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)
10. Procedure
10.1 Turn on the apparatus. Make all electrical connections and open the water lines.

10.2 Before beginning, be sure that the bomb and its fittings are completely dry, inside and out.

10.3 Measure a piece of firing wire 100 mm long and attach the wire to the bomb electrodes forming a U-shaped loop.

10.4 Pipet 1.0 cm3 of water into the bomb and cover with a watch glass.

10.5 Mass of Sample:
10.5.1 Weigh the sample cup to 0.01 mg on a semimicro analytical balance. Place a piece of pressure-sensitive type (Note 6) across the top of the cup, trim around the edge with a razor blade, and seal tightly. Place a 3 by 12-mm strip of tape creased in the middle and sealed by one edge in the center of the tape disk to give a flap arrangement. Weigh the cup and tape. Remove from the balance with forceps. Fill a hypodermic syringe with the sample. The volume of sample necessary to produce a temperature rise equivalent to approximately 30 000 J can be estimated as follows:
V = (W x 0.0032)/(Q x D)
where:
V = volume of sample to be used, cm3,
W = energy equivalent of the calorimeter, J/°C,
Q = approximate heat of combustion of the sample, MJ/kg, and
D = density, g/cm3, of the sample.

NOTE 6 - For relatively high-boiling samples, such as non-volatile (i.e. IBP above 180°C) kerosine-type jet fuels, it is not necessary to use tape.

10.5.2 Add the sample to the cup by inserting the tip of the needle through the tape disk at a point so that the flap of tape will cover the puncture upon removal of the needle. Seal down the flap by pressing lightly with a metal spatula. Reweigh the cup with the tape and sample. Take care throughout the weighing and filling operation to avoid contacting the tape or cup with bare fingers. Place the cup in the curved electrode and arrange the fuse wire so that the central portion of the loop presses down on the center of the tape disk.

10.6 Bomb Assembly - Assemble the bomb and tighten the cover securely. Connect the bomb to the oxygen cylinder and slowly admit oxygen until a pressure of 3.0 MPa is attained. Do not purge the bomb to remove entrapped air. Disconnect the bomb from the oxygen cylinder and replace the valve cover. (Warning - A violent explosion may occur.) Be careful not to overcharge the bomb. If by accident, the oxygen introduced into the bomb does exceed 4.0 MPa, do not proceed with the combustion. A violent explosion, capable of rupturing the bomb, might occur. Detach the filling connection and exhaust the bomb in the usual manner. Discard the sample.

NOTE 7 - Pressures within the range of from 2.5 to 3.55 MPa may be used, provided the same pressure is used for all tests, including standardization.

10.7 Calorimeter Water:
10.7.1 Adjust the temperature of the calorimeter water. The choice of the temperature to which the water is adjusted before weighing depends on a number of factors, including room temperature, the desired initial temperature of the experiment, and the relative heat capacities of the calorimeter bucket, water, and bomb. No definite rule can be given, but the operator will learn by experience how to select the proper temperature under the conditions of his particular laboratory and apparatus. The following can be used as a guide:
Isothermal method: 3.0 to 3.5°C below jacket temperature
Adiabatic method: 1.5 to 1.8°C below room temperature

10.7.1.1 Isoperibol Method - Adjust the temperature such that after assembly of the calorimeter bomb and bucket its temperature will be a few tenths of a degree below the desired initial temperature.

10.7.1.2 Adiabatic Method - Adjust the temperature so that the initial temperature of the determination will be as close to some fixed values as possible. Control the mean temperature of all determinations within more than ±0.5°C and the temperature rise for all determinations within ±0.3°C.

10.7.2 Weigh the calorimeter bucket to ±0.05 g on a heavy-duty analytical balance. After once establishing the dry bucket weight, it need only be checked occasionally. Fill with the desired quantity of water (2000 to 2100 g) and reweigh to 0.05 g (Note 6). The exact quantity of water is not important as long as it is enough to cover the bomb and its fittings and is the same in each determination.

NOTE 8 - The change in the mass of the water in the calorimeter bucket due to evaporation after weighings will affect the energy equivalent. The effect of this loss is small and cancels if the procedure of placing the bomb in its bucket and completing the assembly of the system is carried out in the same manner and in the same length of time in the calibration experiments as in the measurement of the heat of combustion.

10.7.3 Immediately after weighing, place the bucket in position in the calorimeter jacket, carefully place the bomb in the bucket, and complete the firing circuit. Close the calorimeter cover and lower thermometers and thermistors.

