ASTM D4809 Test Method for Heat of Combustion of Liquid Hydrocarbon Fuels
ASTM D4809 Test Method for Heat of Combustion of Liquid Hydrocarbon Fuels by Bomb Calorimeter (Precision Method)
11. Calculation
11.1 Temperature Rise Isoperibol Method - Using data obtained in Section 10, plot a graph of readings of temperature versus time and calculate the corrected temperature rise, Δt, in °C as follows:
Δt = tf - ti - r1(b - a) - r2(c - b)
where:
Δt = corrected temperature rise, °C,
a = time of firing,
b = time (to nearest 0.1 min) when the temperature rise reaches 63 % of total (obtained graphically or numerically),
c = time at beginning of final period in which the rate of temperature change with time has become constant,
ti = temperature at time of firing, °C,
tf = temperature at time c, °C,
r1 = rate at which the temperature was rising during the initial period before firing, °C, and
r2 = rate at which the temperature as rising during the final period, °C.

11.2 Temperature Rise, Adiabatic Method - Using data obtained in Section 10, calculate the temperature rise, Δt, in °C, as follows:
Δt = tf - ti
where:
Δt = corrected temperature rise, °C,
tf = final equilibrium temperature, °C, and
ti = temperature at time of firing, °C.

11.3 Thermochemical Correction (Annex A2) - Calculate the following corrections for each test:
e1 = correction for the heat of formation of the HNO3, J = cm3 of standard (0.0866 N) NaOH solution used in titration x 5,
e2 = correction for the heat of formation of sulfuric acid (H2SO4), J = 58.6 x percentage of sulfur in sample x mass of sample, g.
e 3 = correction for the heat of combustion of pressure-sensitive tape, J = mass of tape, g x heat of combustion of tape J/g.
e4 = correction for heat of combustion of firing wire, J = 1.13 x millimetres of iron wire consumed = 0.96 x millimetres of Chromel C wire consumed

11.4 Gross Heat of Combustion - Calculate the gross heat of combustion by substituting in the following equations:
Qg (gross t°C) = (Δt x W - e1 - e2 - e3 - e4)/1000 M
Qg (gross, 25°C) = Qg (gross, t°C) + A(t - 25)
where:
Qg(gross, t°C) = gross heat of combustion at constant volume and final temperature of the experiment, expressed as MJ/kg,
Qg(gross, 25°C) = gross heat of combustion at constant volume expressed as MJ/kg,
Δt = corrected temperature rise, °C,
W = energy equivalent of calorimeter, J/°C
M = mass of sample, g,
t = final temperature of combustion, °C,
e1, e2, e3, e4 = corrections as described in 11.3, and
A = correction factor, MJ/kg °C to correct from final temperature of combustion to 25°C where values of factor A are given in Table 1.

NOTE 11 - 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 %

11.5 Net Heat of Combustion - Calculate the net heat of combustion as follows:
Qn(net, 25°C) = Qg(Qggross, 25°C) - 0.2122 x H
where:
Qn(net, 25°C) = net heat of combustion at constant pressure, MJ/kg,
Qg(gross, 25°C) = gross heat of combustion at constant volume, MJ/kg, and
H = mass percent of hydrogen in the sample.

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