M a y 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
The knock-inducing effect of ethyl radicals may be still further illustrated by the following simple experiment which incidentally correlates explosion ahead of the flame front, in other words, knock, with explosion of the entire charge induced by the introduction of a radical-producing substance. In this expe’riment a n engine was cranked at a compression ratio of 10 to 1 with cyclohexane as a fuel a t the normal air-fuel mixture ratio but without spark ignition. Cranking at this compression ratio, which is five compression ratios above t h a t for incipient knock for normal operation at 600 r.p.m., no autoignition takes place with cyclohexane alone, but if a drop of diethylmercury is introduced with the intake air a violent explosion follows for several cycles. Firing stops when the diethylmercury has been consumed. No explosion takes place when benzene is substituted for cyclohexane as might be expected from the relative inertness of benzene with respect to ethyl radicals. Ethyl nitrate and acetylene may be substituted for diethylmercury as a source of ignition. This experiment strikingly illustrates how a radical-producing substance, which is known to induce cracking at temperatures of the order of 50’ C. below t h a t for appreciable cracking normally, can induce reaction between certain hydrocarbons and oxygen resulting in explosion.
891
This suggests t h a t the reactions ahead of the flame front that result in knock involve a similar process.
Literature Cited (1) Badin, Hunter, and Pease, J . Am. Chem. Soc., 70, 2055 (1948). ( 2 ) Boord, presented before Division of Pet1 oleum Chemistry, at
112th Meeting of AMERICAN CHEMICAL SOCIETY, New York, N. Y . (3) Cramer, J. Am. Chenz. SOC.,60, 1406 (1938). (4) Jost and Croft, “Explosion and Combustion Proresses in Gases,” Chap. 11and 12, New York, McGraw-Hill Book Co., 1946. ( 5 ) Ibid., p. 437. (6) Lewis and von Elbe, “Combustion, Flames, and Explosions of Gases,” Chap. 4, London, Cambridge University Press, 1938. (7) Lovell, Campbell, and Boyd, IND.ENG. CHEM.,23, 26, 555 (1931).
(8) Rossini. Prosen, and Pitaer, J.Research Nutl. B u r . Standards, 27, 529 (1941) (9) Steacie, “Atomic and Free Radical Reactions,” Chap. 6, New York, Reinhold Publishing Corp , 1946. (10) Taylor and Smith, J . Chem. Phye., 7 , 390 (1939): 8, 543 (1940). (11) Walsh, Trans. Faraday Soc., 42, 269 (1946). I (12) Withrow and Rassweiler, S.A.E. Journal, 39, 297 (1936) ; IKD. ENG.CHEM.,25, 1359 (1933). RECEIVED September 27, 1948.
Effect of Additives on Gasoline Engine Deposits R. E. Albright, F. L. Nelson, and L.Raymond SOCONY-VACUUM LABORATORIES, PAULSBORO, N. J.
1
Gasoline additives such as antioxidants and tetraethyllead have been evaluated for their effect on engine varnish and sludge deposits by means of both laboratory and field tests. Passenger car field tests have shown small and relatively insignificant differences in the deposit forming tendencies of several gasoline antioxidants; the differences in engine design factors being of far greater importance than fuel composition variables. Laboratory tests were made also, using the low temperature CRC FL-2 procedure which has been shown in some instances to correlate with commercial vehicle operations. By this means, it has been shown that some gasoline antioxidants tend to increase engine varnish and sludge deposits; the extent of deposit formation is dependent on the hydrocarbon composition of the base gasoline. Tetraethyllead was found to have no significant effect on varnish and sludge deposits in laboratory engine tests. Experimental fuel additives, which will provide large reductions in engine varnish and sludge deposits, have been developed also. These materials, however, are not yet suitable for commercial use.
