GB/T 384-2025Determination the heat of combustion for hydrocarbon fuels — Bomb calorimeter method (English PDF)

3.1 Bomb heat of combustion

The heat released, when a unit mass of specimen is completely combusted in a constant-volume bomb calorimeter which is filled with high-pressure oxygen, except for water which condenses into a liquid state, nitrogen oxides and sulfur oxides which dissolve in water to form nitric acid and sulfuric acid, respectively, the remaining substances (oxygen, nitrogen, and carbon dioxide) of combustion are in a gaseous state.

Note. The sample contains only carbon, hydrogen, oxygen, nitrogen, sulfur elements. The initial temperature of the specimen and oxygen, and the final temperature of the products, are both 25 °C.

3.2 Gross heat of combustion

The heat released, when a unit mass of specimen undergoes complete combustion in a constant-volume bomb calorimeter filled with high-pressure oxygen, producing gaseous oxygen, nitrogen, carbon dioxide, nitrogen oxides, sulfur dioxide, while water condenses into a liquid state.

Note. For liquid fuels, only the heat of combustion of carbon, hydrogen, nitrogen, oxygen, sulfur is calculated.

3.3 Net heat of combustion

The heat released when a unit mass of specimen undergoes complete combustion under constant pressure, producing gaseous oxygen, nitrogen, carbon dioxide, nitrogen oxides, sulfur dioxide, water.

3.4 Energy equivalent

Energy equivalent for water The energy required to raise the temperature of the calorimeter system by 1 °C.

Note. The unit is megajoules per degree Celsius (MJ/°C).

5.1 Benzoic acid standard sample. Certified standard sample with specific calorific

value.

5.2 2,2,4-Trimethylpentane (isooctane) standard sample. Purity not less than 99.75%. 5.3 Gelatin capsules. 5.4 Mineral oil.

5.5 Oxygen. It shall not contain hydrogen or other flammable impurities; electrolytic

oxygen shall not be used. Commercially available oxygen produced from liquid air can be used without purification.

5.6 Pressure-sensitive tape. Celluloid tape, free of chlorine and sulfur.

6.1 Schematic diagram of the manual calorimeter dish (small dish) is shown in

6.2 Isothermal automatic testing system. This includes the testing chamber, oxygen

bomb, calorimeter, jacket, thermometer, accessories. The requirements shall meet those outlined in B.2.

Note. An isothermal automatic calorimeter can be used.

6.3 Ignition wire. Ni-chromium alloy, iron wire, copper wire, or other ignition wire with a diameter not exceeding 0.2 mm, cut into equal segments of 60 mm ~ 120 mm (depending on the structure of the oxygen bomb accessories and the ignition wire system). Weigh a bundle of 10 ~ 15 wires to determine the mass of each metal wire;

automatic instruments generally use 100 mm long ignition wires.

6.4 Oxygen bomb, pressure gauge, and oxygen connection tubing. These shall be tested

under hydrostatic pressure as needed, at least once a year. The oxygen bomb shall be tested at a pressure of 9.81 MPa (100 kg/cm2). Lubricating grease is strictly prohibited on the connecting parts of compressed oxygen equipment. If the oxygen bomb or oxygen connection equipment becomes oily due to contact with lubricating oil or other oils during testing or handling, it shall be carefully washed with gasoline first, then with ethanol or ether. 6.5 Metal clamps. 6.6 Pipette. 1 mL. 6.7 Stopwatch. 6.8 Syringe.

6.9 Analytical balance. Graduation value 0.1 mg.

6.10 Conventional balance. Load 5 kg, graduation value 0.5 g.

6.11 Volumetric flasks. 1000 mL and 2000 mL.

6.12 Desiccator. Contains concentrated sulfuric acid or phosphorus pentoxide.

6.13 Thermometer. Platinum resistance thermometer, with a resolution of not less than

0.001 °C, short-term repeatability not exceeding 0.01 °C, long-term drift not exceeding 0.05 °C within 6 months. A general calorimeter with a graduation of 0.01 °C or a Beckman thermometer may also be used; it shall be checked by a national metrology authority every 1 °C; its calibration error shall not exceed 0.005 °C.

8.1 Sampling

Sampling shall be performed according to the methods specified in GB/T 4756 or GB/T 27867 For samples containing volatile components, the sample container shall be opened only before the test; the sample shall be analyzed as soon as possible after removal.

Wax-containing, viscous, heavy oils shall be heated to 40 °C ~ 50 °C, mixed thoroughly, then sampled.

8.2 Filtration

Some fuels contain water and particulate matter (ash) that can lower the calorific value.

If it is necessary to measure the calorific value of clean fuels, the sample can be filtered before testing to remove free water and insoluble ash.

8.3 Sample mass estimation

The mass of the sample (including all additional fuels) shall be controlled within a certain range, so that the temperature rise generated by its combustion is equal to the temperature rise of 0.9 g ~ 1.1 g of benzoic acid.

If the approximate heat of combustion of the sample is known, the sample weight can be estimated according to formula (1).

Note. The calorific value of the sample is in the range of 37 MJ/kg ~ 44 MJ/kg; the sample weight is 0.71 g ~ 0.60 g. Where.

me - Estimated sample weight, in grams (g);

26.454 - Parameter for calculating sample weight;

Qs - Approximate heat of combustion of the sample, in megajoules per kilogram (MJ/kg).

8.4 Preparation of dish

To avoid residual substances in the dish affecting the test, the dish can be calcined at 750 °C ± 5 °C for 10 min before measurement, cooled, then weighed to an accuracy of 0.1 mg.

