Solutions of polyisobutylenes L160, L200, B200, and B230 in Jet-A were prepared at concentrations up to 3000 ppm. These polymers have molecular weights in the range 5 to 9 x 1,00,000 and have previously been shown to induce anti-misting properties in Jet-A. In connection with the pumpability of such solutions, especially at low temperatures, the shear viscosity, eta, of these solutions was measured at temperatures 25 C, 0 C, and -25 C. Concentration-dependence of eta was very similar for all four polymer solutes, the increase of eta(c) at 3000 ppm being roughly four-fold (relative to Jet-A) for the L-series and five-fold for the B-series. This behavior prevailed at all temperatures, and there was no evidence of phase separation or other chemical instability at -25 C at any concentration. In the more practical c-range for anti-misting applications, say within 1000 ppm, the increase of eta(c) was only twofold

Grens, E. A., II

Williams, M. C.

English

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https://ntrs.nasa.gov/search.jsp?R=19830008272 2020-03-21T05:43:46+00:00Z
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Final Technical Report
VISCONETRIC AND MISTIM PROPERTIES
OF POLYMER—MOD IFIED JET FUEL
Supported by a Cooperative Agreement between NASA-Ames Research Center and the
Regents of the University of California.
y
Agreement No. NCC 2-163
Agreement Period Nov. 1, 1981 - Sept. 30, 1982
Principal Investigators
	 E.A. Grens, II and M.C. Williams
Chemical Engineering Department
University of California, Berkeley
Berkeley, CA 94720
NASA Technical Officer 	 R .L. Altman
Chemical Research Projects Office, 223-6
NASA-Ames Research Center
Moffett Field, Qk 94035
ONO" PM
y	
OF FM ^
SIlI9B4R
Solutions of polyisobut ass U60, L200 9 	.3230 In g were
prepared at concentrat ions
 up to 3M ppm. Thy polymershaves ssl*cular
weights in the range
 5 to 9 x 108
 and have previously been shove to induce
anti-slating properties to Jest A. ]k connection with the pumpahilty
solutions, especially at low temperatures, the shear viscosity ,n of the
solutions was measured at temperatures 25 •C, O•C, and -25'C.
Concentratio"opendence of n was very similar for all four polymer
solutes, the increase of n(c) at 3000 ppe being roughly four-fold (relative to
Jet-A) for the L-series and five-fold for the B-series. This b.,^havior
prevailed at all temperatures, and there was no evidence of phhsc separation
or other chemical instability at -25 •C at any concentration. In the more
practical c-range for anti-Aisting applications, say within 1000 ppae. the
increase of n(c) was only twofold.
BACICROUND
It has been amply demonstrated' that a small amount of polymeric solute
dissolved in a kerosene-based jet fuel reduces the ignition and flammability
of fuel sprays. Interest in this phenomenon stems from its potential for
suppressing fires in aircraft suffering crash landings that are otherwise
survivable. The mechanism for fire suppression involves polymer-induced
alteration of fuel rheology, so that crash impacts at normal speeds will
produce sprays having very few of the fine droplets (D p < 10 pm) which are
needed to propagate an ignition event.
There remain a number of practical problems, however. One of these is
the question of fuel pumpability. Rheological alterations in the fuel include
an increase of viscosity and the appearance of elasticity, both of which can
make the liquid more difficult to pump from fuel tank through fuel lines and
filters to the engines. Even without the induced elasticity, which retards
stretching notions (e.g., in droplet formation), the viscosity enhancement is
potentially a source of concern because of the additional pressure needed to
produce shear flows within the fuel delivery system.
The latter concern was the one addressed in the present work. There is
general acknowledgement that easily-dissolved linear polymers (e.g ,
polyisobutylenes, PIB) function effectively as antimsisting agents, but the
extent to which they increase fuel viscosity--especially at low temperatures--
was not known. Our project objective was therefore to determine the Newtonian
viscosity n of PIB solutions In Jet-A fuel over a range of practical polymer
concentrations and realistically low temperatures.
EXPERII ENTS
Materials. Four linear PIB's of commercial origin wer used here; these and
others were characterized by GPC in our previous work, so their molecular
weight distributions and averages are well known. These four samples were
L160 and L200 "Vistanex" from Exxon, and 3200 and B230 "Oppanol" from B&►SIP.
	
