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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-
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1949
i
Figure 1. Chevrolet 40-Hour Low Temperature Test Lejt. \'alve chamber I.ouer lejt. Piston B p l o z . Side plate Laker rrgbt. Crankcase pan
ture present a far more severe condition than the high load and temperature levels reached in automotive equipment from the standpoint of proper utilization of the fuel and lubricant.
Significance of Engine Temperature The deleterious effect of low temperatures on engine cleanliness was studied in the laboratory under closely controlled conditions. As a n example, a multicylinder engine in good mechanical condition operated at temperatures of 85' F. inlet water, 155 ' F. crankcase oil, and 95" F. air-fuel mixture produced deposits on various engine parts as shown in Figure 1. These deposits take the form of sludge which tends t o plug oil passages, oil screen, and oil rings, and also lacquerlike material which coats pistons and packs behind rings, decreasing clearances and, in extreme cases, interfering with proper functioning of the engine. The effect of inlet water temperature of the cylinder jacket on sludge deposition and oil contamination is illustrated by the following 40-hour single-cylinder engine test: Coolant Inlet Temp.,
F. 85 160
O
Oil Temp.,
F.
150 150
Engine Sludge, Grams 18.5 0.7
Used Oil Properties Isopentane- BenzeneInsol. insol., % insol., % ' resins, % 1.68 1.35 0.33 0.35 0.27 0.08
I n this test a 96% reduction in sludging and an appreciable reduction in oil contamination resulted from a n increase in inlet water temperature from 85" to 160' F. Although piston lacquer is usually associated with very high temperatures, it is also materially influenced by very low engine temperatures. A Chevrolet engine run under identical operating conditions except for variable jacket water temperature revealed 8 marked increase in lacquer a t temperatures below 140" F. The relationship established is shown in Figure 2. With regard to crankcase oil temperatures, little or no oxidation of the oils now in use would be expected at anything except relatively high temperatures. The well known influence of temperature on oxidation of lubricating oil can be illustrated by oxygen absorption (4) tests on several oils shown in Figure 3.
Table I.
Fuel Commercial motor gasoline Aviation gasoline (no TEL) Isopentane
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Here it is indicated that a t temperatures below 190' F. oxidation would be negligible. Crankcase oil temperature is important, however, from the standpoint of deposition difficulties in engines. Two points are of major interest. At low temperature water (from combustion of fuel) will be left in the oil and relatively little will escape through vaporization. In engine tests crankcase oil temperatures above approximately 130' F. have been found necessary to eliminate water. "Blowby" gases and liquids entering the crankcase past the pistons will not be driven from the oil. As indicative of the effect of allowing this material to remain in the crankcase either through low temperature or poor scavenging by inadequate crankcase ventilation, some test results on a single-cylinder engine are shown in Figure 4. With the oil temperature a t 180" F. where scavenging would be effective high rates of ventilation practically eliminated sludge deposits. As it is apparent that deposits in the engine a t low temperatures are derived from the fuel, completeness of vaporization and combustion of the fuel would be expected to play an important part. This was borne out in comparative tests of several fuels in an engine using an air-fuel mixture temperature of 95' F. and a jacket water inlet temperature of 85' F. (Table I).
Effect of Completeness of Vaporization and Combustion (Lubricant. SAE 20 motor oil) End Point,
F.
Engine Sludge, Grams
Used Oil Properties Isopentane- BenzeneInsol. insol., % insol., % resins, %
395
18.5
1.68
1.3;
0.33
285 95
9.1 5.1
0.45
0 36 0.46
0 09
0.57
0.11
Substitution of aviation gasoline for commercial motor fuel decreased sludging by 50%. and replacement with the still more volatile isopentane (2-methylbutane) reduced the quantity of sludge obtained by 73%.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Mechanism of Lacquer and Sludge Formation in Low Temperature Engine Operations The crankcase lubricating oil is contaminated by a number of mat
