What Aluminum is used to make cylinder heads?

[mikeseli]

I don't know if I'm approaching this the right way, but doesn't an aluminum head or any head in general get exposed to temperatures of 1000F+ during the combustion process? I know that they last a fraction of a second but after a while the head's combustion area will reach a temperature steady state. I'm guessing it should be about 500F or 600F (these are guess), since the fresh intake charge cools it off and also because of the water jackets absorbing that heat.

What kind of aluminum can sustain temperatures of that extreme?

I found out that some aluminum heads are made from A356 T6, but this type of aluminum is not made to handle temperatures above 300F.

Am I looking at this the wrong way?

 

[Latexman]

The heat transfer coefficient in the combustion chamber is relatively small since it is based on gas properties. The heat transfer coefficient in the walls and cooling water jacket is relatively large since they are based on water/EG and metal properties, respectively.

Let me refresh your recollection of heat transfer calcs with the fact that [Δ]T across a resistance (film theory) is proportional to 1/htc of that resistance. Therefore, the combustion chamber is hot as hell in the center and not so hot at the walls, i.e. large [Δ]T. The cooling water/EG is the coolest thing in the system and since it's htc is large and [Δ]T is small so is the walls.

Good luck,
Latexman

 

[EngJW]

Air cooled aircraft engines are allowed to run somewhere around 400 F. This is not all over. It is supposed to be the hottest point in the head, which is usually the solid metal area between the valve seats that doesn't get a lot of cooling. A hole is drilled toward it and a thermocouple installed. The pilot has to watch this temperature as it is affected by the mixture control.

The heads that I know of are made from 356-T6.

 

[NickE]

A316 is also used in automotive heads.

 

[izzmus]

Wankel engines see high exhaust gas temps (up to 1800-2000F) directly on the aluminum at the exhaust ports, with no other cycles in that area to cool it down. 100% cooled by the water jackets, with no apparent problems.

There are some engines with unjacketed exhaust runners - the Pontiac V8 comes to mind - that also have no apparent heat issues when the heads are made of aluminum. The same company also used to make aluminum exhaust manifolds, which did have some erosion problems.

 

[ivymike]

Al pistons (made of piston mfr's special blend) can withstand continous metal temperatures of 350C or higher.

 

[mikeseli]

350C is low in my opinion, since I would think that the top surface of the piston will reach at least 500C, since the exhaust temperature reaches that temperature.

Can someone confirm to me, that during the induction stroke, does the entire chamber and top of piston gets cooled rapidly, therefore the average temperature is the exhaust temperature and intake charge temperature divided by two.

 

[ivymike]

why would you expect the average gas temp to match the metal temp?

 

[NickE]

Here is a hint as to why aluminium, which all alloys are molten at temps >~655C. (Exhaust gas temp on my 2.0L-turbocharged motor reaches ~870C at the collector of #1cyl.)

DELTA T

 

[ivymike]

Sorry, missed the point - what were you trying to say?

 

[patprimmer]

I think he is saying heat transfer from gas to metal is poor or slow, and aluminium conductivity is high and there are heating and relative cooling cycles in a reciprocating engines operation.

Regards

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[NickE]

Thanks pat, thats exactly my point.

Its the same reason a copper lance can be shoved into molten Iron. A high conductivity metal with sufficient cooling jackets can handle very high temperatures.

 

[reidh]

I'm a few posts late on this response, but 1800-2000 degree EGT seems awfully high for a rotary engine.

During a recent development program of a rotary engine we performed a temperature map all over the engine (including exhaust temps), and never saw anything close to 2000 degrees. 1300-1400 was the maximum measured temperature that we saw.

-Reidh

 

[carockwell]

The Mazda rotaries used in the normally aspirated RX-7 typically hit 1650 F exhaust gas temps at full throttle measured about 12 inches from the exhaust manifold gasket. Probably a lot more if turbocharged. You need a really tough exhaust system on a rotary.

 

[thundair]

mikeseli
No one has mentioned this so I will chime in...There is a boundary layer as flame front grows that helps protect the surface temperature. This is not true in the exhaust port but there is a cooling intake reversion wave that helps the port and especially the valve seat...Preigniton (a much discussed subject) will blow away the boundary layer and you will burn a piston..
For my part there are more disadvantages to using aluminum heads then the weight advantage..I favor meehanite castings IMO.

Cheers

I don't know anything but the people that do.