T
HE formation of deposits in internal combustion engines, until fairly recent years, has been blamed generally on the Iubricating oil used in the engine. However, the development of detergent and heavy-duty type oils in the mid-thirties and their widespread use during the war years focused attention on other factors which may at times be of such importance as t o nullify in large part the effediveness of the newer lubricants. Recently published papers (1, 9, 4-6, 8) have indicated that, while heavyduty oils are generally effective when used under the conditions for which they were designed, their performance is interrelated with other parameters. It is now recognized that there are four major factors affecting the formation of engine deposits, namely:
engine design, operating conditions, fuel, and lubricant. A fifth factor, mechanical condition of the engine, may be added t o this list. Since 1945, the Socony-Vacuum Laboratories have been conducting independent but coordinated investigations t o determine the area of influence and the magnitude of importance of each o f these five factors. While it is impossible t o separate completely the contribution of any single factor from the others, this paper will deal with investigations of deposits in gasoline engines in which the fuel effect was of primary interest.
Deposit Types Gasoline engine deposits, due t o the fuel, fall into two main categories: induction system deposits and power section deposits. The former, for t h e most part, are caused by preformed gum and, occasionally, fuel additives. While induction system deposits can have important performance consequences, the present discussion is limited to power section deposits as influenced by additives and associated fuel characteristics. The relation of lubricating oils will not be discussed although there is substantial evidence t h a t the lubricant can cause controlling differences even under conditions accentuating fuel deposition tendencies.
Test Procedures Most of the laboratory engine evaluations described hereiirl have been made by the CRC FL-2 Procedure (a) in which a Chevrolet engine is operated at fairly high load and speed but at low oil and water temperatures. These low temperatures minimize deposits resulting from oil deterioration and emphasize the fuel effect. Key operating conditions for this procedure are given in Table I. Over-all performance in this test is based on a rating system in which varnish and sludge deposits on the following engine parts,
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
898 Table I.
CRC FL-2 Procedure Operating ConditionsChevrolet Test Engine Test duration (continuous), hocrs Engine speed, r.p.In. Brake load, hp. Oil temperature, F. Jacket inlet, F. Jacket outlet,, O F. Air fuel ratio Crankcase ventilation
40 2600
are evaluated on a scale of 100 for a perfectly clean engine or part and zero for a dirty engine or part: pistons, cylinder ~valls,oil pan, push rod cover, rocker arm assembly, and oil pump screen. While t,he over-all engine rating combines the above individual items in one value and is so used, the single inspection item which appears to be most critical to changes in fuel characteristics is the piston skirt varnish rating. Both of these ratings are used in this Pafer. , . n addition t o analyses and comparison of t,he FL-2 Procedure data as such, the relation of these laboratory engine results to field performance as studied also and is discussed herein. For the field test work, sixteen privately owned and operated passenger cars representative of the four most popular makes were used. Prior to test,, engines on all cars were overhauled and all deposits removed. The field test continued for 1 yeay; in this time each car covered approslnlately 13,000 miles, mostiy in the south Jersey area.
Laboratory Tests Commercial Gasolines and Reiinery Base Stocks. Table I1 gives the piston skirt varnish and over-all engine ratings of several finished commercial gasolines and refinery base stocks tested under the FL-2 Procedure. Since the tests on these particular fuels extended over several months, protection against deterioration in storage was necessary in some cases while tetraet,hyllead had t o be added to others t o meet t,he octane requirement of the engine. To reduce variations due to these effects, all of the refinery stocks in Table I1 were inhibited and leaded t o a common level.
