engine lubricating oils

ENGINE LUBRICATING OILS. 371

ENGINE LUBRICATING OILS.

BY W. R. ORYANDY, D.So., AND J. H. LESTER, M.8c.

The Problem Stated.

Most of the articles on this subject contributed to the motoring journals seem calculated to give the reader the impression that the subject of lubrication is one for experts, thoroughly understood by them, and reduced in the minds of the writers to something very nearly approaching an exact science. Whilst, of course, a knowledge of physics and of chemistry is necessary to the appreciation of many finer points of controversy, there is yet much for the layman or the amateur to follow if he can be shown that practice is still far ahead of theory, so far as concerns the application of liquids for the purpose of keeping metallic surfaces out of contact with each other, and so preventing undue wear. It is true that research is not lacking into the realms of capillarity, of surface tension, and of sundry other scientific bases pertaining to the problems invohcd, but very little work has been done upon the point which redly interests us most, that is, with regard to the conditions existing at the surface of the metal and of the lubricant. It may at least be said that a practically useful outcome from such resemch is either entirely lacking or is hidden away in the minds of those whose knowledge of practice is not sufficient to enable them to interpret their results. We shall, perhaps, make surer progress by the admission of a vast amount of ignorance than by parading the importance of our little pet theories.

Methods of Testing. Quito a large numbcr of instruiiicnts liilvc bcen designed

specially for testing oils as to their lubricating qualities, and they have been bought and used by hundrcds of oil users with the idea of selecting the best and cheapest oil for their purpose, but it can scarcely be said that they generally satisfy their purchasers, beoause they do not shorn the differences in lubricating value

A ..\ 2

372 THF, INSTlTUTION OF AUTOMOBILE ENGINEERS.

expected by the user or perhaps guarantecd by the dealer. They give an indication of viscosity, of course, but that can be ascer- tained in a much inore simple manner. We are bound to think sometimes that the seller of oil cannot demonstrate the superiority of his prodnct in any other manner than by appeal to theoretical jargon which he knows thc user cannot understand.

Blind Faith. The iliain coiisicleratioiis in selecting an engine oil are even

now not at all well understood. Too mnch reliance is placed on vague inferences as to the virtues of viscosity and flash point without troubling to think just what these things mean. These claims are not always nilsubstantiated either, as figures are given to show that viscosity and flash point are indeed as claimed; but seldoni is an explanation offered a9 to what is the practical purpose to which the figurw can bc turned, and, for all the user knows, they may be very good or quit0 poor, but he assumes, as they are specifically mentioned, they must be very good. It is true that a few car makers have coiiducted experiments to find out how f a r certain recognisod brands can be recommended for their engiiiw, but rhcy i11’c iii a iuinority.

lechnicnl Terms. Before describing the results of a considerable number of ex-

periments mhich the authors have. carried out, it is necessary to explain some of the technical terms which are of necessity used in dealing even in a popular manncr with a technical subject of this nature.

It is clear that the prime purpose fulfilled by lubricating oiI is to keep apmt metallic surfaces moving onc over the other. We reqpire for this purpose a material which will “wet” the metallio surfaces in question. It must creep between surfaces which are almost in contact, and while wetting both surfaces must form a liquid film. In place of rubbing a metal on a metal we desire to rub oil on oil, that is, to displace solid friction by liquid friction. It is obvious that i f the oil employed be very thin it will the more readily penetrate between metallic surf aces, but it is also obvious that a thin oil will more readily be squeezed out than a thick oil, Here, then, we meet the first ground for compromise. We should use a thick oil as being less liable to be pressed out, but on the other hand a thin oil aa being best able to penetrate between the surfmea to be protected.

Capillary a id Hurfnce lension,

The particulax property of a liquid whereby i t is drawn into narrow openings is known as capillarity, and the capillary power of a liquid is dependent on what is known as the surface tension. It is in this particular branch of the application of science to practice that there is the greatest scope for investigation.

There is no doubt but that there me very considerable varia- tions in the behaviour of different classes of oil in respect to this ability to stick to a metallic surface. Wo may take two oil9 of about the same degree of fluidity and put a drop of each on to a newly planed metallic surface, and it will be found that one spreads wikh great rapidity over a large surface, whereas the other moves much inore sluggishly, and it is in this particular realm that animal and vegetable oils show great advantages over the pure mineral oils. This branch of the subject of lubrication is, however, not that with which we wish to deal particularly.

viscosity. The film of oil between the metallic surfaces in motion with

regard to one another is being continuously displaced, and the liquid is subject to what is known as internal friction. Obviously of two oils that which will allow of one portion to move over another with the least friction will be most advantageously employed. This property is referred to as the viscosity of the oil, and it is the property which is most relied upon in investi- gating the relative value of lubricating materials. I t is evident that, although viscosity may ;be of value in deterinining in some respects the relative value pf a number of oils, nevertheless viscosity in itself is no measure of lubricating quality. This becomes obvious when it is coiisidered that i t is possible to have materials such as treacle or a solution of gum ttrabic or gelathe with a viscosity equal to that of a lubricating oil, but none of these could very well be recommended for crank case purposes.

That peculiar property which we all understand by the term “oiliness” may be in 8ome measure expressed in terms of viscosity, but i t is not casually connected therewith.

I n the work which follows there will be numerous referenem to the viscosity of oils as determined a t various temperatures, and it will be well at this point to describe briefly the weans employed for determining viscosity and expressing the results as B number. The instrument chiefly used is the Redwood Viscosi-

37 4 THE 1NSTITUTION OF AUTOMOBILE ENGINEERS.

meter. This consists in principle of a vessel lo contain the 0iI to be tested surrounded by an outer vessel containing a liquid which can be heated so tts to bring the oil to be tested to any required temperature. Having once attained the desired temperature, a given bulk of the oil is allowed to run through a small hole at the bottom of the vessel, and note is taken of the time in seconds which is occupied by a predetermined bulk of the oil to pass through this opening. The size of the hole employed was quitc empirically fixed a t about 1.7 nim. in diameter and approximately 12 inm. long. This size of hole is found to allow 50 cc. of rape oil to flow through it at a temperature of 60" F. in 535 seconds. The timc taken by the standard quantity of oil to flow through this hole is taken as being a measure of the viscosity. This is not strictly accurate, particularly with thin liquids, but it is sufficiently near for all practical purposes when dealing with lubricating oils such as those employed for the most part in crank case work. Thus tho statement that a certain oil has a viscosity of 500 at 100" F. and 90 at 200" F. means that a t these temperatures 50 cc. of the oil took 500 seconds and 90 seconds respectively to run through the standard opening. A glance at the figures in the Tables will show what an enormous difference in viscosity is caused by increase in temperature. This again is an item of very great importance, because of two oils of equal viscosity at 18 low temperature, that which better retains its viscosity a t high temperature mill be superior. The percentage difference between the viscosity of mineral oils grows less the higher the temperature, and the ratio of falling off in viscosiQ, is greater in the case of mineral oils than in the caee of vegetable oils.

