Comparing the Energy of Natural Gas and Gasoline
By Erine Parker, CFPAI, CFPSD, CFPS, CFPMM, CFPMT, CFPMIP, CFPMMH, CFPMIH, CFPE
When you see a vehicle driven on natural gas, do you ever wonder how far it can go on a tank of fuel? How many times larger would a container of natural gas at 3,000 psi (207 bar) have to be to hold the same amount of energy as in a gallon of gasoline? Use 1,000 BTUs for a cubic foot of natural gas at atmospheric pressure and 125,000 BTUs for a gallon of gasoline.
See the Solution
P1V1 = P₂V₂
14.7 x 1 = 3014.7 x V₂
V₂ = .004876 (volume of 1 cubic foot of gas when compressed to 3,000 psi [207 bar])
1 / .004876 = 205.08163 SCF are compressed into 1 cubic foot container
205.08163 x 1000 BTUs/SCF = 205,081.63 BTUs/SFC
1 cubic foot = 7.48 gallons
7.48 x 125,000 = 935,000 BTUs
935,000/205,082 = 4.56 times as much energy.
1. You would have to pressurize a container to 13,747 psi (948 bar) to get the same energy
2. Gasoline will vary in BTUs depending on the season. The vapor pressure is lower in cold weather for easier starting, but you will lose some miles per gallon.