Flexible Fuel Vehicles – The Fuel

In an earlier post, The Path from Coal to Hydrogen, I discussed a House bill requiring auto engines to run on multiple fuels: ethanol and methanol blended with gasoline, gasoline only and biodiesel.

Since methanol and ethanol do not contain as much energy per unit volume, for example, a gallon, as gasoline, we have to look at it a little differently. Take a look at this simple table:

Heating Value	Gasoline	Diesel Fuel	Methanol	Ethanol
BTUs per gallon	116,090	128,450	57,250	76,330
BTUs per pound	18,676	18,394	8,637	11,585

The figures are from the American Petroleum Institute. When we think about gasoline, the standard we use is miles per gallon because we all buy a gallon of gasoline that contains a similar amount of energy. However, when we begin to use other fuels, a gallon is no longer a standard measure of energy content. We have to go back to the basic energy measure, the British Thermal Unit or BTU. As a refresher, a BTU is the amount of energy required to raise one pound of water one degree Fahrenheit.

A gallon of gasoline costing $3.00 would require about two gallons of Methanol (theoretically costing about $1.50 per gallon) and about 1-½ gallons of Ethanol (costing about $2.00 per gallon). These would be the equivalent costs for the same amount of energy—BTUs—to fuel an engine.

Cost per BTU, just for purposes of illustration, would be $3.00 or 300¢ (cents) divided by 116,090 BTUs per gallon of gasoline or 0.0026¢ per BTU. A better way to look at it is in terms of cost per million BTUs, since a full twenty gallon gasoline tank contains over 2 million BTUs.

In that case, one million BTUs costs about $26.00, whether you are purchasing gasoline, diesel, methanol or ethanol. At 20 miles per gallon of gasoline, you’ll burn about 5,800 BTUs per mile. In a future post: Flexible Fuel Vehicles – The Engine.