ASTM D3338 Test Method for Estimation of Net Heat of Combustion of Aviation Fuels
6. Procedure
6.1 Determine the aromatic content of the fuel to the nearest 0.1 % vol as described in Test Method D1319.
6.1.1 Test Method D6379 or IP 436 may be used as an alternative to Test Method D1319 for determining fuel aromatics content for use in this test method.

6.1.2 If Test Method D6379 or IP 436 is used, multiply the total aromatics content in vol% by 25/26.5 (=0.9434), and use this corrected value in place of aromatics determined by Test Method D1319 in Eq 2.

6.2 Determine the density at 15°C or the API gravity of the fuel to the nearest 0.1 kg/m3 or [0.1° API] as described in Test Method D1298 or in Test Method D4052.

6.3 Determine the 10 %, 50 %, and 90 % boiling points of the fuel to the nearest 1°C or [1°F] as described in Test Method D86. Average these three temperatures to obtain the T value (°C) or the V value [°F] used in the equations of 4.1. For a pure hydrocarbon, T or V is the normal boiling point.
6.3.1 Test Method D2887 may be used as an alternative to Test Method D86 for determining fuel volatility for use in this test method. The average of the 10 %, 50 %, and 90 % boiling points determined by Test Method D2887 may be used directly in place of the corresponding average determined by Test Method D86.

6.4 Determine the sulfur content of the fuel to the nearest 0.02 % sulfur as described in Test Methods D1266, D1552, D2622, D3120, D4294, or D5453, depending upon the volatility of the sample.

7. Calculation and Report
7.1 SI Units:
7.1.1 Calculate the net heat of combustion, sulfur-free basis, using Eq 2 of 4.1. Round the value obtained to the nearest one-thousandth.
Example:
Sample: Kerosine
Determined Values:
Aromatics, A = 12.5 % volume
Density, D = 805.0 kg/m3
Distillation
T10 = 203°C
T50 = 233°C
T90 = 245°C
T = (203 + 233 + 245)/3 = 227°C

Calculated Value: A x T = 2837.5
Substituting into Eq 2 in 4.1:
Qp2 = [5528.73 - 92.6499(12.5) + 10.1601(227) + 0.314169(2837.5)]/805.0 + 0.0791707(12.5) - 0.00944893(227) - 0.000292178(2837.5) + 35.9936
Qp2 = 43.411015 = 43.411 MJ/kg, sulfur-free basis

7.1.2 Calculate the net heat of combustion corrected for the sulfur content of the fuel using Eq 3 of 4.2. Round the value obtained to the nearest one-thousandth.
Example: Qp2 = 43.411 MJ/kg
Determined Value: Sulfur, S1 = 0.10 mass %
Substituting into Eq 3 in 4.2:
Q = 43.411[1 - 0.01(0.1)] + 0.10166(0.1)
Q = 43.3778 = 43.378 MJ/kg

7.2 Inch-Pound Units:
7.2.1 Calculate the net heat of combustion, sulfur-free basis, using Eq 1 in 4.1. Round the value obtained to the nearest integer.
Example:
Sample: Kerosine
Determined Values:
Aromatics, A = 12.5 % volume
Gravity, G = 44.2° API
Distillation
T10 = 398°F
T50 = 451°F
T90 = 473°F
T = (398 + 451 + 473)/3 = 440.7°F

Calculated Values:
G x V = 19 478.9
A x G = 552.5
A x G x V = 243486.8

Substituting into Eq 1 in 4.1:
Qp1 = 16.24(44.2) - 3.007(12.5) + 0.01714~19 478.9! - 0.2983(552.5) + 0.00053(243 486.8) + 17 685
Qp1 = 18 663.3 = 18 663 Btu/lb, sulfur-free basis

7.2.2 Calculate the net heat of combustion corrected for the sulfur content of the fuel and round the value obtained to the nearest integer.
Example: Qp1 = 18 663 Btu/lb
Determined Value: Sulfur, S1 = 0.10 mass %
Q = 18 663[1 - 0.01(0.1)] + 43.7(0.1)
Q = 18 648.7 = 18 649 Btu/lb