s
Values of	 a:id VR. obtained frce GP9 traces were: 5.0 x 106 , 3.2 for
L160; 5.4 x 10 , 4.9 for `90; 6.0 x 10 , 4.3 for B200; and 9.0 x 10 , 8.2 for
B230. Values of
	 obtained from viscosity data on solutions (extrapolated to
1	 _ __
e - 0 to obtain intrinsic viscosity ( q ( that is correlated with N) were
always slightly smaller than the cited % values, as must be so.
Jet-A was obtained, freer Shell Oil Co. at Oakland Airport. Solutions Vero
prepared with extreme care, to prevent mechanical degradation of the polymer
solute. Firely e1vided clunks of they rubbery polymer were placed in a flask,
covered with Jet-A, and the flask slowly rotated (by motor drive) at an angle
in a warn water bath. la this way, stock solutions of 3000 ppm by weight were
prepared over a period of several days, and solutions of lower concentration
were obtained by successive dilution. At all times during preparation and
storage, solutions were covered to prevent vaporization of the lighter
components of Jet-A and inadvertent concentration change.
Apparatus. The original intent was to test viscosities down to -45.6%
(-50.0'F). However, with the modified budget ($11,451 in direct costs) and
less than a year to work, this objective could not be achieved. The necessary
refrigeration system was designed, components ordered, and assembly begun.
When it was noted that the system could not be ready by the Agreement
termination date, an alternate strategy was devised and a simpler system built
that could be used to acquire data down to -25.0°C (-13.0'F).
This latter system was a "phase change" thermostat, consisting of a
constant-L:sperature bath (in which viscometers were immersed) filled with a
liquid undergoing a slow freezing/melting process at temperatureT. Thus, T
- 0°C was achieved with a bath medium consisting of ice and water is
equilibrium, and T - -25.0'C was achieved in a bath of carbon tetrachloride
( Tf - -25° C) that was cooled by a jacket of dry ice (Tf - -44° C) .
Measurements at room temperature (24°C) were made as usual.
Viscosities were measured with U-tube Ubbelohde capillary viscometers.
The time t needed for fluid to flow through the capillary from one level to
another by gravity is proportional to n/p, where p is density, but since p was
not affected by the presence of trace polymer we have n a t (neglecting
correction factors that were always small).
RESULTS
Viscosity of the Jet-A at 20°C was 1.78 mPa • s (cp), as determined from q
Bt where B was determined by calibration with water at this temperature. At
other temperatures, the same B was used because capillary performance is only
slightly affected by thermal changes in this range.
Results are displayed as n(c) for the Vistanex polymers in Fig. 1 and for
the Oppanol polymers in Fig. 2. In each case, data correspond to the three
temperatures -25°C, 0°C, and +25°C. Sensitivity of viscosities explicitly to
temperature is given in Figs. 3 and 4 for polymers with c - 500 ppm and 3000
ppm, respectively. In each case n(T) for Jet-A is given for comparison.
There was no evidence with any of the PIB solutions that chemical
Instability occurred. Fluids even at -25°C were found not to gel and not to
produce visible cloudiness, as might be expected for cases of colloidal
precipitation. Thus, even for the highest molecular weight (B230 with F^ _
9 x 10 ) at the highest concentration (c - 3000 ppm) and the lowest
temperature achieved here (T	 25°C), PIB solutions in Jet-A appear to be
2
L, PAGg
Of Pt ^
short of saturation and chemically stable. Ws desirable situation is not
matched by all polymers being considered as antlaisting candidates.
DISCUSSION
Figures 1 and 2 (note the logarithmic ordinate scale) show the expected
monotonically increasing behavior of n(c). At each temperature, the two
Vistanex polymers (Fig. 1) achieve viscosities at 3000 ppa roughly four-fold
larger than Jet A, while the two Oppanols (Fig. 2) increase roughly five-
fold. it is likely that aircraft fuel pumps would be able to handle vis-
cosities that are only four or five times that of Jet-A.
It is also true that concentrations as hith as 3000 ppm should not be
necessary. Using sparks of 0.5 J, Chao et al. showed that c z 10 to 100 ppm
should suffice for B230 under circumstances of spark ignition. Furthermore,
Xapelke found with a large-scale flame-ignition device (adopted by the
Federal Aviation Administration) that c - 1000 ppm of B230 was at least as
effective there as 3000 ppa of FM9. It is significant that n(c)-increases
with B230 in this practical and effective range--100 to 1000 ppm--are only
two-fold (Fig. 2) at most.
It should also be noted that the other PIB's have n-increases comparable
to that of B230--i.e., two-fold at c - 1000 ppa. Dilute-solution shear
viscosities a •e rather insensitive functions of polymer molecular weight. In
view of She clear superiority of B230 as a flame suppressant/antimisting
agent, - it seems reasonable to focus attention on polymers only of the
highest possible molecular weight--actually, [n] - A' seems to be the best
correlating parameter —and thus on the production or extraction of PIB's with
R still higher than that of commercial B230. The penalty in terms of
increased n is trivial in comparison with major improvements in AM behavior as
R (or [ n]) increases.
The very modest polymer-induced increase in viscosity is reflected also
in Fig. 3 (c - 500 ppa) where curves for all PIB solutions are quite close to
the Jet-A curve. The T-dependence of n(T) for all solutions follows closely
the solvent behavior, as expected, and this fact is likely to prevail down to
-45.6°C (-50°F) as well. Thus, if n(T) for Jet A were known at -50°A, the
viscosities of PITS solutions at 500 ppm could be estimated with some accuracy
--provided that saturation limits were not exceeded at the lower temperatures.
Figure 4 shows this same TL-dependence to be manifested at 3000 ppm as
well, although the upturn for L160 at -25°C (suggested by one point) would
seem to violate this. While this higher-than-expected n at 3000 ppm might be
explained at -25°C as due to colloidal precipitation, no such event was
actually observed and seems unlikely in view of the normal behavior of n(T)
for the higher-M polymers (B200, 8230) which seem better candidates for having
limited solubility. It is more likely that the single high point in Fig. 4
for L160 (at -25°C) is spurious, representing data scatter. This view is
reinforced by Fig. 1, wherein the same point is seen to be inconsistent with
the trend of all data shown there as well.
Even though magnitudes of n(c,T) for PIB's in Jet-A seem small enough, it
is good to bear in mind that fuel pumpability depends on other factors as
well. In particular, fluid elasticity enhances greatly tho elongational
3
viscosity fl that may play a major role in pump and filter performance.
CONCLUSION
Increases in the shear viscosity n(c,T) for P IB solutions in Jet-A we
quite modest, down to -25'C, and no signs of chemical instability are found.
The highest value recorded here Was for B230 at 3000 ppm at -25'C, for which
n - 24 cp. If is expected that viscosities for the range -46' to -25'C Will
exhibit the same trends as found in the present data, but measurements of
these must await further funding.
REFERENCES
1. W. D. Weatherford and B. R. Wright, in "Aircraft Fire Safety," AGARD Cbnf.
Proc. No. 166,.1. 1 (1975).
2. R. H. Ahlers, "Full-Scale Aircraft Gash Tests of Modified Jet Fuel,"
Report No. FAA-RD-77-13 from Nat'l. Tech. Info. Service, Springfield, VA
(1977).
3. A. San Miguel, "Antimisting Fuel Kinetics Related to Aircraft Crash
Landings," J. Aircraft, 15, 137 (1978).
4. K. K. K. Chao, C. A. Child, E. A. Grens, and M. C. Williams, "Ihe Anti-
Misting Action of Polymeric Additives in Jet Fuels," AIChE J,
.
29
(1983) ... in press.
5. M. S. Kapelke, "The Anti-Flammability Effectiveness of Polymers in Jet
Fuel," Final Report on Grant NOC 2-140, NASA-Ames Research Center, Moffett
Field, CA (1981) .
4
i41
20
L-160,r Jet A
0 - 25*C
A 0°C
O + 25*C
L-200/ Jet A
• - 25*C
A	 0*C
0 + 25*C
4 =
OAO
U
V
E+ 
5
N
N
O
•U
y
M
2
ORIGIIIAL PAGE IS
OF POOR QUALITY	 wo/
q
0
J
I
	
