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Thread: Clear gas in Oregon

  1. #19
    Registered User Styhl's Avatar
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    Ya you mentioned all that in my car thread I have to get some money and jog down to Dallas and find a tune shop

  2. #20
    Registered User Other_Erik's Avatar
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    Unfortunately don't have "before" data in the RS, but I can speak to local blends here from other vehicles

    Previous car: 2002 Grand Prix GTP (Supercharged 6-cyl, "Bulletproof" GM 3800 Series 2 Engine)
    Gas mileage on Premium (93 Octane) before Ethanol mandate wiped out clear gas in my area:
    21.2mpg calculated, info center in the car displayed 21.9-22.1mpg. This was 90% city, 10% highway driving
    Only have a single 400-mile road trip to compare for more highway driving: 27.7mpg calculated, 27.0mpg on the infocenter at 99% highway, 1% city

    Gas mileage on Premium (93 Octane) after Ethanol mandate: 12.2mpg calculated, 12.4mpg infocenter. 90% city, 10% highway driving
    Road trip mileage: 15.4mpg calculated and spot on on the infocenter, 95% highway, 5% city driving on 3 road trips at 250-400 miles each

    And now I'm starting to see the signs on the gas pumps change. Thankfully VA law states they must label the pump with the blend they use. Recent change has been the 10% sticker getting covered up with a sticker that states the gas may be up to 15% ethanol.
    What in the ever-loving fuck?

    Some simple data for you, pruned from http://www.afdc.energy.gov/fuels/fue...ison_chart.pdf

    Gasoline energy content: 116090 btu/gal. Dependent on additives, octane ratings commercially available between 81 and 110 R+M/2
    Ethanol energy content: 76330 btu/gal. Generally accepted as 127 octane (dervied from the same R+M/2 formula)

    Taken a step further, if you want 93 Octane in a 10% ethanol blend, you mix the following:
    0.9 gallons of clear-gas 90 octane (104481 BTU)
    0.1 gallons of ethanol 127 octane (7633 BTU)
    and end up with 1 gallon of blend, with an approximate energy content of 112114 BTU (96.5% of the energy content of clear-gas)

    But wait, you say, shouldn't I get 96.5% of my old gas mileage? In a perfect world, yes, you should.
    However, since burning clear gas and burning ethanol emit different chemical signatures, you are tricking your vehicle in two ways:
    1st, with the lower energy content (even at best, only 3.5% lower) of ethanol-blended gas, your car must increase fuel flow by 3.5% to compensate for the energy content difference. By increasing the fuel flow, your car must also take in more air to reach what it believes is stoichiometry (in clear-gas only, that's 14.7 parts air to 1 part fuel in the combustion chamber at time of detonation), BUUUUUUT ethanol has a different stoichiometric ratio, at roughly 9 parts air to 1 part fuel. This means your 14.7 parts of air to 1 part of ethanol blend is really LEAN (too much air) (14.7 * .9)+(9*.1)=14.13 parts of air to 1 part of fuel in true stoichiometry for 10% ethanol. Your fuel consumption is up 3.5%, your air intake is up 3.5%, but your air:fuel mixture is out of whack by ~4% to the lean side. This makes your oxygen sensors read too much air in the mix, which causes the car to push more fuel into the combustion chamber to compensate (by ~4.17%) to reach the 14.13:1 stoichiometric ratio needed. This skews your STFT and LTFT (Short Term, and Long Term Fuel Trim) tables, by ~7.5%.

    I could go on, but I'm already hurting my own head with this. I've given you guys the first couple paragraphs of what I could expand into a doctoral thesis. Questions?

    O_E
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  3. #21
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    Doesn't the computer just look at the lambdas and adjust from that? Therefore eliminating any difference from fuels?

  4. #22
    Registered User Other_Erik's Avatar
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    Quote Originally Posted by JayB View Post
    Doesn't the computer just look at the lambdas and adjust from that? Therefore eliminating any difference from fuels?
    Eventually it's supposed to, but as the STFT's transition to LTFT's, lambda levels out and pretty much tricks the ECU into sticking with dumping ~7.5% extra fuel.

    The single upside to this situation is that we run just a hair cooler since ethanol has a higher flash point but slighly lower burn temp. Maybe not even an upside when you consider that we're basically negating that by running twin turbocharged...


    Long story short: It's a much more complicated system with more variables than would fit in less than a whole lot of pages, but any environmental good they determine comes from using 10% (or more) ethanol is negated and then some because you're burning 7.5% more fuel (again, or more...)
    #905530 - Brilliant Black on Ebony. Sorted, running strong, ready for a new owner.
    No, I am not the board admin - that's Erik (from Sweden), I'm Other_Erik (from the US)

  5. #23
    Registered User lswing's Avatar
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    Funny, my logs say I'm dumping in 25% extra fuel...oh wait, I did that with the tune Think I lost about 1mpg around town...depends on the lead foot.
    Ace/Edge TC - Tozo Trans - MTM TCU - REVO/ME7 tune - Wagner IC's w/ Venair Hoses - Aux Radiator delete - Hotchkis Sways - Hawk HPS Pads - Koni Sport Struts - Scroll KO4 Turbos - Devil's Own WM - 421whp/452wtq on Mustang Dyno - http://www.audirssix.com

  6. #24
    Registered User Other_Erik's Avatar
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    Quote Originally Posted by lswing View Post
    Funny, my logs say I'm dumping in 25% extra fuel...oh wait, I did that with the tune Think I lost about 1mpg around town...depends on the lead foot.
    You... you're a funny man, Sol. Tell you what - just for that, I'll kill you last. How's that sound?

