Tuning issues...
04-22-06, 11:09 PM
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rotary sensei
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Tuning issues...
Saw this on another forum...
Reformulated gasoline (RFG)..........tuning issues?
If ethanol (stoich AFR of 9) is mixed with gasoline (stoich AFR of 14.7) the resulting gas has a lower stoich AFR than 'pure' gasoline. As the fuel injection is tuned to mix a certain amount of fuel for a given amount of air, the resulting mixture would be leaner when using a fuel with lower stoich AFR.
This can be calculated:
sAFR = (%ofAdditive * sAFRadditive + (90-%ofAdditive) * sAFRgas) /100
where:
sAFR is resulting stoich AFR
%ofAdditive is amount in % of mass of additive (ethanol) mixed in
sAFRadditive is stoich AFR of additive (9 for ethanol)
sAFRgas is stoich AFR of base gasoline (14.7)
For a 10% mixture of ethanol to gasoline by mass the resulting stoich AFR is 14.13
So, for an engine that's tuned to certain AFR at a certain load and RPM on straight gas, the resulting (gasoline equivalent) AFR when running the mixture can be calculated as:
new AFR = tuned gas AFR * (gasoline stoich ratio) / blend stoich ratio
An engine tuned to 12.5 gas AFR will run at the equivalent of 13 gas AFR with a 10% ethanol blend. This is what these people were seeing.
Of course, when running in closed loop, the engine will run at 14.13 AFR instead of 14.7. O2 sensors (incl. widebands) don’t measure AFR, but Lambda. Lambda is defined as actual AFR/stoich AFR. It's a ratio. In closed loop part throttle the engine is just running at Lambda 1.0, regardless of fuel. The same would be true for other Lambda values when running closed loop at WOT using a wideband. The engine would run at the tuned Lambda and everything would be fine. Open loop systems would need to be retuned for alcohol blends though.
The bad news is that WOT fueling in the cars I have knowledge of is a form of open loop so you will be fine driving around day to day but WOT fueling will be effected, this becomes particularly inportant in Forced Induction applications.
Ok, So I guess we need to know the stoich of the old MBTE and % used or whatever the stuff is, that this ethanol is replacing.
Some more details:
http://yarchive.net/car/oxygenates.html
Now I will have no choice...............this pretty much covers it:
Chevron Gasoline Questions and Answers - Federal Reformulated Gasoline
What is reformulated gasoline?
Reformulated gasoline (RFG) is a general term for federally mandated gasoline that is specially processed and blended to reduce the emission of pollutants such as hydrocarbons, toxics, and nitrogen oxides. When compared to typical gasoline that you have used in the past, RFG reduces hydrocarbon emissions by at least 15%, according to EPA estimates. While all suppliers and marketers of RFG are required to meet federal specifications for the base product, Chevron blends RFG with our exclusive Techron® additive to ensure unbeatable performance.
Where in Chevron's gasoline marketing area is reformulated gasoline required?
RFG is currently required in California (Los Angeles, San Diego, and Sacramento), Texas (Houston and Dallas-Fort Worth), Kentucky (Louisville and Covington), Virginia (Richmond and Norfolk), and Washington, D.C.
Will I notice a change in my car's performance using RFG?
You should not notice any changes in the way your car drives as a result of using RFG. However, the introduction of RFG brings several federally mandated changes to gasoline chemistry, which raise some performance issues. These potential changes in performance affect all gasolines in an RFG regulated area and are not unique to Chevron.
RFG contains "oxygenates," which lower emissions but also produce less energy, so RFG will yield two to three percent lower mileage than non-oxygenated gasoline.
RFG will have an odor slightly different from that of conventional gasoline.
The rubber that is used in fuel system parts, such as seals and hoses, may shrink, swell, or lose strength when exposed to RFG. This reaction could cause fuel system leaks in a very small percentage of vehicles. Because RFG differs only slightly from the gasoline that you have used in the past, auto manufacturers do not expect RFG to cause fuel system leaks in the majority of vehicles, particularly newer vehicles. However, if your vehicle is older (more than 10 years old) or has high mileage (more than 100,000 miles), you may be at greater risk of developing a fuel leak. Because fuel leaks can cause vehicle fires, Chevron recommends that you consult a qualified auto repair technician to discuss whether your fuel system parts should be checked for repair or replacement. If you suspect a form of leakage, which can often be detected by smelling gasoline at times other than when fueling, consult a qualified auto repair technician immediately. Do not drive a vehicle with a fuel system leak.
All gasoline, including RFG, is very flammable and always should be used and stored with extreme care. In order to reduce pollution, RFG sold during the spring and summer is designed to evaporate less than the gasoline you have used in the past. This could cause the vapor in an RFG storage container to contain oxygen, which would make the mixture flammable at very cold temperatures (less than 20 degrees Farenheit). If you expect that you may store or use spring or summer RFG in very cold temperatures, it may be prudent to keep your storage container as full as possible to minimize vapor space, and to ensure that the container does not have sources of ignition.
During the spring, when less evaporative RFG is phased in for summer use, starting your engine may be more difficult when it is unseasonably cold because RFG, with its lower tendency to evaporate, will not ignite as easily.
One of the local fellow gear heads I trust.............
Ok so where is the big advantage of having to burn more "clean gas" I know when I lived in Ca. and had to deal with this crap gas that I had to back the timing down in my HCI 306 mustang and my mileage was ****. When I drove back east I strarted getting 3- 4 mpg more as I got away from the "clean" gas of Ca and started running the dirty stuff. So 4 mpg is roughly a 20% increase in fuel economy. Does this "clean" gas drop emissions by that? If not its pointless and just another way to make us buy more gas. It doesn't take a genius to figure out that if you use more oxygen in a closed loop efi motor that it is going to have to use more fuel to achieve the same AFR.
