# Mobil selling ethanol at $2.69 a gallon, but it's hidden from view 1. Jan 14, 2008 ### LightbulbSun My local news station visited a local Mobil station that sells ethanol. It sells for$2.69 a gallon, but the sign is hidden from view. I didn't know Mobil was selling this, and was wondering if ethanol is really that big of a threat to oil companies?

2. Jan 15, 2008

### Mech_Engineer

Ethanol is not a viable source of energy to completely replace petroleum right now because the infrastructure to manufacture it doesn't exist.

Ethanol for $2.69/gal sounds like a good deal, but is it? Ethanol has approximately 23.5 MJ/L, whereas regular Gasoline has 34.8 MJ/L. This is a 32% decrease in available energy when compared to gasoline, but only about 10% reduction in price per gallon (assuming regular gas is$3.00/gal).

So, a car that gets 30 mpg on the highway with gasoline, will get about 20.2 mpg with ethanol. This works out to about $0.10/mi for gas, and$0.13/mi for ethanol. Doesn't sound like a very good deal to me... regular gas would have to cost about $4.00/gal to equal the price per energy of ethanol at$2.69/gal.

...and lets not forget the raised prices on all corn products due to the B.S. hype on Ethanol right now. Milk, beef, corn syrup, other crops... all more expensive because of the increased demand for corn.

Last edited: Jan 15, 2008
3. Jan 15, 2008

### brewnog

Unfortunately, that comparison can't be made on energy density alone.

Ethanol is far more knock resistant that petrol, so higher compression ratios and more advanced ignition timings can be used, thus improving specific power output. Gains are also available from the increased charge density which can occur as a result of ethanol evaporation following atomisation.

4. Jan 15, 2008

My last tank of gas was $2.79/gallon. 5. Jan 15, 2008 ### BobG This is true, but then the vehicle could only take ethanol fuel. The 'green' cars that can take E-85 haven't modified their engines to take advantage of ethanol's properties so mech engineer's comparison is more accurate today. I understand what car companies are trying to do. You can't make an ethanol fuel car if there's nowhere to get it refueled. The E-85 option theoretically creates a transition between gasoline and ethanol. Unfortunately, it's so inefficient that only the most dedicated envrionmentalists would choose E-85 fuel over gasoline after a few tankfuls. The end result is such a black eye for ethanol as a fuel that future more efficient ethanol-only cars will be even harder for the public to accept. It will be similar to GM's hasty conversion of their 350's into deisels back in the early 80's. After a few years, GM was putting out quality deisel engines but their reputation was trashed so badly by the first couple years that no one was willing to buy them. 6. Jan 15, 2008 ### Mech_Engineer In my opinion, ethanol has been WAY overhyped as a potential fuel source to take us into the next century; bio-diesels are a much better option in that arena. Specific power output aside, the available energy from combustion of gasoiline and ethanol remains the same; therefore, the energy available to accelerate a car to a sepcific speed (and maintain that speed) remains about the same, and so the mileage remains the same regardless of compression ratio or knock resistance. Higher compression ratio engines will tend to be more efficient than lower compression ratio engines, which means more energy will make it to kinetic energy in the car; but, it can already be seen that the knock resistance of a fuel can and probably will be nullified with the advent of direct injection engines in the mass market (which dramatically increases burn efficiency) like the ones currently being made by VW/Audi. When you think about it, the best choice for a new fuel would be something that is easy to make out of something that we don't use (algae farm bio-diesel plants are a good option in this respect, and bio-diesels can be made out of waste products from the food industry as well). What we DON'T want to do is make our next-gen fuel using a product that is already in high demand everywhere (e.g. corn)! Last edited: Jan 15, 2008 7. Jan 15, 2008 ### brewnog I quite agree. It's a much easier step to make between Diesel and biodiesel than between gasoline and biodiesel, which is why this fuel source is much more readily available in the UK (and I presume mainland Europe) than North America. Bliss! I paid £1.08 per litre today. ($9.62 per gallon). Grrr.

8. Jan 15, 2008

### NateTG

9. Jan 15, 2008

### Staff: Mentor

I couldn't afford to drive to work if gas cost that much.

10. Jan 15, 2008

### brewnog

I suspected as much. The same is true in the UK; prices are around 15-20% lower than Diesel.

I'm about to start preparing my car to run on biodiesel, and some colleagues and I are looking at starting biodiesel production ourselves.

11. Jan 15, 2008

### Ivan Seeking

Staff Emeritus
At about 120 gallons per acre-year net yield [about 30% production and processing efficiency] there is not nearly enough land in the US to convert to ethanol; even assuming that we forget about growing food and convert all land to ethanol production.

At about 50 times the yield per acre-year, biodiesel from algae is the only viable solution.