INDUSTRIAL A N D ENGINEERING CHEMISTRY
502
Vol. 18, No. 5
Motor Carbon Deposits Formed under Controlled Conditions from Typical Automobile Oils By C. J. Livingstone, S. P. Marley, and W. A. Gruse MELLONINSTITUTE OF INDUSTRIAL RESEARCH. UNIVERSITY OF PITTSBURGH, PITTSBURGH, PA.
A small single-cylinder motor has been provided with a special lubricating system, permitting circulation of a very small charge of lubricating oil, and with devices enabling the operator to control very closely the head, oil, and intake air temperatures, the amount of fuel, and the composition of the fuel mixture, as well as the load on the motor and its speed. The modified motor can be so operated as to permit close duplication of conditions. With a given lubricating oil the carbonaceous deposits in the combustion chamber can be checked very closely in a series of runs.
ERY little has been published concerning the “carbon
V
deposits” formed in the combustion chambers of internal combustion engines. Although a considerable amount of experimental work has been performed, practically all the investigators seem to have met the same difficulties in obtaining reliable results. The average gasoline motor as ordinarily operated is not a precision apparatus, and the duplication of results, especially as regards the amount and nature of carbon deposits, has been practically impossible. This difficulty is mentioned by Orelup and Lee.’ A subsequent study by Brooks2 was somewhat more successful. He used the device of throwing together the carbon deposit from all the cylinders of a multi-cylinder engine, thus avoiding the extreme variations from cylinder to cylinder observed by Orelup and Lee. Both investigators reasoned that the carbon deposit is influenced directly by the amount of oil reaching the combustion chamber. I n order to make this supply uniform, both adopted the device of mixing 1 per cent of lubricating oil with the fuel. This ratio of lubricant to fuel was estimated as being the average for most automobiles. By supplying lubricant with the fuel the oil is subjected to conditions it does not meet in general service. I n actual use lubricant is splashed into the gas space to a slight extent, but most of the carbonization takes the form of a “broiling” of a more or less continuous liquid film spread on metal surfaces and exposed to flame. Here ease of volatilization will be an important factor in the fate of the oil. It is generally believed that oils of different types will produce carbonaceous deposits differing in nature and amount, but no studies giving definite support to this belief have been published. Believing the fuel-lubricant mixture method to be inadequate for the purpose, the authors have followed the other alternative. They have controlled the operation of a small single-cylinder motor in such a way as to keep constant all variables but one-the nature of the lubricant-and have allowed carbon deposits to build up in the natural way. The differences in deposit obtained with different oils, using this method, are believed to be real and significant. Apparatus
The basic apparatus was an 850-watt Delco farm lighting unit provided with a specially designed water-cooled head containing a protected thermocouple immersed in a lead bath, a water-jacketed cylinder (interchangeable with an air-cooled cylinder), and a water-jacketed sump replacing 1 2
THISJOURNAL, 1’7,731 (1925). J. SOC.Automoltve Eng , 18,48 (1826).
the bottom of the crank case. A special lubricating system which circulated the oil was installed, whereby a very small charge of oil served for an entire run. This system comprised a small cup fitting under the oiling gear, supplied with oil by a gear oil pump, mounted on the camshaft, pumping from a graduated glass reservoir under the sump. Crank-case drainage oil and overflow oil from the oiling cup drained into this glass reservoir for recirculation. The motor was furnished with fuel through a small carburetor, which was controlled by timing the flow of a measured volume of fuel from a pipet. The air entering the carburetor was warmed to a definite temperature by means of a stove heated by the exhaust. Load on the generator was controlled with resistances. Cooling coils were provided for controlling the temperature of the water supplied to the different parts of the motor. Make-up oil was added by means of a sight-feed lubricator connected to the glass reservoir. A revolution counter was connected to the flywheel end of the crankshaft, and access to the crank case was provided by a covered peephole. Procedure
After a careful adjustment of all parts of the motor, including particularly the exact timing of the spark and valve action and the grinding of the valves, a 1-liter charge of oil was introduced into the reservoir. The engine was started by using the generator as a direct current motor, and the ~ E R M o c o U p L E .
