Combustion Chamber Modifications

[Nick Campagna]

The following is a thread I started on another board. Except for one response, the thread died. Does anyone know the surface temperature of a combustion chamber at its hottest working temperature ( full lean ?)

I am considering doing some combustion chamber modifications, and the question came up " What is the temperature of the surface of the combustion chamber" ? I am considering a powder fusion process with a Ni, B, Si, Fe powder.

Good question,Nick. It's lower than the auto-ignition temp of the fuel/air mix.....but that's about all I know.
Terry

Thanks for the comeback. The process I'm looking at can lay down a surface to any thickness, with from Rb90 - Rc40 in hardness, with 1200*F working temp. A change in chemistry can go to 1900*F but the hardness goes to Rc60. Definite grind territory, not tool steel or carbide. The exhaust temp is up there, but is not cooled by the water jacket. The observation of auto ignition of gas-air at intake (atmospheric pressure) is a good clue. At 180 psi over atmospheric could relate to detonation due to auto ignition. Need to do some research.

[automotivebreath]

In general there is no specific answer to your question. Surface temperature will vary
with the hottest places being the spark plug ground electrode, the exahust valve and
valve seat at peak toque.

You thoughts of using the fuel autoignition temperature as a guide is a good one; with
gasoline that would be ~ 246° C or 475° F.

Combustion temperature is much higher; the boundary layer becomes the insulator.
Autoignition will begin to burn away the protective layer exposing the combustion
chamber surfaces to full heat of combustion, that's likely the biggest concern.

[Nick Campagna]

I'm more concerned with the surface of the chamber, since I wish to change the shape of the chamber without a welding process on the cast iron.

[automotivebreath]

Hi Nick,
I believe I understand your question, you are planning on coating the combustion
chamber surface using a powder fusion process and asking about the the surface
temperature of the combustion chamber at its hottest working temperature.

The actual surface temperature will vary greatly depending on many variables,
there is no specific number that can be stated. Normally the air/fuel mixture doesn't
burn all the way to the combustion surface forming a boundary layer, insulating the
metal from the heat of combustion. This insulating layer normally keeps the surface
temperature below 475° F. The hottest regions in the cylinder can get hotter than
this but the heat transfers away before the next intake stroke avoiding per-ignition.
Surface temperature of ~650° F can begin to damage engine parts.

Can the surface temperature get above this? Yes, especially when the engine is
running with a significant amount of autoignition. The protective layer is burned
away exposing the surface to the full heat of combustion.

[stealthfti]

If I am understanding correctly what you are asking, then I would suggest that you check out the temperature capability of the coatings that outfits like Swaintech offers for coating the combustion chambers and piston crowns.

I agree with AB's answers regarding the boundary layers' protecting the metal surfaces from the temperatures occurring during the combustion process. But, I think that what you are needing to be able to do with your coating is to actually withstand the combustion temperatures themselves. Which will be somewhere between 2500F and 3000F. [...you were asking about the 'max' temperatures possible, right?].

So, finding out what temperatures commercially available coatings for CCs are capable of withstanding should help you determine if either of your formulations can take the heat that they will see in there.

I like your idea. To be able to reshape the CCs of my iron SBC heads into shapes of a fastburn layout without welding would be really nice.

good luck

TF

[Nick Campagna]

Thanks for the replies everyone. The reason we are worried about the surface temp, is that the coatings simply wet the surface during the ~700*F application,also, the normal insulating coatings are not suitable for ~3/16" buildup. In researching this, PTA (plasma transfer arc) seems to be the process of choice. Since this is an electrode negative process, a modified TIG head, with the powder introduced with the normal argon gas flow, could be the ticket. The head should be preheated to ~500-600*F, and the TIG current turned down so we would be using the TIG for a buttering pass on the head (just a light surface melt) to form a good metallurgical bond to the substrate. The normal powder fusion process is more of a brazing process. The substrate is not melted. Once the buttering pass is done, the powder fusion may be used for the build up, or just continue with the "powder TIG". Low current TIG units can be had fairly inexpensively. The powder can also be applied with the argon carrier gas with a separate wand than the TIG head.

[automotivebreath]

Here's a link to some good discussion on spray welding iron heads. Joe Stockton of
JBV HEADS would be a good person to talk to, it sounds like he has a good bit of
experience with this.

Spray Welding Cast Iron Heads?

jbv-heads

[Nick Campagna]

That was very informative, thanks.

[MadBill]

Another way to arrive at an approximate value would be to recognize that when doing repairs to aluminum heads, it is generally recommended that they not be heated above ~300° F., as loss of heat treatment may occur. From this is could be deduced that no part of the head would ever exceed this temperature under even extreme operating conditions, so long as coolant is present.