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)
8. Preparation of Apparatus
8.1 Arrangement of Apparatus - Install the thermometers as recommended by the manufacturer of the calorimeter. Position the liquid-in-glass thermometer so that the bulb is halfway to the bottom of the bucket and locate the thermistor with its sensing element at about the midpoint of the thermometer bulb. Mount these elements so that exactly the same length is immersed each time the calorimeter is used. Install a thermistor in the water jacket with the element immersed to the same depth as in the bucket. It is helpful, but not necessary to have liquid-in-glass calorimetric thermometers in both the bucket and jacket for quick temperature observations. Thermistors can be taped to these thermometers. If the thermistors are taped to the thermometers, it can be done in such a manner that the sensing elements are at the midpoint of the thermometer bulbs. The thermometer bulbs and temperature-sensing elements shall not touch the bomb, bucket, or water jacket.
8.2 Calorimeter Jacket Controller and Auxiliary Equipment - Adjust the jacket controller, valves, heater, etc., as recommended by the calorimeter manufacturer.
9. Standardization
9.1 Energy Equivalent of the Calorimeter - Benzoic acid shall be used as the primary standard (Warning - Oxygen vigorously accelerates combustion. See A3.1). Choose a sample mass so that the temperature rise is approximately equivalent to an energy change of 30 000 J. Initially determine the energy equivalent by averaging six determinations made using benzoic acid over a period of at least 3 days.
9.1.1 A relative standard deviation (RSD) of 0.1 % or less for the six determinations must be achieved. If not, continue to run until six determinations establish a value that has a RSD of 0.1 % or better. If this degree of precision cannot be achieved, review the procedure, critical measurements, mechanical operations and everything that may contribute to scatter in the results. After establishing an energy equivalent value, determine the value at frequent intervals using benzoic acid (every 1 or 2 days of testing) with the average of the last six determinations being used for the energy equivalent as long as the last six determinations have a RSD of 0.1 % or less.
9.1.2 If any part of the equipment is changed or any part of the procedure is altered, redetermine the value. Make each determination in accordance with Section 10. Determine the correction for nitric acid (HNO3) as described in 11.3 and substitute in the following equation:
W = (Qb x m + e1)/Δt
where:
W = energy equivalent of calorimeter, J/°C,
m = mass of benzoic acid, g,
Δt = corrected temperature rise, as calculated in accordance with 11.1 or 11.2, °C,
e1 = correction for heat of formation of nitric acid, J, and
Qb = heat of combustion of benzoic acid, J/g calculated from the certified value in kilojoules per gram mass given for NBS Standard 39i. Multiply kilojoules per gram mass by 1000 to obtain joules per gram (Note 5).
NOTE 4 - 2,2,4-trimethyl pentane may be used for checking the energy equivalent of the system for use with volatile fuels.
NOTE 5 - Multiply the heat evolved by combustion of the standard sample by the following factor.
1 + 10(-6)[197 (P - 3.04) + 42((m/V) - 3) + 30((Mw/V) - 3) - 45(t - 25)]
where:
P = initial absolute pressure of oxygen, MPa at temperature t,
m = mass of benzoic acid, g,
Mw = mass of water placed in bomb before combustion, g,
V = internal volume of bomb, L, and
t = temperature to which the combustion reaction is referred, ° C (final temperature of the calorimeter).
9.2 Heat of Combustion of Pressure-Sensitive Tape - Determine the heat of combustion of the pressure-sensitive tape in accordance with Section 10 using about 1.2 g of tape and omitting the sample. Make at least three determinations and calculate the heat of combustion as follows:
Qpst = (Δt x W - e1)/a
where:
Qpst = heat of combustion of the pressure-sensitive tape, J/g
Δt = corrected temperature rise, as calculated in accordance with 11.1 or 11.2, °C,
W = energy equivalent of the calorimeter, J/°C,
e1 = correction for the heat of formation of HNO3, J, and
a = mass of the pressure-sensitive tape, g.
9.2.1 Average the determinations, and redetermine the heat of combustion of the tape whenever a new roll is started.