OIL BAFFLE
OIL SPLASH GEAR
OIL OVERFLOW
SUMP JACKET
Figure 1-Cross
Section of Carbonization Test Motor
apparatus was brought to the selected conditions as quickly as possible, to avoid dilution of the oil. Room temperature mas kept constant throughout each series of runs, since slight variations in head temperature, as read on the thermocouple shown in Figure 1, seriously influenced the amount and nature of the deposit obtained. This temperature was kept constant within 3 ” C. The oil temperature, taken a t the pump and controlled in the jacketed sump, was important from the standpoint of oil consumption. This
INDUSTRIAL A N D ENGINEERING CHEMISTRY
May, 1926
503
T a b l e I-Lubricating Oils Used VISCOSITY SAYBOLT NO.
1 2 3 4 5 6
SOURClZ
Pennsylvania Midcontinent blend Gulf Coast Pennsylvania blend Midcontinent distilled Gulf Coast
.
AT 15.5' C. GRAVITY (60" F.1 Sp. gr. A. P. I. 30.2 018753 0.9034 25.2 0.9370 19.5 ;30.4 0.8745 0.9024 25.3 20.3 0.9320
(SECONDS) AT:
37.8' C. (l0OOF.) 365 357 358 307 302 300
temperature and the size of the perforations in the oil baffle beneath the cylinder are the two chief factors i n determining the consumption of an oil of given viscosity. The speed of the motor as measured by revolutions per minute was kept constant to 0.5 per cent. Throttle setting was practically constant. The total number of revolutions in each run of a series was duplicated to the same degree of accuracy. At a constant motor speed the gasoline input was kept constant by adjusting the metering pin of the carburetor, giving uniform air-fuel ratios, as determined by exhaust gas analyses. Intake-air temperature was controlled to iyithin 0.5' C. Maintaining the constancy of the conditions mentioned above, it was observed that the power output was constant t o an average of 1 per cent. On an average, 200 w . of make-up oil were added during a run of 15 hours, starting with a charge of 1liter. Gravity,' A. P. I. Over Dry 105' C. (221' F.) 140' C. (284' F.) 200' C. (392'' F.) Per cent 10 20 30 40 50 60 70 80 90 Recovery
T a b l e 11-Gasolines Motor 60.4 37.8' C. (100: F . ) 224" C. (435 F.) 32 7 0 53.8% 90.3% c. ' F. 63 145 82 180 101 214 117 243 134 273 149 300 165 329 180 356 199 391 96%
Flash
99' C. (210' F.)
' C.
Carbon residue Conradson
Fire
F.
(Open cup1 C.
440 412 358 424 422 350
O F .
490 474 408 476 476 400
% 0.51 0.64 0.12 0.44 0.26 0.03
of the deposits so obtained can be attributed to the fuel. and this question is being studied further. It will be observed that both the total weight of carbon deposit and the carbon value (grams of carbon per liter of oil consumed) are markedly lower for the Coastal oil than for the Pennsylvania and Midcontinent products. Data in succeeding tables indicate that the difference. shown are real and significant. T a b l e IV-Series C and D Head temperaRoom tempera- Oi! temperature, 204' C. ture, 23' C. ture, 37' C Duration, 15 hours Speed 1090 Power, 700 Air-cooled cylinI. p. m. watts der used Fuel consumption Dilution negligible constant Oil Car- Chrhon - .. conTotal bo; deposit Carsump- carbon valuea lessoil bon tion deposit (un- a n d a s h valueo Run 011. Cc. Grams cor.) Grams (cor.) Air-fuel ratio, 12:l
Series C
Used Antiknock 58.9 51 C. (124' F.) 224O C. (434' F.) 24.5Y0 51.3% 90.4% (3. ' F. 83 I82 99 210 112 234 126 258 13s 28 1 151 304 166 330 1i 9 3.54 199 391 96 570
Bt the completion of a run the system was thoroughly drained, drainage loss corrections being applied. The head was removed and the carbon deposits were scraped from the piston and head, the two deposits being kept separate. 9 pan, fitting down over the cylinder, was used to prevent carbon losses. The carbon, after weighing as recovered. was extracted with petroleum ether and was then ashed. T a b l e 111-Series B Head temperaOil temperaRoom temperature, 185' C. ture, 30' C. ture, 23" C. Duration, 36 hours Speed, 1140 Power, 700 Cylinder coolingr. p. m. watts water, 12.5' C. Fuel consumption constant Oil consumpCarbon tion (cor. for deposit less Cor. dilution) Dilution oil and ash carbon Run OIL cc. Grams valuea Molor Fuel 330 12.5 5.278 1fi.O DE-1 No. 1 Pennsylvania 330 12.0 5.105 15.4 DE-8 hTo.2 Midcontinent blend 320 11.5 DE-2 No. 3 Gulf Coast 3.086 9.6 Anriknock Fuel DE-5 No. 1 Pennsylvania 270 8.0 4.520 16.7b DE-6 No. 1 Pennsylvania 300 8.5 3.830 12.8 DE-3 No. 3 Gulf Coast 290 9.5 2,508 8.7 S o . 3 Gulf Coast 280 8.5 2.718 9.7 DE-4 Grams of carbon per liter of oil consumed. b T h e head temperature was low during this run. Note-In this series t h e engine was run past the dilution equilibrium point. It may be noted t h a t with t h e same fuel the dilution attained by different oils is constant. Air-fuel ratio 1O:l
Discussion
Series B (Table 111)presents a set of runs made with a rich mixture (1O:l) and low temperature of both head and lubricating system, conditions favoring dilution of oil and heavy .carbon deposit. It is believed that a considerable proportion
'2-37 C-40 (2-45 (2-46
No. No. No. No.