8.5 Loading of non-volatile samples

When measuring non-volatile samples (initial boiling point above 180 °C), weigh the specimen to an accuracy of 0.1 mg, recorded as m, in grams (g).

8.6 Loading of highly volatile samples

8.6.1 For highly volatile liquids, use pressure-sensitive tape (following 8.6.2 ~ 8.6.3) or

gelatin capsules/mineral oil (following 8.6.4) to seal them, reducing calorific value loss due to the volatilization of light components.

8.6.2 Place a piece of pressure-sensitive tape on top of the dish; trim the edges with a blade; seal. Take another 3 mm x 12 mm strip of adhesive tape; fold it in half; attach one half to the center of the sealing layer. Use the other half to seal the pinhole later.

Record the tape mass as mp. Remove it from the balance with tweezers.

8.6.3 Insert the syringe needle through the pressure-sensitive adhesive tape strip and

inject the specimen into the dish. After withdrawing the needle, gently press the folded edge with a metal scraper. Weigh again, accurate to 0.1 mg; record the specimen mass as m (grams). Handle weighing and filling carefully, avoiding direct contact between fingers and the tape or dish. Place the dish under the arc electrode and adjust the ignition wire, so that the center of the ignition wire is pressed downwards onto the center of the adhesive tape strip.

8.6.4 Weigh the gelatin capsule and record it as mp. Add the sample to the capsule;

weigh again, accurate to 0.1 mg; record the sample mass as m (grams). To prevent poor combustion of the capsule, a few drops of mineral oil can be added to the capsule; then it shall be weighed again. Place the sample dish in the curved electrode and adjust the ignition wire, so that the center of the ignition wire contacts the capsule (and the mineral oil). The capsule shall be handled with tweezers.

8.7 Verification of measurements of highly volatile samples

The measurement results of the high-volatility sample are verified using a 2,2,4- trimethylpentane standard sample. If the difference between the obtained result and the nominal value of 2,2,4-trimethylpentane is not greater than the repeatability of the method, the measurement process is considered to meet the requirements. If the difference is greater than the repeatability, the sample processing method needs to be changed. If the deviation still exists, test 2,2,4-trimethylpentane according to 10.1, to determine the energy equivalent of the high-volatility fuel measurement system.

9.1 Water injection into the oxygen bomb

Inject 1.0 mL of distilled water into the oxygen bomb.

9.2 Sealing the oxygen bomb

Fix the sample dish containing the specimen onto the ring of the oxygen bomb electrode, ensuring the plug passes through the opening of the ring. Connect both ends of the ignition wire to the electrode; then tighten the oxygen bomb.

9.3 Injecting oxygen

Warning - When operating with compressed oxygen, the operating procedures must be followed.

Warning - The oxygen bomb must not be overcharged. If oxygen is accidentally introduced into the oxygen bomb at a pressure exceeding 4.0 MPa, combustion shall not continue. An explosion may occur; the oxygen bomb may violently rupture. Disconnect the filling connection and vent the gas as usual. Discard the specimen and reload it.

With the test sample and fuse in place, slowly introduce oxygen to a gauge pressure of 3.0 MPa at room temperature. There is no need to purge the oxygen bomb to remove trapped air.

The initial oxygen pressure shall be controlled within the range of 2.5 MPa ~ 3.5 MPa;

all tests (including calibrations) shall be performed at the same pressure.

9.4 Water for calorimeter

9.4.1 Before measurement, the container shall be dried; approximately 2000 g of

distilled water shall be poured into the calorimeter, weighed to the nearest 0.5 g. If the measurement is always performed within the same temperature range (temperature variation within 5 °C), the water can also be quantitatively measured using a volumetric flask. The amount of water added shall be such that the oxygen bomb is submerged in water up to 2/3 of the way up the locking nut of the inlet valve. The same amount of water shall be used for all subsequent measurements of the specimen.

9.4.2 For calorimeters with an energy equivalent of approximately 10.2 kJ/°C, to ensure

the final temperature is slightly higher than the calorimeter jacket temperature, adjust the calorimeter water temperature to be 1.6 °C ~ 2.0 °C lower than the jacket temperature before weighing. Alternatively, a lower initial temperature can be chosen, so that the final temperature is slightly lower than the jacket temperature. All tests (including calibration) shall be performed under the same temperature conditions.

9.5 Instrument preparation

Slowly submerge the oxygen bomb into the water-filled calorimetric container, avoiding water loss. Connect the leads to the oxygen bomb electrodes; close the lid;

then start the stirrer. The thermometer and stirrer shall not touch the walls of the oxygen bomb or calorimetric container. The center of the thermometer's sensing element shall be located at 1/2 the height of the oxygen bomb. The stirring part of the stirrer shall not protrude above the water surface. Start the calorimetric test, after the equipment has equilibrated for 5 minutes.

The rotation speed of the calorimeter stirrer shall ensure rapid stirring of the water in the container without splashing; the temperature rise caused by stirring shall not exceed 0.01 °C every 10 minutes. The vertical stirring speed shall not be less than 50 r/min;

the speed of the helical stirrer shall not be less than 400 r/min.

Use a voltage lower than 12 V for ignition. The energizing time shall not exceed 1 second. Indicator lights should be connected in series in the circuit to facilitate observation of ignition. When there are significant voltage fluctuations in the circuit, DC power should be used for the calorimeter.

9.6 Temperature recording

9.6.1 The manual calorimetric test is divided into three phases. ......