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air fuel ratio #4768338
05/25/18 09:11 PM
05/25/18 09:11 PM
Joined: Jan 2018
Posts: 265
KS
red7404 Offline OP
red7404  Offline OP
Joined: Jan 2018
Posts: 265
KS
What characteristic of a liquid fuel sets the A / F ratio?

Re: air fuel ratio [Re: red7404] #4768402
05/25/18 11:15 PM
05/25/18 11:15 PM
Joined: Mar 2016
Posts: 1,745
Western S.C.
CR94 Offline
CR94  Offline
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Posts: 1,745
Western S.C.
Air/fuel ratio is not a characteristic of the fuel. It's the ratio air mass to fuel mass in the fuel-air mixture. Stochiometric ratio for air:gasoline is about 15:1.


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Re: air fuel ratio [Re: red7404] #4768561
05/26/18 07:58 AM
05/26/18 07:58 AM
Joined: Mar 2018
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Hammehead Offline
Hammehead  Offline
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Stochiometric ratio is a result of the calorific power of the fuel. The higher the cp, less fuel is used in the stoichiometry of its mix.

Last edited by Hammehead; 05/26/18 08:00 AM.

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Re: air fuel ratio [Re: red7404] #4768573
05/26/18 08:22 AM
05/26/18 08:22 AM
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NH
supton Online content
supton  Online Content
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NH
Not a chemist but what the heck, I'll play one for now.

Most fuels are composed of hydrogen and carbon. In order to fully release all the energy stored in the fuel, there is an ideal amount of oxygen required for the chemical reaction. Too little air and it doesn't fully react. Too much, seems hard to occur but it certainly does inside of an internal combustion engine (due to the small window of time for it to do "useful" work and the need for the flame to go from combustible molecule to another one). Ultimately you get carbon dioxide and water--and heat which is what is usually we are after--and to do that there is a proper amount of oxygen (from the ambient air) required.

Now I realize fuels can be other than hydrogen and carbon based, and often there is stuff in the fuel which also requires combusting (which may or may not help with releasing heat) but most stuff that we like to burn is largely hydrogen&carbon (oil, gas, wood, coal).


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Re: air fuel ratio [Re: red7404] #4768580
05/26/18 08:26 AM
05/26/18 08:26 AM
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Leo99 Offline
Leo99  Offline
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NJ
When we talk about the stoichiometric ratio, that the is the ratio of air to fuel for a "perfect" burn. For gasoline it's 14.7:1. If other fuels can burn with less oxygen, the A/F goes down. If they need more oxygen, the A/F goes us.


Without data you're just another person with an opinion. W. E. Deming

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Re: air fuel ratio [Re: red7404] #4768665
05/26/18 10:20 AM
05/26/18 10:20 AM
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Illinois
SHOZ Offline
SHOZ  Offline
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Illinois
My A/F gauge can be programmed for whatever stoichiometric ratio you want. I use E10 all the time so I set it at 14.2. Lambda is much better to use.


2008 Hyundai Accent 1.6L 5 sp manual hatchback
2010 Hyundai Genesis Coupe Track 2L Turbo 6sp manual
Re: air fuel ratio [Re: Hammehead] #4768727
05/26/18 11:30 AM
05/26/18 11:30 AM
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ME
eljefino Offline
eljefino  Offline
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Originally Posted By: Hammehead
Stochiometric ratio is a result of the calorific power of the fuel. The higher the cp, less fuel is used in the stoichiometry of its mix.


This is a good answer.

Another is that if you examine the exhaust gases, neither oxygen nor fuel particles remain as everything was used up and converted.

If one introduces nitrous oxide, they have to run much richer fuel. But they make more power as the oxygen content of the "air" inside is higher than 21%. Some NOS systems are "wet" and include the needed fuel; others require ECM mods and bigger injectors.

The Space shuttle had to carry liquid oxygen so it could have a stoichometric burn in outer space where there was otherwise no other oxidizer available.

Ethanol for all its issues splits apart and leaves a little extra oxygen in the combustion chamber, so if you're tuned for it, even 10%, you can make more power than with pure gasoline alone.

Re: air fuel ratio [Re: red7404] #4768732
05/26/18 11:39 AM
05/26/18 11:39 AM
Joined: Apr 2018
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Texas & Global
talest Offline
talest  Offline
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Posts: 68
Texas & Global
Originally Posted By: red7404
What characteristic of a liquid fuel sets the A / F ratio?


As mentioned, for pump gas it is 14.7 to 1, or 14.7:1

This would be the ideal mix for the best, and most complete, burn in combustion per stroke.

Re: air fuel ratio [Re: talest] #4768757
05/26/18 12:14 PM
05/26/18 12:14 PM
Joined: Jun 2003
Posts: 5,973
Illinois
SHOZ Offline
SHOZ  Offline
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Posts: 5,973
Illinois
Originally Posted By: talest
Originally Posted By: red7404
What characteristic of a liquid fuel sets the A / F ratio?


As mentioned, for pump gas it is 14.7 to 1, or 14.7:1

This would be the ideal mix for the best, and most complete, burn in combustion per stroke.
And the highest exhaust temps.


2008 Hyundai Accent 1.6L 5 sp manual hatchback
2010 Hyundai Genesis Coupe Track 2L Turbo 6sp manual
Re: air fuel ratio [Re: red7404] #4769057
05/26/18 08:10 PM
05/26/18 08:10 PM
Joined: Mar 2018
Posts: 142
Hammehead Offline
Hammehead  Offline
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Yes with ethanol, the 14.7:1 doesn´t apply for ages. Only for the scarce E0. E15 may use 13.9:1 or even a tad less, hence the higher fuel consumption of these oxigenated gasolines, since you´re adding a lesser cp to the final fuel.

And thank you Eljefino

Last edited by Hammehead; 05/26/18 08:13 PM. Reason: cp

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Re: air fuel ratio [Re: red7404] #4773551
05/31/18 02:57 PM
05/31/18 02:57 PM
Joined: Jan 2011
Posts: 280
California
DGXR Offline
DGXR  Offline
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California
Shell fuels provide the best air-fuel ratio :P


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2003 Honda XR400R
Re: air fuel ratio [Re: DGXR] #4776956
06/04/18 07:19 AM
06/04/18 07:19 AM
Joined: May 2010
Posts: 1,176
Ocala, Florida
racin4ds Offline
racin4ds  Offline
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Posts: 1,176
Ocala, Florida
Originally Posted By: DGXR
Shell fuels provide the best air-fuel ratio :P


Let me fix that for you-

The vehicle's ECM or tune provides the best air-fuel ratio wink

Last edited by racin4ds; 06/04/18 07:19 AM.

Just say NO to thin oils and M1!
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Re: air fuel ratio [Re: racin4ds] #4779274
06/06/18 02:21 PM
06/06/18 02:21 PM
Joined: Jan 2011
Posts: 280
California
DGXR Offline
DGXR  Offline
Joined: Jan 2011
Posts: 280
California
Originally Posted By: racin4ds
Originally Posted By: DGXR
Shell fuels provide the best air-fuel ratio :P


Let me fix that for you-

The vehicle's ECM or tune provides the best air-fuel ratio wink


Clearly. We really need to develop a sarcasm font. I thought my tongue out thingy would indicate a comment in jest.


1995 Corvette coupe LT1 6-speed
2006 Tacoma 2.7 2wd access cab
1999 Yamaha YZ400FL
2003 Honda XR400R

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