But with a 10:1 compression ratio it should benefit from less knock on higher octane than 87. BTU's aside.
E15 acts differently in my 2 cars.
- Thread starter Pete in PA
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The difference in fuel economy isn't very much between E0, E10, and E15.
E10 gets -3.25% worse fuel economy than E0.
E15 gets -4.85% worse fuel economy than E0.
E85 gets -29.9% worse fuel economy than E0.
Let's take a theoretical truck getting 20.00 mpg at steady highway cruise. To obtain this with E0 and stoich AFR, over the course of that 20 miles, that truck's engine is consuming 91.29 lbs of air and 6.21 lbs of fuel. (14.7:1 AFR)
Let's say that truck switched to E10 which has a stoich AFR of 14.14. It commands more fuel but the air ingested is the same at 91.29 lbs.
91.29 / 14.14 = 6.46 lbs of fuel
Since ethanol is slightly more dense than gasoline (SpG = .79 vs .74), we have to account for that. A gallon of straight gasoline weighs 6.21 lbs while a gallon of ethanol weighs 6.59 lbs. Thus, a gallon of E10 weighs 6.25 lbs.
6.46 / 6.25 = 1.0336 correction factor for volume
20.00 mpg / 1.0336 = 19.35 mpg (-0.65 mpg or -3.25%)
That same engine switching to E15...
91.29 / 13.85 = 6.59 lbs of fuel
(6.59 x .15) + (6.21 x .85) = 6.27 lbs per gallon for E15
6.59 / 6.27 = 1.051 correction factor
20.00 mpg / 1.051 = 19.03 mpg (-0.97 mpg or -4.85%)
If you're seeing a larger difference than that, something else is causing it. (usually driver input)
We'll throw in E85 (AFR = 9.8, weight = 6.53 lbs/gal) just for S&G.
91.29 lbs / 9.8 = 9.32 lbs of fuel
9.32 / 6.53 = 1.427 correction factor
20.00 mpg / 1.427 = 14.02 mpg (-5.98 mpg or -29.9%)
E10 gets -3.25% worse fuel economy than E0.
E15 gets -4.85% worse fuel economy than E0.
E85 gets -29.9% worse fuel economy than E0.
Let's take a theoretical truck getting 20.00 mpg at steady highway cruise. To obtain this with E0 and stoich AFR, over the course of that 20 miles, that truck's engine is consuming 91.29 lbs of air and 6.21 lbs of fuel. (14.7:1 AFR)
Let's say that truck switched to E10 which has a stoich AFR of 14.14. It commands more fuel but the air ingested is the same at 91.29 lbs.
91.29 / 14.14 = 6.46 lbs of fuel
Since ethanol is slightly more dense than gasoline (SpG = .79 vs .74), we have to account for that. A gallon of straight gasoline weighs 6.21 lbs while a gallon of ethanol weighs 6.59 lbs. Thus, a gallon of E10 weighs 6.25 lbs.
6.46 / 6.25 = 1.0336 correction factor for volume
20.00 mpg / 1.0336 = 19.35 mpg (-0.65 mpg or -3.25%)
That same engine switching to E15...
91.29 / 13.85 = 6.59 lbs of fuel
(6.59 x .15) + (6.21 x .85) = 6.27 lbs per gallon for E15
6.59 / 6.27 = 1.051 correction factor
20.00 mpg / 1.051 = 19.03 mpg (-0.97 mpg or -4.85%)
If you're seeing a larger difference than that, something else is causing it. (usually driver input)
We'll throw in E85 (AFR = 9.8, weight = 6.53 lbs/gal) just for S&G.
91.29 lbs / 9.8 = 9.32 lbs of fuel
9.32 / 6.53 = 1.427 correction factor
20.00 mpg / 1.427 = 14.02 mpg (-5.98 mpg or -29.9%)
Ethanol has less energy when only looking at the fuel alone. However, we don't burn fuel alone. It's an air/fuel mixture by mass. Thus, you have to consider stoichiometry. When factored for stoich AFR, ethanol produces more energy than gasoline.
Gasoline = 20,012 BTU/lb ÷ 14.7 AFR = 1,361 BTU/lb of stoich air
Ethanol = 12,506 BTU/lb ÷ 9.0 AFR = 1,390 BTU/lb of stoich air
The octane rating doesn't correlate well with ethanol and methanol due to factors that are outside the control of octane testing, mainly heat of vaporization. (cooling factor) The octane rating is just a measure of the auto-ignition point of the end gases and nothing more. Ethanol has +455% better air charge cooling than gasoline and that cooler air is more resistant to detonation and pre-ignition. An "88 octane" E15 is roughly equivalent to a 91 octane straight gasoline in terms of detonation resistance due to this cooling factor.
Gas = 9.7 BTU/lb of stoich air (cooling)
E10 = 13.1 BTU/lb of stoich air (+35%)
E15 = 14.9 BTU/lb of stoich air (+54%)
E85 = 38.9 BTU/lb of stoich air (+401%)
This is why E85, with a loose octane rating of only ~100, has equivalent detonation resistance of ~116 octane race gas.
With modern pentroof chambers and direct injection, an engine with 10:1 static compression will likely produce max power available on regular 87. The chamber shape makes a huge difference in mitigating conflicting flame fronts that promote hot spots and detonation.
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OK. does it call for just 87 octane or more?
It might be putting the 88 octane to good use and supercedes the less energy available.
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This is what I would theorize.
While it only calls for 87 octane, it does have a knock sensor and the 88 octane E15 might allow for a little more timing advance.
Blame the autism.
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What I think is going on is that Chevy and maybe more makers only "say" it only requires 87 octane.
Would be a sales killer to say 93 required.
The facts are with a turbo, knock sensor, etc. Yes, it runs on 87, but it's not optimal.
You get more power and mpg on higher octane.
This has been the concensus on the Cruze forum.
Doesn't explain the Trax though. I should try another tank in it.
Would be a sales killer to say 93 required.
The facts are with a turbo, knock sensor, etc. Yes, it runs on 87, but it's not optimal.
You get more power and mpg on higher octane.
This has been the concensus on the Cruze forum.
Doesn't explain the Trax though. I should try another tank in it.
I think in my truck, when towing a 7k trailer, the slight increase in throttle angle needed with e-15 especially on a slight grade, causes the ecm to move up a gear( down?) for more rpm, and holds that rpm vs 93 octane e-10.
There shouldn't have been a change in throttle opening, only a change in injector pulse. The power output should've been the same with fuel management just commanding +1.6% more fuel.
Dodge product problems
He should try efree as I recommended, some vehicles do better on it, others worse.
If he does better on efree RUG, we know the reason, if he does worse on <=93 efree, we also know the reason.
It wouldn’t surprise me if a Dodge product is getting better MPGs and spewing higher amounts of a particular type of pollution on 93.
If he were to monitor and tune he could probably do better on whatever fuel he wants to target.
