No gains from e85
Ugh.
First, the stochiometric ratio used is from gas stochiometry, thus using molecular mass. That's why gasoline's 14.7:1, instead of the more obvious 12.5:1, as the reaction would normally imply.
http://en.wikipedia.org/wiki/Stochio..._stoichiometry
Gasoline: 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O
Ethanol: C2H5OH + 3 O2 → 2 CO2 + 3 H2O
Stochiometric points: http://ethanolpro.tripod.com/id213.html
Energy densities of different fuels:
http://en.wikipedia.org/wiki/Energy_...nal_components
OK. Now, basic math. To get from 1.0 to 1.5 you add half of the original back to the original. That's +50%. (And not 33%; you're stating a percentage of the original, not a percentage of the final product.)
If you're only running 25% more fuel than you were before you're either running dangerously lean, or you *were* running stuidly rich beforehand. In which case you *still* might be running lean.
Also, that doesn't take into account how the E85 cools the intake charge when atomized more than gasoline, and thanks to the Ideal Gas Law, the charge would decrease in volume (meaning more charge in the same volume, since your intake pipes don't shrink), thus needing even more fuel than the 50% increase. My post was just a point that for a given volume, a stochiometric blending of gasoline and air produces less heat energy than a stochiometric blending of E85 and air.
Something you're gonna want to look out for is that because you're running a whole lot more fuel, there's an increased risk of hydrolocking your engine, especially with high-compression pistons and heads.
OK. MPG's are a different thing. From Wyotech, the average MPG loss converting a naturally-aspirated engine to E-85 is about a 20% - 25% loss or so. Forced-induction engines only suffer about a 10% loss. The difference from the 50% more fuel and the 25% MPG loss probably comes from the efficiency increase that comes with burning a simpler fuel. (And forced-induction engines suffer less of a loss because they're able to take advantage of E85's higher octane rating easier than a naturally-aspirated engine, thus increasing efficiency more.)
First, the stochiometric ratio used is from gas stochiometry, thus using molecular mass. That's why gasoline's 14.7:1, instead of the more obvious 12.5:1, as the reaction would normally imply.
http://en.wikipedia.org/wiki/Stochio..._stoichiometry
Gasoline: 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O
Ethanol: C2H5OH + 3 O2 → 2 CO2 + 3 H2O
Stochiometric points: http://ethanolpro.tripod.com/id213.html
Energy densities of different fuels:
http://en.wikipedia.org/wiki/Energy_...nal_components
OK. Now, basic math. To get from 1.0 to 1.5 you add half of the original back to the original. That's +50%. (And not 33%; you're stating a percentage of the original, not a percentage of the final product.)
If you're only running 25% more fuel than you were before you're either running dangerously lean, or you *were* running stuidly rich beforehand. In which case you *still* might be running lean.
Also, that doesn't take into account how the E85 cools the intake charge when atomized more than gasoline, and thanks to the Ideal Gas Law, the charge would decrease in volume (meaning more charge in the same volume, since your intake pipes don't shrink), thus needing even more fuel than the 50% increase. My post was just a point that for a given volume, a stochiometric blending of gasoline and air produces less heat energy than a stochiometric blending of E85 and air.
Something you're gonna want to look out for is that because you're running a whole lot more fuel, there's an increased risk of hydrolocking your engine, especially with high-compression pistons and heads.
OK. MPG's are a different thing. From Wyotech, the average MPG loss converting a naturally-aspirated engine to E-85 is about a 20% - 25% loss or so. Forced-induction engines only suffer about a 10% loss. The difference from the 50% more fuel and the 25% MPG loss probably comes from the efficiency increase that comes with burning a simpler fuel. (And forced-induction engines suffer less of a loss because they're able to take advantage of E85's higher octane rating easier than a naturally-aspirated engine, thus increasing efficiency more.)
Energy density of E0 (regular petrol) = 34.2 MJ/L
Energy density of E85 = 25.65 MJ/L
25.65*(1+x) = 34.2... solve for x. Its about 30% more E85 to match energy density of regular gas.
