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Hi,

I'm attempting to convert 2 air cooled single cylinder 3hp 4 cycle
lawmower engines into a type A Stirling engine, and it's not yet
running and I'd like some debugging tips, please.

A brief description, first, so you all can tell me if I'm totally
screwed in my setup.

I've stripped the two engines down to just the crankcase, cylinder, &
head. I've pulled the valves, and plugged the valve stem holes with
bolts, and sealed one side of the manifold with a metal plate &
gasket. I use the other side of the manifolds to connect the two
engine's cylinders via copper pipe through a recycler made of pvc pipe
& steel wool. The two engine's crankshafts have sprockets on them and
are connected via a roller chain. I've set the two pistons to 90deg
out of phase with each other (e.g. when one piston is all the way up,
the other one is half way up). A spring held tensioner keeps the
chain in place.

When I apply heat (for now, just via a propane torch) to one cylinder
nothing happens. If I rotate the thing by hand with heat applied I
feel no difference in resistance through any part of a full rotation,
nor, this applies when hand rotating the engine either direction.

Assuming that my basic design is okay, I've got several ideas on my
own why it doesn't run, hopefully, I'm on the right line of inquiry in
one of these:

First: rolling resistance # I've been tuning the chain and tensioner.
I can now more or less easily spin the assembly. When I pressure
tested it (more about this later), the engines would spin at about
10psi (as measured by my bicycle air pump)

Second: pressure seal # I'm having problems keeping a tight pressure
seal. When I pressure test the assembly (I've rigged an air stem &
valve from a bicycle innertube) I've noticed that it doesn't keep
pressure for more than a second or maybe two. The main leaks appear
to be around the cylinder # e.g. the piston is loose. I confirmed
this partially by tipping the engine(s) up so that the piston heads
would be flat, and pouring a few tbs of oil into each via the spark
plug hole # it held pressure notably better for a short while, as if
the oil were semi-sealing the cylinders

Third: heat transfer to&from the air contained in the cylinders #
these are air cooled engines, and the outsides of the cylinders and
heads are covered in cooling fins. The insides however, are, of
course, smooth cylinders. I've thought to perhaps get flat but 1-2in
thick blocks of aluminum of appropriate size, and drill numerous holes
in it perpendicular to the flat dimension, then to bolt these between
the cylinder head and body & heat or cool this aluminum block to
increase internal heat transfer. Is this worth it?

Fourth: getting the phase offset between the two cylinders right #
I'm not sure if the hot cylinder should lead the cold cylinder by
90deg, or lag it by 90deg. However, I'm not certain that it matters,
it just means a difference in which direction the engine runs

Fifth: still missing a flywheel # I don't have one yet. a. I'm not
yet certain that there won't be enough momentum just in the roller
chain, and b. I should at least get the darn thing to rotate 1/2 cycle
even w/o a flywheel

Anyway, thanks to anyone who's willing to answer. I look forward to
hearing from you!

# Pat

Hi Patrick,

I am new to Stirlings. I am an audio engineer by profession. So take this with a little
sodium chloride...

Heat engines are not usually too happy to start on their own. If it takes 10 psi to move the
pistons, then the air pressure inside the engine must build to 10 psi very quicky or the
engine's leaks will not allow the engine to run. The slow heat buildup with a torch will
likely not do it.

But if the engine is spinning fast enough, the heat now being exchanged would not have
time to bleed away past the engine's rings, and it should run.

I would suggest adding a flywheel, heating one cylinder, then giving it a spin. I'll bet it will
run.

Also, how much dead (unswept by a piston) space is there? The compression ratio of a
lawn mower engine might be like only 8 to one, assuming valve-in-block layout. Try
minimizing the dead space and see if that helps a tad.

One more thing, are you using a regenerator such as an expanded steel wool pad? If not,
that could raise the efficiency enough to help. If you are already using one, make sure it is
not restricting air exchange too much.

Good luck,

Richard