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Mudflap wrote: ↑

16 Nov 2020, 05:18

Bolting a presumably aluminium piston running close to 300C with steel bolts through the crown is a recipe for disaster...

Why assume "steel bolts"?

Thermal expansion compatible Ti studs/countersunk sleeve nut fasteners instead, perhaps?

Ti has a very similar coefficient of thermal expansion to steel so it doesn't make a difference in that regard.

Also having crevices in the piston is not a good idea for combustion.

Correct Mudflap, it should be bolted from behind into a blind hole, maybe a locking washer or wire tie as insurance.

Mudflap wrote: ↑

17 Nov 2020, 11:13

Ti has a very similar coefficient of thermal expansion to steel so it doesn't make a difference in that regard.

Also having crevices in the piston is not a good idea for combustion.

Yet the alloy composition of the piston can be suited to the fasteners, TE-wise
then add - sodium-filled cylindrical studs too - if you'd like more heat transfer.

& if you'd like less, then a concentric ceramic crown, could also be considered.

What significant "crevices" would there be, with a flush-capped sleeve nut?
(& 4T poppet valve piston clearance "crevices" seem to manage combustion ok, no?).

Unfortunately it doesn't look simple to bolt from the other side in this scheme.

My biggest gripe with the piston bolt is that it introduces a high mean stress in a component which is subject to thermal stresses, creep and large alternating loads.

Aluminium pistons creep below 300c (about 40% of the material melting point) but they are not normally subjected to high constant mean stresses so it is rarely an issue.

How practical would it be to bond(stick) the surfaces?

Well he may just have to rewrite the rules and circulate some oil through plate to cool it all down yes?

Even if you invent an adhesive strong enough, it will be so strong it will turn the whole thing into a permanent assembly at which point it probably defeats the purpose?

There is another evolution update, not far from a feasible design, i think he will roll the dice with cap screws through the piston crown, clearly not a puritanical aproach. Youtube is his forum, he answers helpful advice.

If the goal is to build an engine that just runs under its own power that will probably do.

In that case the engine won't really amount to anything more than a curiosity.

No idea about the person behind this, but the software world has been like this for a while, people throw proof of concepts up on GitHub - it's usually when they are looking for a new job. It could also just be for curiosity of course, or I could be wrong.

I'm not sure that random solidworks cartoons would get you a job as an engine designer, but perhaps that is the way it works these days. Or not.

Cad is fun as a hobby, but sitting at desk pumping detail after detail requires different temperance.

coaster wrote: ↑

19 Nov 2020, 22:40

Cad is fun as a hobby, but sitting at desk pumping detail after detail requires different temperance.

Yeah, I used to do that, both in aerospace and marine engineering; my productive work time was about four hours, 6:00 am till 10:00 am and then I was sapped of creative juices and simply did grunt stuff to make the day end. There was a lot of tedious work, checking clearances and travels and stuff like that, as well as making sure it could be built; I got burned out and became a winemaker.

I don't really see how the crank, gears, and pistons can be assembled on this thing but have only looked at it briefly; I imagine the case will be split, which might get rid of the piston head bolts - they aren't a good idea.

Interesting.