From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical discussion on fuels, lubricating oils, combustion, and deposit formation in early internal combustion engines, including a table of elemental composition.
| Identifier | ExFiles\Box 144\1\ scan0009 | |
| Date | 11th July 1911 guessed | |
| 4 Spec. Grav. v.{VIENNA} Boiling Point. In the earlier days of the motor trade it was assumed that spirit of 680 sp.{Mr Spinney} gr.{George Ratcliffe} possessed all the necessary properties and that this gravity offered the motorist all the guarantees required. By and bye, in consequence of the scarcity of spirit of this gravity, motorists were constrained to accept spirit of higher gravities, and I understand that now-a-days spirit of 720 and 726, and in some cases even up to 760, sp.{Mr Spinney} gr.{George Ratcliffe} is used. I have, however, argued, ever since the introduction of engines using petroleum spirit as fuel, that specific gravity is by itself, if not entirely negligible, by no means the final or a trustworthy criterion of the value of spirit for this purpose, and that apart from specific gravity the truly essential condition is that, whatever the gravity of the spirit may be, the spirit should have as nearly as possible a constant boiling point in order that the bulk, if not the whole, shall be easily volatilized under the normal working conditions of the engine. Abnormal spirits may be produced in two ways. First, and honestly enough, by the refiners, who, in order to increase the production of spirit, run together a wide range of fractions of distillates with widely differing boiling points, the mean of which produces a spirit having the required sp.{Mr Spinney} gr.{George Ratcliffe} for the time being. Dishonestly, by 'cute manufacturers who mix together very light spirit with cheaper and heavier distillates to produce the required sp.{Mr Spinney} gr.{George Ratcliffe} In the early days of the petroleum trade we had practically only one brand of refined petroleum lamp oil which had sp.{Mr Spinney} gr.{George Ratcliffe} about 800 and was generally described as "good merchantable." This was produced by running together the distillate which came off after the heavier spirit or naphtha had been removed and continuing the distillation till the intermediate or gas-oil made its appearance. By and bye it occurred to some of the American refiners that an exceptionally fine oil might be produced by dividing the distillate into three fractions—1st, 2nd, and 3rd, and, after withdrawing the 2nd for sale as water-white oil of low sp.{Mr Spinney} gr.{George Ratcliffe}, fine colour, and great illuminating value, mixing the first and third portions. This mixture produced an oil corresponding in appearance and physical properties—colour, sp.{Mr Spinney} gr.{George Ratcliffe}, flash point, etc.,—indistinguishable from the original "good merchantable," but sadly deficient in burning properties. There was much grumbling on this side about the change, so emissaries were sent here from America, who tried to convince us that our lamps and our wicks were wrong, and, although we assured them that we were using the same old lamps and the same old wicks, we got no satisfaction. Elements of Fuel and Lubricating Oils. It is well within my knowledge, and it is probably equally well known to you, that despite the former popular idea that fatty (compound) oils were inadmissible in internal combustion engines, the use of compound oils as lubricants is largely extending, while in several instances even pure vegetable oils are used in competitions and trials in which it is desired to get absolutely the best results from an engine. This leads us, therefore, to consider the constituents of various oils, including spirit, mineral or hydrocarbon lubricating oils, and animal and vegetable oils. The appended table shows the elementary composition of leading members of each group:— TABLE A.{Mr Adams} Material. Carbon. Hydrogen. Oxygen. Motor Spirit ... ... 82.99 16.08 0.93 Royal Daylight ... ... 85.09 14.38 0.53 Alcohol, Ethyl ... ... 52.17 13.04 34.79 Refined Distillate, ·905 87.05 12.56 0.39 „ „ „ ·910 84.77 12.67 2.56 Cylinder Oil, Natural .. 85.02 13.92 1.03 „ „ Charcoal Refined 85.43 13.17 1.40 Huile D.{John DeLooze - Company Secretary} ... ... ... 86.02 13.33 0.65 Gas Engine Oil, Light 85.66 12.53 1.81 „ „ „ Heavy 86.69 11.86 1.45 Motorine A.{Mr Adams} ... ... 84.45 13.04 2.51 Tallow Oil ... ... ... 77.4 11.8 10.8 Coconut Oil ... ... 75.3 11.8 12.9 Rape Oil ... ... ... 78.0 11.4 10.6 Castor Oil ... ... ... 74.0 11.4 14.6 Before we consider the behaviour and effect of these various elementary substances either as fuel or as lubricants in the internal economy of the engine let us pause for a moment to examine the conditions to which they are all to be exposed, the first of these being combustion with its attendant flame and heat, and all the complex problems they involve. Elements of Combustion. Combustion depends mainly upon the chemical combination of carbon and hydrogen, with oxygen, the former two being the elements of constituent matter animal, vegetable, and many minerals, in our system, while the third (oxygen), which represents one-fifth of our atmosphere, and about eight-ninths of all the water in the world, is equally all pervading. All of us recognise, without hesitation, that form of active combustion to which we apply