AIDS FOR ANALYTICAL CHEMISTS Analyzer for Determining Fuel Vaporization Pressure Curves of Gasoline and Gasoline-Alcohol Fuels John H. Baudino, Frank J. Chloupek, and Arthur W. Crowley" Atlantic Richfield Company, Harvey Technical Center, Harvey, Iilinois 60426
Volatility characteristics of gasolines have been related to engine performance as detailed in a review by G. H. Unzelman and E. S. Forster of Ethyl Corporation ( 1 ) . T h e typical volatility characteristics of fuels RVP, To( V / L 20) and 10, 50 and 90% evaporated temperatures are measured by ASTM Methods D-323, D-2533, and D-86 or D-216, respectively. These fuel properties, which are used as production specifications, are all measured under equilibrium conditions or as a function of changing temperature and are method dependent. This paper describes the development of an analyzer for determining a nonequilibrium volatility characteristic of fuels. T h e characteristic is the pressure increase with time resulting from the vaporization of a fuel. T h e property is measured while vaporizing a fuel sample under conditions of constant volume, temperature, and initial reduced pressure. This characteristic should be more representative of fuel performance t h a n one measured under equilibrium conditions because fuel vaporization does not reach equilibrium in the intake system of an engine ( 2 ) . T h e analyzer a n d method have been named the Fuel Vaporization Pressure Analyzer (FVP Analyzer) and Fuel Vaporization Pressure Test (FVP Test), respectively. T h e output of the analyzer is the fuel vaporization pressure curve, a pressure vs. time curve, which is unique for each fuel. T h e fuel is injected with a snap sample injector into a vaporization chamber and the pressure of vaporization is recorded on a calibrated strip-chart recorder. Only a small quantity of fuel (40-80 pL) is required for the measurement. The use of a snap sample injector, described in the paper, makes it possible t o introduce a known quantity of fuel into the analyzer while having a minimum effect on the vaporization pressure results. T h e test conditions of the vaporization chamber can be varied to provide the capability of determining vaporization pressure curves of fuels over a wide range of conditions. In addition t o the analyzer design, this paper covers the results of experiments which show the effects of sample size, initial pressure, and temperature on the fuel vaporization pressure curves. T h e precision of the test method is demonstrated by repeatability experiment results using isooctane and Indolene clear gasoline. Also reported are the vaporization pressure curves of fuels containing alcohol. These fuels have been difficult t o characterize by the usual test methods (3-5). I n general, using this analyzer and method, fuels can be characterized by their vaporization pressure curves rapidly with good precision. T h e potential of predicting a fuel's performance from its vaporization pressure curve has been demonstrated using gasoline and gasoline-alcohol fuels ( 4 ) . Experiments are in progress to further demonstrate the applications of the FVP Test results and will be the subject of a future paper.
EXPERIMENTAL Apparatus. The Fuel Vaporization Pressure Analyzer consists of a nominal 1-L spherical glass vaporization chamber, diagramed 2368
ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977