Plashpoint. The flashpoint of an oil is that temperature at which it evolvea

a vapour which will burn in the air. Petrol evolves a vapour which will explode when mixed with air at ordinary temperatures, although on some cold minter mornings the man who perspires i n vain at the Btarting handlo may be excused for doubting it. Ordinary paraffin oil may require heating to 100" F. or more before evolving inflammable vapours, and sonic lubricating oils ma)- require heating to over 500" F. before a sufficiently volatile material is given off to causc n flash.

I n the pmt there is no doubt that far too mnch importanoe has been attached to this tcst. considered in conjunction with

other resulk it is of value, but as mill be showii later it is possible to have oils flashing at little over summer temperatures which perform their duty in the crank case in an entirely satisfactory manner.

Heat Loss. The last technical tern which we shall frequently come across

is heat loss. An oil may have a comparatively high flashpoint and yet, if heated to a temperature below the flashpoint for a considera.ble period, it may lose a large percentage of its weight. It is this property of oils which has not hitherto received the attention it deserves, for by means of a comparatively simple experiment it is possible to distinguish among a number of samples those which are most likely to give satisfactory results when employed for crank case work. The temperature which the authors employed in the test here aescribed was arbitrarily fixed at 400" F., this being a temperature comparatively easily obtained with paraffin bath. A number of small beakers were employed, in each of which a small weighed quantity of oil was placed, and these 'were heated to 400" F. for a varying number of hours and the loss i n weight a,scertained from time to time.

The most {astonishing diff cremes were discovered. Losses under the above condition in six hours were found to vary from below 2 per cent to over 60 per ccnt. Not only must tho loss $gum be kaken into consideration, but also the physical nature of the residue. Some oils after B comparatively small loss left a gummy residue, others 'after a comparatively high loss left a residue which remained fluid and satisfactory. The authors' ow11 experiments go to show that the oil which loses the least whilst leaving a residue a8 little altered in chnmcter 08 possible will give the best results.

It is obvious that compamtivo tests of a number of oils could, be carried out with no special apparatus by the layman by ex- posing in similar vessels eqiial amounts of the various oils to a comparatively high teinpcrature, say, that of an ordinary oven, for a considerable period nad thcn examining the residues for quantity clnd properties.

Having now explained in a general way the terins to be employed, we will turn to more detailed consideration of t,ho a.ctual experimenb.

Some years ago the authors carried out tests 011 a wide range of petrol engine oils in thc belief that the simple heat.ing of one gramme of oil to 400' F. for six lioiii-s ~voold show really appreci-

376 THE INSIITUTION OF AUTOMOBILE ENGIXEERS.

able differences and furnish a test of practical value. Others have worked on similar lines, and the authors found that Messra. Henry Wills and W. Scott Tsggart had published similar results on the examination of steam cylinder oils.

Generally speaking, gas engine oils and the cheaper oils gave the worst results, though the thick steam cylindcr oils gave results practically equal to the most expensive air-cooled oils. The viscosity of the black steam cylinder oils was, of course, against their use for petrol engines, but the authors ventured to experiment with one obtained at l l d . per gallon and mixed with 10 per cent of ordinary paraffin to reduce it to a reasonable viscosity. The original oil had an exceedingly small loss on the heat test, and after the addition of 10 per cent of paraffin i t was found that the total loss was only 6 per cent, showing that something like half the paraffin was retained by the lubricating oil even after six hours' heating at 400" F. Five gallons of the mixture were used on two different cars, and no difficulty of any kind w w experienced in use. Although fairly high compressions were used, the carbonisation wits not more than usual with other oils.

One of the engines upon which the experiment was made has been treated at various times with cheap gas engine oils, heavy air-cooled oil, light engine oil, and with many of the advertised brands of both compound and hydrocarbon oils, the object being to find out whether any of these were really unsuitable from any point of view when carefully used in reasonable quantity. As a result, the authors cannot say that any of the samples were unsuitable if used in correct quantity, though some were much more economical than others. I t is consequently difficult to believe that tales as to the marked superiority or inferiority of any of these oils are. in fact, well founded. The authors mould, of course, hesitate to recommend any motorist to lay in a stock of their particwlar paraffin mixture, but they do say that their testa point clearly in the direction of great economies being effected in the future, when running costs must become of greater importance than they are to-day.

Table I. contains a collection of results of experiments ou a large nuniber of oils carried out for the most part a oonsidcrable number of years ago. All the proprietary oils were purchased in the ordinary way, and the authors are indebted to Mr. E. W. Wollaston, of Manchester, for his kindness i n providing them with the oils which are aesignated by letters.

The heating experiments were carried out in all c&9w 011 one

ENGINE LUHRICATINQ OILS. 377

gramme of the oil in small beakers about 1 in. diameter heated in a paraffin bath. At the end of the test the oil waa allowed ,to cool down to room temperature and the beaker inclined. Obvi- ously, the oil which loses the least and leaves a residue ’most like the original oil is the most desirable sample.

TABLE I. .

Oil.

Price’s Gas Engine ........ Heath’s Gas Engine .. , . . , . . Price’s Motorine G. ........ Vacuum N (air cooled) .... Vacuum A (water cooled) , , A. Dark Cylinder.. ........ B. Filtered Cylinder ........ C. Heavy American.. ...... D. Heavy Russian ........ E. Gas Engine Basis ...... F. Blended Oil . . . ......... (3. morris'^ Speedon (air-

H. Morris’s Speedon (water cooled) ..............

I. American. ............. J. Similar to I. ........... E. Fine Filtered .......... L. Similar to I( ........... M. Heavy Russian ........ Autolubrine .............. .Price’s lldotorine A ........ Q.B. 1 (Bir-cooled) ........ Q.B. 2 (water-cooled) ...... Wellsaline (air-cooled) . . , . N. Mixed I( and I 411. ..... Belsize Oil. ............... Humber Oil .............. Pennsylvania .............. Snowdon ..................

cooled) ..............

D.l

Viscosity.

At 0 8 F. - sees. 44% 45 71 118 54 160 118 71 55 47 ’75

107

77 50 46 152 160 73 61 130 60 71 90 127 68 56 80 59

~

At 400° F.

sew.. 29

35 35

293)

31& 36& 37

30 31 32

38

36 31 31 394 42 34 32.9 37 30 33 35 39 34 31

33

..

. . - -

R.-Doee not run. S.L.,-RIUU .lightly. R.R.-Rnns readily.

Close Teat

Flash- point.

O F .

401 365 392 419 383 473 464

349 374 424

455

428 428 416 500 509 428 374 492 383 410 414 464 401 383 464 390

-

..

-

-___

Low Tests 6 Hrs. 408 F.

Per Gent. 61-35 86.95 22-52 7-54 45.12 1-46 8.10 56.04 54.3’7 65-43 56.16

7-71

16.41 25.88 40-94

1-51 2’1 1 14.65 33-15 7.60 63-83 50.30 33-79 18-10 21-80

&‘78 38.63

Effect,

S.L. D.N.R. R.R. R.R. R.R. D.N.R. D.N.R. D.N.R. D.N.R. D.N.R. S.L.

R.R.

R.R. R.R. R.R. D.N.R. D.N.R. R.R. R.R. R.R. D.N.R. S.L. D.N.R. D.N.R. .. .. .. ..

