Chicken Wings Forum

Roost Air Lounge => The Classroom => Topic started by: Stef on June 08, 2008, 09:35:20 PM

Title: fuel to air ratio
Post by: Stef on June 08, 2008, 09:35:20 PM
Hi Fellas! I have a quick and simple question (which no doubt will spawn into a 100 post thread, but nevertheless  ;) )

What is the average fuel to air ratio in a Cessna like Chuck's?  ???
Title: Re: fuel to air ratio
Post by: Oddball on June 08, 2008, 09:44:11 PM
as in carburation stef?
Title: Re: fuel to air ratio
Post by: Stef on June 08, 2008, 10:10:39 PM
as in carburation stef?

Well, obviously it's good to have a lot of air around you and a lot of fuel in the tank!  ;D But indeed, I was rather thinking about the "mixture" that goes into the engine!
Title: Re: fuel to air ratio
Post by: Rooster Cruiser on June 09, 2008, 01:39:08 AM
Optimum Air/Fuel ratio in an Internal Combustion engine is approximately 7:1.  Air cooled engines are often run at a lower ratio (richer mixture) than this while operating at higher power settings in order to help keep cylinder head temperatures within limits and prevent detonation.  Liquid cooled engines can run at the optimum air/fuel ratio all the time due to the more efficient heat conduction of the cooling system compared to air.  This also allows much higher cylinder compression ratios in liquid cooled engines which leads to still more efficient combustion and better power output for a given fuel consumption.

OK guys, what'd I miss here?

RC
Title: Re: fuel to air ratio
Post by: Mike on June 09, 2008, 01:46:06 AM
you missed an internal discussion where my brother and I couldn't agree if it was 4.1 to 1 or 14.1 to 1 . . .
guess we were both wrong.....

Title: Re: fuel to air ratio
Post by: Frank N. O. on June 09, 2008, 05:47:22 AM
I thought the optimum fuel/air-ratio, also known as Lambda 1, was 14.7:1 ?? Some cars can easily drive with less, like my old Orion (that had a vacuum-regulated Weber carburator) could do a lot less, not sure how much but maybe 18:1 or more? Some modern cars do this too, but it's been comming in the carmagazines that they don't do it all the time and in the other times they switch it totally off to give power and then the fuel-economy goes to heck. The early Mitsubishi Carisma 1.8 GDI (gasoline direct injection) claimed 20% better economy but that lean-burn function it had was disabled when you used more than just a little throttle, and permanently when the car was driving over 80 kph. I have no idea why the car's speed should have any direct impact on the engine settings but that's what I've read several cars have, perhaps due to maximum speed where the goverment tests official car polution figures used for car taxes in some countries. Just weird the car can't drive at optimum combustion all the time, but I guess that would be too perfect ::)

I must say, it sounds wild if aircraft engines run at 7:1 but I guess I it sounds logical about the engine temperature in this case, but wouldn't that advocate for liquid-cooled aircraft engines?

Frank
Title: Re: fuel to air ratio
Post by: Oddball on June 09, 2008, 08:45:53 AM
i shall hang my head in shame that was one of the things i had in one of my previous exam papers  was caught at a weak moment last night.     :-[  :-[
Title: Re: fuel to air ratio
Post by: airtac on June 09, 2008, 02:29:39 PM
HMMM---Google fuel/air ratios, there's some interesting stuff there that might change those numbers a little  ::thinking::
Title: Re: fuel to air ratio
Post by: leiafee on June 09, 2008, 07:55:46 PM
I learned 12:1 Air:Fuel...

Though the engine will run albeit less eficientny either side of that. 

Am I missing something?
Title: Re: fuel to air ratio
Post by: Mike on June 09, 2008, 09:52:13 PM
woah ! ::unbelieveable::

looks like we have as many different ratios in here as we do members  ::rofl::

should we ask in the AOPA forum?!
Title: Re: fuel to air ratio
Post by: Oddball on June 09, 2008, 09:56:31 PM
now now mike dont be so hasty you might get as many answers there as well!!!!  ::unbelieveable:: ::eek:: ::eek:: ::loony::
Title: Re: fuel to air ratio
Post by: Stef on June 09, 2008, 11:02:07 PM
... thanks for all the hard thinking on your part guys! Somehow I get the feeling that no matter what ratio we would use in this potential strip, somebody's definitely going to write us and say we're wrong!  ;D
Title: Re: fuel to air ratio
Post by: AirScorp on June 09, 2008, 11:53:03 PM
I too have learned about grossly 15:1 which seems to be the one most of us agree on (14.7:1)

However, 14.7:1 is a "Theoretical" ideal.. And that to my ears sounds like: perfect fuel (iso-octane), a test engine and perfect conditions (1 atm pressure, 20 degs Celcius or whatever)
With normal fuel, I'd expect everything to be one or even two points lower, maybe as low as 12.5:1 on low-octane fuel..
Then you have detonation, and everything shifts again to the safe side which is the rich side.. Remember rich is less efficient, lean is more heat and more dangerous to detonate.

