Effect of Sulf ustion of Lea H. K.LIVINGSTON, J. L. HYDE, AND M. H.CAMPBELL E. I. d u P o n t de Nemours 8c Company, Wilmington, Del. S u l f u r compounds i n gasoline combine directly or i n directly with tetraethyllead i n t h e engine cylinder t o produce a lead reaction product of reduced antiknock activity. The extent of t h i s reduction i n antiknock activity is greatest for t h e more reactive s u l f u r c o m p o u n d s s u c h a s hydrogen sulfide, s u l f u r dioxide, mercaptans, or disulfides. Sulf u r compounds t h a t a r e very unreactive at low temperatures probably only affect t h e antiknock action of t e t r a ethyllead by c o n t r i b u t i n g s u l f u r dioxide a n d trioxide t o t h e burned gas formed o n combustion. A s m a l l a m o u n t of t h i s burned gas remains i n t h e engine cylinder a f t e r t h e exhaust stroke a n d mixes with t h e fresh fuel-air mixture. The s u l f u r oxides from t h e unreactive s u l f u r c o m p o u n d s
t h e n i n t e r a c t with t h e tetraethyllead t o reduce its a n t i knock efficiency. Variation of t h e Cooperative Fuels Research (CFR) engine spark advance, t o produce a large change i n pressure-temperature-time relations existing i n t h e fuel-air mixture, did n o t a l t e r t h e antiknock efficiency of tetraethyllead when sulfur-containing fuels were compared a t a c o n s t a n t level of knock intensity. T h e sulfur-tetraethyllead interaction is remarkably insensitive t o engine conditions. Analyses of combustion chamber deposits from engines operating on leaded s u l f u r - c o n t a i n ing gasolines show deposit composition t o depend o n sulfur concentration i n t h e gasoline. Lead oxysulfates a r e more c o m m o n t h a n lead oxide or sulfate i n typical deposits.
HE trend tuMald higher wlfur concentlationq 111 American gasolines (7, 20) has made it desirable to examine the impor-
carbon) 1 sulfide, and suliul hexafluoride weie chosefl f o r this purpose. These coinpoundP, which are gaseous undw ordinary conditions, were introduced into the engine by adding the puw gases to the inlet air at ii lcno~vnflow rate of gas and R known raie of fuel consumption. The results are 5ummarized in Table r.
rance of sulfur in all the various phases of gasoline production and use. The influence of sulfur on the antiknock performance of leaded gasoline is of pari icular impox tance. Schulze and Buell (81)wexe the first t o describe in quantitative terms the pronounced decrease in octane number produced by adding sulfur compounds to leaded gasolines. Their results \\ere later verified by a nuniber of investigatois (8,8,11,12,1.4,19,$3).
Table I. Octane N u m b e r s of 60 Iso-octane-40 Heptane Reference Fuel a s Affected by Gaseous S u l f u r Compounds (Fuel contained 3 nil, of TCL pes gallon)
EFFECT OF VARIOUS SULFUR COMPOUNDS ON OCTANE NUMBER O F LEADED FUELS
Xt is believed that the critical interaction between sulfur compounds and tetraethyllead, causing a marked reduction in the effectiveness of this antiknock compound, occurs before the fuelair mixture is completely burned in an eiipinc (aylinder. This is based on the folloning reasoning:
Sulfur Compound None HiS
1. Different sulfur oompounds have substantially different effects on tetraethyllead--for example, it has been established (8, 16, 19) that at equivalent sulfur concentrations thiols and disulfides reduce the antiknock effect of tetraethyllead more than do sulfidrs, which are themselves more harmful than thiophenes 2. . On combustion. sulfur compounds of the type found in gasoline yield water, carbon dioxide or monoxide, and sulfur oxides. Bince all organic sulfur compounds give the same combustion products, they should have the same effects if the critical reaction interfering with tetraethyllead occurs after all of the iuel-air mixture has hurned. This, honever, does not agree n i t h experimental facts. 3. Before actual combustion, but a t temperatures correspondin to those reached by portions of the unburned mixture in a cyfinder just prior to complete combustion, different sulfur compounds undergo markedly different rractions. Moreover, it is probable that at such temperatures thc rcactivities of organic sulfur compounds fall in approximately the same order as that of thcir lead antagonism effects.
