ASTM D4868 Estimation of Net and Gross Heat of Combustion of Burner and Diesel Fuels
5. Procedure
5.1 Determine the density to the nearest 0.1 kg/m3 as described in Practice D1298, and Test Methods D1480, D1481 or D4052.

5.2 Determine the sulfur content of the sample to the nearest 0.01 mass % sulfur as described in Test Methods D129, D1266, D1552, D2622, D4294, or D5453.

5.3 Determine the water content of the sample to the nearest 0.05 mass % water as described in Test Methods D95, D1744, or D1796.

5.4 Determine the ash content of the sample to two significant figures as described in Test Method D482.

6. Calculation
6.1 Calculate the gross heat of combustion of the fuel corrected for the sulfur, water and ash content in accordance with the following equation:

where:
Qv = gross heat of combustion at constant volume, MJ/kg,
d = density at 15°C, kg/m3,
x = mass fraction of water (% divided by 100),
y = mass fraction of ash (% divided by 100), and
s = mass fraction of sulfur (% divided by 100).

6.2 Calculate the net heat of combustion of the fuel corrected for the sulfur, water and ash content in accordance with the following equation:

where:
Qp = net heat of combustion at constant pressure, MJ/kg,