in Figure 1, equipped with two pressure transducers (Validyne DP-15), a sheathed thermocouple, a nominal 500-mL reference pressure reservoir, and a fixed-volume snap sample injector. The sample injector is positioned so that vaporization takes place in the center of the sphere. A catch pan is positioned immediately below the end of the sample injector rod t o retain all of the fuel in the center of the chamber. The snap sample injector is detailed in Figure 2. It is a modification of the type previously offered by Precision Sampling Corporation for injection of smaller size samples (6). A calibrated circular groove in the injector rod holds a known volume of sample when the rod is withdrawn into a Teflon sleeve. In this position, the sleeve seals the sample until injection, and the sample injector can be dried, heated, or placed in a vacuum without loss of sample. This type of injector was chosen so that the small fuel samples could be accurately injected with a minimum effect on the vaporization pressures caused by the injection. The chamber and other items shown in Figure 1 are mounted in a constant temperature box and attached to a standard vacuum system for evacuating and adjusting the test pressure. This system consists of a vacuum pump, manometer, 0.0 to 20.0 mm Hg range Dubrovin vacuum gauge, and cylinder of dry, hydrocarbon-free air. The transducers are connected t o demodulators (Validyne CD-15) calibrated to different sensitivities and the output signals are recorded on a variable chart speed, two-channel recorder (Hewlett-Packard Model 7100B with Model 17501A multiple span modules). Temperatures are recorded on a multipoint recorder. The chamber temperature and initial pressure can be adjusted within the ranges of -18.0 to +38.0 f 0.03 "C and 0.1 mm Hg to atmospheric pressure, respectively. The precision of these test pressure measurements is fO.02 from 0.1 to 20.0 mm Hg and f0.5 mm Hg from 20 mm Hg to atmospheric pressure. The two valves located at the bottom of the chamber are Fischer & Porter Co. Quick Opening Threaded Glass Valves with Teflon stems and a 4-mm base size. Reagents. The analyses of the Indolene clear gasoline and other test fuels are given in Table I. Procedure. A 100-mL sample of fuel to be tested is conditioned to a constant temperature (4.0 to 24.0 f 0.02 "C) in a sealed bottle using a constant temperature bath. A volume of the fuel is then sampled with the snap sample injector, taking precautions to ensure that no air is taken in with the sample. The injector is positioned and secured in the center of the vaporization chamber while maintaining the chamber at the test temperature under a slight positive pressure with dry air. The system is evacuated to 0.1 mm Hg, pressurized back to atmospheric pressure and evacuated to 0.1 mm Hg again to purge the chamber of any hydrocarbons remaining from the previous run. The pressure is then adjusted to the desired test pressure. After the system is equilibrated at the test temperature and pressure (about 10 min), valves 1 and 2 shown in Figure 1 are closed. The differential pressure is set at zero and observed to ensure no leaks and complete equilibration of the system before injection of the fuel sample. The recorder is started (2.54 cm/s) and the sample is injected into the vaporization chamber. As the fuel vaporizes, the increasing pressure is detected by the pressure transducers and the different sensitivity outputs are recorded continuously on the strip-chart recorder. The outputs are set to give full scale readings of 6.33 f 0.007 and 19.00 f 0.02 mm Hg t o cover the vaporization pressure ranges of most fuel samples.
Table I. Analyses of Test Fuels Fuel Indolene Clear Alcohol, vol % 0 RVP, psia 10.2 T F ( V / L 20)b 132 O
Distillation ( D 8 6 ) , " F 7% Evaporated IBP 10 20 30 40 50 60 70 80 90 EP a
89 128 154 181
205 225 243 264 29 1 327 408
A 0 11.0 124
B
C 0 13.2 14.4 110 112
99 120 136 158 181 205 230 259 301 343 420
81 103 114 127 142 164 189 215 229 254 375
D 0 9.9 140
0
Modified to use no water for fuels containing alcohol.
E 0 9.4
...
EA 5 13.0
...
F 0 9.2
...
:FA 5 11.9 . , .
.. 100 97 95 92 '35 90 137 137 116 123 109 155 183 185 147 142 116 205 214 208 204 158 145 216 229 227 225 179 1'71 219 239 237 236 207 198 224 250 244 245 233 2'23 228 270 257 258 269 261 234 326 286 286 322 316 247 398 353 356 351 345 379 488 469 460 439 4.32 Modified to use mercury for fuels contaming ,
G 0 13.8
...
87 102 112 125 141 163 197 227 245 277 405 alcohol.
GA 5 16.7
...