    But seriously. Driving an RS6 and worrying about poor fuel mileage is like driving a boat and worrying about it getting wet.
    I'm only annoyed because the same number of miles, I could be making about a quarter less stops to gas up.

    Enough with the beating of the dead horse, I suppose.

    Back to your regularly scheduled thread, already in progress...
    #905530 - Brilliant Black on Ebony. Sorted, running strong, ready for a new owner.
    No, I am not the board admin - that's Erik (from Sweden), I'm Other_Erik (from the US)

  7. #25
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    I want to beat the dead epa horse!

  8. #26
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    Best post of the year! Thank you for the input.

    Start a new thread with this topic

    Quote Originally Posted by Other_Erik View Post
    Unfortunately don't have "before" data in the RS, but I can speak to local blends here from other vehicles

    Previous car: 2002 Grand Prix GTP (Supercharged 6-cyl, "Bulletproof" GM 3800 Series 2 Engine)
    Gas mileage on Premium (93 Octane) before Ethanol mandate wiped out clear gas in my area:
    21.2mpg calculated, info center in the car displayed 21.9-22.1mpg. This was 90% city, 10% highway driving
    Only have a single 400-mile road trip to compare for more highway driving: 27.7mpg calculated, 27.0mpg on the infocenter at 99% highway, 1% city

    Gas mileage on Premium (93 Octane) after Ethanol mandate: 12.2mpg calculated, 12.4mpg infocenter. 90% city, 10% highway driving
    Road trip mileage: 15.4mpg calculated and spot on on the infocenter, 95% highway, 5% city driving on 3 road trips at 250-400 miles each

    And now I'm starting to see the signs on the gas pumps change. Thankfully VA law states they must label the pump with the blend they use. Recent change has been the 10% sticker getting covered up with a sticker that states the gas may be up to 15% ethanol.
    What in the ever-loving fuck?

    Some simple data for you, pruned from http://www.afdc.energy.gov/fuels/fue...ison_chart.pdf

    Gasoline energy content: 116090 btu/gal. Dependent on additives, octane ratings commercially available between 81 and 110 R+M/2
    Ethanol energy content: 76330 btu/gal. Generally accepted as 127 octane (dervied from the same R+M/2 formula)

    Taken a step further, if you want 93 Octane in a 10% ethanol blend, you mix the following:
    0.9 gallons of clear-gas 90 octane (104481 BTU)
    0.1 gallons of ethanol 127 octane (7633 BTU)
    and end up with 1 gallon of blend, with an approximate energy content of 112114 BTU (96.5% of the energy content of clear-gas)

    But wait, you say, shouldn't I get 96.5% of my old gas mileage? In a perfect world, yes, you should.
    However, since burning clear gas and burning ethanol emit different chemical signatures, you are tricking your vehicle in two ways:
    1st, with the lower energy content (even at best, only 3.5% lower) of ethanol-blended gas, your car must increase fuel flow by 3.5% to compensate for the energy content difference. By increasing the fuel flow, your car must also take in more air to reach what it believes is stoichiometry (in clear-gas only, that's 14.7 parts air to 1 part fuel in the combustion chamber at time of detonation), BUUUUUUT ethanol has a different stoichiometric ratio, at roughly 9 parts air to 1 part fuel. This means your 14.7 parts of air to 1 part of ethanol blend is really LEAN (too much air) (14.7 * .9)+(9*.1)=14.13 parts of air to 1 part of fuel in true stoichiometry for 10% ethanol. Your fuel consumption is up 3.5%, your air intake is up 3.5%, but your air:fuel mixture is out of whack by ~4% to the lean side. This makes your oxygen sensors read too much air in the mix, which causes the car to push more fuel into the combustion chamber to compensate (by ~4.17%) to reach the 14.13:1 stoichiometric ratio needed. This skews your STFT and LTFT (Short Term, and Long Term Fuel Trim) tables, by ~7.5%.

    I could go on, but I'm already hurting my own head with this. I've given you guys the first couple paragraphs of what I could expand into a doctoral thesis. Questions?

    O_E

  9. #27
    Registered User ben916's Avatar
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    Quote Originally Posted by DHall1 View Post
    I want to beat the dead epa horse!
    This post is worthless without the Benny Hill Dead Horse gif...
    Last edited by ben916; July 21st, 2014 at 22:59. Reason: not Monty Python
    SOLD - 03 RS6 Avus (905355)
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