ASTM D6446 Estimation of Net Heat of Combustion of Aviation Fuels
ASTM D6446 Standard Test Method for Estimation of Net Heat of Combustion (Specific Energy) of Aviation Fuels
3. Summary of Test Method
3.1 The hydrogen content, density, and sulfur content of the sample are determined by experimental test methods and the net heat of combustion is calculated using the values obtained by these test methods based on reported correlations.

4. Significance and Use
4.1 This test method is intended for use as a guide in cases in which an experimental determination of heat of combustion is not available and cannot be made conveniently, and in which an estimate is considered satisfactory. It is not intended as a substitute for experimental measurements of heat of combustion (see Note 2).

NOTE 2 - The procedures for the experimental determination of the net heat of combustion are described in Test Methods D240 and D4809.

4.2 The net heat of combustion is a factor in the performance of all aviation fuels. Because the exhaust of aircraft engines contains uncondensed water vapors, the energy released by fuel in vaporizing water cannot be recovered and must be subtracted from gross heat of combustion. For high performance weight-limited aircraft, the net heat of combustion per unit mass and the mass of fuel loaded determine the total safe range. The proper operation of the aircraft engine also requires a certain minimum net energy of combustion per unit volume of fuel delivered.