NOTE 9 - The bomb should be lowered into the calorimeter without touching the water with the fingers. This can be done by using a hook on which the bomb can be hung and which can be removed after the bomb is in place in the calorimeter bucket. A hook made of a piece of brass rod about 1.6 mm in diameter has been found satisfactory. The hooked ends of the rod are inserted into holes on opposite sides of the screw top of the bomb and are easily removed after the bomb is in place. It is very important that all operations in the experimental procedure be carried out in an identical manner throughout for the energy equivalent and heat of combustion measurements.

10.8 Procedure for Isoperibol Method:
10.8.1 Start the stirrer motor and the controller on the jacket heater to bring the temperature of the water in the jacket to 28°C. Take time and temperature readings over a 25-min period. During this period there are three definite time intervals:
10.8.1.1 An initial period of about 6 to 9 min during which the temperature change results solely from thermal leakage and heat of stirring.

10.8.1.2 A middle period of about 12 min, at the beginning of which the charge in the bomb is fired, and during which the temperature change is due primarily to the heat liberated by the combustion reaction in the bomb and partly to thermal leakage and heat of stirring, and

10.8.1.3 A final period of 9 to 11 min during which the temperature change is again due solely to thermal leakage and heat of stirring.

10.8.2 Allow the temperature of the calorimeter water to drift up to the starting temperature and then make and record readings of the time and temperature of the initial period. During this initial period when the rate of temperature rise is constant, make observations of temperature at 1-min intervals. The starting temperature always has the same value as determined from the calibration runs.

10.8.3 When the firing temperature is reached, fire the sample by closing the firing circuit through the fuse wire in the bomb by depressing the button on the ignition unit. The pilot light should glow momentarily and the temperature should start increasing in about 15 s. If the circuit does not close, or if it remains closed, or if the temperature does not start rising, the experiment has misfired and must be discontinued. After the combustion of the sample and during the middle period when the temperature is rising rapidly, take temperature measurements at 30s intervals. After about 3 min, the rate of temperature rise will decrease so that temperature readings may be taken with more accuracy. These readings shall be continued until the rate of temperature change has been constant for at least 10 min. The readings made after the rate of temperature change has become constant constitute the final period.

NOTE 10 - During the initial and final periods the thermometer should be read with the highest possible care, since the overall precision of the determination depends directly upon these temperature measurements. During the middle period, because of the very rapid rate of temperature rise, it is not possible to make readings as carefully as during the initial and final periods. This is not important because the readings of the middle period are used only for calculating the relatively small correction for thermal leakage and heat of stirring.

10.9 Procedure for Adiabatic Method:
10.9.1 Start the stirrer motor and turn on the calorimeter controller. Use the manual control switch of the controller to bring the jacket temperature in close agreement with the bucket temperature. Allow the controller to automatically control the temperature and wait 15 min for equilibrium to be attained. At this point, and at the end point also, control the temperature of the jacket to the same temperature as the bucket, or slightly (0.005°C at most) below. Make readings at 1-min intervals until three consecutive readings show no change. Fire the sample by depressing the button of the ignition unit. The pilot light should glow momentarily and the temperature should start increasing in about 15 s. (If the temperature does not start rising, the experiment has misfired and must be discontinued.) Read and record the initial resistance, estimating the value to the nearest 0.00005°C.

10.9.2 After 6 min from firing, begin reading temperature every minute. Continue until three consecutive readings show no change, or the readings decrease. Read and record the final temperature reading estimating the value to the nearest 0.0005°C.

10.10 Analysis of Bomb Contents:
10.10.1 Turn off the controller and stirrer and remove the bomb from the calorimeter. Open the needle valve and allow the gas to escape at a uniform rate such as to reduce the pressure to atmospheric in not less than 1 min. Open the bomb and examine the interior for unburned carbon. If any trace of unburned carbon is found, the experiment should be rejected. Wash the interior of the bomb including the electrodes and the sample cup with a fine jet of water and quantitatively collect the washings in a 500-cm3 Erlenmeyer flask. Use a minimum amount of wash water, preferably less than 300 cm3. Titrate the washings with standard alkali solution using methyl red indicator.

10.10.2 Determine the sulfur content of the sample to the nearest 0.02 % sulfur as described in Test Method D129, D1266-IP 107, D2622, D3120, D4294, or D5453 depending upon the volatility of the sample.

10.10.3 When iron or Chromel C wire is used, remove and measure the combined pieces of unburned firing wire, and subtract from the original length. Record the difference as wire consumed.