85 94 101
108 129 157 191 224 245 276 402
Table 11. Repeatability Data PVP, mml Hg
SAMPLE INJECTOR
Time,s 0.50 1.0
TVP, 3.0 6.0 12.0 30.0 m m H g Indolene clear
Run No. 1
VAPORIZATION CHAMBER
TRANSDUCER
THERMOCOUPLE
PAN
TRANSDUCER
2 3 4 5 6 Av Std dev Range
1.02 0.91 0.99 0.89 0.85 0.90 0.93 0.06 0.17
1.49 1.37 1.45 1.31 1.33 1.35 1.38 0.07 0.18
2.34 2.94 2.19 2.75 2.25 2.81 2.21 2.80 2.20 2.83 2.16 2.74 2.23 2.81 0.06 0.07 0.18 0.20 Isooctane
3.58 3.40 3.43 3.41 3.50 3.38 3.45 0.08 0.20
4.61 4.46 4.45 4.42 4.55 4.44 4.49 0.08 0.19
10.14 10.04 10.08 10.06 10.06 10.16 10.09 0.05 0.12
0.10 0.07 0.08 0.10 0.10 0.09 0.10 0.09 0.01 0.03
0.17 0.14 0.15 0.17 0.16 0.16 0.16 0.16 0.01 0.03
0.45 0.42 0.43 0.44 0.43 0.44 0.44 0.44 0.01 0.03
0.86 0.80 0.81 0.83 0.82 0.83 0.84 0.83 0.02 0.06
1.32 1.25 1.27 1.28 1.29 1.29 1.32 1.29 0.03 0.07
1.74 1.73 1.78 1.74 1.84 1.83 1.86 1.79 0.05
9.00 9.02 9.04 9.00 9.02 9.00 9.02 9.01 0.02 0.04
Run No. GLASS TUBING
VALVE 2 RESERVOIR
Figure 1. Schematic drawing of fuel vaporization pressure apparatus
When the pressure approaches a constant value, the recorders are turned off, valve 1 is opened to equalize the pressure between the chamber and reference reservoir and then valve 2 is opened. The system is pressurized to a slight positive pressure and the sample injector is removed and made ready for the next sample. Calibration. The responses of the transducers are set at the desired sensitivities by pressurizing the system with air to the desired full scale pressure and adjusting the output of the demodulators to full scale. The analyzer is zeroed before each run and the calibration is checked daily or when necessary. The check is made by measuring the vaporization pressure of a span liquid under total vaporization conditions (0.1 mm Hg and 24 "C). The normal span liquid is isooctane. To check the span at lower temperatures, n-pentane is used. The snap sample injector volumes are calibrated using isooctane vaporization pressures obtained at 0.1 mm Hg pressure and 24 "C and then back-calculating the liquid volume injected using the ideal gas equation. The volumes of the sample injectors used for this study were determined to be 76.7, 58.1, and 38.8 f 0.2 PL. Since each injector rod occupies a certain volume, which results in a pressure increase when the sample is injected, a correction in the pressure readings is necessary. The pressure correction for this volume is determined by injecting an empty sample injector, with the sample space a t the same pressure as in the chamber, into the chamber and measuring the increased pressure under test conditions. In addition, the vaporization pressure data
1 2 3 4 5 6 7 Av Std dev Ranee
0.11
reported in this paper are corrected to a standard chamber volume of 1.00 L.
RESULTS A N D D I S C U S S I O N T h e vaporization pressure curves of isooctane and Indolene clear fuel in Figure 3 were determined with the FVP Analyzer. A 76.7-pL sample was vaporized a t 24 "C and an initial reduced pressure of 660 mm Hg. These curves show the pressure rise with vaporization for 30 s, b u t data were recorded until all the fuel vaporized or a constant pressure was approached. Vaporization of the sample occurs a t the center of the chamber. T h e pressure increase in the chamber was found t o be uniform, as indicated by identical responses by the two transducers. Under these test conditions, the total vaporization pressure of some fuel samples is approached within 10 min. However, with the initial conditions of 24 "C and 0.1 mm Hg pressure, most samples approach total vaporization within 5 t o 6 s. Results obtained a t 0.1 mni Hg reduced pressure will be referred t o as total vaporization pressures (TVP's) and those a t higher pressures as partial vaporization pressures (PVP's). ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977
