ASTM D2533 Test Method for Vapor-Liquid Ratio of Spark-Ignition Engine Fuels
11. Procedure
11.1 Read and record the barometric pressure.
11.2 With the V/L buret at room temperature or somewhat above (Note 12) and everything in readiness, carry out the following steps as quickly as possible. Open the chilled sample container, tip it so as to reach the liquid with the hypodermic syringe needle, taking caution to prevent water from reaching the sample and partially fill the syringe. Point the needle upward and dispel the contents to eliminate all air bubbles. Immediately refill the syringe from the sample container and check for air or vapor in the syringe (Note 13).
NOTE 13 - Glycerol (mercury) in the buret may be somewhat above room temperature due to warming in the previous test, but should not be so warm as to cause the sample to vaporize when injected.
NOTE 14 - Vapor may form if the sample is drawn in too rapidly. If this happens, repeat the sampling with a clean, chilled syringe.
NOTE 15 - Use cotton gloves to reduce heat transfer from the hands to the syringe.
11.2.1 Depress the plunger exactly to the mark for the sample size desired, then, taking care not to disturb the plunger position, insert the needle through the rubber septum full length into the V/L buret. Depress the plunger all the way to inject the sample, and withdraw the needle. Use a 1-mL sample if the highest V/L ratio expected for the sample is less than 35. For higher V/L ratios, use a smaller sample sufficient to give 20 to 35 mL of vapor at the highest temperature to be tested.
11.3 Record the volume of sample charged, corrected by means of the calibration specified in 9.1 and 9.2.
11.4 Transfer the charged buret to the water bath set at the desired temperature and position so that the water level comes above the stopcock barrel.
11.5 As vapor forms in the buret, adjust the height of the leveling bulb to give the desired pressure on the sample. If glycerol is used as the confining medium, raise the level of glycerol in the reservoir 10.80 mm above the level of the glycerol in the buret for every mm of mercury that the barometric pressure is below 760 mm Hg; or lower it by a like amount for every mm that the barometric pressure is above 760 mm Hg. If mercury is used as the confining medium, raise the level of the mercury in the reservoir 1.0 mm above the level of the mercury in the buret for every mm of mercury that the barometric pressure is below 760 mm Hg; or lower it by a like amount for every mm that the barometric pressure is above 760 mm Hg.
NOTE 16 - If the difference between the atmospheric pressure in the laboratory and the pressure for which the V/L measurement is desired is too great for convenient correction by means of the leveling bulb alone, use the mercury-filled manometer described in 6.2.4 to set the pressure. Keep the level of glycerol in the leveling bulb the same as that in the buret and apply pressure or vacuum gently to the air space in the leveling bulb as needed to obtain the desired pressure on the manometer.
NOTE 17 - With some narrow boiling gasoline fractions, super heating may occur and no vapors are formed in the buret, even after immersion for as long as 15 min or more. When vaporization takes place, it does so rapidly and sometimes explosively. With these samples, it is recommended that injection be carried out with warm glycerol in the buret, such that a few millilitres of vapor are formed immediately after injection. The temperature of the glycerol is dependent on the sample composition but in general should not be more than 50°F (28°C) above ambient. With mercury as the confining medium this phenomenon has not been observed.
11.6 Without removing the buret from the water bath, shake it sufficiently to agitate the liquid sample, but not so vigorously as to disperse droplets of sample into the glycerol.
NOTE 18 - Shaking is not necessary if mercury is used as the confining liquid because the superior heat transfer properties of the mercury will result in rapid thermal equilibrium of the system. With mercury as the confining liquid shaking is discouraged because of the danger of breakage of the glass caused by accidental impact.
11.7 Readjust the height of the leveling bulb, if necessary, to give the desired pressure on the sample. Because of mercury's high density, the use of a cathetometer or similar optical leveling device is necessary to minimize pressure errors.
NOTE 19 - Any spilled mercury, and any that may be purged from the equipment, should be placed in an airtight closed vessel. This recovered mercury may be sent to a reprocessor, who can provide shipping instructions. (Names of mercury reprocessors are available from ASTM Headquarters.) To minimize spillage, a catch pan that is large enough to contain all the mercury in case of failure should be placed under the apparatus.
It is useful to have a 1 L vacuum flask available connected to a vacuum source. Introduce a few ounces of a solid mercury vapor absorbent in the flask. Connect one end of a piece of tubing to the top of the flask and insert a glass eyedropper at the other end. Use the eyedropper end to pick up spilled mercury and to remove the spent sample and excess mercury from the top of the burets at the end of the run.
11.8 Read the volume of vapor to the nearest 0.1 mL. Repeat until the volume remains constant for at least 2 min. Record the volume, corrected by means of the calibration specified in 9.1 and 9.3, the bath temperature, and the pressure.
11.9 If the vapor-liquid ratio is also desired at another temperature, either adjust the temperature of the bath accordingly, or transfer the buret to another bath at the desired temperature. Repeat the operations described in 11.5 and 11.8.
NOTE 20 - During the cleaning procedure note that small amounts of hydrocarbons can be trapped between the glass and the Hg column. If they are not removed, they may contaminate the next sample. After removal of the spent sample at the end of the run, close the valve at the top of the tube and immerse the tube in the hottest bath available at that moment for about 5 min. Then raise the tube 50 to 75 cm and hold in this position for 5 to 10 s. The trapped hydrocarbons will rise to the top of the tube, from where they can be removed.
12. Calculation
12.1 For each determination calculate the vapor-liquid ratio as follows:
Vapor - liquid ratio = A/B
where:
A = volume of vapor, mL and
B = volume of sample charged, mL.
