Fuel ?
06-13-2011, 08:22 AM
#1
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Fuel ? Not sure where to post this...
Tow rig, 07 Yukon Denali w/ 6.2L. Load, 3,500# boat. The first part of the trip I was running 93 octane ethanol fuel averaging 9.9-10. mpg. I stopped and filled up from 3/8 of a tank with 87 octane pure-gas non ethanol and was averaging 9.5 mpg on the dot. My question is, does the octane/ethanol change sound correct for MPG change? Denton, TX 93 octane was $3.90/gal and the 87 octane pure-gas was $3.44/gal. The pure-gas at this station in Witchita Falls had some major price jumps in octane levels, it jumped $3.44, $4.01, $4.51. I was shocked it jumped more than a dollar but it was 93 octane there as well. Let me know what you guys think of the pure-gas low octane running against ethanol high octane.
Tow rig, 07 Yukon Denali w/ 6.2L. Load, 3,500# boat. The first part of the trip I was running 93 octane ethanol fuel averaging 9.9-10. mpg. I stopped and filled up from 3/8 of a tank with 87 octane pure-gas non ethanol and was averaging 9.5 mpg on the dot. My question is, does the octane/ethanol change sound correct for MPG change? Denton, TX 93 octane was $3.90/gal and the 87 octane pure-gas was $3.44/gal. The pure-gas at this station in Witchita Falls had some major price jumps in octane levels, it jumped $3.44, $4.01, $4.51. I was shocked it jumped more than a dollar but it was 93 octane there as well. Let me know what you guys think of the pure-gas low octane running against ethanol high octane.
06-14-2011, 11:22 AM
#2
Given that gas gives you better mileage than the corn syrup, IMO octane is irrelevant unless you are having knocking issues.
The mileage calculations you got were probably not telling of the differences between Ethanol and Gas. Towing will make things very different depending if you are going up hill or down hill. Also, your tank was mixed. What does your owners manual say about this.
My understanding of dual fuel engines is that they sense the type of gas and adjust the engine accordingly. Not sure, but a mix might give you some odd results or the engine may take a conservative approach. I'll bet that if you drive without the tow and do a full tank of each, you'll find that the gas will give you better mileage.
The mileage calculations you got were probably not telling of the differences between Ethanol and Gas. Towing will make things very different depending if you are going up hill or down hill. Also, your tank was mixed. What does your owners manual say about this.
My understanding of dual fuel engines is that they sense the type of gas and adjust the engine accordingly. Not sure, but a mix might give you some odd results or the engine may take a conservative approach. I'll bet that if you drive without the tow and do a full tank of each, you'll find that the gas will give you better mileage.
06-14-2011, 09:31 PM
#3
you were running 10% ethanol 93 octane correct?
ethanol has a much lower air-to-fuel ratio, as a result you will burn more of it. An offset to ethanol blended fuel is that ethanol inherently has a higher octane rating so you can and should run a much higher compression ratio. The engine cannot change compression ratio, but what it can do is advance ignition timing to increase cylinder pressures and extract the power out of the ethanol. So from your observation I would guess the E10 at 93 octane while having lower A/F ratio ran much more ignition advance and you got the economy you did. And the 87 octane non-ethanol fuel ran with less ignition timing but had higher A/F ratio to offset it and economy was about the same.
I know on my ss which is a 6-speed I can hold 1500 rpm and under around town and up hills in 5th and 6th gear much better with 93 octane vs 87 octane, and all our gas is E10.
The real test would be to run a 93 octane gasoline with no ethanol and see what you get,
although real world driving like this can have too many variables to draw good conclusions, not to mention how much gas was in your tank before filling up.
ethanol has a much lower air-to-fuel ratio, as a result you will burn more of it. An offset to ethanol blended fuel is that ethanol inherently has a higher octane rating so you can and should run a much higher compression ratio. The engine cannot change compression ratio, but what it can do is advance ignition timing to increase cylinder pressures and extract the power out of the ethanol. So from your observation I would guess the E10 at 93 octane while having lower A/F ratio ran much more ignition advance and you got the economy you did. And the 87 octane non-ethanol fuel ran with less ignition timing but had higher A/F ratio to offset it and economy was about the same.
I know on my ss which is a 6-speed I can hold 1500 rpm and under around town and up hills in 5th and 6th gear much better with 93 octane vs 87 octane, and all our gas is E10.
The real test would be to run a 93 octane gasoline with no ethanol and see what you get,
although real world driving like this can have too many variables to draw good conclusions, not to mention how much gas was in your tank before filling up.
