ASTM D2274 for oxidation stability of distillate fuel oil (Accelerated method)
11. Procedure
11.1 Preparing the Sample - Place one filter (described in 7.7) on the filter support and clamp the filter funnel to the support as shown in Fig. 2. Apply suction (approximately 80 kPa (12 psi). Pour 400 mL of the fuel through the filter (see 7.7) into a clean (10.1) 500-mL glass suction flask. Repeat preparation for each sample to be run. After filtration is complete, discard the filter media. Never use the same filters for a second increment of fuel, because any material deposited on the filters by a previous increment of fuel can result in a greater removal of solids from the next increment.
11.2 Assembling the Oxidation Apparatus:
11.2.1 Place a clean oxygen delivery tube into a clean oxidation cell (Section 10) and pour 350 more or less 5 mL of the filtered fuel into the cell. As soon thereafter as possible, but in no case greater than 1 h after measuring the fuel, immerse the test cell in the 95°C (203°F) heating bath. During any interim period store the cell in the dark. The level of fuel in the oxidation cell shall be below the level of the liquid medium in the heating bath.
11.2.2 Place a condenser over the oxygen delivery tube and oxidation cell; connect the condenser to the cooling water. Connect the oxygen delivery tube to the oxygen supply through the flowmeter and adjust the oxygen flow to 3 more or less 0.3 L/h. Make sure samples are protected from light. When the number of test cells is less than the capacity of the heating bath, fill the empty positions with dummy oxidation cells containing 350 mL of a stable petroleum liquid with physical properties similar to those of the fuel being tested.
11.2.3 Record the time the first oxidation cell is placed in the bath as zero time.
NOTE 3 - Military Specification MIL-F-16884 permits the use of a modified Test Method D2274 procedure in which the time in the heating bath is extended to 40 h. Periods other than 16 h may also be used in research or in other specifications. However, the precision values given in Test Method D2274 apply only to the 16 h period in the heating bath.
11.3 Cooling the Sample:
11.3.1 Sixteen more or less 0.25 h from zero time, remove the samples from the heating bath in the same sequence as they were placed therein. Cover the opening of each cell with a piece of aluminum foil or plastic to prevent entrance of dirt, dust, or moisture. Record the time the first cell is removed.
11.3.2 Place in a dark, ventilated site at room temperature, which shall be above the cloud point of the fuel, until the fuel attains room temperature but for no longer than 4 h.
11.4 Determining Filterable Insolubles:
11.4.1 Assemble the filter apparatus as illustrated in Fig. 2, using one set of matched pair filters. Apply suction or vacuum as necessary to filter the sample in an adequate time (approximately 80 kPa (12 psi); pour the cooled sample through the filter. Pull all fuel through the filter before pouring isooctane rinses into the filter assembly.
NOTE 4 - If the filtration of the sample cannot be completed within 2 h as a result of severe filter plugging, filter the remaining fuel through a separate set of filters.
11.4.2 On completion of filtration, completely rinse the oxidation cell with three separate 50 more or less 5 mL volumes of isooctane from a squeeze bottle or vessel capable of directing a fine stream of isooctane. Pass all rinsings through the filter assembly.
11.4.3 After filtration and rinsing of the oxidation apparatus is complete, wash down the sides of the funnel with an additional 50 more or less 5 mL of isooctane directed as a fine stream. The stream of isooctane should be directed in a manner that, where possible, would push particles to the middle of the filter pad.
11.4.4 After filtration is complete, disconnect the top part of the filter assembly and wash down the rim of the filter media and adjacent parts of the filter assembly with a further 50 more or less 5 mL of isooctane. Be certain the area of the filters previously under the filtration funnel is adequately rinsed to eliminate any presence of residual distillate fuel. Discontinue the vacuum and disconnect the filter assembly. Discard the filtrate.
11.4.5 Dry the two filter media at 80°C (176°F) for 30 min, cool them for 30 min, and weigh the upper (sample) and lower (blank) filters separately to the nearest 0.1 mg.
11.5 Determining Adherent Insolubles :
11.5.1 After the final rinsing of the oxidation cell and the oxygen delivery tube with isooctane, dissolve adherent insolubles from the surfaces of these pieces using three equal rinses totalling 75 more or less 5 mL of trisolvent.
11.5.2 Examine the oxidation cell and the oxygen delivery tube for evidence of stain or color indicating incomplete removal.
If such stain or color is noted, rinse with a fourth 25-mL volume of trisolvent.
11.5.3 Evaporate the trisolvent from the rinsings in either of two ways.
11.5.3.1 Collect the rinsings in a tared 200-mL tall beaker. Place the beaker and contents on a hot plate and evaporate the trisolvent at 135°C under a hood. When all the solvent has evaporated, place the tared beaker in a desiccator without desiccant to cool for 1 h. When dry and cool, weigh the beaker to the nearest 0.1 mg.
11.5.3.2 Optionally, collect the rinsings in one or two 100-mL beakers of the type specified for Test Method D381 and evaporate the trisolvent at 160°C by the Test Method D381 air-jet method.
11.5.4 Run an adherent insolubles blank by evaporating a volume of trisolvent equal to that used in the test and correct for the presence of impurities in the solvent.