TABLE II.

390 38.6

464 3.8

392 22.5

464 8.1

Close Test Flauhpoint, O F . . . . . . . 349 1 365 374 1 374 383 Heat L o ~ s 6 Hours, 400° F.",', . . 54.3 87.0 65.4 33.1 63.8

CloscTestFlashpoint, O F . ....., 419 424 428 428 428 Kent Loss 6 Hours. 400° F . O / , .. 7.5 56.2 14.6 16.4 25.9

383 1:: 455

18.1 45.1

7-7 18.1

401 61.3

492 7.8

TABLE IV.

410 50.3

500 1.5

B.

"I" 2.49 8.21 8.10

LORE on Heating-- 5 Hours at 350' F. . . .. . .

48 Hours at 350" F. . . . . . . 6 Hours at 400° F. . . . . , ,

401 21'8

473 1.5 -

Pike's GaS

Engine.

OIO

28-66 59.68 61.35

" l o ,5:/:58 I 10.18 85.13 23.94 86.95 1 22.52

I

414 33.8

509 2- 1

" l o 1 " lo " l o 1.93 17'22 1 1.00 6'00 51'07 1 1-74 7'54 1 45.1'2 j 1'46

416 40.9

% 22,74 56.5 56.04

C. I D. 1 E.

O 10 "I0 26.92 29.10 51.44 66.09 54-37 65-43

I-l-

TLs Hgz8 En@ne. Engine.

B. C. I

Motorine N. I A. ~

Price's vacuum v m u m 1 A.

F.

"!O

11.75 37-66 56.16

D. I E.

.. .. ..

F.

Ole 75.0 ..

ENGINE 1,UHKICATING OILS. 879

Relation between Flashpoint and Heat Loss. d cursory glance suffices to show that there is very little con-

nection between the flashpoint of an oil and the result of the heat loss test. I n order to bring this better into prominence, Table 11. shows the oils arranged in the order of the flashpoint with the corresponding heat loss at 400" F. given below. Fig. 1 shorn these results graphically, and the frequent occurrence of a number of oils of the same flashpoint and very different heat loss empha- sises the impossibility of relying too fully on flashpoint figures. From the curve, however, it is clear that, generally speaking, the heat loss is greater in oils with a low flashpoint. Subsequent

FIG. 1 .-Curve sliowiug connection betweeii Flash Point and Heat Loss.

results will show that a flashpoint may be reduced by the presence of a small amount of a comparatively easily volatile impurity or constituent. I n such a case the flashpoint would give an entirely false picture as to the quality of the oil.

Experiments on the rate of loss in weight of an oil at two or three temperatures render it possible to tell whether the oil as a whole is fairly homogeneous or whether it contains several constituents of very different character.

Fig. 2 shows the loss in weight on heating a sample of Vacuum A for various lengths of time at various temperatures. At 300" F. in twenty-four hours the oil has lost 23 per cent of

its weight. From the uppearancc of the curve it monld appenr that further heating would have resulted in further loss. The siiigle experiment at %O" F. for five hours shows that this sainc oil lost as much as it mould huve lost in about fifteen hour* at 300 F., and in two hours at -100" F. i t had lost as much in weight as in twenty-four hours at 300' F.

Table 111. records a series of expciiincnts on the heat lossrs of various oils at various temperatures. and i t is interesting to notc that in almost all cases the loss i n six hours at 400" F. i b

almoit always equal to the loss in foyty-eight hours at 350" F . and that the order of the losr remains pretty moll the samc within the times and range of temperature of the experiments.

90

100 2 4 6 X 10 12 11 10 18 20 "2 24

Hours' Heating.

Frc;. ?.--Effect of Teiii1)crature nud Tiiiie on Heat Loss.

Gei~ernl Consideration of Ci~iiih. Cusc I,ubt ictrtioii

ISefore endeavouring to arrive at any conclusions as to t l i u probable iiature of a satisfactory oil for crank case lubricatioii, it would be well to consider Briefly the conditions under which such an oil has to work. The big ends, the main journal bearings on the crankshaft and the gudgcon pin, have to be lubricated m well as the cylinder itself. The pressure on the gudgeon pin is excessive. but the angular motion is irery slight, and little diificulty is experienced at this point. The pressure on the big end bearing3 and on the crankshaft bearings is also very high, but is alternating in character, and it is this alternating character

ENGINE 1,L H l t l c A r l S G OILS. :18 1

of the load which enables satisfactory results to be obtained under pressures which would be disastrous if continuously applied in one direction.

A thin oil is preferable in that it absorbs less power than a t,hick oil when separating metallic surfaces moving at a high velocity over each other. On the other hand, such thin oils are more easily displaced from between the bearing surfaces. A heavy cylinder oil would perhaps be too thick i f the temperature of the oil remained at that of the surrounding atmosphere, but this we know does not occur. Those who have allowed the oil to run out of a crank case immediately after the car has returned from a run know how very fluidly it comes out compared with its behaviour when the engine is cold.

This Lriiigs us to the consideration of the influence of temperature on the viscosity, that is, the thickness of lubricating oil. Most of the available data are those dealing with viscosity of oils between ordinary temperatures and 200" F., but in crank mse lubrication we have to do with temperatures on tho cylinder walls which much exceed these, and the authors have carried out ft number of experiments ou the viscosity of oils at higher tcin- peratnres, thc result.; of which nrc cnntninecl in Table IV.

Temp era t u re and Viscosity. It will be seen that the differences in the viscosity are com-

paratively slight a t higher temperatures. This is a characteristic, particularly of mineral oils. The rate of falling off in viscosity of animal oils, such as sperm and lard oils, and of vegetable oil, such as castor oil, is not quite so rapid, and this property, conjointly with the extra oiliness of animal and vegetable oils, has led to their utilisation in racing car engines. Owing to the comparatively high temperatures of oil in the crank case, there is no danger that i t will be too thick when once it has got into use in the crank case. Wc must, however, use an oil which at ordinary temperature is sufficiently fluid to pass through the con- strictions of the lubricating system, and this alone marks the maximum limit of allowable viscosity.

'Original v. Crank Case Oil. Having been struck by the great fluidity of oil taken from the-

crank case wlien i t was not very warm, tlic authors determined

382 THE I NSTII‘ U’l’ION OF AUTOMOHI 1.1.: EXGl N E EKS.

to investigate samples taken from the crank case after ude, ttud this led to some interestiiig discoveries. A certain oil before being used gave heat losses as shown in Fig. 3. The plain line shows the amount evaporated on heating the original oil (i.e., before use), and the dotted line shows the amount lost on heating the crank case oil (i.e., after use) under similar conditions. I t will be seen that the total loss in this case was greater with the crank cme oil, but the most striking feature is the increased loss at low teniperatures, the subsequent course of the oil being practically parallel to that of the original oil. The specific gravities of the two oils are very close. that of the crank case oil being taken on the filtered sample.

Further experiments detailed in Table V. mere carried out on oil from another engine. The crank case oil was filtered in each case before the physical constants wcrc determined.

