Significance and Use
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 D 240 and D 4809.
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.
Scope
1.1 This test method covers the estimation of the net heat of combustion (specific energy) at constant pressure in SI units, megajoules per kilogram, from the fuel density, sulfur, and hydrogen content.
1.2 This test method is purely empirical, and it is applicable only to liquid hydrocarbon fuels derived by normal refining processes from conventional crude oil that conform to the requirements of specifications for aviation turbine fuels of limited boiling ranges and compositions, as described in Note 0 and permitted by each specification.
Note 0
The estimation of the heat of combustion of a hydrocarbon fuel from its hydrogen content, density, and sulfur is justifiable only when the fuel belongs to a well-defined class for which a relationship between these quantities has been derived from accurate experimental measurements on representative samples of that class. Even in this class, the possibility that the estimates can be in error by large amounts for individual fuels should be recognized. The classes of fuels used to establish the correclation presented in this test method are represented by the following specifications:
1.3 The heat of combustion can also be estimated by Test Methods D 1405, D 3338, and D 4529.