SFe
It is plausible to assume that it is the precombustion reaction products of organic sulfur compounds that actually interfere with the antiknock action of tetraethxllead. The observed different effects of the various types of auliur compounds nould then be due to different reaction tendencies. I n order to explore this i \ p e of reasoning further, it is neces+ary t o study the effevt on tetraethyllead antiknock efficiency of 4ome veiy simple sulfur compounds, of known chemical reacbivity at low temperatures. Hydrogen sulfide, sulfur dioxide,
son
cos
Sulfur Added, % 0 : 06
0.13 0.13 0.13 0.06
0.10 0.40
A. 8.T. 3'1 Motor Method Oothne X o * 83 74 70 72 80 81 r9 76
heduction in Oct,ane
No. Caused by Sulfur
Compound 0 9
13 11
3 2 4 7
These results shon that sulfur dioxide and hydrogen sulfide are much more harmful to the octane number of leaded gasoline than are carbonyl sulfide or sulfur hexafluoride. Hydrogen sulfide is the only one of the four gases that has a noticeable effect on the octane number of unleaded fuels a t the indicated concentrations. It decreases the octane number of reference fuel two units, which is equal to the effect of mercaptans at the same sulfur concmtration. The slight effect of csibonjl sulfide arid sulfur hexafluoride on leaded fuel is particularly significant when the oxidation characteristics of these compoifndi arc considered. These can he summarized as follows:
1. Carbonyl sulfide (COS) and sulfur hexafluoride (SF6) art' extremely resistant to slow oxidation or preflame reactions at, temperatures as high as 800" C. (9, 1 7 , $5'). 2. Hydrogen sulfide and sulfur dioxlde undergo oxidation and radical-type reactions at temperatures as low as 320" C . (4, 6). The temperature of the hottest portion of the unburned fuel-air mixture (the end gas) in the engine cylinder under motor method octane rating conditions (A.S.T.M. Method D 357-47) has heen calculated to be not over 700" C. (at 6 to 1 compression r:%tio). 2 722
INDUSTRIAL AND ENGINEERINQ CHEMISTRY
December 1949
Under these conditions carbonyl sulfide and sulfur hexafluoride would be expected to undergo little or no reaction in the engine cylinder before actual combustion. On the other hand, both hydrogen sulfide and sulfur dioxide would be very likely to enter into reaction well before all of the fuel-air mixture is burned. The facts that (A) the sulfur compounds which resist preflame oxidation have little effect on tetraethyllead efficiency and (B) the sulfur compounds which react readily have a large effect support the theory that preflame oxidation products or other reaction products of sulfur compounds are the materials which interact with tetraethyllead to reduce its antiknock effect. The general rule that the more oxidizable sulfur compounds are the more deleterious in leaded gasoline seems to apply to the common organic sulfur compounds as well as to the simple compounds in Table I. Mercaptans and disulfides, which are the strongest antagonists for tetraethyllead, would also be expected to undergo reaction a t low temperatures much more readily than the less reactive thiophenes.