TABLE V.

Original Crank Case Oil. Oil.

‘Specific Gravity.. ...................... Flash point ............................ Viwosity at 7a0 F.. ....................

I , looo F.. ..................... ,, 1 2 P F ....................... ,, 150°F. ...................... ,, ZOOo F.. ..................... ,, 400n F.. .....................

Mineral Oil.. .......................... Fatty Oil ............................. Effect ................................ Loss on Heating 6 Hour@ at 4003 F. ......

0.900 2i6O F.

725 sea. 267 8808. 140 secs.

36 secs. 99.77 p. cent 0.23 ,,

20.3 ,, Runs slightly

1,530 WCR.

76 8eCb.

0 904 230° F.

1,390 WB. 670 secs. 259 Rem. 138 mm. 74 f3ecB. 35 8em. 98.74 p. cant. 1-20 ,, 22.6 ,,

Runs modcrately

Tliesc resulk, \\ere in 6011ie directions unexpec:td. Tlic gicxat increase in the fatty oils requires investigation, and we can oficr 110 explanation beyond that of possible oxydation. Tho loss on heating seemed at first sight abriornial ‘1’11~ viscosity test showr that the crank case oil is distinctly more fluid, especially when cold, but the niore tho oil is wariiiecl the closer become the viscosities. This points to the presenco of some easily volatile constituent.

I t must be buriie in Iiiiiid that the crank case oil is sphslicd on the piston inid on to the cylinder walls, where i t is exposed


Original Mixture.

:wc F. 93 8PCS. a9 SWA. 10.1 er cent.

Runs sfghtly

to a very high temperature, and the oil is then in the form of a thin film, which enables these physical changes to be brought about very rapidly. As will be scen later on, there is, however, another explanation which did not then occur to the authors, but which further experiments havc proved to play an important role.

The fact that the flashpoint of the crank case oil has gone up after removal of the easily volatile constituents boiling below 160" C. proves that the increased fluidity of the heated oil at low temperaturc is not, due to the splitting up of the oil into a volatile portion leaving a heavy residue. I t would rather seem due to internal alteration in the molecular structure, though little importance can be attached to this conclusion until it has been confirmed by further investigationq.

Crank Case Mixture.

32O0 F. 1 1 5 Recs.

43 seas.

, Runs slightly 7.0 per aent.

TABLE T7I.

FlaRhpoiut ........................... 400° F. ....................

Effect ................................ Viscosity at ZOOo F. . . . . . . . . . . . . . . . . . . . H&'koss Teat 6 Hours at 400° F. ......

Arguing from the staudpoint that the crank case oil after we became more h i d from the presence in it of some emily volatile constituent, the amount of which, however, did not seem to increase beyond a certain limit, the authors decided to use a heavy cylinder oil so viscous that a t ordinary temperature it would scarcely run through a :in. pipe. In order to make this oil suitable for drip feed lubricating arrangements 10 per cent of ordinary paraffin was added. This dark mixture then had a viscosity about equal to an average motor oil for water-cooled engincs. Table VI. shows the properties of this mixture before use and whcn taken from tho crank case after use.

I t will be seen that whatever was lost of the paraftin contents in tho crank case was practically made up by something which the crank case oil gained in the cylinder, or on the cylinder walls, because the flashpoint remained constant.

Impravmzent of Crank Case Oil by Heatiny . a s these experiments have been carried out on oil used 011

somewhat old types of engines, the authors arranged t u obtain some crank case oil from a inore modern engine. Table V I I . gives the results of the exaiiiination of the oil takeii from the crank ca5e of a +cylinder Wolseley (102 min. by 130 mm.).

The enormous reduction in the flashpoint and in the viscosity of the crank case oil, its shown in the last Table, led the authors to try the effect of heating the crank case oil for onc hour to 300' F. I t will be seen that. this raised the viscosity both at low and high temperatures to something over that of the original oil. This points to the fact that the low flashpoint was duc to the preicwce of ;L sinall quantity of very volatile ingredicnt, which

TABLE VII.

Flashpoint . . . , . , . . . , . , , . , . . , . . 120° F.

Vieooeity at 1000 F. . . . . . . , . , . . . ,, 200°F. ...... ,. .. .. 55 B W .

Crank Case Oil after Heating to

300° F. for 1 Hour.

610 a m .

90 flea.

also aftected the viscosity, whereas tho bulk of the oil was improved in quality.

The results of these experiments led the auth6rs to the conclusion that the crank case oil became contaminated with the fuel employed, and that during compression strokes some pro- portion of the charge leaked past the piston rings towards the crank case. If this be true, then on every compression stroke of the engine a small percentage of air saturated with fuel gets into the crank case, where it is met by an oil spray. Such an oil spray is an ideal means for washing volatile fuel oils out of a gas, and is indeed the method eniployed to-day for recovering benzol from colre-oven gas. Obviously, the oil in the crank case would continue to wash out petrol from the charge escaped past the rings until the vapour tension of the oil-petrol mixture at the temperature uf the crank case resisted further solution.


Flashpoint .................... Yisco.rity at looo F. ............

,, 200°F. ............ Loss 0x1 Heating at 400° F. for

6 Hours ....................

I f this explanation be correct, it should be possible to distil off from the crank case oil a small amount of petrol-like fuel at

408" F.

670 sew.

67secs.

35.1 p. cent

Moo F. N O o F. 4 W F. Original Oil (before use) S.G. 0.8995. Crank Case Oil (after uae) - - - - - - - S.G. 0.8993.

FIG. 8.-Heating for one hour at increasing Temperature.

a low temperature. A consideration of Fig. 3 would lead to aa expectation of something like 2 per cent of volatile material being the limit of solubility under average crank case conditions. 9

TABLE VIII.

Original Oil.

Crank Case Oil.

130° F.

450 aeos.

55 @em.

28.3 p. cent

Crank CaRe Oil after Heating for

1 Hour to 300° F.

355O F.

596 secs.

72 8808.

32'1 per cent.

sample of the unused oil employed in the crank case of a 6-cylinder Sunbeam engine (90 niin. by 160 mni.) and also the contents of the crank case taken from the engine were then obtained. Therct

0 RMAN1)T. R 13

was in all about two gallons of oil, and the authors are informed that such care was taken in emptying the crank case that not more than half a teacupful was lost in all. The engine had run 1,250 miles since the crank case was filled, and during this period half a gallon of oil had been added to keep up the level. Fable VIII. gives the physical constants.

As regards the flashpoint, the results are practically the same as those found in the oil from the Wokeley car, and the sahe drop in viscosity is observable. Heating the crankcase oil to 300" F. for one hour showed that it was more fluid at low tempcra- ture and less fluid at high temperature than the original oil. Obviously, this heating removed the material which was the cause of tho low flashpoint. A litre of the crank case oil was heated, and Fig. 4 shows the results. The distillate, which was exactly 2 per cent of the original sample, had a specific gravity of 0'7656,

Lwx)o F. 3ooo F. 4CQwp F. 6000 F. Sp. Gr. of Dbtillate 0,7656.

FIG. 4.-Temperature of Distillation.

and was soinething between ordinary petrol and paraffin oil in its nature.

