Nickel Plating piston tops etc: more timing advance
 

These guys say:
"Gasoline engines achieve maximum efficiency when operated at the knock limit. Knock control ignition systems enable an engine to operate in either continuous or intermittent light knock...
Experience with knock control engines in passenger cars has shown erosion damage on pistons...
Nickel coating has been developed as an effective and reliable technique to protect pistons from combustion knock erosion.
Additional benefits of nickel coated pistons include:

• Reduced piston deposits
• Increased wear resistance in the top ring groove
• Reduced cylinder head temperatures"

https://www.sae.org/publications/tec...ontent/900453/

These guys add "Heat reflection" to the list:
https://auto.jepistons.com/blog/what...ng-for-pistons

I DON'T 'see' the "Reduced cylinder head temperatures" unless the head (and valve bottoms) is also coated and reflecting IR etc light/heat back into the chamber..?
The pics also don't seem to show any piston top polishing to increase reflection and reduce heat absorbing surface area.
So perhaps the claims are made based on Nickel's low thermal conductivity of 90 W/mK, vs 250 W/mK for Aluminium.
BUT
at a thickness of 25 to 100 microns..??!


Now I'm going to take this straight to the Unicorn Corral again! :)
Steam Reformation is the process of reacting steam with a hydrocarbon (fuel) to form Hydrogen and CO (burnable) as a by-product.
Nickel is the catalyst used.

(The process generally happens at the temperatures and pressures found in diesel engines rather than gasoline engines, but bear with me here)

Perhaps just maybe a very thin and diffuse layer of hydrogen forms on the piston surface and if/when knock starts; said layer causes the flame to spread out over a larger area, decreasing the corrosive etc effects..?
P=F/A after all.
And the flame speed of H2 is WAY higher than that of HCs.

Lets take this idea further:
Lets say the whole head and the valves are also coated with Nickel and you have a 'Nickel' Spark Plug.
(Perhaps even the cylinder walls: Nikasil...

Lets also say you also have a some steam or water mist injection going on.

H2O and HC is in contact with the hot intake tract and valve during the compression, power and exhaust stroke and even more so during intake! (much flow).
Then in the cylinder during intake and compression and even the power stroke:
During compression temperatures and pressure (amount of gasses in contact with surfaces) goes up.
Even more so during the power stroke.

Also keep in mind that the flame front dies out about 2.5mm before the cylinder wall, leaving a 2.5mm thick 'pipe' of 'unburned' air/fuel.
Less for pistons and exhaust valve as they're hotter, but still.
Now if there's a slight increase in the amount of H2 close to these surfaces..?
(See Quench Distance)

Having a bit more H2 in the 'Nickel Spark Plug' region would get the fires started a bit faster too, which relates into more pressure at usable crank angles and slightly delayed ignition timing, reducing losses.

Then there's the reflected light/IR/heat during combustion.
That helps on it's own, but water is known to dissociate a bit better in IR light too.

Even without a Nickel surface: Thermolosis:
The decomposition of water into H2 (and OH, O3, etc type radicals) happens from around 2200 C, which is below the temperature of combustion..!

Sooo...
What are the chances that one could mod one's engine unto a slight Syngas etc factory, to produce a tiny but useful bit of H2..???
Especially in Diesel engines.
And what else could one do to increase the effect, of any???

One last thought:
Those HHO cells tend to be hot, steamy things.
Perhaps the steam is turned into Syngas etc more than even the HHO nuts realise..?
They do seem more effective in Diesels where pressures and compression temperatures are higher...

You want maximum heat energy at the top of the piston stroke, not heat being absorbed to break apart molecules that then recombine later when they provide less useful work on the piston.

The only thing I would contemplate coating a piston top (or cylinder head) with is a little bit of thermal barrier coat only if there is extra knock resistance headroom. That raises the surface temperature so less heat is conducted away, but you lose knock resistance.

I.e. if you have an E85 engine and you are okay with only running high octane gasoline or high ethanol fuel in there.

I read the Nickel as a reflective catalyst.

Compare with ceramic coating, or Nickasil.
Porsche use the stuff.
But that's the cylinder not the piston?

Nikasil is just nickel plating so silicon carbide can be embedded in the cylinder liner for wear resistance. Plating is easier to apply than depositing iron spray or casting in silicon carbide matrix into the liner or pressing in a separate liner.

The "laziest" bore hardening technique is just casting the block out of hypereutectic aluminum so the silicon precipitates form the wear surface, or casting the block out of iron.

Heat reflection is a fruitless idea, because pistons don't stay clean.

That's just what a search turned up. From memory Porsche used a nickel-silver alloy to match the heat expansion of the cylinder to the piston (or vice versa), but DuckDuckGo doesn't support the contention.

What I found interesting was that chemical deposition is more uniform than electro-plating. I suspect that's because electroplating is sensitive to the placement of the anode.

Hmmm... good point.

However Hydrogen has a MUCH higher flame speed (1.85 vs ~0.4m/s) and
Diffusion coefficient.
So it will get the fuel lit faster.

It also has a much lower quench distance (0.64 vs ~2mm)
So will burn closer to the cylinder walls and piston and head surfaces where it should be more concentrated thx to the Nickel catalyst.

Also, a bit should be be produced in the intake tract wile waiting for the intake valve to open and during intake (much flow) and compression.

Also a lower ignition energy which should ad to getting things lit a bit sooner.

Hopefully these effects would make up for any heat losses during combustion.

Then there's the fact that hopefully you're burning a tiny bit of water, rather than fuel..? :)

Links:
https://mdpi-res.com/d_attachment/en...ion=1634797654

https://h2tools.org/bestpractices/hy...ed-other-fuels

Knock is from the shock waves caused by multiple flame fronts interacting, doing damage. You really do not want multiple ignition points.

While I'm thinking about it, years back Honda experimented with FRM cylinder liners, which had much greater hardness than typical cast iron liners. What they found in practice was that piston rings wore more quickly, and practically all of the engines with these liners began burning oil (and a lot of it) quite early. For whatever reason, they went back to cast iron liners and haven't deviated since.

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.

Nickel plating is something one could do at home on their kitchen table.

Technically, yes as the processes use low voltage DC, but the chemicals are on a restricted list with really extensive and expensive hazmat mitigation. Aerospace was moving away from that back in the '80s