ASTM D240 for Heat of Combustion of Liquid Hydrocarbon Fuels by Bomb Calorimeter
10. Calculation
10.1 Temperature Rise in Isothermal Jacket Calorimeter - Using data obtained as prescribed in 9.5, compute the temperature rise, t, in an isothermal jacket calorimeter as follows:
t = tc - ta – r1(b - a) - r2(c - b)
where:
t = corrected temperature rise,
a = time of firing,
b = time (to nearest 0.1 min) when the temperature rise reaches 60 % of total,
c = time at beginning of period in which the rate of temperature change with time has become constant (after combustion),
ta = temperature at time of firing, corrected for thermometer error (10.1.1),
tc = temperature at time, c, corrected for thermometer error (10.1.1),
r1 = rate (temperature units per minute) at which temperature was rising during 5-min period before firing, and
r2 = rate (temperature units per minute) at which temperature was rising during the 5-min period after time c. If the temperature is falling, r2 is negative and the quantity - r2(c - b) is positive.

10.1.1 All liquid-in-glass thermometers shall be corrected for scale error, using data from the thermometer certificate prescribed in Annex A1, A1.5.1, or A1.5.2. Beckmann thermometers also require a setting correction and an emergent stem correction (Annex A2, A2.1.2). Solid-stem ASTM Thermometers 56F and 56C do not require emergent stem corrections if all tests, including standardization are performed within the same 5.5°C interval. If operating temperatures exceed this limit, apply a differential emergent stem correction (Annex A2, A2.1.1) to the correct temperature rise, t, in all tests, including standardization.

10.2 Temperature Rise in Adiabatic Jacket Calorimeter - Using data obtained as prescribed in 9.6, compute the temperature rise, t, in an adiabatic jacket calorimeter as follows:
t = tf - ta
where:
t = corrected temperature rise,
ta = temperature when charge was fired, corrected for thermometer error (10.1.1), and
tf = final equilibrium temperature, corrected for the thermometer error (10.1.1).

10.3 Thermochemical Corrections (Annex A2) - Compute the following for each test:
e1 = correction for heat of formation of nitric acid (HNO3), MJ = cm3 of standard (0.0866 N) NaOH solution used in titration x 5/10(6),
e2 = correction for heat of formation of sulfuric acid (H2SO4). MJ = 58.0 x percentage of sulfur in sample 3 mass of sample/10(6),
e3 = correction for heat of combustion of firing wire, MJ,
= 1.13 x millimetres of iron wire consumed/10(6),
= 0.96 x millimetres of Chromel C wire consumed/10(6), and
e4 = correction for heat of combustion of pressure-sensitive tape or gelatin capsule and mineral oil, MJ = mass of tape or capsule oil, g x heat of combustion of tape or capsule/oil, MJ/kg/10(6).

10.4 Gross Heat of Combustion - Compute the gross heat of combustion by substituting in the following equation:
Qg = (tW - e1 - e2 - e3 - e4)/1000 g
where:
Qg = gross heat of combustion, at constant volume expressed as MJ/kg,
t = corrected temperature rise (10.1 or 10.2), °C,
W = energy equivalent of calorimeter, MJ/°C (8.1),
e1, e2, e3, e4 = corrections as prescribed in 10.3, and
g = weight of sample, g.

NOTE 7 - The gross heat of combustion at constant pressure may be calculated as follows:
Qgp = Qg + 0.006145H
where:
Qgp = gross heat of combustion at constant pressure,MJ/kg, and
H= hydrogen content, mass %.

10.5 Net Heat of Combustion:
10.5.1 If the percentage of hydrogen, H, in the sample is known, the net heat of combustion may be calculated as follows:
Qn = Qg - 0.2122 x H
where:
Qn = net heat of combustion at constant pressure, MJ/kg,
Qg = gross heat of combustion at constant volume, MJ/kg, and
H = mass percent of hydrogen in the sample.

When the percentage of hydrogen is not known, determine the hydrogen in accordance with Test Methods D1018 or D3701.

10.5.2 If the percentage of hydrogen in aviation gasoline and turbine fuel samples is not known, the net heat of combustion may be calculated as follows:
Qn = 10.025 + (0.7195)Qg
where:
Qn = net heat of combustion at constant pressure, MJ/kg,
Qg = gross heat of combustion at constant volume, MJ/kg.

NOTE 8 - Eq 12 is recommended only if the percentage of hydrogen is not known. It is based on Eq 11 and an empirical relation between Qn and the percentage of hydrogen in aviation gasolines and turbine fuels, developed from data by Jessup and Cragos.