Some General Conclusioias.

There is much experimental work to be done in connectioii with crank case lubricating oils, and the authors propose to continue thi3 work on the general hie5 developed here. For thc present i t niay be said to be denionstrated that for cpank caw plupo3eu it is preferable to use an oil with a high flashpoint, p low heat loss, and D very high viscosity, and that it is quite in older to iuake use of an oil, which in itself is too thick for meclianical reasons, reduced in its viscosity by thc addition of ordinary paraffin oil. In order to prevent the accumulation of \ olatilc material in the lubricating oil exceeding a reasonable

ENGINE T~DHHICATING OILS. 387

limit, it would appear to be good practice to take the air for carburation from the crank case, since obviously such air will not only be warm, but will contain a certain amount of fuel which will thus be utilised. But the prime object of the air current is to remove the petrol vapour from the sphere of action of the lubricating oil. In view of the increased use of benzol, which leads to somewhat greater heating effects on the piston, it might be well to direct the cold incoming air into the crank case towards the underside of the piston, thus helping at the same time to keep this cool.

Petrol-Parafin Fuel and Big End Bearings. I t has been stated that great trouble has been experienced

in motor cabs which have been attempting to run on mixtures of paraffin and petrol owing to frequent failures of the big e d bearings. In the light of what has gone before, the cause is possibly t o be found in the gradual acciunulation of paraffin washed out by the crank case oil. In the case of petrol, the accumulation cannot exceed a comparatively small amount, owing to the high vapour tension of petrol, even at crank case temperatures, but with paraffin the case is different, and this inatcrial would tend to accumulate in the lubricating oil until the latter became too thin to serve its purpose, with the consequent perishing of the big end bearings. It would probably be found that heating the crank case lubricating oil for a short time with agitation to 300" or 400" F. would render such lubricating oil in every way fit for further use. To a certain extent it is possible that the lubricating oil, which is drawn up on to the cylinder walls and then carried by the piston motion back into the crank case, may dissolve a certain amount of volatile fuel oil, and in this manner bring a certain amount into the crank case, but, however it arrives there, the fact is undoubted that the fuel is to be found in the crank case.

For racing engines, where owing to heavy load and high temperatures lubrication difficulties beconie vastly increased, castor oil is frequently employed because it is not readily soluble in petrol, and consequently remains longer on thc cylinder Rides. ('nutor oil, however, according to Archbutt and Deeley, is capable of dissolving allnost its own weight of petroleum spirit, and this oil will become thinned in the mme way as mineral oil. In racing engines i t mould seem more than ever necessary to take the air

13 n 2

388 THE INSTITUTION O F AUTOMOBILE ENGINEERS.

for carburation through the crank case, with a view to reducing the temperature and keeping up the viscosity of the lubricant, not only by the temperature reduction but by the removal of these volatile constituents which cause such rapid thinning.

If by the use of thick oils and by taking comparatively simple precautions aeroplane engiues and racing engines can be saved from the necessity of using external oil cooling devices, it would be a great advantage both on account of simplicity and the saving in weight. I n certain industrial operations, as, for instance, in transmitting considerable power through worm reduction gears, i t har been proved worth while to add oil pumps and oil cooling apparatus, since by so doing it is pwsiblo to make use of a gear which, while mechanically strong enough for its purpose, would be incapable of continuing in steady w c owing to the fact that the lubricating oil, i f not cooled externally, would become so hot, and consequently so thin, that undue wear would take place on the rubbing surfaces. In such cases the cost of the addition of the oil cooling devices is more than justified by the ability to use small, and conreqnently cheaper, gears with equally satisfactory results.

The authors are informed by Messrs. Wallwork that a certain gear 36 in. diameter, Fig. 5, Plate XI. , was constructed to transmit 200 h.p. at about 1,200 revs. per minute. The loss was about 1 5 h.p., and the heat was removed by a radiator placed in the path of the oil from the sump to the worm. Bad there been no added cooling arrangements the natural cooling area of the worm gear would only have allowcd the gear to transmit 80 h.p. with thr same maximum temperature of lubricating oil.

Tlie whole of the foregoing experiments were carried out at the Mancliester Chamber of Uoiiimerce Testing House, and the authors’ thanks are due to Mr. Barwick (himself a keen motorist) for his kindness in allowing the experiments-started at the Testing House under Mr. Lester when the latter was manager- to be completed by Mr. Edwards there, so that it was possible to carry out the final work m d e r the same conditions and with the same apparatus as wst9 eiiiployed in the earlier experiments.

ENGINE LURRICATlNQ OILS. 389

THE DISCUSSION.

Mr. A. LUDLOW CLAYDEK, in opening the discussion, said: Can the authors tell us the effect of adding only 4 per cent of paraffin to the hoavy oil which, with 10 per cent of paraffin added, showed a subsequent loss, on re-heating, of 6 per cent? Was this loss partly parafin and partly something else that was in the oil? Can they also tell us the normal temperature in the crankcase? that is to say, which of the temperatures given is closest to ordinary crankease conditions? Then again, would it pay to take oil from the crankcase continually, heat it, perhaps by ex- haust treatment, m d then cool it, and return i t to the crankcase? Would that result in economy, would it result in improved lubrication, and, above all, would it result in reduced carbonisation? Carbonisation is, I think, one of the inost interesting points in connection with oil at the present day. I believe inost people who have had much experience of motor cars are aware that there is not much difference between a very large number of the oiLs now on the niarlret. The choice is largely one of personal predi- lection. In my own case, I know half a dozen oils that do not contain grit, and I stick to them, but there is not much diff'erence between them in their lubricating qualities or in their liability to deposit carbon. It seems to me that modern engines carbonise much too freely. I f we can find an oil that does not carbonise, it is worth wliilc making some sacrifice on the score of expense. The difficulty is, however, that the oil used in bearings and that used on the cylinder walls require to possess different character4 istics. The oil for use on the cylinder walls must resist heat and retain its lubricating qualities at the highest possible temperature. Directly i t is past the piston rings and in the combustion chamber it must either not burn at all or it must burn up completely; there must be no deposit of solids in the combustion chamber. Will the authors tell us whether their experiinents have given them anv idem on that point? Will they also tell us how long it would take for a crankcase oil to return to its original state i f placed in the crankcase after the lighter constituents have been driven off by heat? I n other words. does i t pay to treat used oil in this way ?

390 THE ISSTITUTION Or' AUTOMOIIII,E ENGlNEEKS. (Mr. A. Ludlow Clayden.)

The authors recommend that the air for carburation should be taken from the crankcase in order to prevent the oil from taking up petrol which passes the pistons. Would not this tend not only to take away petrol which passes the pistons but much of the oil too? In Knight engines it is customary to take a small pro- portion of the air from the crankcase with the idea of drawing up oil spray into the combustion space on to the sleeve. I take it that most of the oil passed through the engine is for a good. portion of its life in the form of spray, and any air drawn from the crankcase would carry such spray with it. Mr. Morcom, in his paper on " Forced Lubrication,"" given before this Institution in London in 1910, mentioned the partiality of oil for petrol, and recommended the re-use of oil from the crankcase heated for a certain length of time and then returned, but he did not say whether the oil after such treatment was really better than when it was new.