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Figure 2. Schematic drawing of snap sample injector. Cut-away schematic drawing of packing to hold fuel sample is shown in insert. a = 41.3 f 0.5 mm, 6 = 4.648 f 0.013 mm, c = 6.35 0.02 mm, d = 1.24 f 0.38 mm, e = 6.0 f 0.5 mm, f = 50.8 f 0.5 mm, g = 9.52 f 0.10 mm, h = 0.51 -I- 0.02, -0.04 mm, i = 5.97 f 0.02 mm, j = 2.007 f 0.025 mm, k = 4.648 4~ 0.025 mm i.d., 8.560 -k 0.000, -0.051 mm od, I = 2.381 i 0.013 mm, rn = as required for sample size
*
60
$ 2 0
2 o r
00
00
40
E0
120 TIME
160
20C
240
280
Figure 3. Vaporization pressure curves
The repeatability of the test method is very good under both of t h e above conditions. Repeatability data using Indolene clear and isooctane are given in Table 11. The PVP data were obtained using 76.7-pL samples a t 24 "C and 660 mm Hg initial pressure. The maximum pressure ranges with Indolene clear a n d isooctane are 0.2 and 0.1 mm Hg, respectively. As expected, the data using the pure material, isooctane, is more repeatable. Also given in Table I1 are the T V P results for Indolene clear and isooctane. These tests were made using 76.7-lrL samples a t 24 "C and 0.1 mm Hg initial pressure. These d a t a indicate t h a t TVP's can also be measured with good precision. E f f e c t of V a r i a b l e s . All measurements are made a t the same chamber volume of 1 L b u t the sample size, initial pressure, and temperature can be varied to determine a fuel's vaporization pressure curve under different test conditions. T h e effects of these variables on vaporization curves were evaluated using a typical full boiling range gasoline, Fuel A. T h e effect of sample size on the vaporization curve was determined a t 24 "C and an initial reduced pressure of 660 m m Hg. Three different sample injectors were used to inicot 76.7, 58.1, and 38.8 pL. The Figure 4 curves show the greaL, st effect of sample size to be on the initial vaporization pressures, i.e., within about the first 24 s. The effect then decreases with time until the vaporization pressure increases are directly proportional to t h e increase in sample size. T h e effect of initial pressure was determined using a 76.7-pL sample a t 24 "C and two initial reduced pressures of 660 and 350 m m Hg. T h e maximum effect, as shown in Figure 5 , 2370
00
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SECGUDS
ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977
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2C0
240
28C
SECGUDS
Figure 4. Effect of sample size on FVP curves with Fuel A 6 3 1
1
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I 120 Tl',IE
1 160
I 200
I 240
I 280
1
SECOXDS
Figure 5. Effect of initial pressure on FVP curves with Fuel A 60
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SECOhDS
Figure 6. Effect of temperature on FVP curves with Fuel A
occurs after 2 s of vaporization. The effect then decreases and becomes insignificant as vaporization nears completion. T h e effect of temperature on t h e vaporization pressure curve is shown in Figure 6. T h e three vaporization pressure
Table 111. Partial and Total Vaporization Pressure Data o n Test Fuels PVP, mm Hg Fuel
Time, s
A B C D E EA F FA G GA
0.50 0.75
1.0
3.0
6.0
12.0 30.0 60.0
120
240
360
600
900
TVP, mm Hg
1.3
1.5 2.1 1.8
2.6 3.6 2.6 1.6 1.6 2.5 2.8 3.1 3.6 4.4
3.4 4.5 3.1 2.0
4.2 5.5 3.7 2.4 2.4 3.6 4.4 4.9 5.5 6.5
6.9 8.0 6.2 4.5 4.8 6.0 6.8 7.9 8.6 9.6
7.6 9.5 7.5 5.5 5.8 7.0 7.4 8.5 9.3 10.3
8.1 9.9 8.3 6.1 6.1 7.6 7.8 8.8 9.6 10.6
8.5 10.1 9.1 6.7
8.7 10.2 9.8 7.0
9.4 10.6 10.6 7.9 8.4 9.5 9.1
1.0 1.3 1.4 0.8 0.7 1.0 0.9 1.1 1.0 1.8
1.9
1.6 1.0 0.9 1.4 1.2 1.5 1.9 2.4
1.1 1.0
1.6 1.5 1.8 2.2 2.8
2.0
3.1 3.7 4.0 4.6 5.5
80
60
5.3 7.0 4.4 3.1 3.2 4.4 5.4 6.2 6.9 8.0
6.1 8.0 5.3 3.6 3.9 5.1 6.1 7.1 7.8 8.8
... ... ...
... ...
... ... ... ...
10.1
... ...
10.6 11.6
80
1 -
...
