Due primarily to high costs of gasoline, a wild frenzy for alternative fuels has recently mushroomed across the nation. The Energy Policy Act of 1992 named ethanol and ethanol blends as a commercially available alternative fuel to typical gasoline. E85, comprised of approximately 85% ethanol and 15% gasoline, is surrounded by myth and misinformation. It is my intention to shed some light on this subject.
Gasoline vs. E85
The two most common details utilized by individuals either for or against the use of E85 are the octane levels and power output. The pro-E85 crowd will point to the high octane levels and insist that this equates to more power. Meanwhile, the anti-E85 crowd explains that the lower BTU output of ethanol means that power production is diminished. Unfortunately, both ideas are essentially correct.
Pure ethanol has an octane rating of about 116 which makes it an excellent and relatively cheap octane booster. Most E85 blends hover around 100 - 105 which puts them in the range of moderate race fuels. However, octane is not a measure of power production. The octane rating is simply a value of resistance to pre-ignition.
To confound the problem, E85 contains roughly 27% less energy per gallon of standard gasoline. Gasoline has an average energy content of 125,000 BTU while E85 has only 80,000 BTU. Therefore, you must burn more E85 to get an equal amount of power output as gasoline.
The Switch
Simply going to the gas station and filling up your car with E85 will do you zero good. In fact, you will experience lower fuel economy, less power, and more money out of your wallet than if you had used gasoline. Running your non-adjusted Mustang with E85 will result in a lean condition in carbureted motors and an overworked and underpowered motor in EFI instances. Luckily for us modification freaks out there, with a small amount of tinkering we can utilize the benefits of ethanol.
Air/Fuel Ratio
Ideal combustion occurs at different levels for different fuels. Under stoichiometric conditions, this implies a complete burn resulting in no significant amounts of unburned fuel exiting the exhaust.
Typically, the conventional air/fuel ratio for standard gasoline is 14.7:1 on up to 12.5:1 for rich max power setups. E85, on the other hand, experiences a stoichiometric air/fuel ratio of 9.7:1 with a rich max power ratio of 6.9:1. This means that an unmodified engine may experience piston/head damage without the customary “knock” associated with pre-ignition.
Fuel Consumption
As mentioned previously, you must burn approximately 40-60% more E85 in order to obtain an equal amount of energy output as a gallon of gasoline. This translates into larger injectors and a beefier fuel system. A person must keep these things in mind when contemplating a switch to E85.
Ethanol is a partially oxidized fuel and, as noted, needs to be burned at a much richer mixture than gasoline. Consequently, the increased volume of fuel burned per injection cycle compensates for the lower energy content per unit.
Horsepower!
Although the thermal energy per gallon of E85 is significantly less than a gallon of gasoline, the power potential is greater for E85. The specific energy at stoichiometric air/fuel ratios (energy released per AFR) of E85 is actually higher than gasoline. This allows for a greater release of energy per volume of air. In other words, E85 burns faster and creates more exhaust gas for a given weight than gasoline.
The average thermal energy content for gasoline is 19,000 BTU/lb while E85 lags behind at only 13,465 BTU/lb. However, a motor is essentially an air pump. Utilizing an air consumption of 100 lbs, the power outputs would be as follows:
Gasoline:
14.7:1 air/fuel = 6.8 lbs fuel @ 19,000 BTU/lb = 129,252 BTU
E85:
9.7:1 air/fuel = 10.3 lbs fuel @ 13,465 BTU/lb = 138,814 BTU
Essentially, you would experience a 7% increase in energy which would increase to 28% in rich max power ratios. Keep in mind, however, that you will be burning 52 to 81% more fuel per cycle.
Compression
The real beauty of E85 comes into play under boosted applications. Current trends on turbocharged vehicles show boost numbers upwards of 30 psi without experiencing knock. E85, being an alcohol derivative, has much higher evaporative cooling abilities than gasoline. This allows the intake air to cool significantly enabling a larger amount of oxygen to enter the combustion chamber. Re-introduce the high octane rating and bump up the timing and we find ourselves with a compression friendly fuel!
Conclusion
With the proper setup, you can create plenty of power with E85. There are a couple of key things to keep in mind though: 1) Fuel consumption is increased. Adjust your fuel system accordingly. 2) The stoichiometric ratio is different for E85. Don’t tune for 14.7:1!