Mr. A . E. TUCKER: The authors were careful to avoid theoretical considerations, or at any rate to skim over them lightly. They suggested the impossibility of using solutions of sugar, molasses or glycerine as lubricants. I do not aee any reason at all for not using these materials if conditions admit, and I would be glad to know if they can indicate any physical reason why they should not be used. I am speaking of lubrication per se. We know that glycerine is used as a lubricant, and I should expect that a solution of sugar of suitable viscosity would prove to be a lubricating medium. In connection with the lose on heating, the authors touched on a point which is rather double- edged. I have had occasion to examine a large number of lubricating oils, and I think they will agree that while there is a heat loss on raising the temperature of the oil through a lengthened period there may also be a gain, especially in the cases of vege- t.able oils, so that both the gain and the loss must be taken into consideration. I n some cases the gain in weight is considerable, and is due to oxidation, and that has a profound influence on the character and value of the oils, because it clearly points to burning, and the sticky residne which results leads, of course, to increased friction on the surfaces. This test of loss on heating may, therefore, fail under certain conditions. The use of a mixture of paraffin in the oil would appear, according to the authors,

* See Proc. I. A.E., Vol. IV., p. 351.

to afford a very simple way of getting an efficient lubricant, and paraffin is very much cheaper than ordinary lubricating oils. If the authors are right, it would be a very great help to consumers, but I submit that the paraffin will find ite way into the combustion chamber, where it will probably lead to carbonisation; i t will certainly lead to disturbed carburation, which is very unde- sirable in any case.

I now come to the question of the poasibility of the presence of such a material rn petrol in the oil in the crankcase after continued use. It seems to me that such an occurrence points to one of two things, namely, either that i t is possible for the petrol to find its way, through the oil itself as the conveying medium, into the crankcase, or there must be a mechanical leakage of the mixture past the piston. It seems to me in practice that either conditiou is improbable. We know that the tendency of the oil is upwards into the combustion chamber; under what conditious therefore, can the petrol get past the pistons in rt downward direction? O n the other liand I would submit that a possible explanation, i f it is really petrol in the used oil in the crankcase, is given in Mr. Morcom’s paper and the discussion on it. Mr. Morcom recogniued that in sniall engines, so far from it being impossible to mix oil and wator, they were capable of being verj perfectly mixed, and of giving a most perfect eiuulsion, so perfect. indeed, that i t was quite impossible to separate the oil and the water from each other by ordinary means. We know that during the operation of producing this emulsion therc is oxidation going on under most unfrtvourable circumstances. I suggest, then, that the presence of this small quantity of petrol is due rather to obscure chemical action than to the passage of petrol from the combustion ohamber.

Mr. C. G. TUCKER: I t would appear from tho mass of figures the authors have given us that those oils which have an open flashpoint of about 400” F. are the moat suitablo for usc on motor cars for all average purposes.

I woulcl like to mention that it is common practice in Wolselcy cngines of high efficiency to take air for the carburettor froin the crankcase. Though the paper was announced 5s bcing upon “ Lubricating Oils,” I think it is rather a pity that greases were not referred to. There are a number of grea3es which, on the Thurston test, show better results at inoderate temperatures than many oils; one, indeed, gives a lesfi friction angle than a fail-ly

3 92 THE lNS'I'I1UTION OF hU'~OMOHl1.E hAGIA'hEH*. (Mr. G . C. Tucker.) good cylinder oil. Analysis of one of the greases which was not so good as this particular one showed that there was a fais percentage of calcium present, which I haidly think is a very good lubricant; it was probably introduced to give it a good body, aiid to make it look as though it was a good grease.

Mr. A. E. TUCKER: Steatite is coiiirnonly used. Mr. C. C: TIJCKER: With regard to the addition of parallin to

oil, I have frequently soen the oil froin a Belliss paraffin engine taken out after being in use for a month and put into a flask, when i t showed a layer of paraffin separating out quite distinctly from the oil. This is quite distinct fro111 an eiiinlxion which does not separate As regards putting up the viscosity, I believe at the present tiine thore is a doubtful niethod of doing this by adding graphite. I know a case in which $20 had to be paid for damages to an engine arising from the use of oil thus treated.

Mr. J. 5 NAPIER: I ani sorry that tlio heat losses shown in Fig. 2 were taken at such high temperatures as 400" Fahrenheit, as I thiiilr this is higher than obtains in practice in a crankcase. I have carried out some experiments conncctecl with the temperatures of oils in crankcases, and I have not been able to obtain more than 205", even aftor throe days and three nights continnous running under full load.

Dr. ORAIANDY: By taking the temperature at 400" results are obtained in six hours which woulcl take sixty hours at the lower temperatures Three hours at 400" is equal to twenty-four hours at 800". and twonty-four hours at 300" mould be equal to about three hours at 400'. We adoptod the hiqh teinperaturw to save time.

Mr. NAPIER: I would like to ask the authors to tell 119 the viscosity of the mixture of heavy oil with 10 pcr cent of paraffin before i t wi is put into the engine and also after it came out of the engine. I gathered from the paper that they prefer a heavy oil to a light oil for engine lubrication, but this leads to difficulty in starting up the motor, especial1.v in cold weather, aiid to loss of power in the engine. Some years ago I had to CBI'PJ' ont some test? in order to discover the oil which would allow an engine to develop its greatest 11.11 1' , I found that the difference betmeeii one of the oils iiientioned iii the paper, Prices' Heavy Gas Engine Oil, and a w r y thick oil slipplied by the Vacuum Compaiir was over 9 per cent in favour of tlio former

I xas interested to hear that the authors' cxperimmts showed

that oil can be used in the crankcase for a very long time without any great depiwiation of its lubricating properties. This fully bears out my own experience. I am one of those who believe that a motor car ought to be left alone until something really goes wrong or appears to be going wrong. I once ran a car for two years, about 10,000 miles, and during that time I never cleaned out the crankcase; all that was done was to add oil to make up the loss from time to time, and I never suffered any trouble from improper lubrication. The average consumption worked out at one gallon for every 500 to 600 miles. A great deal of trouble has been experienced in racing engines at very high speeds on account of the big end bearings giving out. The remedy for that is to cool the oil either by means of a special radiator or to have a very thin corrugated metal bottom to the crankcase exposed to the passing air.

Mr. G . H. LANCHMTER: Mr Napier mentioned 205' F. 88

being the temperature of the oil in the base chamber, but in the combustion chamber the temperature is nearer 400", and it is in the combustion chamber that carbonisation takes place.

Mr. NAPIER: I have no doubt that it is 400", and it may be a great deal more, but we do not want oil on the pistons; we want to avoid it. The figure I quoted referred to the temperature of tho mass of oil in the crankcase, and the temperature at which it would be used for lubricating purposes.

