Do You Agree With This?

[chris]

Hey guys,

I know I've asked a lot of questions regarding mixture control lately, but I have one more

I hate to beat this dead horse with a stick, but I really would like some feedback.

In one book, I read the following:

" An aircraft's engine will run hotter with a lean mixture than with a rich mixture because the leaner mixture is slower to burn, exposing the cylinder walls to high temperatures for longer periods of time. A richer mixture will burn faster, exposing the cylinders to high temps but for a relatively shorter period of time." This came from the book "From The Ground Up."

What do you think about this?

I always thought that the leaner mixture is burning faster, and this speeds up the combustion cycle as more heat is produced, and more work is being done.

Also, in an article (again, the Deakin one) I read that as you lean, the mixture begins to burn faster, and the Peak Pressure Point (PPP) will occur closer to Top Dead Center, resulting in higher pressure and higher temps- this is the direct cause of the high CHT with a leaner mixture (assuming you're not lean of peak). This seems to contradict what I read above.

What am I missing?

Thanks in advance.

 

[agcatman]

[ QUOTE ]
Hey guys,

I know I've asked a lot of questions regarding mixture control lately, but I have one more

I hate to beat this dead horse with a stick, but I really would like some feedback.

In one book, I read the following:

" An aircraft's engine will run hotter with a lean mixture than with a rich mixture because the leaner mixture is slower to burn, exposing the cylinder walls to high temperatures for longer periods of time. A richer mixture will burn faster, exposing the cylinders to high temps but for a relatively shorter period of time." This came from the book "From The Ground Up."

What do you think about this?

I always thought that the leaner mixture is burning faster, and this speeds up the combustion cycle as more heat is produced, and more work is being done.

Also, in an article (again, the Deakin one) I read that as you lean, the mixture begins to burn faster, and the Peak Pressure Point (PPP) will occur closer to Top Dead Center, resulting in higher pressure and higher temps- this is the direct cause of the high CHT with a leaner mixture (assuming you're not lean of peak). This seems to contradict what I read above.

What am I missing?

Thanks in advance.

[/ QUOTE ]

I can't say that I've heard that as the reason that a richer mixture burns cooler. But I've heard lots of other reasons. The unburnt fuel in the richer mixture helps cool. The increased volume of fuel and the cooling effect of its evaporation has been noted by some. There are lots of theories but I've never heard of one that could claim to be the "end all be all" of the subject.

Understand that there's a point where theory is just that- theory. And while understanding the theory is great and will not hurt you as a pilot don't think that you must understand the minutae of the system to make it work. You know that rich means more fuel in the mixture and lean means less. You know that a richer mixture will burn cooler and a leaner mixture will burn hotter.

So get off it and go fly, willya?

 

[mtsu_av8er]

Man, this is too deep for me...I just lean it till it runs rough, then a little richer...then I'm good to go!!!

I'm just a pilot, not a tech!!!

(humor!!!)