1 L	 __	 1	 . I	 1	 1	 !
	
0	 500
	
1000
	
1500	 2000	 2500	 3000
C 0 N C E N T R A T ION ( ppm
Fig. 1. Viscosity dependence on concentration for two PIB polymers (L160,
L200) dissolved in Jet-A. The polymers are compared at -25°C (top
two curves), 0°C, and +25 9 C (bottom two curves).
000^
.0
1.— 0	 A
e
40
20
B 202Z Jet A	 8 230/ Jet
n - 25 0C 	 q - 25*C
A	 00C	 A	 0'C
0 + 25 * C	 0 + 25'C
OR-IGIrIAL PAGE 13	
Je
OF ;;AR QUALffy	 q
.0%
as
U10
I
2
0 500	 1000 1500 2000 2500	 3000
C O N C E N T R A T ION PPM
Fig. 2.	 Like Fig. 1, except that the two polymers are B200 and B230.
T EMP ERATURE ('C)
Fig. 3. Viscosity dependence on temperature for three PIB polymers (L160,
B200, B230) dissolved in Jet-A, and also for Jet
-.k itself. Polymer
concentration is 500 ppm.
W*
ORIGINAL PAGE 15	 • B 230
of POOR QUAL"	 • B200
n L 160
o Jet 
^O
Jet A
—0	 w^O
,t
40
20
10
a 8
u
..
a 5
H
U)
O
u
.yN
25"
	
	
v
TEMPERATURE (*C)
Fig. b. Like Fig. 3, except that the concentration is 3000 ppn.
l .^


Viscometric and misting properties of polymer-modified fuel

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