<VV> Effects of thermal coating in combustion chamber

[FrankCB]

     Tom didn't believe my assertion that thermally coating the inside of the combustion chamber might cause combustion problems due to the extra heat retained so I sent his response to son Jim who is an engineer at Delphi involved in engine design.
     Here's Jim's answer shown in line-by-line response to Tom's comments.  The most important point Jim makes is that REDUCING the heat flow through the head (by thermal coating) INCREASES the peak pressure which makes knock more likely, even while it is increasing the torque.
     Looks like a case for adding water injection to keep peak pressure under control.  (I "may" have mentioned that previously.<GGG>)  Or at least use electronic knock control like Ray Sedman's SafeGuard (see www.american-pi.com).
     Frank Burkhard

In a message dated 09/06/09 18:49:28 Eastern Daylight Time, 64vair at absolutetops.com writes:
Frank, do you really believe that?  Do you actually think that heat can conduct that fast?   

Yes, it can.

 Let's say that I have a motor with a head held on by a zipper so it can come off in a second, (Wouldn't we all like that for real!).  WE take a cold motor, say 80 degrees, put the foot to the floor, and start it at WOT.  When the engine hits 5500 we shut it down and unzip the head.  How much you want to be that the head is no more than 5 or10 degrees hotter than before the motor started. 

It will be a LOT hotter!

   Heat cannot conduct that quickly.   

Yes it can

 There are many reasons why a cold motor may be less prone to rattle than a hot motor.  A cold motor has a colder intake charge,  

That is true.

 the hot motor heats the a/f mixture before it ever gets to the cylinder.  

that is true

  The cold motor does not have hot spots in the chamber like the hot motor does. 

true

   a cold motor is running richer than a hot motor, (choke on carburetter motors WUE on EFI). 

true, but what's a WUE, warm up enrichment?  FIrst time I ever heard that acronymn.
   
IT does not matter if you road race, auto cross, or drag race.  Ceramic thermal barriers reduce an engines tendency to detonate.  If you have a motor that has coatings and detonates, it is not because of the coatings.  any stories you may have heard, you need to remember that most people will not do what is really required for an accurate test.  They may coat pistons, change jetting, and go to a thinner head gasket, then when it detonates blame it on the coatings.  (come on, we all know guys like that!) 

Tom's final point is  true, this is something difficult to test without controlled conditions and that is the sort of thing few folks have the resources for.  

If one does anything to increase the thermal efficiency of the engine by reducing heat transfer through the head, it will increase torque (a good thing), but it raises peak pressure and that might make knock more likely.  It's akin to increasing the compression ratio perhaps ... there are some good things, but also some risks.

J


Tom


On Sun, Sep 6, 2009 at 12:09 PM, FrankCB <frankcb at aol.com> wrote:

Tom,
     If that's true then why are we more likely to get improper combustion noise ("rattling") when our engines are HOT than when they are COLD.  The COLD engines are sucking out more of the combustion heat than those same engines do when they get HOT.
     Frank Burkhard

In a message dated 09/05/09 22:51:31 Eastern Daylight Time, 64vair at absolutetops.com writes:
Coating the pistons and chambers REDUCES the chance of detonation. The heat
is not until after the ignition, and it goes out the exhaust. The chamber
and piston deck stay cooler. this is not conjecture on my part, this is
documented both on the track and in the dyno room.
Tom