Making this a separate post as I would like to hear other inputs on this particular subject.


I did some testing of my own with tech-line brand thermal barrier coating and I got not postive results whatsoever. A couple of my friends don't think my testing method was valid for a piston coating, and that's partially right, but I still think the results are very telling.
I used a propane torch an inch away from the center of the piston deck and a thermocouple placed against the underside of the deck held in place by a given mass of playdough.
Each test started cool at a measured room temp, and lasted one minute with my torch at its fullest setting.
The coating survived the torch which did surprise me, but showed no reduction in temperature at all... zero.

This isn't how a piston operates, but I still think a thermal barrier should at least slow the heat down to some measurable degree.

On a positive note, I tried the old-school method of polishing the piston top to a mirror like finish and tested that. The results were amazing with a very large temp drop over the control tests.

Amount of heat gained during test:

+135*F both uncoated and coated with techline

+91*F for the polished piston

That looks like a 33% drop to me.
I did test each way at least twice on the first run, and then twice on a second run. That meant roughing the surface back up, testing again, then coating & testing, then re-polishing.
The results stayed the same, so I know I didn't goof it.

After thinking about the conditions of the test I tend to think that my test used more conductive heat from the air to the piston, than radiant heat. I'm pretty sure that if I used only radiant heat in the test that the polished surface would have made even more difference. My point being that I think it is radiant heat from the burning mixture that primarily heats the piston in operation. Maybe I will rig up another test for this.

I have read about the ceramic coating and I know ceramic is a great insulator, but I've also heard rumors that the thickness neccessary to provide working insulation are too much, and that it will not stick to the metal in operation due to a large difference in thermal expansion rate.
If anybody knows the real story please add what you know.

 

well the radiant heat thing would make sence! i was always led to bielive that there is a thin film of gas that sits just above the piston. i was allso told that dep. can upset this layer and thus cause higher piston temps (due to conduction).

but coatings also help with dep. resistance and provention! but still very interesting findings. be really good to see if anyone else was any findings of their own!

Chris.

 

curious if the type of piston would matter... i/e forged/cast?

 

I think that caste doesn't conduct heat through its mass nearly as fast as forged. This is good for efficiency, but not good for racing since heat will build up quicker at the surface of the piston causing hot spots.

 

does anyone make a thermal "reflective" coating????????

it would be ace if you could combined the supposed thermal barrier benifits with the radients heat benifits you have seen from polishing!

Or someone could kjust make a piston from a pollimer thats lighter and stronger than steel, with a steel top to take all the shock loading! but alas, im breaming again!

Chris.

 

The only possible weakness in the experiment that I can see is that the coating could in theory be resistant to heat absorption for a very short period of time. This would cut down on heat absorption during a short combustion event but not show on your blow torch testing.
But if it did that, I'd assume it would also slow down absorption on a continual basis.

I'm rather impressed with the results of the polished piston..

 

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The problem you have is that you did not measure the heat input power nor have a proper time measurement.

Heat transfer is mainly based on differential temperatures and if the top of the ceramic coating is closer to the temperature of the combustion chamber, you will have less heat transfer into the piston.

Your test showed no measurement of how much Energy you placed into each piston, nor what the flame temperature was.

Not to mention, the piston rings are responsible for approximately 70% of the heat transfer from the piston top to the cylinder walls. and you did not take that into account either..

 

H8 Luzn has a very valid point. Heat transfer and temp with the thermal barrier coating cannot accuratly be measured unless there is something for the pistons to transfer heat into. Of course, with the pistons out of the block, they're going to maintain gaining heat, whereas in the block, there is a chance that they would transfer the heat from the piston to the block.
And I'm not 100% sure on the thermal barrier coating. I've heard many things about it, but in all honestly, I believe it's primarily a little something to reduce friction in the cylinder instead of actually "reduce heat" placed on top of the piston. Because we all know that friction = heat, reductions in friction will yield reductions in heat. There are a lot of variables that weren't taken into account on this test.

 

chevy high performance did a write up about the coatings one time. they performed the torch test until both pistons melted. the coated one lasted twice as long before melting down, but the middle caved instantly instead of slowly melting away. the conclusion was that the coating pulled the heat away from the flamefront but when the piston could no longer transfer the heat away it had much more heat soak and melted quicker. i personally had my piston and combustion chamber of my 400 single dirt bike motor coated by highperformance coatings. i don't know how much it helped because i did several things at one time, but the cylinder and head really heat up fast.

 

Time and distance were kept a constant for every test.
The lack of heat sinking via rings was also a constant during every test.
FYI, maintaining constants during a scientific experiment negates the need for tracking the measurment of those qualifiers.
Time and distance were measured. The amount of heat energy is not a factor in the test.

I'm not sure how you would set up your own experiment, but I'm sure it would sound interesting.

 

Correct. A true insulator would slow the rate of the piston mass gaining heat. This is what was measured over a fixed amount of time.
The heat source was a constant level and distance.
Temperature levels were measured with a K-type thermocouple.

 

If you ever rig up another test, it would be interesting to see the difference in time when the polished piston and the stock piston melted.

Nice test anyway, I`m amazed with the polished piston result.

 

Nice experiment, but here's the problem: You need to measure the transient heat gain. The ceramic coating will slow down the rate of heat transfer, but given the same mass and rate of heat transfer to the ambient air, both parts will stabilize to a max temperature. A minute is just too long. The polished piston is great, but wouldn't its benefits decrease with combustion deposits?

 

I used to not be such a believer in the heat barriers because I'd seen quite a few coated and uncoated pistons blow through in Nitrous applications. We did a test a short time ago in our R&D department here at Wiseco. We dyno'd a single cylinder test engine run extremely lean for 3.5 hours at wot. Two identical pistons except for the heat barrier on one. The uncoated one went from rockwell b of 75 into the mid 30's. The coated one hung in the low 70's with the same number of cycles. Not everyone needs coatings, but they can be useful for some. -Brian Nutter

 

TBCs only work with active cooling, which a piston has (oil, moving through crank case, cold intake charge).

edit: as said above, this is because it slows heat transfer.

 

Thats a valid explaination right there.

 

Just wondering how the TBC's would work on aluminum intake runners. Thinking of coating the inside of my TPI runners and manifold. With the cool air flowing through them it sounds like the TBC's would work.

 

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No expert & will never claim to be. N2O pistons are much more forgiving & reliable in my experience with a heat coating. I use skirt coating on N/A & N2O. Have never tried coatings on intakes or heads. Some guys go nuts with coatings.

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