Now I’ve heard of many guys switching to e85 but I don’t understand how you adjust fuel trims based on lambda values(assuming you have the injectors and fueling needed to do so) According to this graph Lambda for e85 at its stoichiometric efficiency would be 9.7:1 which would = 1 for lambda even thought for gas 14.7 = to 1L also. I don’t understand how the lambda values would be different for max load being too rich or lean if the stoichiometric values are the same. Someone help I’m confused…
Because Lambda is a ratio of AFR/AFR Stoich
RIght I know this but the problem is wouldn’t the lambda be different being that the 02 requirements are different so the lambda calculated by the ecu should be different.
… 02sensors tell the ecu how much 02’s in the exhaust so the product of combustion should be different. Say if max power lean and rich were between .9 and .85 with gasoline and e85 is between .86 and .71 shouldn’t lambbda with e85 be somewhere around .9 being stoichiometric if the product of 14.7:1 = 1 lambda for gasoline ?
English? What are you trying to do? Like I said Lambda = AFR/AFRstoich. Lambda is a ratio and is figured on the type of fuel you are using gasoline, E85, methanol, etc.
AFR is the AIR FUEL ratio and is independant on what type of fuel you are using. 13.0 AFR is the same no matter what fuel you use. The only thing that changes is what AFR that fuel is Stoich at
lets say I install 630cc injectors and a new inline pump to compensate for the fuel needed to have a stoichiometric A/F ratio. I get software for 630cc injectors but is for 93octane. I have to tweek primary fuel settings for this on the file. Would using my lambda values be the same with e85 as it would with regular gas trying to fine tune the software.
From talking to the swoleguy on vortex he said that the ecu has the ability to adjust fuel as long as the system has the capability to provide, I am still rather confused on it also. I think Lambda of 1.0 = 14.7:1 (on 93) = 9.75 (E85).
I think our confusion is we are trying to say that 1 on 93 is the same AF as 1 on E85, while stoichometrically they are but in AF terms they are different. I dunno correct me if I am wrong.
Don’t use Lambda when determining fuel requirements if the fuel has changed. The computer, if not designed to be a flex fuel vehicle, won’t know you have a different kind of fuel. Tune it for a desired air/fuel value based on the first column in the chart posted.
Also, if the car is not designed to run on E85 the fuel lines and some other associated components may not last as long as you’d like.
Most fuels today like from sunoco for instance can contain 5-15% ethanol. Vechicles post-1988 started to use different fuel system components because of corrosion. For instance my car has nylon fuel lines along with a inline/intake fuel pump that is more resistant to corrosion. I’m not certain about the intake mani gasket or head gasket and how well they’ll resist to corrosion but there have been a few running e85 for over a year on my engine. Also many subie and evo owners are switching over and have run e85 with no problems whatsoever for over 2 years.
There is a difference between 5% and 85% ethanol, one is obviously more effective at destroying fuel lines than the other. And many companies do build/buy better, more resistant fuel lines nowadays. Not all, and certainly not for older cars. It’s more of a blanket caution than an absolute rule.
And for any “mod” or “upgrade” people make, there is a chance it won’t work the same for you.
Max power rich and max power lean are guidelines/guesstimates of the lamda at which max power will be made assuming the proper timing adjustments for each lamda. They’re just guidelines and they assume zero knock limitation. You rarely end up at those values on gas, for example.
I think you’re also getting confused thinking about looking at AFRs on a gas calibrated sensor while running E85.
That is the same mistake I was making.
[I]What is the stiochiometric air-fuel ratio?
Internal combustion engines burn fuel to create kinetic energy. The burning of fuel is basically the reaction of the fuel with the oxygen in the air. The amount of oxygen present in the cylinder is the limiting factor for the amount of fuel can be burnt. If there’s too much fuel present, not all fuel will be burnt and un-burnt fuel will be pushed out through the exhaust valve. When building an engine, it’s very important to know the air-fuel ratio at which exactly all the available oxygen is used to burn the fuel and all the fuel is burnt completely. This ratio is called the stoichiometric air-fuel ratio.
Calculation
As already stated, the stoichiometric air-fuel ratio is the ratio at which all oxygen is used up and all fuel is completely burnt. This ratio is a basic property of a fuel and is the result of its chemical composition. Let’s for example look at natural gas (methane). When burning any carbon-based fuel, carbon dioxide and hydrogen are formed. Going back to the octane example, the following reaction equation describes the oxidation of the fuel:
CH4 + 2O2 -> CO2 + 2H20
of the atoms that make up octane and oxygen, we get the following numbers:
Carbon (C): 12,01
Oxygen (O): 16
Hydrogen (H): 1,008
So 1 molecule of methane has a molecular weight of: 1 * 12,01 + 4 * 1,008 = 16,042
One oxygen molecule weighs: 2 * 16 = 32.
The oxygen-fuel mass ratio is then: 2 * 32 / 1 * 16,042 = 64 / 16,042 = . So we need 3,99 kg of oxygen for every 1 kg of fuel. Since 23,2 mass-percent of air is actually oxygen, we need : 3,99 * 100/23,2 = 17,2 kg air for every 1 kg of methane. So the stoichiometric air-fuel ratio of methane is 17,2.
Common fuels
When the composition of a fuel is known, this method can be used to derive the stoichiometric air-fuel ratio. For the most common fuels, this, however, is not necessary because the ratio’s are known:
Gasoline: 14.7
Natural gas: 17.2
Propane: 15.5
Ethanol: 9
Methanol: 6.4
Hydrogen: 34
Diesel: 14,6
Interesting to see is that methanol and ethanol both have a very low air-fuel ratio, while the carbon chain length is comparable to methane and ethane. The answer to that is that alcohols like methanol and ethanol already carry oxygen themselves, which reduces the need for oxygen from air.
Conclusion
In order to be able to judge if an air-fuel mixture has the correct ratio of air to fuel, the stoichiometric air fuel ratio has to be known. If the composition of a fuel is known, this ratio can be calculated rather easily.
[/i]
Thank you 