Auto Fuel Mileage Comparisons

This dragster runs on one of the most expensive and efficient fuels out there.

A lot of factors go into a car's net fuel economy: engine design, aerodynamics, tire design and driving style all play a part. However, few factors are so inflexible or consistent as what kind of fuel it uses.

Energy Content

All combustible substances on earth contain a certain amount of stored chemical energy. This energy potential is measured in BTUs (British Thermal Units) per gallon. Think of this measurement as the substance's "calorie" content, which is, in itself, another measure of energy potential.

BTU Content

Diesel and gasoline are by far the most energy dense road fuels at 128,450 and 116,090 BTUs, respectively. Propane is next down the list at 84,250 BTUs. Both corn ethanol and the more sustainable cellulosic ethanol are good for 76,330. The racing fuels methanol and nitromethane contain 57,250 and 125,412 BTUs, respectively.

Other Factors

While BTU content is the primary indicator of a fuel's theoretical economy, the higher octane ratings of ethanol, methanol and propane (110 octane) allow for much higher compression ratios, which make more power and deliver more economy per unit of fuel used. Diesel and nitromethane have both a high BTU rating and high octane rating, making them the two most efficient fuels available today.

References

• Alternative Fuels & Advanced Vehicle Data Center: Fuel Properties Table
• Louisiana Government: Methanol--An Alternative Fuel
• Klotzwarehouse Nitromethane: Nitromethane Properties
• Patooyee: How to Convert Your Engine to Propane