c
n
EFFECT OF RESIDUAL BURNED GASES IN FUEL-AIR MIXTURE The automotive engine leaves a small amount of burned gas in the cylinder a t the end of each exhaust stroke. This burned gas enters into the make-up of the fuel-air mixture to be burned in the next cycle. T h e exact amount of residual gas depends on engine conditions, but in the CFR knock-test engine under fuel rating conditions i t is of the order of 5y0. I n terms of a sulfur balance, this means that 5y0 of the sulfur in the fuel will reappear in the next cycle as sulfur dioxide or trioxide. It L l L l 0 2 0.3 0.4 06 0.8 Lo 2 0 3 0 4 0 50 has been shown that sulfur GRAMS SULFUR ADDED PER KO FUEL dioxide lowers the antiknock Figure 1. Logarithmic effects of t e t r a e t h y l l e a d 'lot Of Antagonism markedly (Table I). NothData with Corrections for Residual Burned Gas ing is knownabout theantagonism of sulfur trioxide, but it is a less common combustion product (S), and it is possible that the bulk of the exhaust gas effect is due to sulfur dioxide. The effect of the sulfur oxides in the residual burned gas is to increase the apparent antagonism for any given sulfur compound above the value due to the original unburned compound. Previous work (16) has shown that the ratio of inactive to active tetraethyllead-equal to (L/lOO-L),where L is the percentage of decrease in tetraethyllead antiknock efficiency due to sulfur-in sulfur antagonism studies, when plotted against suIfur concentration on logarithmic coordinates, gives straight lines. These data are replotted in Figure 1 together with a correction for the estimated effect of the sulfur oxides in the residual burned gas. This correction is slight for thiols, disulfides, and sulfides, but a large proportion of the thiophene effect is contributed by the sulfur oxides in the burned gas (Figure 1). The previous observation (16)that the slope of the antagonism-concentration curve for thiophenes differed from that for sulfides, disulfides, and thiols was due to failure to correct for this effect of residual burned gases. New data, based on octane ratings of four different fuels containing tetraethyllead and 3-methylthiophene, show the slope for thiophenes to correspond to that for the other types of sulfur compounds when this correction is applied (Figure 1). The sulfur compounds of very low antagonism (COS and SF6) have only a slight effect, in excess of that due to the sulfur oxides, that they contribute to the residual burned gas (Table 11). The greater antagonism of SFGmight be due to the fact that the prodI
d
*
2'123
Table 11. Octane Numbers of 60 Iso-octane-40 Heptane Reference Fuel (Fuel contained 3 ml. of TEL per gallon) Observed Predicted Motor Method Motor Method Sulfur Compound Sulfur. % Octane No. Octane No. 83 83 None 0.1 79 81" SFe
...
cos
0.1
81a
80
Predicted from known octane number of this base fuel containing 0.005% S a8 902,whioh corresponds t o 6% residual burned gas in the fuelair mixture when the fuel contains 0.1% S. a
ucts of combustion are not only SO2 but also HF, which itself would interfere with the antiknock action of tetraethyllead. This work suggests that refining processes leading to the conversion of sulfur compounds into forms resistant to low temperature oxidation would lead to increased octane numbers (with leaded gasoline), but there is a limit to the improvement that can be obtained by this method of reducing sulfur antagonism. This limit is set by the effect of the sulfur oxides in the residual burned gas on the tetraethyllead in each fresh charge of fuel introduced into the engine cylinder.
ENGINE CONDITIONS FOR SULFUR ANTAGONISM The results of a comprehensive study of sulfur antagonism in leaded fuels under standard knock-rating conditions (motor and research) have been published previously (16). This work has been extended in a series of experiments in which the engine conditions were changed so as to alter the time-temperaturepressure relations to which the last unburned portion of the fuel-air mixture is subjected before it knocks. This was done by operating a CFR engine under motor method octane rating conditions (A.S.T.M. Method D 357-47) but with widely varied spark advance. Measurements were made of the compression ratio which gave standard knock intensity, with the spark advance changed over the range 6" t o 40' before top center.
Ot3.0 CC.TEL/GAL. 60 t 1.5
CC.TE.L /GAL.
60 t 0.5 CC.TEL./GAL.