Newbie
Joined: Jun 2012
Posts: 4
Likes: 0
From: Sacramento, CA
You can't solely go off of energy density of the fuel.
That only specifies how much energy is in each unit volume of the liquid stuff.
Because E-85 has a lower stoichiometric ratio, you need more of it per cylinder, which would give you more energy in each cylinder.
One day I really nuked the hell out of the formula, and found out the actual densities of the different fuels, the density of air at sea level, and the actual volumetric ratios of how much air and fuel there would be for a complete burn in a fixed-sized container. And here's what I'd gotten:
Given:Gasoline:34800 MJ of energy per m3 of fuel
Ratio for AFR : 14.7/1 (that's a mass, not a volume)
density: 748.91544 kg / m3 of fuel
E85:25200 MJ of energy per m3 of fuel
Ratio for AFR: 9.855/1
density: 778.87203 kg / m3 of fuel
density of air at sea level, 0*C, no humidity: 1.294 kg / m3
OK. Derived information:
For 1 kg of gasoline you'd need 19.0218 m3 of air, and the fuel would take up .00134 m3.
For 1 kg of E85 you'd need 12.7537 m3 of air, and the fuel would take up .00128 m3.
Combined:
AFR mix of gas: 19.0231 m3, which produces 46.632 MJ of energy.
AFR mix of E85: 12.7537 m3, which produces 32.256 MJ of energy.
...But with engines you need a set volume.So, with some manipulation:
The gas produces 2,451 kJ per m3 of air/fuel mix.The E85 produces 2,529 jJ per m3 of air/fuel mix.
...And then consider that gasoline's octane is about 91, and E85's is 105, meaning you can compress an E85 air-fuel mixture more than gasoline, pulling more useable power out of it.
That only specifies how much energy is in each unit volume of the liquid stuff.
Because E-85 has a lower stoichiometric ratio, you need more of it per cylinder, which would give you more energy in each cylinder.
One day I really nuked the hell out of the formula, and found out the actual densities of the different fuels, the density of air at sea level, and the actual volumetric ratios of how much air and fuel there would be for a complete burn in a fixed-sized container. And here's what I'd gotten:
Given:Gasoline:34800 MJ of energy per m3 of fuel
Ratio for AFR : 14.7/1 (that's a mass, not a volume)
density: 748.91544 kg / m3 of fuel
E85:25200 MJ of energy per m3 of fuel
Ratio for AFR: 9.855/1
density: 778.87203 kg / m3 of fuel
density of air at sea level, 0*C, no humidity: 1.294 kg / m3
OK. Derived information:
For 1 kg of gasoline you'd need 19.0218 m3 of air, and the fuel would take up .00134 m3.
For 1 kg of E85 you'd need 12.7537 m3 of air, and the fuel would take up .00128 m3.
Combined:
AFR mix of gas: 19.0231 m3, which produces 46.632 MJ of energy.
AFR mix of E85: 12.7537 m3, which produces 32.256 MJ of energy.
...But with engines you need a set volume.So, with some manipulation:
The gas produces 2,451 kJ per m3 of air/fuel mix.The E85 produces 2,529 jJ per m3 of air/fuel mix.
...And then consider that gasoline's octane is about 91, and E85's is 105, meaning you can compress an E85 air-fuel mixture more than gasoline, pulling more useable power out of it.
Newbie
Joined: Jun 2012
Posts: 4
Likes: 0
From: Sacramento, CA
It looks like E-85 actually runs cooler, as the ignition temperature of ethanol is lower.
And if you know something about cars you'd know that they've *already* been running on ethanol blends for decades now. E-85 isn't the scary thing that some neophobes here make it out to be.
http://www.change2e85.com/servlet/Page?template=Myths
And if you know something about cars you'd know that they've *already* been running on ethanol blends for decades now. E-85 isn't the scary thing that some neophobes here make it out to be.
http://www.change2e85.com/servlet/Page?template=Myths
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