Mr. B W. SHILSON: I should like to ask the autlinrr their opinion on the subject of mixing-definitely inixing--oil with the fuel for two-stroke engines. There are a number of two- stroke engines on the market in which this practice is adopted, but I gather from the paper that it is to be deprecated. We have had a number of very interesting figures on the viscosity and other properties of oil, but the viscosity in most caws is taken at ordinary temperatures, and not a t working temperatures. I think it would have been very interesting if we could have had a curve slwwing the ratio of viscosity, starting at teniperatures such $19 those which prevail in winter up to the working temperatures in the engine. I should also like some information as to the advantages of one type of oil over others in regard to carbonisation, that is to say, whether they give a hard or a soft carbonisation. I n some cases an engine carbonises very quickly, but the carbon can be scraped off very easily; but in other caSes a hammer and chisel have to be used.

394 THE INSTITL'TION OP AUTOMOHILE ENGINEBKS.

Mr. WEARHAM: I should like to ask the authors a question regarding the corrosive action of oils on steel. The results of some experiments carried out in this connection were published recently in The Engineer, and these seemed to prove conclusively that vegetable oils were particularly bad in this respect; especially was this so with castor oil. There is on the market at the present time an oil by the name of '' Castrol," which is extensively used on Brooklands track i n high speed engines. Could ylo authors say if this contains much castor oil? Do they consider the presence of castor oil detrimental, or is the corrosive action neutralised by the admixture of the mineral oil, and therefore not worth consideration?

Mr. A. A . REMISGTON: May I ask whether the petrol taken up by the oil, as mentioned in the paper, was taken up fairly quickly and then remained constant, or whether i t was taken up gradually during the whole time? A number of experiments I have inadc lead nie to think that it i u taken up quickly, and the percentage remains constant afterwards. I n order to prove whether it is petrol from the fuel that is takeii up, I suggest that experiments should be made o n oil used in the gear box, where it i e churned up just about as much as in the onginc, rqs in this case the oil could not possibly take up any fuel.

With regard to taking air froru tlic crankcase, the results of experinients lead me to suspect that oil spray in a crankcase is notable by its absence. The air will be practically f'ree fsom oil if tho spot fkom which it ia taken is t3elec.t.ed with care, and drawing air from the crankcase need make no perceptible or memumble differeiicc to the oil consumption of tho cngine.

I suggesl that there is a considerable difference in respect of tho carbonisation effect between many oils which arc appa- rently otherwise similar. Personally, I should like to know son~c- thing about the properties of oil that lead it to carbonisc, and also what are the properties that make it deposit lmrd or soft carbon. I have had a large number of experiments made in this direction, but cannot get any satisfactory results to SCPYH

as a basis upon which to experiment further. The only thing I could see as a result of the experiments was that the carbonisation in an engine running on the road is just aboyt the same in character and coniposition as in an engine running at sea. The carbon content of the deposit in both cases is about 95 por cent

or 96 per cent, and the small yerceutagc remaining is very mis- cellaneous-traces of metals used in construction, silica, eta.

Mr. P. L. RENOUF: The paper shows that we do not know so much about this subject as we ought to know, and I hope that the authors will be able to follow up their investigations at some future time, and lay the results before this Institution. With regard to the comparison made by Mr. A. E. Tucker 3s to what is a lubricant and what is not, I personally have always considered that a lubricant is really a substance which consists of a mass of molecular balls lying in a fluid. If that can be imagined, it would account to a large extent for the fact that oil used again after treatment by heating might be more efficient than i t was in the first instance, because practically the balls would have been ground down into a greater number, and consequently with a greater effective distributing surface. Sugar will be found to consist of small particles of crystalline forin; these crystals, of course, would scrape and scratch the surfaces to which they were applied in comparison with a true lubricant.

Dr. ORMANDY, in replying on the discussion, said: Mr. Clayden asked whether, if 10 per cent of paraffin were added to the lubricating oil, the loss on re-heating was due to the paraffin or to something removed from the oil itself. We submitted the same oil to which the paraffin was added to heating at the same temperature as the mixture, and to very much higher temperatures than in ordinary work, namely, between 400" and 500" F., and nothing was lost. The crankcase temperature is seldom above ZOO" F.; this temperature arises from a number of things, partly from primary friction on the cylinder walls and in the bearings, but to a lai-ger extent from convection of the currents of oil in the interior of the cylinders. I n spite of cooling at the bottom of the crankcase, the temperature there may be 200°, but the temperature of the oil above is much higher, possibly reaching 500" to 600". Mr. Clayden asked whether the crankcase oil ,should be heated and used again; undoubtedly it should. After crankcase oil has been re-heated it is a better oil by far as regards viscosity and heat loss at high temperatures than it was before. I pay nothing about carbonisation, because that is a subject which requires investigation. Carbonisation on some engines, especially on the old engines upon which the experiments were made, w& very pronounced. The engines had fairly high compression, and were made with a less degree of accuracy than is now cii$tomarj->

396 'I'HP. IXSTI'L'U'I'ION OP'AU'I'OMOHI1,E ENGINEERS. (Dr. Ormandy.) which seems to me to be a possible explanation. There was every tendency for oil to be brought up past the piston rings, and we could not go more than a thousand iniles without scraping the cylinders. The result, of scraping did not confirm the chairman's statement. The carbon content of the material removed did not approach 96 per cent; more than 50 per cent of it was practically road dust, and there was a considerable amount of zinc and copper in it,, the presence of which has not been adequately explained.

As to air being drawn out of the crankcase, one speaker states that i t is easy, another says it is a difficult problem; I prefer to leave the motor car manufacturers to fight it out amongst themselves. All I say is, that other things being equal, it is a good thing.

Mr. Lanchester thought I was hard on the inakers of thegas engines of t'he early days to which I referred. I was for some tinie in a works where large gas engines were introduced on the grounds of economy, and the result was that the cost of &l just ahut nullified the h e 1 advantages which arose by thc use of tho gas engines. The lubricating oils which were available were not of the class which can now be obtained. There is no doubt that the modern requirements of high speed engines and high temperature machines working within exceedingly fine limits have caused a demand for greatly improved lubricating oils.

One of the difficulties is to know whether an oil is a straight oil or a blended oil. I tried my best to get certain oils, and I asked one of our first authorities to say whether hc t.hought the oils with which we experimented were what we supposed thein t,o be, aiid he said: "I€ yon have siicceedetl in getting the oil you desired you have done inuch more than I have been able to do." We cannot get hold of oils with any definitc knowledge of what t,liey really are in order to base our experiments upon them.

With regard to the question of carbonisation, I prefer an oil wit,h an exceedingly high flashpoint, which will not burn on the cylinder walls, and which will resist as far as possible tho teinpe- ratnres to which it will he exposed in the cylinder, rather than to use an oil which will burn away, beoaose the burning of oil leaves a residue, and I prefer an oil wliich will leave no residue. I also believe in having a, high riscosit;v oil ns me11 as an oil with a high flashpoint.