Vol. 41, No. 5
Table I1 s h o m that there are wide differeiices in the ratings of the three commercial fuels as well as in the ratings of the refinery base stocks, particularly in piston skirt varnieh. As can be seen, the refinery base stocks which cause deposits are cracked stocks. However not all cracked stocks lead to the f'ormat>ionof deposits. Further examination of this table shows t h a t neither fuel volatility nor olefin content (bromine number) is related, per se, to deposit ratings. Effect of Tetraethyllead Fluid. The effect of additions of tetraethyllead t o gasoline \?-as evaluated only in a straight run stock, both uninhibited and inhibited n-ith 25 puurids per 1000 barrels of di-sec-butylphenylenediamine. These results are plot,t,ed in Figure 1 as engine rating against ietraet.hyllead content in ml. per gallon (Ethyl Corporation 62 Mix). From this it will be seen that the effect of tet,raethyllead fluid on the ratings of both the inhibited and uninhibited fuels is rather small and variable in direction. Further, sirice the differences noted are probably xithin the limits of reproducibility of the FL-2 test, the conclusion can be drawn that tet,raethyllead fluid has no significant effect on varnish and sludge deposits in t,his low temperature type of test. Effect of Gasoline Antioxidants. Figure 1 may bc used also t o evaluate the effect of the addition of 25 pounds per 1000 barrels of di-sec-butylphenylenediamineto this st'raight run gasoline. As indicated, the piston skirt) varnish rating is dccreased by this concentration of addit~iveby approximately 20 points t o an average rating of 7 5 whereas the decrease in overall engine rating is smaller. The concentration of antioxidant in commercial practice is of the niagnitude of 5 t,o 10 pounds per 1000 barrels. This work was ext,eiided to the evaluation of the effect on engine deposits of a number of other gasoline antioxidants when added t o a straight run gasoline containing 1.5 ml. per gallon of tetraethyllead (62 Mix). The data plotted iri Figure 2 show that di-sec-butyl ca,techol and 2,B-di-tert-butyl cresol have no major effect on engine rating while a-naphthol, di-sec-butylphenylenediamine, and n-butyl-paminophenol increase engine deposits,
I
T a b l e 11. CRC FL-2 Low Ternperature Chevrolet Engine Deposit Tests on Commercia1 Gasolines and Refinery Base Stocks
Gravit OA P I . A.S.T.4. D&:, OF. Initial b. p.
2 y
3 Z
10% Rec. 50% Rec. 90% Rec. End point Bromine No. Tetraethyllead, ml./gal. Inhibitor conc Ib./i008 bbl. Inhibitor type"
COMMERCIAL FUEL A 60.5 92 140 240 362 392 0 2.0 Unknown Unknown
COMMERCIAL FUEL 8 58.2 108 150 246 35 1 409 27.8 2.5 Unknown Unknown
COMMERCIAL FUEL C 57.5
STRAIGHT RUN 60.0
98
in6 16 1 248 324 360
149 - ._
269 364 410 40.8 1.3 Unknown Unknown
0
1.6 25
THERMALLY CRACKED A 64.4
THERWLLY CRACKED B 54.3
CATALYTICALLY CRACKED A 55.9
96 118 102 130 178 136 ~ - . .. 2i n 276 244 304 379 356 364 423 386 65.1 45.2 24.7 1.5 1.5 1.5 25 32 25 Di-sec-butylphenylenediamine ~
~~
~
CATALYTICALLY CRACKED B 58.1 go 126 244 380 420 25.6 1.6 35
May 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
n-BUTYL-PARAAYIIIO P n E i n L
90
899
U
Di-SEC-!Ulll PIIEIYLEEYE D l A M l l E
70
I
I
I
DI-SEC-BUTYL CATECHOL 2 , 6 4 I-TERT-8UTVL CRESOL ALPHA w P n T n o L
z
5;
I
01-SEC-WTYL DIAMIHE
20
ID
0
lNHlBlTC4 COIITEYT,
Figure 2.
