now, there really isn't too much that hasn't been tried...I have a book from the early 1920's, & the knowledge they had about engines at that time was amazing-about the only new thing since then is electronics & computers, as far as engine controls...
I kinda have to say, if an engine with that long a stroke was the best idea, it would be more in use-which seems to be not the case...as i was saying above, it's a pretty mature technology.

[GlennW]

Make that 140 years now!

I dunno a whole lot about engines, but I have a book somewhere that is a reprint of a 1870's book on internal combustion engines, and they pretty much had it all figured out. Can't remember the title.

[camerart]

"Linear engine"? No TDC? How about a sketch or something?

Ronm,
I have attached an example that shows no TDC (no Top Dead Centre as there is no flywheel) so the compression is variable.

You're losin' me here...I hate to throw cold water, but the internal combustion engine has been experimented with for over 100 years now, there really isn't too much that hasn't been tried...I have a book from the early 1920's, & the knowledge they had about engines at that time was amazing-about the only new thing since then is electronics & computers, as far as engine controls...
I kinda have to say, if an engine with that long a stroke was the best idea, it would be more in use-which seems to be not the case...as i was saying above, it's a pretty mature technology.

I have attached an example of a long stroke diesel engine, not sure how well it works.
I think for normal transmission the stroke would be different from what I am trying to do, but I imagine I will take the power off as a generator.

I try to be inventive which sometimes takes me away from the conventional, so please don't throw too much water on me.

[ronm]

OK-a free-piston engine-wondered if that's what you were talking about...
lots of info available...I'll let you do the looking for stroke length-
http://www.google.com/search?client=ubu ... 8&oe=utf-8

[camerart]

From what you all say, it seems that longer strokes lose too much energy as heat, and 1:2 is what would be the longest recommended.

I suppose if heat was needed for another reason, longer strokes might be a more efficient heater?

I would have preferred longer, but until anyone give a reason, I'll make my first test as 1:2 ratio.

Thanks for you help.

[ronm]

The big Diesel you posted a pic of is a large slow-speed ship or powerplant engine-probably runs like 150 RPM or so...a long stroke is feasible on such an engine, whereas the piston speed would get excessive with higher speed. You have to take into account the ability to hold the engine together...again, the free-piston is a whole different animal, not having to worry about connecting rods or crankshafts...so, like said before, experiment away...

[camerart]

I'm expecting much faster than 150rpm. I'll take your point and keep it short.

As my tests will be much smaller than that big diesel, I should be able to hold them down. Let's see!!

Another reason, I thought a longer stroke might be good for my tests is, I imagine it would be less fierce than a shorter stroke? While I get the feel of things.

[Doug4d3s]

Normal piston engines have issues with stroke/bore ratios much longer than about 1.3:1, due to connecting rod/cylinder interference.

The big ship engines are called "cross-head" engines. They have a short piston on an articulated connecting rod, allowing longer strokes than usual. Up to about 8:1 (stroke/bore) has been used, but typical is around 4:1. And they are 2-stroke (blown) diesels so there's a lot of other weirdness going on in there, but there is no reason they cannot be built as 'regular' gasoline or diesel engines.
http://en.wikipedia.org/wiki/Crosshead

Crosshead internal-combustion engines were a carryover from steam locomotives. Like steam locomotives, they are best at putting out relatively large amounts of torque at rather low RPMs.
For as high as the efficiencies claimed for ship engines, it is rather odd that they aren't used for anything else these days.

[camerart]

Hi,

Thanks for all of your replies.

I have attached an animation of the design. I hope this is interesting and possible.

Cheers, Camerart.