Fuel ratio????
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Drifting
Joined: Oct 1999
Posts: 1,722
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From: Gloucester Va
Fuel ratio????
OK I am wondering why does a rich mixture not allow for best HP.
I was thinking that if you had plenty of fuel then it would burn what ever it could and the rest just left alone thus giving you the best power, but It doesn't seem to work this way. WHY?
I was thinking that if you had plenty of fuel then it would burn what ever it could and the rest just left alone thus giving you the best power, but It doesn't seem to work this way. WHY?
Burning Brakes
Joined: Apr 2000
Posts: 980
Likes: 2
From: Chandler AZ
Re: Fuel ratio???? (88_vette)
You need to achieve total combustion to create the most power. Too little fuel? It's easy to burn all the fuel in the cylinder. If you have too little fuel when it burns you don't have the maximum expansion of gasses in the cylinder. Too much fuel and it doesn't burn efficiently. If this is the case it doesn't create the largest possible amount of expansion due to unburned fuel cooling the burning mixture. Fuel vapor is easier to ignite than liquid. Add air or sparks or pressure to compact the mixture and you can add more fuel. So get an MSD and a higher compression and go for it.
[Modified by VAHROOM, 10:52 PM 4/27/2004]
[Modified by VAHROOM, 10:52 PM 4/27/2004]
Burning Brakes
Joined: Apr 2000
Posts: 980
Likes: 2
From: Chandler AZ
Re: Fuel ratio???? (nonetooclose)
The ideal ratio for power is 12.6:1 and does change slightly from engine to engine.
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: Fuel ratio???? (88_vette)
Think of how the burn progresses...at the spark the charge energy becomes high enough for molecules of air & fuel to combine and break down (oxidize) the fuel and the flame kernel is formed. For the burn to propegate through the entire charge kinetic energy must be transfered to the molecules to cause more fuel oxidazition, as the flame front progresses through the charge. If there are too many molecules of air the kinetic energy is lost between them instead of being used to oxidize the fuel; if there are too many molecules of fuel the kinetic energy is also lost between them instead of doing fuel oxidization.
So, indeed there is "best power" ratio of air to fuel that can be determined empirically with a WB A/F gauge and a dynomometer.
The shape of that curve is domed, so that the peak power occurs at about 12.6:1 and power falls off on either side of that ration. The fall off is at first gradual, so that if you are close to ideal you are pretty good. But if youi deviate very far from the "ideal" ratio, power begins to fall off rapidly.
So for optimum power you need to tune the A/F ratio at WOT across the RPM power band of your engine.
So, indeed there is "best power" ratio of air to fuel that can be determined empirically with a WB A/F gauge and a dynomometer.
The shape of that curve is domed, so that the peak power occurs at about 12.6:1 and power falls off on either side of that ration. The fall off is at first gradual, so that if you are close to ideal you are pretty good. But if youi deviate very far from the "ideal" ratio, power begins to fall off rapidly.
So for optimum power you need to tune the A/F ratio at WOT across the RPM power band of your engine.