I "
0
3
2
I
Figure 1. Effect of Tetraethyllead on FL-2 Ratings of a Straight Run Gasoline
particularly on the piston, t o a marked degree when used in higher than normal concentrations. Further investigations have shown t h a t the detrimental effect of di-sec-butylphenylenediamineon the FL-2 rating of a gasolilie is a function of hydrocarbon composition of the fuel. As shown in Table 111, addition of 25 pounds of this antioxidant t o LOO0 barrels of pure hydrocarbons and blends of pure hydrocarbons resulted in the following reductions in piston skirt varnish ratings: isoparaffins, 3 points; naphthenes, 8 points; olefins, 16 points; and aromatics, 32 points. The formation of undesirable products from an interaction of chis additive with certain types of hydrocarbons is indicated also by the behavior of the same antioxidant when used in commercial refinery base stocks. As recorded in Table 111, the piston skirt varnish rating of a straight run fuel containing no olefins and 15% aromatics was reduced by 17 points; a thermally cracked fuel containing 26Y0 olefins and 15% aromatics was reduced in rating by 20 points; and a catalytically cracked stock containing 13y0olefins and 2070 aromatics was reduced by 31 points. From this work with both pure hydrocarbons and commercial Jtocks it would appear that while the combination of di-sec-butylphenylenediamine with any hydrocarbon type is detrimental t o engine cleanliness, the effect is most pronounced with olefins and a r o m a t i c s , particularly the latJter.
Field Tests Effect of Gasoline Antioxidants. All of the foregoing discussion has been based on the performance of fuel additives as determined by the low temperaturehigh load laboratory FL-2 Procedure. Inasmuch as these results indicated some of the antioxidants t o be detrimental to engine cleanliness, proof t e s t i n g of t h e d e p o s i t
,
30
YO
L E S l l O M BELS.
Effect of Antioxidant Inhibitors on FL-2 Ratings of a Straight Run Gasoline
All runs made with fuel containing 1.5 ml. of tetraethyllead per gallon
TETRAETHYL LEAD. n1/6AL
4
I
PHEIYLEIE-
forming tendencies of these materials in the field appeared logical. For this purpose a base fuel composed of straight run, thermally cracked, and catalytically cracked stocks plus tetraethyllead fluid was inhibited with 20 pounds per thousand barrels of 2,6-di-tert-butyl cresol, di-sec-butyl catechol, and di-sec-butylphenylenediamine, respectively. The test fleet consisted of sixteen privately owned passenger cars operated by the owners in normal everyday driving. The cars were divided into four groups of four cars each; each group contained one each of the four most popular makes. Each group of four cars was assigned one of the four test fuels-that is, the base fuel or a blend of the base fuel with one of the three additives mentioned above. At the end of a year of operation the cars had accumulated an average of 13,000 miles each with t h e results shown in Table IV. Analysis of the data indicates t h a t the passenger cars rate the additive blends in approximately the same relative order as the laboratory FL-2 engine, but the spread in ratings among the various blends is considerably smaller than in the case of the FL-2 ratings. For example, the FL-2 Procedure shows the spread in piston skirt varnish rating t o be 38 points between t h e best and worst combination of fuel and additive whereas the field test showed a spread of only 8 points. The same is true for the over-all engine ratings where the laboratory engine indicated a spread of 9 points and the field test 6 poinfs.
Table 111. Effect of Di-sec-butylphenylenediamine Addition on FL-2 Rating of Base Stocks
Base Fuel Tetraethyllead ml./eal. Hydrocarbon t h e , vol. % Aromatics Olefins Parafins Naphthenes Piston skirt varnish rating (100 = clean) Without inhibitor With inhibitor Reduction in rating
(Addition, 25 pounds per CataTherlyticmally ally Straight Cracked Cracked Run B A 1.5 1.5 1.5
1000 barrels base stock) Iso-octane (2 2 450% Diisobutylene triAelhyl- Cyolo- 25% Triisobutylene pentane) hexane 25% Isopentane 1.5 1.5 1.6
0 62 2.7
15 26 35 2.5
20 13 43 24
0 100 0
100
88 71 17
Ya 32
59 28
99
20
31
98 90 8
15
0
96 3
0 0 0
0
75 25 0
95 79 16
409' Benzene 3 0 9 Toluene
30g Cumene 1.5
100 0 0
Q
82
50
38
INDUSTRIAL AND ENGINEERING CHEMISTRY
MILES OK
TEST
(I" Thousand.)