Most of what I said is from intuition, I don't have internal combustion engines in my curriculum , but Leia's 12:1 makes the most sense to me..
R/C, maybe the 7:1 was for diesel fuel or a compression ratio or something? It's too low to make sense unless I'm completely wrong about everything..

AOPA forums won't do much good, pilots were never meant to know such things.. ::rofl:: Maybe you should ask *gasp* an engineer??????? (Oddball, you're the man on this)

Ok, for a question now: How much is the air to fuel ratio on a pilot's brain?????
Title: Re: fuel to air ratio
Post by: TheSoccerMom on June 10, 2008, 03:09:32 AM
 ::whistle::

I think we know how much AIR is in the pilot's brain.............   ::whistle::

The dusty old FAA Flight Handbook says: 
"Mixtures as rich as 8:1 and as lean as 16:1 will burn in the cylinder of an engine that develops maxiumum power with about a 12:1 ratio."

I think we should ask CHUCK....   ::silly::

 :D
Title: Re: fuel to air ratio
Post by: G-man on June 10, 2008, 03:18:19 AM
(http://i76.photobucket.com/albums/j35/helokat/givedamn.gif)

Ya'll just try to overcomplicate stuff--I mean really

(http://i76.photobucket.com/albums/j35/helokat/8uzn8y1164932566.jpg)

(http://i76.photobucket.com/albums/j35/helokat/k035.gif)(http://i76.photobucket.com/albums/j35/helokat/k035.gif)(http://i76.photobucket.com/albums/j35/helokat/k035.gif)(http://i76.photobucket.com/albums/j35/helokat/k035.gif)(http://i76.photobucket.com/albums/j35/helokat/k035.gif)(http://i76.photobucket.com/albums/j35/helokat/k035.gif)(http://i76.photobucket.com/albums/j35/helokat/k035.gif)(http://i76.photobucket.com/albums/j35/helokat/k035.gif)(http://i76.photobucket.com/albums/j35/helokat/k035.gif)(http://i76.photobucket.com/albums/j35/helokat/k035.gif)
Title: Re: fuel to air ratio
Post by: TheSoccerMom on June 10, 2008, 03:32:02 AM
Personally, I pay a lot more attention to the CCC-to-A/C Ratio --- (Company Credit Card-to-Aircraft Ratio)....     :P

As long as it's at least 1:1, no worries...   And 2:1??  Even better.....    ;)

 ::whistle::

Title: Re: fuel to air ratio
Post by: G-man on June 10, 2008, 03:36:30 AM
Personally, I pay a lot more attention to the CCC-to-A/C Ratio --- (Company Credit Card-to-Aircraft Ratio)....     :P

As long as it's at least 1:1, no worries...   And 2:1??  Even better.....    ;)

 ::whistle::

2 company cards--now thats just greedy---have them increase the limit.. Better yet--borrow one of the other pilots CCC.. ::whistle:: ::whistle::
Title: Re: fuel to air ratio
Post by: TheSoccerMom on June 10, 2008, 03:38:19 AM
Well, actually, I USED to have two, now I have 17, it's sure simple ever since I got that little laminating machine for Christmas... 

Shh-hh-hh, don't tell the Boss....   :-X

 ;)
Title: Re: fuel to air ratio
Post by: Oddball on June 10, 2008, 09:43:54 AM
 :-[ sorry airscorp I let the side down on this one a bit. I'm now waiting for one of my ex-lecturer's to throw a white board pen at me  to wake me up and remember everything he taught me......................but some how i cant see how to smuggle cigarettes and booze in a Avro Shackleton's mid-upper turret ring and in the rear of the inboard engines has anything to do with air/fuel ratio's.  ::thinking::  ::loony::
Title: Re: fuel to air ratio
Post by: Rooster Cruiser on June 10, 2008, 11:32:45 AM
Ok, ok.  I'm being hammered on being way off on air/fuel ratio!  I was drawing from memory something I read in my private pilot ground school textbooks in high school 30 years ago!  Please forgive my faulty memory if it was that.  Maybe back then that was the optimum air/fuel ratio for air-cooled engines or for all engines prior to computerized fuel injection systems that can directly measure the oxygen content of the intake air (something I just read in Wikipedia).  <pant, pant>  Whew!  That was a mouthful for a single sentence from me!