the term flame or diffused fire, but in recognising in the sudden ignition of gas—which we describe as an explosion—a manifestation of combustion in another form. To flame, in the ordinary sense of the term, we apply the term “slow” combustion. To explosions we apply the term “rapid,” although even in regard to explosions of gas it is usual to discriminate between the speeds of the propagation of ignition. But in recognising these two forms of combustion we have not disposed of all the manifestations of this principle, as it is not less true, though less generally recognised, that our own health and life depend upon the ceaseless removal from our bodily systems of waste gases and impurities evolved in our bodies by exercise, and that this beneficent function is performed by the assimilation of the lungs of oxygen from the atmosphere, i.e., by another form of very slow combustion. The Chemistry of Combustion. And there are yet still other kinds of slow combustion seldom recognised as such, in regard to which Professor Vivian B. Lewis says:— “Ordinary combustion, therefore, may be defined as the evolution of heat and light during rapid and energetic chemical action, but there are many cases of chemical changes which are so gradual that the heat evolved, being spread over a long period of time, becomes inappreciable to our senses, and such cases we call slow combustion.” “A tree left to rot upon the ground gradually disappears in the course of years, being oxidized up into carbon dioxide and water vapour and scarcely any evolution of heat is observed, yet as much evolution of heat is generated as if the tree had been cut into logs and burnt.” “When a steel watch spring is kindled in oxygen gas by a piece of German tinder attached to the end of it, the metal burns away with great rapidity, forming oxide of iron and giving out great heat and also light. The same weight of iron rusts; yet no evolution of heat is perceptible, because the time over which the action is spread is so great that at no one moment is enough heat evolved to be perceived by our senses; yet in each case the total quantity of heat evolved is the same. Another example of slow combustion is found in the act of respiration.” In each of the various forms of combustion to which I have referred, no matter whether the material be coal or wood, or whether the combustion takes the form of continuous flame, or sudden explosion, or rust of metal or decay of wood, the essential agent in every case is oxygen, and it, therefore, becomes a matter of immediate interest to know how much oxygen is required for the complete combustion of the various materials which, either as fuel or as lubricants, are introduced to the cylinders of the internal combustion engines. See table B, page 6. Fuel Deposit v.{VIENNA} Lubricant Deposit. From an extensive acquaintance with the management of engines and of oil engines before the advent of the petrol engine, I have found that the chief bugbear to the engineer and the obstacle to the uninterrupted and successful running of such engines, was almost invariably due to the formation of carbonaceous deposits, sometimes in the form of pitch residues; sometimes of dry coke. What appealed to me was the fact that whatever the nature or the condition of the deposit, it was always attributed to the lubricating oil. But from the information given to me by some of the leading makers of gas and of oil engines I am in a position to state that the quantity of oil used in a gas or an oil engine does not represent more than about 2½ per cent. to 3 per cent., and in some cases even a lower proportion of the fuel used as gas or as oil. In the case of a modern motor car using, say, one gallon of spirit per 20-25 miles and running 1,000 miles on a gallon of lubricant, the percentage of oil to petrol is so small that assuming that pure hydrocarbons, having almost identical composition (c.f. foregoing table), are used for both fuel and lubricant, it becomes an interesting question whether the production of carbonaceous deposits is due to the imperfect combustion of the 40 or 50 gallons of carbonaceous fuel or to the one gallon of carbonaceous lubricant. Unfortunately, the numerous analyses which our chemists have made of deposits from cylinders, and valves of motor engines throw little light on their origin, although constant differences present themselves in their appearance. Some exhibit a form of lumpy form like small coke, some being saturated with oil, others dry, while yet others are dry and powdery. In table D (appendix) I give such particulars as have been obtained from recent examinations. From these figures it will be observed that oil matter, which may include heavy residues from spirit, amounts to 40 per cent. to 50 per cent. coke, or carbon, some part of which in the presence of so much oily matter may also be due to unconsumed spirit and amounts to nearly 2s much as the volatile fraction. Ash, which exhibits the greatest range, runs from 8 per cent. to 17 per cent., consisting mainly of copper, iron, lime, for which I do not suppose that the oil can be held responsible. Pure Hydrocarbon Oil v.