70 Q
$
B
g
e.0
5.0
- L d IO 20
0
30
40
SPARK ADVANCE, DEGREES
-
Figure 2. Compression Ratio Spark A d v a n c e Relations for Standard Knock Intensity
0
IO
20
30
40
SPARK ADVANCE,OEGREES
Figure 3. Compression Ratio Spark Advance Relations for Standard Knock Intensity
-
The type of data which are obtained in this manner are shown in Figure 2 for a series of reference fuels; in Figure 3 for reference fuel blends and leaded 60-octane number reference fuel; and in Figures 4 to 7 for reference fuel blends and for 60-octane number reference fuel containing both tetraethyllead and various sulfur compounds a t 0.1% S concentration. From the reference curves for the unleaded and leaded primary reference fuels, octane numbers and lead efficiency decreases may be determined (Table 111). The effect of spark advance on the decrease in tetraethyllead efficiency is slight. There is a tendency for the decrease to be smaller at high advance angles for ethyl sulfide, ethyl disulfide, and isobutyl mercaptan. The
INDUSTRIAL AND ENGINEERING CHEMISTRY
2724
Table 111. Indicated Octane No. a n d Lead Efficiency Data from Figures 4 t o 7 Sulfur Compound
dpark Indicated Advance. Octane
No
Degree-
D~~~~~~~ Relative t o S-Free Fuel
Decrease in T E L EfficieE!5y&C'noorCorrected recteda
Vol. 41, No. 12
vance over the wide range of engine conditions investigated .Actually, this would be expected if the sul€ur-lead interaction occurs a t any time before knock occurs and combustion is completed. If the spark advance and compression ratio were adjusted over a wide range to give a constant level of detonation. the end gas would in each instance pass through intermediatr conditions of pressure, temperature, and residence time tha? would permit relatively reactive sulfur compounds to react. wit,h tetraethyllead. PHYSICAL CHEMICAL INTERPRETATION OF SULFUR-TETRAETHYLLEAD INTERACTION
B
Ethyl sulfide
87 5 76
10 :6 20
7e
78 76
26
30 40
77
dtandarda
75
71
58
63
84 68
58 58 58 53 53 e3
58 53 55 63
58 58
The first attempt a t a physical chemical interpretation of t h r effect of sulfur on tetraethyllead was made by Adirovich ( 1 ) . He concluded that the sulfur must affect the lead rather than the ethyl radicals from tetraethyllead, and therefore the hypothesi? that tetraethyllead owed its antiknock activity to the ethyl radicals must be abandoned; and that the empirical equations of Ryan (19) relating the sulfur concentration to the decrease in lead susceptibility were in accord rrith chain reaction theory of the Semenov type. More recently, it has been shown ( 2 6 ) that the sulfur-t,rt,rn, ethyllea,d interaction may be expressed by an equat,iori
-
which can be derived from the mass iaw for the eyuilihriurn Corrected for the effect of the sulEur compound on the octane number of the base fuel at the indicated spark zdvance. b Spark advance for standard motor method conditions; data from (la). These results are for GO-octane number primary reference fuels containing 3 ml. of tetraethyllead per ga!lon and 0.1% sulfur as one of the above four compounds. The fuels w-ere tested under standard motor method octane rating oonditions, except for the variabla spark advance and the change in compression ratio neoesaary t o maintain standard knock intensity. Decrease in TEL efficiency, L , i s given by the equation y
whert ap = ConcentraLion of tetraethyllead added, and a = aonoentratiori of tetraethyllead i n hhe sulfur-free base fuel having an octane number corresponding t o the octane number observed with the sulfur-containing fuel a t cancentration ao.
