<VV> Ceramic Coatings Questions

[RoboMan91324 at aol.com]

Hello JE,

Thanks for the reply.  I have a few comments/questions regarding some of the 
info in your response.

1.  Yes, "warm up" can mean more than one thing.  Thanks for your response to 
one of them.  Living in LA, I am not overly concerned with the windshield 
frost issue you bring up but others might be which is why I am copying this to 
VV. There is at least one other warm up issue besides the two you bring up.  
Please see below.

2.  You ask why would it be an area of concern that the pistons are insulated 
from the heat.  I am aware that the rings are the seals between the pistons 
and the cylinder walls.  I am also aware of the differential thermal 
coefficients of expansion between the aluminum piston and the steel cylinder.  Reading 
into your response,  I assume that you are too.  I do know that there is a 
specific gap range between the piston OD and the cylinder ID when cold that is 
based on the expected gap once operating temperatures are reached.  Since the 
steel cylinder expands less than the aluminum piston due to increased 
temperature, I expect the gap (when cold) to become reduced at elevated temperatures 
without coatings.  With the use of thermal coatings on the combustion chambers and 
piston heads, I expect that the cylinder will expand more at the elevated 
chamber temperatures and the piston diameter will expand less with its reduced 
temperature thus increasing the gap between them.  My question regarded the 
overall difference between the potentially shrinking gap without coatings vs. the 
increasing gap with the coatings.  In addition, the rings you brought up are 
supported by the slots in the piston.  With the anticipated larger gap, the 
rings will be hanging further out from the slots without the full designed 
support of the slot.  I think that this may also be a factor in the warm up issue 
posed in question number 1 but my main question is, should the piston to 
cylinder gap be reduced when cold to compensate for the reduced increase in the gap 
when hot?  Forgive me for not being more clear initially.

3.  Thanks.  Between your response and others, this has been answered quite 
well.

4.  No, JE, I am not joking with any of my questions but thanks for asking.  
Yes, I agree that insulating anything aft of the turbo will not increase the 
velocity of hot gas through the turbo.  However, it is my understanding that 
increased temperatures through the exhaust system will significantly reduce 
their life span and will elevate the air temperature within the engine bay thus 
increasing the temperature of air to the intake.  As I understand it, the pipe 
wrap in the engine bay is minimal.

5. Yes, JE, this could well be an issue for me and others considering the use 
of thermal coatings.  A "few hundred more degrees" can be significant "in the 
grand scheme of things" when you consider that the body paint is in such 
close proximity to the muffler.  Thanks for the mini lesson in thermodynamics but 
I was looking for some feedback on whether the elevated temperatures caused a 
problem in real use.  Since the muffler is easy to get to and relatively 
inexpensive, I might consider coating the outside with a thermal barrier at the 
cost of reduced muffler life.  It is a whole lot cheaper than a new paint job.

At the risk of sounding pejorative, I guess I do tend to over think things.  
I would think (no pun intended) that thinking (no pun intended) something 
through or even over thinking something is much better than acting without 
thinking (no pun intended.)  It has prevented me from getting into hot water (hot 
air? ... pun intended) on many occasions.  I highly recommend it to anyone out 
there.

