There are really two problems with the "heat value" of gasoline.
The first is that there are two different kinds of heat value (as some of you know). High heat value and low heat value. The difference is the form of the products after the reaction. If you start with the fuel and air at room temperature, and obtain the heat when the products end up at the same temperature, then you have the "high heat value." If you aknowledge that the products leave the engine as gases, you get the "low heat value." And, if you account for the exact temperature of the exhaust, then you can get an even lower "low heat value."
Dcb, your value of 124,000 BTU per gallon is a high heat value. (125,000 is quoted more often for this.) The others are low heat values--that's why this one value is so much different than the others.
The second problem is that there is no clear definition for what "gasoline" actually is. Every refinery makes a different product, subject to an ASTM or a API specification that insures the stuff will burn okay in a car.
Since the chemical compositions are different, the energy content can be a little different too. Sometimes people doing research will specify a particular gasoline formula to guarantee that their data can be reproduced. I have seen isooctane used for this "standard gasoline."
Ernie Rogers
Quote:
Originally Posted by dcb
LOL, even that is not simple 
From the wiki discussions on gasoline:
BTU per gallon of gasoline
- 1 kilowatt hour = 3,412.14163 BTU
But nobody seems to know how much energy is supposed to be in a gallon of gas.
- 1 Gallon = 114,000 Btu/gallon according to NIST. They came up with the GGE concept in 1994.NIST
I will assume NIST's figure for 114,000 Btu per gallon of base gasoline is their standard, since they are the ones behind the GGE concept. EPA's figure agrees with this in most places. Kgrr ( talk) 16:02, 1 January 2009 (UTC)
Even some government institutions cannot be internally consistent:
- 1 Gallon = 115,400 Btu/gallon ORNL
This figure seems to gain a lot of traction:
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