ASTM D2889 Test Method for Calculation of True Vapor Pressures of Petroleum Distillate Fuels
5. Data Requirements
5.1 Distillation temperatures at the initial boiling point (IBP) and 10, 30, 50, 70, and 90 volume % distilled obtained in accordance with Test Method D86.
5.2 API gravity determined in accordance with Test Method D287, or a method of equivalent accuracy.
6. Procedure
6.1 Calculate the 10/70 slope, °F/%, of the Test Method D86 distillation using the 10 and 70 volume % distilled temperature. Using this slope and the Test Method D86 50 volume % distilled temperature, obtain to the nearest +/- 1°F a temperature difference,° F, from Fig. 2. Add °F to the Method D86 50 volume % temperature to obtain the equilibrium flash vaporization (EFV) 50 volume % temperature.
6.2 Calculate the differences between the Test Method D86 IBP and 10 volume %, the 10 and 30 volume %, and the 30 and 50 volume % temperatures. Using these differences, obtain to the nearest 1°F, the temperature differences between corresponding EFV percentages from Fig. 3.
6.3 Calculate the EFV zero volume percent temperature by subtracting the sum of the three differences obtained from Fig. 3, from the EFV 50 volume % temperature calculated in accordance with 6.1.
6.4 Plot a point on Fig. 1 at the coordinates, 14.7 psia and the calculated EFV 0 % temperature. This point establishes the lower end of the phase boundary line commonly referred to as the bubble-point line. If the EFV 0 % temperature at atmospheric pressure has been measured, use the measured value instead of the calculated value.
6.5 Use the following procedure and the curves on the right portion of Fig. 1 to obtain coordinates for the upper end, or focal point, of the bubble-point line. If both the critical temperature and critical pressure of the fuel are known, the calculations described in 6.5.1 through 6.5.4 are not carried out. The critical temperature and critical pressure are used as the coordinates in Fig. 1 to define a critical point to be used instead of the focal point.
6.5.1 Calculate to the nearest 0.1 unit the 10/90 slope of the Test Method D86 distillation curve, °F/volume %, as the difference between 10 and 90 volume % distilled temperatures divided by 80.
6.5.2 Calculate to the nearest 1°F, the volumetric average boiling point (VABP) as the sum of the Test Method D86 10, 30, 50, 70, and 90 volume % distilled temperatures divided by 5.
6.5.3 Calculate to the nearest 0.1 unit the ratio:
VABP/(10/90 Slope + 16.0)
6.5.4 Enter Fig. 1 on the lower right scale at the Test Method D86 VABP temperature. From the intersection of the VABP temperature and the line of constant API gravity corresponding to the gravity of the sample, proceed horizontally to the point of intersection with the line corresponding to the 10/90 slope of the Test Method D86 distillation. From this point proceed vertically to the intersection with the ratio calculated for the sample according to the previous section. This point of intersection establishes the upper end, or focal point of the bubble-point line.
6.6 Draw the bubble-point line on Fig. 1 by connecting the two points (6.4 and 6.5.4) with a straight line.
6.7 Obtain the calculated true vapor pressure psia, at any specified temperature below the critical temperature by reading the vertical pressure scale of Fig. 1 at the intersection of the bubble-point line with the specified temperature.
6.7.1 If either a determined critical temperature or determined critical pressure is known, the point of its intersection with the bubble-point line defines the maximum vapor pressure to be reported.
6.7.2 If neither the critical temperature nor critical pressure is known, obtain a calculated approximate critical temperature from Fig. 4. The point of intersection of the calculated critical temperature with the bubble-point line defines the maximum vapor pressure to be reported.