cbange from 6" to 40" advuriue does not exceed two octane numbers, however; this is not likely to be a significant difference for this type of operation. Therefore, within the accuracy of the test method, the magnitude of the sulfur antagonism is independent of the spark ad-
ns .f T
v
In this equation S represents sulfur-containing molecules, either the original sulfur compounds or their oxidation products; T represents lead in a form possessing ant,iknock activity; and C' represents inactive lead, presumably in combination with sulfur. The exact significance of this equilibrium equation is not known. It lea,ds to an accumte expression of the experimental data, but may not necessarily correspond to any real process. If the equilibrium is real, it would be of interest to characterize il thermodynamically by means of the free energy concept, which expresses the driving force (espressed in calories per gram-mole) of any chemical reaction. In Equation 1 the constant, K , which is the mass law equilibrium constant, is relat,ed to AF O, the standard free energy of the equilibrium reaction, by the equation A F " = -RTln
R
= -4.58 3 ' l o g K
(2)
The octane number data for primary referenre fiiels ci)rit,w,ininp d f u r and tetraethyllead yield the equatinn
(a, - u)/as' .= k
(3)
$Thereu = concentration of effective tetraethyllead; u" = con-
centration of tetraethyllead added; s = concentration of sulfur, expressed as gram-atoms of sulfur per gram-mole of fuel-air mixLure; and k and n are constants. The terms a,ail,and s are related t,o the concentratjons of S, T , and 11 a ? follows: [ T i ] = k, _ ~ I _ -
0
IO 20 M SPARK ADVALCE, DEGREFS
40
- a)
[TI = k t u
o SPARK ADVANCE, DEGREES
Figure 4. compression Ratio Spark Advance Relations for Standard Knock Intensity
Figure 5. Compression R a t i o Spark Advance Relations for Standard Knock Intensity
Bare fuel, 60-octane reference luel: s u l f u r , 0.1% as isobutyl m e r c a p t a n ; m o t o r m e t h o d octane r a t i n g conditiona, exoept Jor spark advance a n d compression ratio
Base fuel, 60-octane reference fuel: s u l f u r , 0.1% as ethyl d i sulfide: m o t o r method octane r a t i n g aonditions, except for spark advance and compression ratio
-
(a0
-
[SI=
(4) (5)
s (k,)l/"
(6)
The new constants k,, kt, and k , can be wrnhined t o give (71
k = ktk,/'kq,
Then Equat,ion 1 can he expanded to
[VI
___=-
[TI [SI"
a0
--a
a (s)"
X - k, = K
ktk.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
December 1949
I t has been found experimentally that for blends of 60 parts isooctane and 40 parts heptane containing thiols or disulfides, n = '/a and Kk,k,/k, = 1400. The rate constants k,, IC,, and IC, cannot be given absolute values without a detailed understanding of the reaction. The best assumption that can be made is that they are of the same order of magnitude and that (Ic,k,/k,) is not very different from unity. The free energy of the reaction
*
IS then, by Equation 2, of the order of - 11,000cal./gram-atom of sulfur, if the effective temperature at which the reaction occurs under engine conditions is 500" C. This seems to be a plausible value for this temperature, since the maximum temperature reached by the end gas a t 6 to 1compression ratio under A.S.T.M. motor method test conditions is approximately 700"C. The negative value of the free energy indicates that the reaction has a definite tendency to move from left to right. If ( - AF") were of the order of 100,000 cal./gram-atom, substantially all the active Lead would be used up in the reaction. The fact that ( AFO) is probably much smaller shows that the concentration of active lead will always be a substantial fraction of the inactive lead concentration, for all practical concentrations of sulfur in gasoline.
1 PbSO+*PbO
L
deposits as affected by sulfur content of leaded fuel are not availsble. Droegemueller (6)has recently discussed the nature of aviation engine deposits from fuels containing 0.0501, sulfur and has given the results of chemical analyses without attempting to determine the molecular form in which the lead compounds occur. He suggests that in addition to lead oxide, lead sulfate, lead chloride, and lead bromide, certain complex saIts are formed. Engine experiments have been performed to investigate the nature of the sulfur effect. Chemical analyses of deposits show, in general, that a higher sulfur concentration in the fuel produces a higher proportion of sulfur in the combustion chamber deposits, although some sulfur compounds may produce a greater increase than others. X-ray analyses of the deposits from sulfur-containing fuels show that normally they contain large amounts of lead oxysulfates-PbSO,.PbO, PbSO4.2Pb0, and PbS04.4PbO. Reference patterns for these materials were obtained from samples prepared in these laboratories. X-ray diffraction data for PbO (litharge), PbS04, and PbSO4.Pb0, the most stable of the oxysulFates (1S), are given in Table IV and plotted in Figure 8. These results offer an example of the ease with which the oxysulfates can be differentiated from lead oxide and lead sulfate. The sharp
0 t 0.5CC.T.E.L./GAL.