C-39 C-43
C-38 '2-41 '2-44
(2-49 C-50 C-48
4 Pennsylvania 4 Pennsylvania 4 Pennsylvania 4 Pennsylvania
blend blend blend blend
310 270 160 270
3: 708 2.780 1.991 2.977
12.0 10.3 12,5 11 . O
No. 5 Midcontinent distilled No. 5 Midcontinent distilled
310 250
2.309 1.886
7.5 7.5
90. 6 Gulf Coast No. 6 Gulf Coast No. 6 Gulf Coast
280 350 300
1.566 1.699 1.646
5.6 4.9 5.6
Series D No. 1 Pennsylvania 260 No. 2 Midcontinent blend 260 No. 3 Gulf Coast 260 Grams per liter of oil consumed.
2.736 2.925 1.431
10.5 11.3 5.5
2.632 1.746 1.192 1.987 Av. 1.693 1.318 Av. 1.022 1.266 1.219 Av.
8.5 6.5 7.5 7.4 7.5 5.5 5.3 5.4 3.7 3.6 4.1 3.8
2.004 2.289 1.047
7.7 8.8 4.0
Series C includes runs made with a rather lean mixture (12:1), higher temperature, and more efficient combustion, thereby minimizing the part the fuel plays in depositing carbon. It will be observed that the Pennsylvania oil gives the heaviest deposit, the Midcontinent distilled oil an intermediate one, and the Coastal oil the lowest. Series D presents values on another set of Pennsylvania, Midcontinent blend, and Coastal oils, under the conditions prevailing in Series C, the oil consumptions being checked exactly. The Pennsylvania oil and the Midcontinent blend gave total carbon deposits and carbon values far in excess of those from the Coastal oil. T a b l e V-Series A Head temperature, 225' C. Power, 620 watts Oil and room temperatures Dilution negligible varied considerably Oil Total CarCarbon de- Carconsump- carbon bon posit less bon tion deposit valuea oil and ash valuea OIL Cc. Grams (uncor.) Grams (cor.) No. 1 Pennsylvania 165 1.941 11.8 1.044 6.3 No. 1 Pennsylvania 155 1.845 11.9 1.110 7.2 No. 1 Pennsylvania 270 2.579 9.6 1.797 6.7 S o . 1 Pennsylvania 230 2.708 11.9 1.880 8.0 Av. 7 . 1 No. 3 Gulf Coast 110 0.694 6.3 0.408 3.7 410 2.018 4.9 1.469 3.6 No. 3 Gulf Coast 1.142 4.1 1.698 6.7 255 No. 3 Gulf Coast 5.4 240 1.285 0.578 3.7 N o . 3 Gulf Coast Av. 3 . 8 Grams carbon per liter of oil consumed.
Air-fuel ratio, 1 2 : l Duration, 15 hours
Run '2-12 (2-13 C-20 C-21 C-14 C-16 C-18 C-19
Series A presents results obtained one year prior to the work reported in Series C and D. The same oils were used,
INDUSTRIAL A 9 D ENGINEERING CHEMISTRY
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but the operating conditions were somewhat different. Because of inadequate control, the oil consumptions in these runs varied rather widely, in consequence of which the total carbon deposits obtained in a given time also varied. I n spite of these differences, the carbon values for the two oils were the same as those obtained for the same oils a year later, and these carbon values bear the same ratios to one another; that is, the Coastal oil gave a deposit, in grams per liter of oil consumed, one-half that given by the Pennsylvania oil. E t h e r E x t r a c t s f r o m C a r b o n s in Series B PETROLEUM ETHEREXTRACT, PERC E N T Piston carbon Head carbon 16.2 1 Pennsylvania 34.9 1 Pennsylvania 17.2 32.7 18.7 1 Pennsylvania 43.0 2 Midcontinent blend 19.6 38.6 13.5 3 Gulf Coast 25.1 11.3 3 Gulf Coast 26.8 3 Gulf Coast 26.3 11.0
T a b l e VI-Petroleum Run DE-1 DE4
DE-6 DE-8 DE-2 DE-3
DE-4
OIL
No. No. No. No.