CCMUERCllL GASOLIHE A COHilERCllL GASOLIHE C COUUERCIAL CISOLIHE D
A
CDUIIERCIAL C A S C L I I f STRA 3 H T R I Y
+
Figure 3. Road Performance of Several Antioxidants ( 2 0 Lb./1000 Bbl.) in a Commercial Type Gasoline Containing 1.5 M1. of Tetraethyllead per Gallon
Table IV.
0 A TJ
ConcenAntioxidant None 2 6-Di-tert-butyl cresol 6-sec-butvl catechol Di-sec-but>lphenylenediamine Maximum spread in ratings
h?ji%O
Bbl
73
38
Average Passenger Car Road Teat Piston skirt Over-all varnrsh engine rating rating
70 70 74
79
68
6 Average Road T e s t Ratings by hIake of Car Piston Skirt Over-a11 Engine Make of Car Varnish Rating A 79 80 B 75 71 C 75 68 , 0 68 61 Maximum spread in ratings 11 19 a Base fuel composition: 33% catalytic, 33% straight run, 2 8 7 , thermal, C,70n-butane, 1.5 ml./gal. tetraethyllead. 34
Even more significant is the fact t h a t the field test results as averaged by make of car show a spread of 11 and 19 rating points for piston &lit varnish and over-all engine, respectively, as cornpaled t o a corresponding spread among the different fuel5 of 8 and 6 points. This tendency for t h e diffeiences among makes of cars t o be greatcr than the differences among the test fuels 1s shown 111 Figure 3 and demonstrates that the effect of the engine design variable is of larger magnitude than the effect of fuel variations. This conclusion 15 confirmed by the results of an ear-
9
Tt,ER!ILLY CRIClED A T l E R N A L L Y CIA:XLD
C
CATALYTICblLI CRACKED l-pars A
V X
C A 7 A L T T ! C l L L Y CRACKED I-PASS B CLTALITICALLY CRACXEO 2 - P I S S
~HDICITLO
Figure 4. Correlation of FL-2 Ratings with Phenol and Naphthalene Content of Commercial Fuels and Base Stocks
Aperage Ratings by Type of Antioxidant 0 20 20 20
V 8
PHEYOL 6 ~ A P d T X I t E Y E D E ~ E R ' 4 I X l T I O H S O D T A I H E O BY P?OCEDUIES I Y TLXT OF P I P E ? .
Laboratory and Passenger Car Road Test Ratings of VaPicms Anti&dants in Commercial Typen Gasoline Blend L a b o r a h r y Engine FL-2 Test Piston skirt Over-all varnish engine rating rating
Vol. 41, No. 5
8
lier 18-month passenger car field test in which the spread in average piston skirt varnish rating among the three test fuels used was 12 point,s as compared to a spread among the four makes of cars of 25 point's. Similarly, the spread in over-all engine rating among the three fuels was 4 points whereas the spread in car averages was 27 points. While passenger cars, which consume about 75 to 80% of the total gasoline marketed for highway use, are not critical with respect t o fuel composition and resulting engine deposits, there are indications t,hat at least some of the commercial vehicle operations utilizing the remaining 20 to 25% of the gasoline are somewhat more sensitive to changes in the fuel. This phase of the problem requires further controlled
s
Figure 5.
FL-2 Test Results on a Dirty Base Fuel without Additive Piston skirt varnish rating 39; over-all engine rating 56
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1949
901
I
Table V. Effect of Trace Components on FL-2 Ratings of Straight Run and C a t a1 y t i c a l l y Cracked GasolinesO
STR.
Run
STR. RUN
STR. RUR
Base fuel additive, wt. $To Phenol 0.05 0.05 &resol ,.. ... Mixed cresols ... .. Naphthalene Axuline ... .. Xylidine ... Di-see-butvlDhenvlenediamine ... .. ._ , Fuel for all runs contained 1.5 ml. of tetraethyllead per gallon.
... .
.
.
.
I
I
field test evaluations before definite and realistic conclusions can be made.