7.0
0
Lead Sulfate d 11'1ma
4.26 3.80 3.61 3.47 3.37 3.25 3.03 2.79 2.71 2.64 2.43 2.27 2.17 2.08 2.04 2.00 1.90 1.81 1.75 1.71 1.66 1.63 1.58
z
z
8
p6.0
P
6.0
B
L
H
5.0
5.0
0
0 10 20 30 SPARK ADVANCE.DEGREE9
40
-
Figure 6. Compression Ratio Spark Advance tions for Standard Knock Intensity Base fuel 60-octane reference fuel ;sulf&,O.l %as ethyl sulfide ; motor method octane rating conditions, except for spark advance and cornpression .ratio
10 20 30 SPARK ADVANCE. DEGREES
40
Figure 7. Compression Ratio Spark Advance Relations for Standard Knock Intensity
-
Base fuel, 60-octane reference fuel; sulfur, 0.1% as 3-methylthiophene: motor method octane rating conditions. except for spark advance and compression ratio
&
o
RADIATION)
Table IV. X-ray Diffraction Data (Powder Patterns) for Lead Sulfate, Oxide, and Oxysulfate
0
B 0
c
maxima a t grating spacings of 2.98 and 2.87 A. for PbSOI.PbO are quite characteristic. All three sets of data were obtained on the same instrument, a Norelco Geiger counter x-ray spectrometer. The reference data are in approximate agreement with the tabulated data of Hanawalt, Rinn, and Frevel (IO)for PbO and PbSO, and of Lander (16)for PbSOd.Pb0. The x-ray patterns due to the lead oxysulfates are given to a greater or lesser extent by substantially all combustion chamber deposits from leaded fuek so far obtained by these laboratories, including fuels leaded with Motor Mix (a mixture of 1 mole of tetraethyllead, 1 mole of ethylene dichloride, and 0.5 mole of ethylene dibromide) or Aviation Mix (an equimolar mixture of tetraethyllead and ethylene dibromide). These compounds *frequently comprise very substantial fractions of engine deposits obtained with leaded gasolines containing appreciable amounts-O.05 to 0.25%-of sulfur. Engine conditions must be controlled very carefully if data of chemical value are to be obtained from deposit studies. Some operating conditions which have been used with laboratory engines for studies of deposit compositions are summarized in
'4
c4
7
Figure 8. Relative Intensities of X-Ray Diffraction Lines
0.5 CC.TE L./GAL.
7.0
A
I
I I
IO BRAGG ANGLE, DEGREE$ (FOR Cu K - a
-
EFFECT OF' SULFUR ON DEPOSIT COMPOSITION Literature data concerning composition of combustion chamber
INTERPiANAR SPACINGS, A? 4 I I
1 7 6 5
8 f 3/2 T --f 3/2 U
2725
a
I I
-
0.90 0.40 0.20 0.30 0.90 0.70 1.00 0.45 0.50 0.10 0.15 0.20 0.25 0.95 0.70 0.25 0.10 0.20 0.10 0.25 0.10 0.30 0.10
Lead Oxide (Litharge) d
5.84 3.06 2.94 2.76 2.36 2.03 1.84 1.80 1.74 1.65 1.53
r/I 0.10 1.00 0.65 0.25 0.20 0.20 0.20 0.10 0.35 0.20 0.15
= interplanar spacing in Angstrom unitor
intensity of diffraction line = intensity of the strongest line for eacb compound Data obtained by F. W. Tober of the Jackson Laboratory.
Lead Oxysulfate5 (PbSOr. PbO) d I/I Pas.