References
http://www.eere.energy.gov/afdc/pdfs/afv_info.pdf
E85 Vs. Gasoline Comparison Test
http://www4.ncsu.edu/~frey/Zhai_et_al_2007a.pdf
Comments, corrections, questions and complaints are all highly encouraged!
Gasoline vs. E85
The two most common details utilized by individuals either for or against the use of E85 are the octane levels and power output. The pro-E85 crowd will point to the high octane levels and insist that this equates to more power. Meanwhile, the anti-E85 crowd explains that the lower BTU output of ethanol means that power production is diminished. Unfortunately, both ideas are essentially correct.
Pure ethanol has an octane rating of about 116 which makes it an excellent and relatively cheap octane booster. Most E85 blends hover around 100 - 105 which puts them in the range of moderate race fuels. However, octane is not a measure of power production. The octane rating is simply a value of resistance to pre-ignition.
To confound the problem, E85 contains roughly 27% less energy per gallon of standard gasoline. Gasoline has an average energy content of 125,000 BTU while E85 has only 80,000 BTU. Therefore, you must burn more E85 to get an equal amount of power output as gasoline.
The Switch
Simply going to the gas station and filling up your car with E85 will do you zero good. In fact, you will experience lower fuel economy, less power, and more money out of your wallet than if you had used gasoline. Running your non-adjusted Mustang with E85 will result in a lean condition in carbureted motors and an overworked and underpowered motor in EFI instances. Luckily for us modification freaks out there, with a small amount of tinkering we can utilize the benefits of ethanol.
Air/Fuel Ratio
Ideal combustion occurs at different levels for different fuels. Under stoichiometric conditions, this implies a complete burn resulting in no significant amounts of unburned fuel exiting the exhaust.
Typically, the conventional air/fuel ratio for standard gasoline is 14.7:1 on up to 12.5:1 for rich max power setups. E85, on the other hand, experiences a stoichiometric air/fuel ratio of 9.7:1 with a rich max power ratio of 6.9:1. This means that an unmodified engine may experience piston/head damage without the customary “knock” associated with pre-ignition.
Fuel Consumption
As mentioned previously, you must burn approximately 40-60% more E85 in order to obtain an equal amount of energy output as a gallon of gasoline. This translates into larger injectors and a beefier fuel system. A person must keep these things in mind when contemplating a switch to E85.
Ethanol is a partially oxidized fuel and, as noted, needs to be burned at a much richer mixture than gasoline. Consequently, the increased volume of fuel burned per injection cycle compensates for the lower energy content per unit.
Horsepower!
Although the thermal energy per gallon of E85 is significantly less than a gallon of gasoline, the power potential is greater for E85. The specific energy at stoichiometric air/fuel ratios (energy released per AFR) of E85 is actually higher than gasoline. This allows for a greater release of energy per volume of air. In other words, E85 burns faster and creates more exhaust gas for a given weight than gasoline.
The average thermal energy content for gasoline is 19,000 BTU/lb while E85 lags behind at only 13,465 BTU/lb. However, a motor is essentially an air pump. Utilizing an air consumption of 100 lbs, the power outputs would be as follows:
Gasoline:
14.7:1 air/fuel = 6.8 lbs fuel @ 19,000 BTU/lb = 129,252 BTU
E85:
9.7:1 air/fuel = 10.3 lbs fuel @ 13,465 BTU/lb = 138,814 BTU
Essentially, you would experience a 7% increase in energy which would increase to 28% in rich max power ratios. Keep in mind, however, that you will be burning 52 to 81% more fuel per cycle.
Compression
The real beauty of E85 comes into play under boosted applications. Current trends on turbocharged vehicles show boost numbers upwards of 30 psi without experiencing knock. E85, being an alcohol derivative, has much higher evaporative cooling abilities than gasoline. This allows the intake air to cool significantly enabling a larger amount of oxygen to enter the combustion chamber. Re-introduce the high octane rating and bump up the timing and we find ourselves with a compression friendly fuel!
Conclusion
With the proper setup, you can create plenty of power with E85. There are a couple of key things to keep in mind though: 1) Fuel consumption is increased. Adjust your fuel system accordingly. 2) The stoichiometric ratio is different for E85. Don’t tune for 14.7:1!
References
http://www.eere.energy.gov/afdc/pdfs/afv_info.pdf
E85 Vs. Gasoline Comparison Test
http://www4.ncsu.edu/~frey/Zhai_et_al_2007a.pdf
Comments, corrections, questions and complaints are all highly encouraged!