Doc (also a PE)
1960 Vette; 1961 Rampside; 1962 Rampside; 1964 Spyder coupe; 1965 Greenbrier; 
1966 Corsa Turbo Coupe; 1967 Nova SS; 1968 Camaro ragtop
~~~~~~~~~~~~~~~
In a message dated 10/25/2008 6:19:23 PM Pacific Daylight Time, 
jekepler at amplex.net writes:

> -----Original Message-----
> From: virtualvairs-bounces at corvair.org
> [mailto:virtualvairs-bounces at corvair.org] On Behalf Of RoboMan91324 at aol.com
> Sent: Saturday, October 25, 2008 1:59 PM
> To: virtualvairs at corvair.org
> Subject: <VV> Ceramic Coatings Questions
> 
> Gang,
> 
> I have been thinking of using ceramic coatings in a rebuild I  am doing and 
> I have a few questions.  These are as follow.
> 
> 1.  Since the head will be thermally insulated from the  heat of the 
> combustion chamber, how will this effect the warm up period of the  engine?
> 
> Define "warm up period"?  Do you mean the time until the engine is at it's 
> minimum designed operating temperature.....or the point where you can melt 
> frost on the windshield?  Since the actual engine operating temperature is 
> largely governed by the oil temp, and That's largely dictated by the 
> cylinders....the coatings should have little or no negative effect.
> 
> 2.  Since the pistons will be insulated from the heat,  they will expand 
> less and/or slower in the cylinder.  I believe that the  expansion of the piston 
> is assumed to be a certain amount when the diameters of  the piston and 
> cylinder are set.  Is this an area of concern?
> 
> Why would it be?  The rings are what seal the bores, not the piston, so who 
> cares!
> 
> 3.  The engine I am rebuilding is a 180 turbo.  Am I  correct to assume that
> 
> I need to also coat components in the exhaust side of the  turbo to protect 
> them from the increased exhaust heat?
> 
> 
> What "components".....you mean the turbo?  That turbine-spool is a 
> Super-alloy.....the same material that the power-section of a jet-engine is made 
> from.....it won't care!  The case is cast steel and isn't going to start being 
> bothered until you are running several orders of magnitude higher exhaust temps 
> than you currently are....Cermet coatings aren't going to do that.  The 
> porous nature of the Turbine housing makes it a poor candidate for coating unless 
> you are willing to send it to someone that knows what the hell they're doing 
> to clean and de-oil it.  I wouldn't screw with the interior surface for a 
> number of reasons; all of them related to issues with that coating bonded on old 
> iron with high-velocity gas in close proximity to a precisely balanced spool 
> rotating at 125,000 rpm....but on the exterior is very attractive if you can 
> get adequate surface-prep done. The guys that do the coatings professionally 
> are generally pretty good at
> their business.....I'd ask them!  Actually, the turbo will LOVE the hotter 
> exhaust and run more efficiently as a result. 
> 
>   If so, which  components?  Also, will the thickness of the coating cause 
> an  interference problem between components and/or balance problem on the  
> rotating member?
> 
> You do NOT want to touch that spool!
> 
> 4.  I assume that the exhaust pipe components must be  thoroughly cleaned 
> before the inner surface is to be coated.  Is it  practical to coat the inside 
> of the muffler considering that the inside can't be  thoroughly cleaned?
> 
> I've never done it to old metal, but I do know that the metal surface MUST 
> be clean (as in fresh metal surface) before the coating will bond.  I'd fab 
> new metal, or be prepared for either some flavor of chemical dipping or VERY 
> creative sand-blasting....either one is going to cost more than new pipes. 
> FWIW.....anything aft of the turbo is meaningless, and you'd be wasting your 
> money screwing with it.  You're joking about the muffler.....right?
> 
> 5.  If I do not coat the interior of the muffler, how  much hotter will it 
> get with this setup and will the increased temperature  cause a problem with 
> surrounding components and paint?  Also, what reduced  life span can I expect 
> for the muffler if it is unprotected?
> 
> Is this really an issue for you?  Corvair mufflers are already running 
> hotter than a Jalapeño fart.....so what's a few hundred more in the grand scheme 
> of things?  Engines are adiabatic machines.  Any heat not converted into work 
> is going to go somewhere, be it a radiator, a fan outlet, or the 
> exhaust.....physics says this is a zero-sum game.....if your exhaust is hotter, your fan 
> outlet is cooler....NO net change (other than less heat being extracted from 
> the system via the cooling system, more work being extracted out of the heat 
> in the fuel, and overall higher thermodynamic efficiency
> 
> I guess that is enough for now.
> 
> With nothing pejorative intended.....it's REAL easy to over-think 
> things...guess where you are?
> 
> Just as an FYI.....my Dodge Dakota POS V-6 makes extensive use of Cermet 
> "Low-E" coatings.....and doesn't glow in the dark!
> 
> JE Kepler, PE


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