Effect of Additives to Increase Deposits The fuel antioxidants reported herein are of the oxyaromatic and amine types. Of the former, the cresol and catechol derivatives did not cause engine deposits in the FL-2 tests in contrast to or-naphthol which, with t h e phenylenediamine and aminophenol derivatives, did increase deposits measurably. T h e d a t a plotted in Figure 4 show a general relation between the phenol and naphthalene content of commercial fuels and increase in engine deposits. The phenol and naphthalene contents were determined after the engine tests were run. Phenol determinations were made
STR.
Run
STR. RUN
...
.. .. ..
...
0.05
...
...
0.8
STR. RUN
... ...
...
...
0.02
STR. R U N
... . .
...
.. ....
CAT. CRACKED
I . .
...
... ...
CAT. CRACKED
...
... 0.05
1.0
0.02
...
0:004
0:004
using the colorimetric procedure for alkyl phenols given in (7). Appropriate correction was made where necessary for any phenolic inhibitor contained in the fuel, Naphthalene contents were obtained b y ultraviolet analysis of t h e aromatic concentrate obtained from t h e test gasolines b y fractionation and silica gel absorption. However, attempts t o reproduce this apparent effect of oxyaromatic and amine constituents by adding phenol, cresols, aniline, and xylidine t o a “clean” (FL-2) fuel were not successful as is shown in Table V. The “clean” fuels included both straight run and selected cracked stocks containing all four types of hydrocarbons. I n view of earlier d a t a indicating interaction of fuel components, the failure of the synthetic blends t o reproduce the effect may be due t o the absence of associated materials which, in combination with these trace components, would cnusc deposits. On the orhcr hand, it is possible t h a t the prescilcc of phenols and nsphthalenes in deposit forming fuels may be coincidentsl.
Effect of Additives to Reduce Deposits -1 logics1 developincnt in the work already described wns the investigntion of fuel additives for the prevention of gasoline engine deposits. Several such materials have been dcveloped which arc cffcctive in reducing or eliininating gasoline engine varnish
Fi ure 6 (Above). FL-2 Test Resufts on a Dirty Base Fuel with 0.1 Weight yc Additive l’tston skirt varnish rating 87; over-all engine rating 04
Figure 7 (Right). FL-2 Test Results on a Dirty Base Fuel with 0.25 Weight 70
Additive
Piston skirt varnish rating 92; over-all engine rating 88
902
INDUSTRIAL AND ENGINEERING CHEMISTRY
and sludge deposits. The results which can be obtained by this means are shown in the before and after photographs, Figures 5 and 6. A small concentration of the additive (0.10 weight yo) provides a remarkable reduction in piston and crankcase deposits. As shown in Figure 7 , an increase in additive concentration to 0.25 weight yoreduces still further the formation of deposits on the pistons and push rod cover plate. However, this is not an unalloyed good, as intake valve deposits caused by the additive increased.
Conclusions From the results reported herein a number of significant clusions may be drawn:
WII-
1. As measured by the FL-2 Procedure, commercial gasolineb and refinery base stocks may vary greatly in their tendency to form varnish and sludge deposits. 2. The significant fuel factors leading to engine deposits according to the FL-2 Procedure appear to be trace components, in particular certain gasoline antioxidants when associated with certain hydrocarbon types-namely, aromatics and olefins. On the basis of limited work, tetraethyllead fluid has no significant effect on the formation of engine desposits. 3. Passenger car field test results rate additive-containing fuels in the same order as does the FL-2 Procedure. However, the spread in fuel ratings is much smaller in the field than in t h e laboratory.
Vol. 41, No. 5
4. ,4s shown also by the passenger. car field tests, engine design factors have a much greater bearing on the formation of engine deposits than do fuel factors. 5 . The formation of sludge and varnish deposits in gasolintb engines can be reduced materially by the incorporation of a suitable additive in the fuel. To date, however, those materials which have been found effective muse the formation of undesirable intake valve deposits.
