Nickel Plating piston tops etc: more timing advance

[Logic]

Originally Posted by Isaac Zachary

I dissagree to some extent. Engines with multiple sparkplugs aren't more likely to have knock, for an example. I believe the multiple flame fronts as being an old myth.

What I understand knock (detonation) to be is when a pocket of air and fuel (regardless of the number of flame fronts) reaches a critical temperature and pressure so that it spontaneously combusts. Normally combustion occurs along a flame front and therefore causes a gradual presure wave. If a whole pocket of air and fuel suddenly ignite then you have a much more sudden expanssion of gasses resulting in a sonic (or maybe even hypersonic??) pressure wave. These knock pressurewaves are very stronge and will bounce around causing spots along the tops of the pistons and in the combustion chamber to have very high pressure and very high temperature compacted ripples of exhaust gas smack into the metal.

Yep; that's the way I understand knock too
but
'sharp-ish' points on the piston face or in the head tend to get hotter than other areas and can also start knock.

IIRC thats why spark plugs often have copper in the electrode; to get the heat out of it and prevent this.

[Isaac Zachary]

Originally Posted by Logic

'sharp-ish' points on the piston face or in the head tend to get hotter than other areas and can also start knock.

That's also been myth-busted. Sharp edges in the right spots can actually decrease knock as it can help fuel to reatomize. One of the worse combustion chambers for knock was the hemispherical head.

https://www.youtube.com/watch?v=f8XG9T8v-ng

https://www.youtube.com/watch?v=BFypM7ADAA0

https://www.youtube.com/watch?v=lcxp9ufC1DY

IIRC thats why spark plugs often have copper in the electrode; to get the heat out of it and prevent this.

Sparkplugs have various levels of insulation to keep their temperatures up. It depends a lot on the application, but the idea is hotter, insulated spark plugs keep the carbon burned off. Too much insulation and therefore too hot of a spark plug could cause a problem such as pre-ignition.

[Logic]

Originally Posted by Isaac Zachary

That's also been myth-busted. Sharp edges in the right spots can actually decrease knock as it can help fuel to reatomize. One of the worse combustion chambers for knock was the hemispherical head.

Thx for the vids: Interesting stuff!
But i think we're mis understanding each other here.
I'w as talking more about burs from machining and unfinished/polished castings than the 'less sharp' edges etc in the vids.

Originally Posted by Isaac Zachary

Sparkplugs have various levels of insulation to keep their temperatures up. It depends a lot on the application, but the idea is hotter, insulated spark plugs keep the carbon burned off. Too much insulation and therefore too hot of a spark plug could cause a problem such as pre-ignition.

I'm aware of the heat range and self cleaning etc.
But the ground electrode can get too hot from what I understand and that's where copper and even silver is employed to conduct the excess heat back into the plug body, keeping the plug temperature more uniform..?
https://www.performanceracing.com/ma...ht-spark-plugs

[Xist]

Hemispherical, as in Hemi engines, with a rabid following?

[Logic]

"...Use of In-Cylinder Catalysts
In order to investigate the application of the concept of
catalytic combustion, various catalysts, such as copper,
chromium, and nickel, were coated on the combustion chamber wall or determining their effects on engine
pcrtormance. combustion, and emissions characteristics...

...Among the
different catalysts investigated, copper was found very
effective in reducing both HC and CO emissions, and brake
thermal efficiency was also improved. At a high CR of 9:1
and with a lean mixture (A/F=15.7), copper catalyst increases
the absolute brake thermal efficiency from 17.7% to 22.8%,
decreases HC emissions from 3200 to 2300 ppm, and lowers
CO emissions from 3.6 to 0.25% by volume when compared
to the normal engine (CR=7.4, A/F=13.2) at 2 kW, 3000
rpm. Ignition delay was lower, combustion duration was
shorter, and cylinder peak pressures were higher with the
copper catalyst at higher compression ratios and with leaner
fuel-air mixtures. Knock-limited power output also increased
by about 12% at a high CR of 9:1 in the presence of copper
catalyst..."
https://digital.library.unt.edu/ark:...dc740511/m1/8/

There's interesting stuff in the rest of that paper too.

Now coating pistons, valves, intake tracts with copper is as easy as a Copper Sulphate solution and some copper wire.
(I played with this as a kid)

Nice too see some vindication of the idea..?

[freebeard]

This video on Fuel From The Air suggests Cerium Oxide as a catalyst. At 1500 degrees (combustion chamber temps?) it turns the CO2 in the air into syngas.

As to how you'd get it to adhere to combustion chamber, I have no clue.

[Piotrsko]

The only places you could plate that would be the top of the piston and the head portion of that cylinder. Could be easier as a fuel additive

[Isaac Zachary]

Originally Posted by freebeard

This video on Fuel From The Air suggests Cerium Oxide as a catalyst. At 1500 degrees (combustion chamber temps?) it turns the CO2 in the air into syngas.

As to how you'd get it to adhere to combustion chamber, I have no clue.

The problem is that at the boundry layer of the combustion gasses it is pretty much impossible to get that high of temps. That's why you end up with unburnt fuel. The coolness of the metal surface (200 - 300 °F is cool in terms of starting and maintaining combustion) quenches the flame front causing it to not reach the very edge.

In a perfect world we'd have a 100% insulating surface with zero thermal mass on all the surfaces in a combustion chamber.

[Piotrsko]

I believe you can get those temps but since the melting point of your pistons is less than 1500f..... I can melt pistons in the F250 by just hauling a big load up grade at full throttle.

Not sure what insulated surfaces inside the chamber would actually get you as a benefit

[Isaac Zachary]

Originally Posted by Piotrsko

Not sure what insulated surfaces inside the chamber would actually get you as a benefit

A theoretical insulation on all surfaces that doesn't exist, at least not yet.

I did put a ceramic thermal barrier on the tops of my pistons and in the combustion chamber and in the exhaust ports on the Bug. But then I had a hard time getting the engine temps up to where they needed to be. Even after bypassing the oil cooler I still would hardly see oil temps above 150 °F IIRC (they never would get to 180 °F).