Ethanol blend question
#1
01-01-2011, 12:40 PM
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Ethanol blend question
I posted this same thread on PHP's forum, but it's pretty slow over there so I figured I would post the same over here to see if I could get some responses.
I have an '07 F150 4x4 5.4L. Ordered a gryphon cs with 3 custom tunes last week (87&93 performance and 87 tow). I swore there was a question on the order form that asked if your area sold ethanol blended gasoline, and I answered no. When looking back over my order today I could not find that question on my form. The problem is I do believe my local gas stations sell an ethanol blend. Will this cause any problems with my custom tunes, since I answered no? Our am I just going crazy and that wasn't even a question on the order form? Thanks for the help!!!
I have an '07 F150 4x4 5.4L. Ordered a gryphon cs with 3 custom tunes last week (87&93 performance and 87 tow). I swore there was a question on the order form that asked if your area sold ethanol blended gasoline, and I answered no. When looking back over my order today I could not find that question on my form. The problem is I do believe my local gas stations sell an ethanol blend. Will this cause any problems with my custom tunes, since I answered no? Our am I just going crazy and that wasn't even a question on the order form? Thanks for the help!!!
#2
01-01-2011, 04:34 PM
This is a fair explanation of what happens with ethanol added:
Tuning Tip: Ethanol Content
"We've had a few reports where users could not “nail down” their tune on the street with the LM-1. The AFR's would jump about 0.5 AFR across the WOT band even in the same weather conditions in the space of a few days. Instead of holding a tune, the engine seemed to slowly “yodel.”
Naturally the first thing to blame was the LM-1. But it turned out that the users filled up at different gas stations, sometimes filling up on gas that had 10% ethanol mixed in. As expected, when Schnapps is mixed with cars, things get a little complicated.
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.
Until next time... Keep On Tuning!"
-Innovate Motorsports
A richer blend is poor for gas mileage, but still safe.
Tuning Tip: Ethanol Content
"We've had a few reports where users could not “nail down” their tune on the street with the LM-1. The AFR's would jump about 0.5 AFR across the WOT band even in the same weather conditions in the space of a few days. Instead of holding a tune, the engine seemed to slowly “yodel.”
Naturally the first thing to blame was the LM-1. But it turned out that the users filled up at different gas stations, sometimes filling up on gas that had 10% ethanol mixed in. As expected, when Schnapps is mixed with cars, things get a little complicated.
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.
Until next time... Keep On Tuning!"
-Innovate Motorsports
A richer blend is poor for gas mileage, but still safe.
#3
01-01-2011, 04:46 PM
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#4
01-01-2011, 05:32 PM
This is from the 2010 MY OBD System Operation, Summary for Gasoline Engines:
Ford Motor Company is cooperating with the Department of Energy in providing customers with vehicles capable of using alcohol-blended fuels. These fuels are renewable and can lower some engine emission byproducts. The original 1993 Taurus vehicle hardware and calibration were designed for use on any combination of gasoline or methanol up to 85% methanol. Current flex fuel vehicles, however, are no longer designed for methanol, but are designed to be compatible with any combination of gasoline and ethanol, up to 85% ethanol.
This flexible fuel capability allows the vehicle to be usable in all regions of the country, even as the alcohol infrastructure is being built. Operation of a vehicle with the alcohol-blended fuels is intended to be transparent to the customer. Drivability, NVH, and other attributes are not notably different when using the alcohol-blended fuels.
The higher octane of alcohol-blended fuels allows a small increase in power and performance (approximately 4%), but this is offset by the lower fuel economy (approximately 33%) due to the lower energy content. Cold starts with alcohol-blended fuels are somewhat more difficult than with gasoline due to the lower volatility of alcohol-blended fuels; 10% vaporization occurs at approximately 100 °F for gasoline vs. 160 °F for 85% ethanol. Ethanol requires approximately 37% more flow than gasoline due to a lower heating value (29.7 vs. 47.3 MJ/kg). Consequently, Flex Fuel vehicles require higher flow injectors than their gasoline counterparts. This results in a smaller fuel pulse widths with gasoline and makes the task of purging the canister more difficult during idles and decels.
In order to maintain proper fuel control, the PCM strategy needs to know the stoichiometric Air/Fuel Ratio for use in the fuel pulse width equation. On pre-2000 MY flex fuel vehicles, the percent alcohol in the fuel was determined by reading the output of the Flex fuel Sensor. The percent alcohol was stored in a register called Percent Methanol (PM). Although current alcohol-blended fuels only include ethanol, the percent methanol nomenclature has persisted. On 2000 MY and later vehicles, the Flex Fuel Sensor has been deleted and PM is inferred. The strategy to infer the correct A/F Ratio (AFR) relies on the oxygen sensor input to maintain stoichiometry after vehicle refueling occurs.
This flexible fuel capability allows the vehicle to be usable in all regions of the country, even as the alcohol infrastructure is being built. Operation of a vehicle with the alcohol-blended fuels is intended to be transparent to the customer. Drivability, NVH, and other attributes are not notably different when using the alcohol-blended fuels.
The higher octane of alcohol-blended fuels allows a small increase in power and performance (approximately 4%), but this is offset by the lower fuel economy (approximately 33%) due to the lower energy content. Cold starts with alcohol-blended fuels are somewhat more difficult than with gasoline due to the lower volatility of alcohol-blended fuels; 10% vaporization occurs at approximately 100 °F for gasoline vs. 160 °F for 85% ethanol. Ethanol requires approximately 37% more flow than gasoline due to a lower heating value (29.7 vs. 47.3 MJ/kg). Consequently, Flex Fuel vehicles require higher flow injectors than their gasoline counterparts. This results in a smaller fuel pulse widths with gasoline and makes the task of purging the canister more difficult during idles and decels.
In order to maintain proper fuel control, the PCM strategy needs to know the stoichiometric Air/Fuel Ratio for use in the fuel pulse width equation. On pre-2000 MY flex fuel vehicles, the percent alcohol in the fuel was determined by reading the output of the Flex fuel Sensor. The percent alcohol was stored in a register called Percent Methanol (PM). Although current alcohol-blended fuels only include ethanol, the percent methanol nomenclature has persisted. On 2000 MY and later vehicles, the Flex Fuel Sensor has been deleted and PM is inferred. The strategy to infer the correct A/F Ratio (AFR) relies on the oxygen sensor input to maintain stoichiometry after vehicle refueling occurs.
#6
01-01-2011, 10:03 PM
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It's different in different areas. Around here you'd be hard pressed to know as all the stations have the stickers that say the gas "may" have up to 10%. I know of just a few stations that will have some straight gas. There is only one very close to me and only 93 is straight gas, only because its a small family owned station and customers have asked for straight 93 especially. Since hardly anyone buys 93 anyway its not a big deal. I have bought it when running my 93 tunes. But I have my tunes setup for blended as you could be anywhere.