ENGINE I. lIHKICA1'ISG OILS. 397

Mr. Tucker suggested the use of sugar as a lubricant. Jt would be interesting to have data upon this subject. We all know that oil is oil and sugar is not. Nobody has yet fully succeeded in explaining why sugar should not act as a lubricant. I do not think it is any aspersion on my abilities to say that I cannot do it. A11 the measurements of surface tension with regard to ail liave been done by two or three methodh, particularly by that of dropping oil from a pointed tube, or by the disk method of pulling a disk up from the surface of the oil and taking out the power necessary to break the oil film round the edge of tha disk. Both these experiments merely show the viscosity of oil in rclation to air. What we want to know is the viscosity of oil in relation to metallic surfaces. There is no experiment by which to measure the surface tension of oil on metallic surfaces; it would require a steel capillary tube which must also be trans- parent. If such a tube could be devised i t would solve the problem. The problem raised by Mr. Tucker may be, and probably is, due to surface tension which exists between the materials in question, which are the oil, and the metallic mrface, but wc have no means of measuring that particular capillarity or surface tension. As to the petrol in the oil being due to oxidation during heating, that is quite iinpossible. I f that were so, there would be a chemical change taking placc under those conditions in the crankcase which would be accompanied by a tremendous increase in the saponifiable equivalent in the oil to form the 2 per cent of petrol in the crankcase oil. This could not arise by oxidation. I n the first place petrol is not made out of heavy paraffin by oxidation; it can only arise by a cracking process. With a cracking process there would be carbonaceous residues and materials going up the whole range. I do not think the conditions obtaining in the crankcase are such as to give cracking. If cracking took place in the crankcase, the loss of oil would be greater. We know from actual experience that 2 per cent of petrol i u present after a rim of a couple of hundred miles in two days. If thero was enough cracking to account for this 2 per cent of petrol it would account for alterations in the physical properties which would be greater than are actually found. On internal evidence, therefore, the explanation that the presence of petrol is clue to cracking or oxidation mould seein inadequate. I think thc intcrnal evidence does not bear that out in any way-

It has something to do with surface tension.

398 THE INST11 UTlON O F AUTOMOBILE ENGIKEERS.

(Dr. Onnandy.) On the other hitiid, I think the evidence does tend to prove that it may be due to the passage of the fuel from the combustion chamber.

The choice of the nse of an expensive oil or of a mixture of thick cheaper oil with 10 per cent of paraffin is a question of economy. The paraffin added to a comnion oil brought it into a state (that was usable for the particular purpose for which we desired to use it.

I n regard to Mr. A. E. Tucker’s refcrence to Mr. Morcom’s paper and the formation of an emulsion in the crankcase by the mixture of oil and water, it must be remembered that oxidation takes place more rapidly in the presence of water, but I have not seen any figures to justify this statement. It is not correct to say that it is impossible to separate the emulsion. It is the $implest thing in the world to do by electrolysis.

Mr. TUCKER: I meant by heating. Dr. ORMANDY: Mr. C. G. Tucker suggests the fixing of a flash-

point for lubricating oils. It seem8 to me, however, that by doing so we should be cutting out quite a number of possibly good lubricants. I n many oils, while the Hashpoint may he wrong, the heat loss may be everything that is desirable. It is impossible to define a good lubricating oil as one having a flashpoint between any two set limits.

I have never carried out any experiments with graphite, or even with flocculated graphite. I hare not enough knowledge to express an opinion on the point.

Mr. Napier says that he used his oil for two years in a crankcase without cleaning it out. I used to run my car regularly for twelve months without cleaning out the crankcasc, and even then it was done more as a matter of a religious duty than anything else. I kept on using the oil and nothing happened. I t was oil that I picked up anywhere, from spindle oil out of a mill to colliery oil, and these substances werc used in the rrank- caw, as I say, for twelve niontlis without being cleaned out.

With regard to the mixing of oil and fuel, a question which was raised by Mr. Shilson, I should not like to suggest using oil and fuel mixed in the present high speed, high compression engines. I know it is used for little engines for attaching to the back qf tlinghies, where there is no means of lubrication except by putting .ibout 5 per cent of mineral oil into the fuel, and that is all the lubrication those engines get. I know qcorcs of thcqe enginw

ENGINE 1,UBItlCATING OILS. 399

running on dinghies, but they are not used to the same extent that the road motor car is used, and that may account for the absence of complaint. They have not got high compression, and altogether the marine man is satisfied with a very great deal less than the motor car man on land; his engines run at a less variable load, and their efficiency is lower to start with.

As to the corrosive action of castor oil, I am not going to venture to express an opinion, nor will I commit myself by making any statement as to the amount of castor oil in the brand of oils known aa “Castrol”; some oils contain very little and some a good deal. I think it depends upon what the oil is going to be used for, that is to say, whether it is going to be sold in the ordinary way of trade, or whether it is to be used on racing engines at Brooklands or elsewhere. Personally, I do not think castor oil added to other oils produces any appreciable results in ordinary practice. It is only when dealing with racing engines where there are difficulties in keeping the oil in the crankcase a t a reasonably low temperature, that the question becomes important, and it is only in these cases t,hat the addition of animal .or vegetable oils to mineral oils is to be recommended.

I n the paper referred to by Mr. Wearhaiii and publislied in the Engineer, it was shown that when 1~111 bearings are esposcd to the action of some oils, certain ingredients of the stcel are eaten away and the shell of the ball becomes broken afterwards. Mr. Wearham thought that there was a special selective action of castor oil which made it particularly unsuitable. That is his research work, but I have no experience of it personally.

The Chairinan asked whether the petrol in the crankcase came there quickly or whether it came gradually during 1,200 miles or so of driving. A8 far as iuy experience goes, I should say 200 miles would be rufficient to get the crankcase oil into a state of equilibrium in regard to the fuel .

Mr. Renouf‘s parallel, or possible mechanical parallcl, between a lubricant and a molecular ball suspended in a liquid, was ingenious, The bulk of the experiments upon which the papel* was founded were made six or seven years ago, and the results have remained in manuscript form till now. Certain questions have arisen out of the researches which me made which have a bearing on the patent laws of this and other countries, and at $he last moment we mere obliged to leave out certain portions

400 (Dr. Omiandy.) which it was considered might possibly giie away niorc inforinn- tion than was advisable.

In regard to the temperaturcs at wliidi n c ~ cqcriinented with the oil for heat losses, I might explaiii that in six hours lit

400" F . we could obtain results which \ \ o d d take four or fivr times as long to obtain at lower teiiipcmturcs. To take the. viscosity under various conditions a t teinperatures of 200", 300" tliid

400" necessitates a very great amount of work, and although i t i. obvious that there are a treniciidous number of qucstions th;i t will repay investigation by thosc who i nake a special busine+ of undertaking such work, it i, i i n p 4 ~ 1 c foy 119, who h a w otliw iiratters to attend to, to investigate d l tlie aspccts of the question. It is in tlie hopc of stiiiiulating others to work in this fidd that we have prepared this paper, and having put forward there results, we trust that others will follow up the investigatiom in the numerous directions in which rcsearch work can be carried on, which ~ 1 1 be obvious to those who wish to pursue the xnattei.

THE IKRI'ITUTION O F A L"~OMORII,E ENGINEERS.

ENGINE LUBRICATING OILS. Plate X I

FIG. 5.-200 H.P. with Cooling ; 80 H.P. without Cooling.

engine lubricating oils

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