6.39 6.19 5.96 4.44 5.19
0.25 0.20 0.15 0.20 0.10
3.72 3.53 3.37 3.20 2.98 2.87 2.61 2.58 2.48 2.44 2.41 2.36 2.27 2.24 a . 12 2.06 1.98 1.92 1.85 1.77 1.74 1.67 1.65 1.63 1.61 1.58 1.57
0.25 0.15 1.00 0.15 1.00 0.50 0.10 0.10 0.25 0.25 0 10 0.10 0.25 0.10 0.10 0.30 0.10 0.10 0.40 0.15 0.20 0.20 0.10 0.10 0.10 0.10 0.10~
INDUSTRIAL AND ENGINEERING CHEMISTRY
4726
Table VII,
Vol. 41, No. 12
Effects of Dissimilar S u l f u r C o m p o u n d s on Combustion C h a m b e r Deposits
Single-cylinder Lauson engine tests. Iao-octane fuel (-0.001 c/o S) c o n k i n ing 3 mi. of tetraethyllead per gallon, as Motor Mix 0.10% S Ad$edjE.Eprm of
Butyl disulfide
__._
Butyl (CnHsO) aulfate aSOv
(CIH9)9S9
"/.
s:
0.03
ENGINE CONDITION:
0.03
0.25
MEDIUM DUTY
0.25
HEAVY DUTY
Analysis of exhauet-valve ClPpoSit
S %
Figure 9. Molar Proportions of Lead Compounds in Cylinder-Head Deposits from 100-HourChevrolet Tests Table V. Typical rebults from a carefully-controlled 100-hour medium duty Chevrolct engine test are shown in Table VI. The deposit analyses fall into two (.lasses: one, high in halide and low in sulfur, applies to the relativelv cool surfaces on the piston, block, and cylinder bead; the other type of deposit, obtained on the exhaust valve surfaces, ahich reach temperatures of the order of 650" C. ( 1 8 ) , contains relatively little halide and consists almost entirely of lead oxysulfates. An example of the effect of sulfur concentration on deposit composition is shown in Figure 9. The sulfur content of the fuel was increased by adding disulfide oil-a commercial mixture of petroleum disulfides obtained from the Standard Oil Company (Indiana)-to the base fuel. Under either medium duty or heavy duty Chevrolet engine test conditions (described in Table V), the lead sulfate increased a t the expense of the lead halide when the sulfur concmtration increased. The results are for oylinder head deposits; on hotter locatiqns, such as exhaust valves, the effect of sulfur is frequently much more complicated, probably because the halide concentration on hot surfaces is so low that simple displacemrnt of PbXi by PhSOd is no longer posGble. The molar ratio of sulfur to lead may be taken as a measure of the amount of lead sulfate in the deposits. For example, if the ratio S/Pb = 1.O the Irad exists entirely a q PbSOl and if S/Pb =
Table V.
Engine Test Operating Conditions
Oil. Heavy duty, 2-104-B type
+ 25%
Fuel. 75% catalytic cracked Sulfur. 0.03 weight % Tetraethyllead. 3.0 ml./gallon
;-Medium duty
2000 speed, r.p.m, 15 Load, brake horseporvw 100 Duration hours 195 Water ou't temp., 0 F. 26.5 Oil temp., ' F. 15 Air-fuel ratio 38al Spark advance, ebefore top dead center
Heavy duty 3000 60 100 195 266 15 42 *l
Lauson, Medium Duty 2000
2.5 76 210
175 14 30
Table VI. Typical Analyses of Combustion C h a m b e r Deposits Obtained Under M e d i u m D u t y T e s t Conditions (Tetraethyllead. 3.0 ml./galion as Motor h7ix. Sulfur, 0.03%) Relatively Cool S u r f 5 Relatively Hot Surfaces Piston Cylinder Block Exhaust Exhaust tops heads topsa valve tops valve tulips 1.36 4.51 1.12 4.84 3, % 1.28 2.73 7.08 1.89 6.97 7.03 Br, % c1, % 12.48 10.73 ?0.22 0.95 2.21 73.08 01.60 76.10 66.68 62.19 Pb, % X-ray PbCli PbC12 PbClz PbSOd.Pb0 PbSO4.PbO patternsb PbSOd.Pb0 PbSOd.Pb0 PbS04.PbO . ... PbSOi PbSOi PbS04 il Block tops &re portions of cylinder blocks not covered b y the cylinder head gasket. Listed in order of relative intensity.