Sorry to cut and run, but I've got a contract flight to do this early morning...
Title: Re: fuel to air ratio
Post by: Mike on June 10, 2008, 06:20:12 PM
on my boat, the ratio seems to be 2:1 . . .  :-\ :'(


Ok, are we agreeing on 14:1 for now ?!  ??? ::unbelieveable::
Title: Re: fuel to air ratio
Post by: airtac on June 10, 2008, 06:44:41 PM
Personally, I pay a lot more attention to the CCC-to-A/C Rajavascript:void(0);
salutetio --- (Company Credit Card-to-Aircraft Ratio)....     :P

As long as it's at least 1:1, no worries...   And 2:1??  Even better.....    ;)

 ::whistle::



RIGHT ON MOMMA !!! |:)\  my feelings EXACTLY |:)\ |:)\
Title: Re: fuel to air ratio
Post by: airtac on June 10, 2008, 06:57:10 PM
Thanks for the Algebra lesson Gordy----I wasted a whole year of college looking for that "X" ::complaining: ----no wonder they kicked me out ::banghead::
Title: Re: fuel to air ratio
Post by: Oddball on June 10, 2008, 07:47:00 PM
I kept on telling them thats where "x" was but they kept on marking me wrong. ::complaining:
Title: Re: fuel to air ratio
Post by: Oddball on June 11, 2008, 12:13:38 AM
ok after looking up some old notes from uni i have found a "chemically correct mixture" (direct quote from the book) mixture ratio of 15:1 and a rich mixture of 10:1 and a lean mixture of 18:1.
Title: Re: fuel to air ratio
Post by: AirScorp on June 11, 2008, 02:25:58 AM
Ok, ok.  I'm being hammered on being way off on air/fuel ratio!  I was drawing from memory something I read in my private pilot ground school textbooks in high school 30 years ago!  Please forgive my faulty memory if it was that.

Truly sorry if it looked that way R/C  ::) Tell you the truth, it was quite the opposite of hammering on you! When I'm making "logical assumptions", like I did, I get excited at the possibility that I'm way off and some new data will make me reconsider all my reasoning or even start anew.. So I was asking for more info on what you said cause you and most ppl round here are around planes and engines waaaaaaaay longer than I am!  ::cowboy:: Just the way I process new information :)
Title: Re: fuel to air ratio
Post by: Rooster Cruiser on June 12, 2008, 04:46:30 AM
Tis Ok Nick!  We can discuss it over a Brew or two whenever we get a chance to meet in person.   ::drinking:: ::drinking:: ::drinking:: ::drinking:: ::drinking:: ::drinking::
Title: Re: fuel to air ratio
Post by: tundra_flier on July 10, 2008, 12:42:51 AM
Are we talking by volume or by weight?  Sorry, the engineer in me just had to ask.   ::thinking::
The 14.7:1 sticks out in my mind as being correct, have to check my hot rod books when I get home.

Phil
Title: Re: fuel to air ratio
Post by: Mic on July 11, 2008, 08:15:39 PM
I've always learn this is 15:1 and this is what we are teaching to our ATPL students.

But as I'm more a glider pilot I'll say that the most interesting thing for me is to have air ... below !!
Title: Re: fuel to air ratio
Post by: Mike on July 11, 2008, 09:03:51 PM
I've always learn this is 15:1 and this is what we are teaching to our ATPL students.


yes, but you're in France!

don't you guys have the metric system over there? ? ?
it's gonna be all different, isn't it?!

 ::rofl:: ::rofl:: ::rofl:: ;D ;)


(I see a new Chicken Wings strip in this . . .)
Title: Re: fuel to air ratio
Post by: airtac on July 12, 2008, 02:52:55 AM
I've always learn this is 15:1 and this is what we are teaching to our ATPL students.


yes, but you're in France!

don't you guys have the metric system over there? ? ?
it's gonna be all different, isn't it?!

 ::rofl:: ::rofl:: ::rofl:: ;D ;)


(I see a new Chicken Wings strip in this . . .)

Now I'm beginning to see how your twisted mind works ::loony:: ::rofl::
Title: Re: fuel to air ratio
Post by: Mic on July 13, 2008, 08:12:22 PM
I've always learn this is 15:1 and this is what we are teaching to our ATPL students.


yes, but you're in France!

don't you guys have the metric system over there? ? ?
it's gonna be all different, isn't it?!

 ::rofl:: ::rofl:: ::rofl:: ;D ;)


(I see a new Chicken Wings strip in this . . .)

Well you're right ! I forgot that a metric ratio is different than a british one !!

It make me remind on comic strip I saw few years ago :

- Weather report from ATC : "horizontal visibility = zero"
- Pilot to tower "Is that in feet or in meter ?"

Title: Re: fuel to air ratio
Post by: Mike on July 13, 2008, 09:56:57 PM
good one!

just read a similar on the other day:


They Walk Among Us!!

*    I used to work in technical support for a 24/7 call center. One day I got a call from an individual who asked what hours the call center was open.  I told him, 'The number you dialed is open 24 hours a day, 7 days a week.' He responded, 'Is that Eastern or Pacific time?' Wanting to end the call quickly, I said, 'Pacific.'
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