6 0 m
I
0
a
40
Y e P
20
00 00
40
80
120 TINE
160 SECONDS
200
240
00
280
40
8.0
12.0 160 TIME, SECONDS
ZOO
240
73.0
Figure 7. FVP curves of typical fuels
Figure 8. FVP curves of fuels with and without alcohol
curves of Fuel A were determined using a 76.7-pL sample at a n initial reduced pressure of 660 mm Hg. T h e fuel sample was vaporized a t 2 4 , 4 , and -20 "C. T h e rate of vaporization is shown to change with temperature and the effect is nonlinear. F V P C u r v e s of T y p i c a l Fuels. T h e differences between t h e vaporization pressure curves of fuels are demonstrated using fuels covering t h e distillation range of most gasolines produced, Fuels A through D. T h e vaporization pressure curves of these fuels were recorded for 15 min using a 76.7-pL sample at 24 "C a n d an initial reduced pressure of 660 m m Hg. Partial vaporization pressure (PVP) readings taken along t h e curves are listed in Table 111, and the first thirty-second section of the vaporization pressure curves are shown in Figure 7. As shown by these curves, each fuel has a characteristic curve which is dependent on t h e composition of the fuel. T h e total vaporization pressures (TVP's) of these fuels are also listed in Table 111. T h e TVP's were determined using 76.7-pL samples a t 24 "C and an initial reduced pressure of 0.1 m m Hg. At these conditions, t h e fuels approach total vaporization within 5 to 6 s with the possible exception of Fuel D, the highest boiling range fuel. T h e T V P of a fuel can then be used along with t h e P V P a t any time t o calculate the percent vaporized. Alcohol-Gasoline F u e l s . T h e usual volatility characterization tests, D-86 distillation, RVP, and T o (V/L 20), all require modifications or additional data interpretation to be applied to alcohol-gasoline fuels. The RVP test must be run dry a n d t h e calculation modified t o measure fuels of this nature ( 7 ) . T h e To( V / L 20) test uses glycerin, but when alcohol is present in the fuel, mercury must be used (7). Normal interpretation of the distillation d a t a will lead t o erroneous driveability conclusions due to the "alcohol plateau" (4). T o determine the potential of t h e F V P test for characterizing fuels containing alcohol, three base gasolines were
formulated t o represent low, medium, and high volatility gasolines, Fuels E, F, and G, respect.ively. T o each of these fuels five volume percent alcohol (4:l volume ratio of methanol t o tert-butanol) was added t o give Fuels EA, FA, and GA. T h e fuel vaporization pressure readings from t h e curves measured using t h e fuels with and without alcohol are listed in Table I11 along with the T V P d a t a on these fuels. T h e curves were determined using 76.7-pL samples at 24 "C and an initial pressure of 660 mm Hg. Figure 8 shows thirty-second sections of t h e vaporization pressure curves of t h e low, medium, and high volatility fuels. T h e effect of adding five percent of the alcohol mixture to the three gasolines, also given in the Figure, is shown to be variable imd may be composition dependent. However, t h e effect on t h e T V P is independent of t h e base gasoline, with a constant 1 mm Hg pressure increase for t h e five percent added alcohol as shown in Table
111. ACKNOWLEDGMENT T h e authors thank J. A. Glover, R. P. Page, D. C. Tong, J. G. Vlasic, and A. G. Widen for their valuable contributions t o t.his study. LITERATURE CITED (1) G. H. Unzelman and E . S. Forster, Pet. Refiner, 39, 109 (1960). (2) E. F. Obert, "Internal Combustion Engines and Air Pollution", Intext Educational Publishers, New York and London, 1973, p 253. (3) E. E. Wigg and R . S. Lunt. SAE Paper No. 741008 (1974). (4) A. W. Crowley et al, SAE Paper No. 750419 (1975). (5) S. J. W. Pleeth, "ALCOHOL-A fuel for Internal Combustion Engines",Chapman & Hall Ltd., London, 1949, pp 21 1-213. (6) Catalog PS-72, Precision Sampling Corporation. (7) P. P. Lifland, Mobil Research and Development Corporation, Paulsboro, N.J., personal communication, October 4 , 1974.
RECEIVED for review May 12,1977. Accepted August 29,1977. This research was conducted under contract of t h e InterIndustry Emission Control Program-2 (IIEC-2) as AtIantic Richfield Program I of Project V (Alternate Fuels).
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