.. ...
4.11 6.17 1.05
71.7
PhSO4. PbO 0.30 0.37
b
87
&'ka l'bS04 0.95 0.68
0.5 the proportions of sulfur arid lead art. app1opriat.e lor turming PbSOr.Pb0. Thib piciure is complicated by the presence of halogens, which ma\ replace part of the PbO by PbX2, and by failure to attain chemical equilibrium, which can result in the formation of such a mixture a 5 PbSO1, PbS04.Pb0 and PbSO, 2 P b 0 all in the same sample. Hornever, the molar ratio of sulfur to lead is very useful in characterizing deposits, and t o a firsi approximation the cornplica tions may be overlooked. The effects on deposit composition of butyl disulfide and butyl. sulfate, each used at a concentration of 0.1% sulfur in leaded isooctane originally containing only about OaOOl % sulfur, are shown in Table VII. It is evident that the fuel containing butyl sulfate produced a deposit with a substantially greater sulCur t o lead ratio and that the lead in the cylinder-head deposit found from this fuel exists almost entirely as PbS04. These tests were run in a singlrcylinder Lauson engine under conditions given in Table i7 Although it is recognized that butyl sulfate is not a type of sultur compound ocrurring in petroleum fuels, it illustrates a11 exn e m e situation in which the type of sulfur rompound has a marked effect on the composition of the mgine deposits and points the way t o further work with more practical sulfin compounds. LITERATURE CITED
alkylate
---Chevrolet
B'r % el: % P b , 70 X-ray patterns 9/Pb ratio in cylinder-head deposit S / P b ratio i n exhaust-valve deposit
...
(1) Adirovich, Acta physicochim. U.R.S.S., 21, 283 (1946) (2) Birch and Stansfield, IND. ENG.CHEM.,28, 668 (1936). (3) Cloud and Blackwood, S.A.E. Journal, 51, 408 (1943). (4) Dooley and Whittingham, Trans. Faraday SOC.,42, 354 (1946). (5) Droegemueller, A.S.T.M. Bull., KO.154, p. 53 (1948). (6) Emanuel, Doklady Akod. N a u k S.S.S.R., 59, 1137 (1948). (7) Fookson and Bell, Petioleurn Refiner, 27, 4.59 (1948). (8) Friedmann, Ibid., 20, 398 (1941). (9) Giiffith and Hill, J . Chem. JSOC., 1938, p. 2037. (10) Hanawalt, Rinn, and Frevel, IND. ENG.CHEX, ANAL. ED., 10, 487 (1938). (11) Hanson and Coles, J . Inst. Petroleum, 33, 589 (1947). (12) Holloway and Bonnell, IND. ENG.CHEM.,37, 1089 (1945). (13) Kelley, U . 8. Bur. Mines Bull., No. 400 (1937). (14) Kobayashi and Kajimoto, J . Soe. Cham. Ind. .Japcm. 39, 354 (1936). 4,174 (1949). (15) Lander, J . Electrochem. SOC., ( 1 6 ) Livingston, IND. ENG.CHEM.,41, 888 (1949). (17) Moissan and Lebeau, Compt. rend., 130, 865 (1900). (18) Newton, paper given a t S.A.E. Tulsa, Okla., meeting (Nov. 6, 1947). (19) Ryan, IND. ENG.CHEM., 34,824 (1942). (20) Scafe, Petroleum Refiner, 25,413 (1946). (21) Schulze and Buell, Natl. Petroleum News, 27, h-0. 41, 25 (1935). (22) Thompson, Hovde, and Cairns, J . Chem. Soc., 1933, 208. (23) Kidmaier, Jahrb. deutsch. Luftfahrtforschung, 1941, 441. RECEIVED M a y 24, 1949. Contribution from Jackson Laboratory, Publication No. 78, and Petroleum Laboratory, E. I. d u Pont de NemourR & Company. Wilminpton, Del.
