ASTM D240 for Heat of Combustion of Liquid Hydrocarbon Fuels by Bomb Calorimeter
8. Standardization
8.1 Determine the Energy Equivalent of the Calorimeter - Average not less than six tests using standard benzoic acid. These tests should be spaced over a period of not less than three days. Use not less than 0.9 g nor more than 1.1 g of standard benzoic acid (C6H6COOH). Make each determination according to the procedure described in Section 9 and compute the corrected temperature rise, t, as described in 10.1 or 10.2. Determine the corrections for nitric acid (HNO3) and firing wire as described in 10.3 and substitute in the following equation:
W = (Q x g + e1 + e2)/t
where:
W = energy equivalent of calorimeter, MJ/°C,
Q = heat of combustion of standard benzoic acid, MJ/g, calculated from the certified value,
g = weight of standard benzoic acid sample, g,
t = corrected temperature rise, as calculated in 10.1 or 10.2,°C,
e1 = correction for heat of formation of nitric acid, MJ, and
e2 = correction for heat of combustion of firing wire, MJ.
8.1.1 Repeat the standardization tests after changing any part of the calorimeter and occasionally as a check on both calorimeter and operating technique.
8.2 Checking the Calorimeter for Use with Volatile Fuels - Use 2,2,4-trimethylpentane to determine whether the results obtained agree with the certified value (47.788 MJ/kg, weight in air) within the repeatability of the test method. If results do not come within this range, the technique of handling the sample may have to be changed (Annex A1.8). If this is not possible or does not correct the error, run a series of tests using 2,2,4-trimethylpentane to establish the energy equivalent for use with volatile fuels.
8.3 Heat of Combustion of Pressure-Sensitive Tape or Gelatin/Mineral Oil - Determine the heat of combustion of either the pressure-sensitive tape or 0.5 g gelatin capsule/mineral oil in accordance with Section 9 using about 1.2 g of tape or 0.5 g gelatin capsule/mineral oil and omitting the sample. Make at least three determinations and calculate the heat of combustion as follows:
Qpst = (Δt x W - e1)/1000 a
where:
Qpst = heat of combustion of the pressure-sensitive tape or mineral oil, MJ/kg,
Δt = corrected temperature rise, as calculated in accordance with 10.1 or 10.2,°C,
W = energy equivalent of the calorimeter, MJ/°C,
e1 = correction for the heat of formation of HNO3, MJ, and
a = mass of the pressure-sensitive tape or gelatin capsule/mineral oil, g.
Average the determinations, and redetermine the heat of combustion of the tape or gelatin capsule/mineral oil whenever a new roll or batch is started.