Reformulated gasoline (RFG)..........tuning issues?
If ethanol (stoich AFR of 9) is mixed with gasoline (stoich AFR of 14.7) the resulting gas has a lower stoich AFR than 'pure' gasoline. As the fuel injection is tuned to mix a certain amount of fuel for a given amount of air, the resulting mixture would be leaner when using a fuel with lower stoich AFR.
This can be calculated:
sAFR = (%ofAdditive * sAFRadditive + (90-%ofAdditive) * sAFRgas) /100
where:
sAFR is resulting stoich AFR
%ofAdditive is amount in % of mass of additive (ethanol) mixed in
sAFRadditive is stoich AFR of additive (9 for ethanol)
sAFRgas is stoich AFR of base gasoline (14.7)
For a 10% mixture of ethanol to gasoline by mass the resulting stoich AFR is 14.13
So, for an engine that's tuned to certain AFR at a certain load and RPM on straight gas, the resulting (gasoline equivalent) AFR when running the mixture can be calculated as:
new AFR = tuned gas AFR * (gasoline stoich ratio) / blend stoich ratio
An engine tuned to 12.5 gas AFR will run at the equivalent of 13 gas AFR with a 10% ethanol blend. This is what these people were seeing.
Of course, when running in closed loop, the engine will run at 14.13 AFR instead of 14.7. O2 sensors (incl. widebands) don’t measure AFR, but Lambda. Lambda is defined as actual AFR/stoich AFR. It's a ratio. In closed loop part throttle the engine is just running at Lambda 1.0, regardless of fuel. The same would be true for other Lambda values when running closed loop at WOT using a wideband. The engine would run at the tuned Lambda and everything would be fine. Open loop systems would need to be retuned for alcohol blends though.
The bad news is that WOT fueling in the cars I have knowledge of is a form of open loop so you will be fine driving around day to day but WOT fueling will be effected, this becomes particularly inportant in Forced Induction applications.
Ok, So I guess we need to know the stoich of the old MBTE and % used or whatever the stuff is, that this ethanol is replacing.
Some more details:
http://yarchive.net/car/oxygenates.html
Now I will have no choice...............this pretty much covers it:
Chevron Gasoline Questions and Answers - Federal Reformulated Gasoline
What is reformulated gasoline?
Reformulated gasoline (RFG) is a general term for federally mandated gasoline that is specially processed and blended to reduce the emission of pollutants such as hydrocarbons, toxics, and nitrogen oxides. When compared to typical gasoline that you have used in the past, RFG reduces hydrocarbon emissions by at least 15%, according to EPA estimates. While all suppliers and marketers of RFG are required to meet federal specifications for the base product, Chevron blends RFG with our exclusive Techron® additive to ensure unbeatable performance.
Where in Chevron's gasoline marketing area is reformulated gasoline required?
RFG is currently required in California (Los Angeles, San Diego, and Sacramento), Texas (Houston and Dallas-Fort Worth), Kentucky (Louisville and Covington), Virginia (Richmond and Norfolk), and Washington, D.C.
Will I notice a change in my car's performance using RFG?
You should not notice any changes in the way your car drives as a result of using RFG. However, the introduction of RFG brings several federally mandated changes to gasoline chemistry, which raise some performance issues. These potential changes in performance affect all gasolines in an RFG regulated area and are not unique to Chevron.
RFG contains "oxygenates," which lower emissions but also produce less energy, so RFG will yield two to three percent lower mileage than non-oxygenated gasoline.
RFG will have an odor slightly different from that of conventional gasoline.
The rubber that is used in fuel system parts, such as seals and hoses, may shrink, swell, or lose strength when exposed to RFG. This reaction could cause fuel system leaks in a very small percentage of vehicles. Because RFG differs only slightly from the gasoline that you have used in the past, auto manufacturers do not expect RFG to cause fuel system leaks in the majority of vehicles, particularly newer vehicles. However, if your vehicle is older (more than 10 years old) or has high mileage (more than 100,000 miles), you may be at greater risk of developing a fuel leak. Because fuel leaks can cause vehicle fires, Chevron recommends that you consult a qualified auto repair technician to discuss whether your fuel system parts should be checked for repair or replacement. If you suspect a form of leakage, which can often be detected by smelling gasoline at times other than when fueling, consult a qualified auto repair technician immediately. Do not drive a vehicle with a fuel system leak.
All gasoline, including RFG, is very flammable and always should be used and stored with extreme care. In order to reduce pollution, RFG sold during the spring and summer is designed to evaporate less than the gasoline you have used in the past. This could cause the vapor in an RFG storage container to contain oxygen, which would make the mixture flammable at very cold temperatures (less than 20 degrees Farenheit). If you expect that you may store or use spring or summer RFG in very cold temperatures, it may be prudent to keep your storage container as full as possible to minimize vapor space, and to ensure that the container does not have sources of ignition.
During the spring, when less evaporative RFG is phased in for summer use, starting your engine may be more difficult when it is unseasonably cold because RFG, with its lower tendency to evaporate, will not ignite as easily.
One of the local fellow gear heads I trust.............
Ok so where is the big advantage of having to burn more "clean gas" I know when I lived in Ca. and had to deal with this crap gas that I had to back the timing down in my HCI 306 mustang and my mileage was ****. When I drove back east I strarted getting 3- 4 mpg more as I got away from the "clean" gas of Ca and started running the dirty stuff. So 4 mpg is roughly a 20% increase in fuel economy. Does this "clean" gas drop emissions by that? If not its pointless and just another way to make us buy more gas. It doesn't take a genius to figure out that if you use more oxygen in a closed loop efi motor that it is going to have to use more fuel to achieve the same AFR.
im still trying to figure out what that says... 
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