No. No. No.
No. 1
Vol. 18, S o . 5 Carbon value (cor.) 7.7 8.8 4.0 7.5 5.4 3.8
OIL Pennsylvania Midcontinent blend Gulf Coast Pennsylvania Midcontinent distilled Gulf Coast
2
3 4 5 6
Conradson carbon residue 0.51 0.64 0.12 0.44 0.26 0.03
The authors believe there is a close connection between the volatility of an oil and its carbon-depositing tendency. If a n oil contains a fair proportion of hydrocarbons nonvolatile a t the prevailing temperature of the metal surface, such as a steam-refined cylinder stock, this residue will progressively crack and oxidize to sticky and asphaltic materials,
Table VI, giving extraction figures on carbons obtained
at low temperature, shows that the carbon from Coastal products contains less oily matter than do the Pennsylvania carbons. This is believed to be due to the more volatile nature of the Coastal oil, which permits it to distil away from the metal surfaces without leaving much deposit. This may also explain the varying nature of the carbon deposits from the different oils. I n all the runs made, no matter what the conditions, the Coastal carbon was, in general, powdery and friable over the hot metal areas and only slightly more coherent over the cooler areas. The Pennsylvania carbon, on the other hand, was extremely hard and adherent over the hot areas, and sticky and asphaltic in appearance over the cooler areas. It was the general experience that the Coastal carbon could be removed from the motor much more easily than the Pennsylvania carbon.
I
I
I
10
Lo
30
I
I
I
40 ?D co PcnCWTML DISTILLLO
I 10
ea
I M
Figure 3
which will gradually bake into dense, adherent deposits. If, on the other hand, the oil can distil off fairly cleanly, i t will probably take much longer to produce a deposit of equal thickness. I n addition, it appears that a deposit from such a volatile oil will contain a smaller amount of binding material, and will therefore be more friable than a deposit from a higher boiling oil. Acknowledgment
The authors wish a t this point to acknowledge their indebtedness to W. F. Faragher, assistant director of the Mellon Institute, for valuable suggestions and constructive criticism in the planning of this investigation, and also to John J. Curry, whose painstaking attention and mechanical skill have been of great assistance in this work.
Calendar of Meetings PCACLKI+~E DISTTIYCD
Figure 2
Figures 2 and 3 give the distillation data a t 10 mm. pressure for the oils used, in two groups of matched viscosities at 37.8" C. (100" F.), It will be noted that the Coastal oils, which gave the lowest carbon deposits, have also the lowest boiling temperature, while for the other oils used the amount of carbon deposited and the boiling temperatures were both higher. It is particularly significant that those oils almost completely volatile below the cracking temperature gave considerably lower carbon values than those containing appreciable proportions nonvolatile below the cracking range. It has been suggested that the Conradson carbon residue of lubricating oils offers an approximate measure of the tendency to deposit carbon in an automobile motor, but little experimental support for this supposition has hitherto been published. The following comparison, however, confirms this view :
American Chemical Society-72nd Meeting, Philadelphia, Pa., September 6 to 11, 1926. 73rd Meeting, Richmond, Va., April 12 to 16, 1927. American Electrochemical Society-Fall Meeting, Washington, D. C., October 7 to 9, 1926. Association of Chemical Equipment Manufacturers-2nd Chemical Equipment Exposition, Cleveland; Ohio, May 10 to 15, 1926. Chemical Section, National Safety Council-Niagara Falls, N. Y . ,May 21 to 22,1926. American Leather Chemists' Association-23rd Annual Convention, Traymore Hotel, Atlantic City, N. J., June 2 to 4, 1926. National Lime Association-8th Annual Convention, French Lick Springs, Ind., June 8 to 11, 1926. American Institute of Chemical Engineers-Berlin, N. H., June 21 to 23, 1926. Fourth Annual Colloid Symposium-Massachusetts Institute of Technology, Cambridge, Mass., June 23 to 25, 1926.
