Can Someone Explain This?

[uwochris]

Can someone please explain why CHTs peak before EGTs, as you lean from full rich? I would have they would peak together, but this is not the case... peak CHT is approximately your Best Power Setting, and Peak EGT is approximately your Best Fuel Economy Setting... why the difference?

Thanks in advance and I hope everyone has a happy new year!!

 

[Typhoon1244]

I'll be more than happy to discuss it with you...after you tell me what "CHT" is.

(Apparently I've missed something in my aeronautical experience...)

 

[PonchoMan]

Cylinder Head Temperature. Your welcome

 

[Typhoon1244]

Cylinder Head Temperature.

Ah. Thank you.

Now...what's a cylinder?



(Just kidding...I'm turbine-spoiled. )

 

[EagleRJ]

Jets are for kids.

Maybe it has to do with how much of the available fuel is burning in the cylinder and how much is going into the exhaust? If the mixture is slightly rich, fuel is left unburned and burns in the exhaust, which raises the EGT.

I remember adjusting the glow of the turbo inlet pipe that was visible behind the nacelle vent of a twin Cessna with the mixture knob. Probably wasn't doing the engine any favors, since I wasn't watching the gauges!

 

[GeorgeTG]

why:

As always
the fun and entertaining John Deakin has written a detailed column on the subject:
http://www.avweb.com/news/columns/182084-1.html

Cheers George

 

[vossdr1]

The actual combustion is occuring inside of the cylinder and causes an enormous rise in the pressure (remember the relationship between pressure and temperature). The exhaust is actually cooler than the combustion process because combustion has ceased.

CHTs will be higer at best power because you are extracting the most heat in the cylinder from the fuel for moving the piston (best power). EGTs are higher at best economy because all of the fuel being delivered to the cylinder is being burned (no fuel to cool).

If the mixture is over rich, some fuel acts to prevent knock and allows for higher brake mean effective pressure (pressure at the point of combustion inside of the combustion chamber). This also means that, since the fuel hasn't got oxygen to combust with, it acts to cool the exhaust and the hydrocarbons wick away the heat out of the exhaust stack.

Happy New Year.