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Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Fri Nov 10, 2017 8:31 am
by n2xlr8n
ptuomov wrote:
Fri Nov 10, 2017 8:13 am
With a twin scroll and E85, you weren't very knock limited, right? The twin scroll (and the long pipes) eliminate the exhaust blowdown interference and E85 evaporization cools so much. So this may be closer to the diesel case than pump gas case.

Out of curiosity, did you have to add fuel because of insufficient evaporization or to keep the AFR the same?
For my application 27 psi on a VF-37 is pushing it out of its' efficiency; the E85 helped, I'm sure. Especially with a stock top mount IC.

The "version 8" EJ, which is the engine I'm referring to, was the best of the best as far as stock Subaru goes. It screamed.

I added fuel to maintain AFR, yes.

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Fri Nov 10, 2017 12:05 pm
by ptuomov
twl wrote:
Fri Nov 10, 2017 8:24 am
I have used Tech-Line Cer-Met coating on chamber, valves , and piston crown, and ceramic only TBC in the exhaust port of every one of our 50 street performance single cylinder aircooled engines for 10 years.

We have never done a/b dyno tests for hp difference. However, we were able to get lower head temps, which I believe helped the engine to take more compression on pump gas than our competitors engines.

My partner Joe Mondello worked on this with me, and the consensus was that this combination of 2 different coatings in different areas was the right way to go in a very difficult application.

In general, a cooler head temp led to less heating of the intake mixture, helping to reduce propensity to have pre-ignition. The cer-met coating has some insulation property that not only helps reduce head temp by slowing thermal transfer, but even a partially effective insulator acts very well during the "flash" peak combustion period where there is extremely high temps and very little time at those peak temps. This helps reduce heat transfer at the extreme delta-t periods wich define rapid heat transfer. Even partial effectiveness at these times is a pretty big deal in aircooled environment. The same is true for the cer-met on the piston. We had virtually zero overheating seizures with this due to less thermal expansion at the skirt on our 2618 forged slug.

Additionally, the metallic (al) component of the cer-met acts to reflect the heat back to the interior of the chamber from the coated chamber/valves/piston, making a better environment for more complete combustion, reducing propensity for detonation, from reduced unused end gas . And the metallic particles are extremely low mass and high thermal conductivity so they give up their heat very quickly during the overlap.

All said and done, my assessment is that it may have helped power in a variety of small ways which just helped the overall application. But it definitely helped in reliability by mitigating heat related problem in a difficult aircooled hemi (no squish) large(105cc) chamber street engine.
I think it makes all the sense in the world that an air cooled gasoline engine will be more reliable if the combustion chamber surfaces are coated. And an engine that is not seized is certainly making more power. However, I was just narrowly wondering about whether the coatings would increase the peak power on a knock-limited pump gas engine.

I think a single cylinder engine might be the one situation in which someone might some day run a test in which nothing else is changed. Most people working on multi-cylinder engines seem to make multiple changes at the same time for cost reasons, and use logic and experience to guesstimate how much each of the changes contributed to the results.

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Fri Nov 10, 2017 7:00 pm
by MadBill
Depending on how deep you want to go, there are many potential secondary gains and effects associated with TBCs. For example:
o TBC on titanium exhaust valves could be a durability game-changer under high boost or low CR conditions, saving crucial weight compared to typical super alloys.
o Lower piston temps could allow tighter bore clearance and thus improved piston stability and ring wear.
o Ditto increases hot strength allowing weight reductions in pistons, with a knock-on for rods and crank.
o Ditto for shorter top ring land and thus improved ring pressure response and reduced crevice volume, as well as reduced heat flux, especially useful with sub-1 mm rings.
o Optimum SA and AFR would need to be revisited.
o Higher CR may be possible.
o Higher EGTs due to internal and header TBCs might require system dimensional changes to harvest the full potential of TBCs.
o I'm sure there are others...

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Fri Nov 10, 2017 9:14 pm
by ptuomov
And it could be that on pump gas the absence of coatings allows for so much higher compression that it more than overcomes all that.

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Sat Nov 11, 2017 9:56 am
by twl
ptuomov wrote:
Fri Nov 10, 2017 12:05 pm
twl wrote:
Fri Nov 10, 2017 8:24 am
I have used Tech-Line Cer-Met coating on chamber, valves , and piston crown, and ceramic only TBC in the exhaust port of every one of our 50 street performance single cylinder aircooled engines for 10 years.

We have never done a/b dyno tests for hp difference. However, we were able to get lower head temps, which I believe helped the engine to take more compression on pump gas than our competitors engines.

My partner Joe Mondello worked on this with me, and the consensus was that this combination of 2 different coatings in different areas was the right way to go in a very difficult application.

In general, a cooler head temp led to less heating of the intake mixture, helping to reduce propensity to have pre-ignition. The cer-met coating has some insulation property that not only helps reduce head temp by slowing thermal transfer, but even a partially effective insulator acts very well during the "flash" peak combustion period where there is extremely high temps and very little time at those peak temps. This helps reduce heat transfer at the extreme delta-t periods wich define rapid heat transfer. Even partial effectiveness at these times is a pretty big deal in aircooled environment. The same is true for the cer-met on the piston. We had virtually zero overheating seizures with this due to less thermal expansion at the skirt on our 2618 forged slug.

Additionally, the metallic (al) component of the cer-met acts to reflect the heat back to the interior of the chamber from the coated chamber/valves/piston, making a better environment for more complete combustion, reducing propensity for detonation, from reduced unused end gas . And the metallic particles are extremely low mass and high thermal conductivity so they give up their heat very quickly during the overlap.

All said and done, my assessment is that it may have helped power in a variety of small ways which just helped the overall application. But it definitely helped in reliability by mitigating heat related problem in a difficult aircooled hemi (no squish) large(105cc) chamber street engine.
I think it makes all the sense in the world that an air cooled gasoline engine will be more reliable if the combustion chamber surfaces are coated. And an engine that is not seized is certainly making more power. However, I was just narrowly wondering about whether the coatings would increase the peak power on a knock-limited pump gas engine.

I think a single cylinder engine might be the one situation in which someone might some day run a test in which nothing else is changed. Most people working on multi-cylinder engines seem to make multiple changes at the same time for cost reasons, and use logic and experience to guesstimate how much each of the changes contributed to the results.
From the experience I have had, I would say yes it can permit compression increase in a knock-limited pump gas application.

In the sort of difficult conditions that we had, including head temps of 300°F, no-squish deep 105cc hemi chamber, and high dome piston with lots of surface area, we were able to increase cold cranking compression from 135psi to 160psi before the on-set of knock.

So, it might be extrapolated from that experience that up to 25 psi increase of cold cranking compression may be possible depending on the challenges of your application. YMMV.