Literature Cited Backoff, W. J., presented at the Summer Meeting of the Society of ilutomotive Engineers. Frenrh Lick, Ind. (June 1 to 6. 1947’1. ( 2 ) Bowhay, E. J.. and Koenig, E. F., Ihid., Summer Meeting, French Lick, Ind. (June 1 to 6, 1947). 13) Coordinating Research Council, New York, Designation FL-2 Teet Procedure. (4) Georai, C. W., I b i d . , Aiinual Meeting, - Detroit, Mich. (Janultrv (1)
1926). ( 5 ) Moir, A. L., and Hemminga-ay, H. L., Ibid., National Fuels and
Lubricants Meeting. Tulsa, Okla. (Nov. 7 and 8 , 1946).
(6) Pilger, 4.C., Jr., Zhid., Summer Meeting, French Lick, Ind. (June 1 t o 6, 1947). 17) Socony-Vacuum Oil Co. and Shell Development Co., Operation. Control Manual-Tannin Solutizer Process, appendix 18 (February 1946). (X) Wolf, H. R., presented at the 45th Meeting of the National Pr-
troleum Association (Sept. 18, 19471.
RECEIVED.Illnu&t 17, 1948.
Deposition of Lacquer and Sludge in Passenger Car Service F. F. Farley and R. J. Greenshields WOOD RIVER RESEARCH
LABORATORIES,
SHELL OIL COMPANY, INC., WOOD RIVER, I L L
In studying the factors concerned in the formation of sludge a n d lacquer deposits i n engines operated at low temperatures, the effects of engine design, operating conditions, fuels, and lubricants are rated i n this order of decreasing importance. T h e deleterious effect of low engine jacket temperatures in promoting sludge a n d lacquer formation has been established in laboratory tests. At low crankcase temperatures lubricating oils do not contribute appreciably to deposition, a n d oxidation proceeds at a negligible rate. Deposits from low temperature engine operation are derived chiefly from the incomplete combustion products of the fuel which pass the piston as blowby, condense in the oil film o n the cylinder wall, and flow with the oil into the crankcase. As the crankcase oil is
recirculated over the pistons it is postulated that oxidation and polymerization of fuel combustion intermediates proceed to form, simultaneously, lacquer on the pistons a n d sludge particles i n the circulating oil. Agglomeration a n d coagulation of sludge particles then occur in cooler a n d more quiescent parts of the engine. Extensive temperature measurements during normal passenger-car service show that i n winter low crankcase oil temperatures a n d low coolant inlet temperatures are the rule rather than the exception a n d confirm the validity of the conclusions from laboratory studies of engine deposition at low operating temperatures. In many respects, low temperature operation presents more. difficult problems than are encountered at high temperature levels.
L
factorily under certain specific conditions and the definition of these conditions is very important in studies of their behavior. Because automotive equipment, and passenger cars in particular, are required to operate a t variable speed and load and under a wide range of atmospheric temperatures, the actual definition of the conditions to which fuels and lubricants are subjected is very difficult and has been the subject of much investigation. I n the past, high operating temperatures in equipment running under high load conditions have been studied very extensively and products with high oxidation stability to combat this situation have been developed. However, it appearp now that for passenger car service high load and high temperatures have been overemphasized and that as far as deposition in the engine is concerned light load m d low temperatures represent the major part of the operation. Light loid and low tpmpera-
ONGER engine life tLt high performance levels has long been the objective of engineers and chemists in the automotive and petroleum industries. There are many ramifications of the problem of obtaining better performance. Petroleum products play a n important part and aside from actual fatigue and wear of parts, the accumulation of deposits from fuels and lubricants accounts for much of the shortened useful engine life. This paper discusses in some detail the factors concerning deposition in engines. Much has been said in the past about the effect of operating conditions and the design of engines in alleviating engine deposition. HolT-ever, an analysis of the problem is presented here, assuming that operational requirements will remain the same as found today and that radical changes in design will not be made in the near future. On this basis, then, fuels and lubricants are required to operate satis-