{VIENNA} Compound Oils. Responsibility for deposits is not, however, limited to spirit and lubricants, but much difference of opinion obtains as to the respective responsibility of pure hydrocarbon oils and of fatty oils of animal or vegetable origin, either when used pure, as in some cases, or when mixed in various proportions with hydrocarbon oils, as in more numerous cases. The original opinion prevalent among Continental engine-makers, and to some extent among British motor engineers, was that fatty oils of all kinds ought to be rigorously excluded from motor cylinders, mainly because it was believed that they would produce gummy deposits, and partly because it was feared they would liberate acids detrimental to the cylinder. It happened, however, in my case that upwards of twenty years ago facts came to my knowledge with regard to the practice of several leading makers of gas engines who, despite the evil reputation of fatty oils and their higher cost as compared with pure mineral oils, not only used compound oils themselves, but insisted on their customers using such oils upon pain of forfeiture of the maker’s guarantee of the engine. I also learned that these makers preferred compound oils, not only on account of reduced friction, reduced gas consumption, and prolonged the life of the engine, but, more remarkably, because they reduced or if they did not entirely prevent deposits. I confess that with such evidence before me, on one hand, of the efficiency and value of the engine, the other of the harmlessness of compound oils, I became a convert by conviction to their efficacy and value. Author’s Experience Cited. But this was not all; I had, subsequently, although before “motors” made their appearance, the opportunity put before me of studying the lubrication of oil engines, and I soon found from personal discussion and experiment with several of the leading makers (whose names it would be invidious to name) that, if the makers of gas engines expressed a preference for compound oils, the makers of oil engines regarded such oils as the only possible lubricants for their engines. Some makers of oil engines are content to use the ordinary compound gas engine oil, others, among whom I may cite a great authority, Mr. Crossley himself, prefer super-fatted oils, while from a few makers of oil engines I have received the assurance that their engines will only run satisfactorily on pure, or nearly pure, vegetable oils. I remember discussing the question with one of the leading motor engineers in the Eastern Counties, and when I expressed surprise at their preference for fatty engine oils he met by the reply, “If we can run our engine, as we can do, in case of need, on pure fatty oil for fuel, surely there can be little harm from the small quantity required for lubrication.” That seemed an unanswerable argument. While I am fully convinced of the superiority of compound oils, I am unable to understand, or to explain to others, why they fail to do all the dire damage expected of them, or why I can do so now, but I can and I am going to cite some suggested explanations for what they are worth:— 5 (1) That the name “oxygen,” which was given to this element by Lavoisier, a French chemist, who shares the honour of its discovery with Scheele, a Swede, and with our own Priestley, is derived from two Greek words, and signifies “acid producer.” (2) That fatty oil combines with nearly all bodies, animal and vegetable oils absorb it with varying degrees of rapidity, and in so doing develop acid and become rancid, and it may be gummy. (3) That mineral oils contain only a minute trace of oxygen and have little affinity for it. (4) That fatty oils contain a lower percentage of carbon and a much higher percentage of oxygen than mineral oils. As they, therefore, contain in themselves a large amount of the oxygen required for combustion, they may be burned in lamps without chimneys, while all mineral oils require lamps with chimneys to provide sufficient atmospheric oxygen to permit of their proper smokeless combustion as illuminants. (5) That when fatty oils are exposed to heat and steam, they absorb oxygen from the steam and the air, develop acid, and attack metal with which they come into contact. While these statements seem to give the case of the fatty oils away, still, when we consider that in the case of gas oil, petrol, engine, nearly all the oxygen which is admitted to the cylinder with the air supply is required for combustion, I think it possible that no free oxygen is left to combine with the small quantity of fatty oil which may be present as a lubricant, and that, therefore, no fatty acids nor deposits are produced from them. (6) That, as it appears that the bulk of the deposits in cylinders consists of carbon, fatty oils which, as shown by the foregoing table B, contain a lower percentage of carbon than pure hydrocarbon oils, are less likely to contribute to the deposit of carbon in the cylinders than the oils, or spirit used for fuel, of which, containing as they do a higher percentage of carbon, much greater quantities are introduced to the engines. Compound Oils Aid Starting and Tests. I should also like to emphasize the fact that, however contrary to popular belief or prejudice it may be, it is the fact that oil engines generally require compound oils and sometimes pure fatty oils to secure successful lubrication. Perhaps you will realize the importance of this better if I narrate, without giving names, an incident which led one great firm of oil engine manufacturers to adopt fatty oils for their engines. Two apprentices had been told off to test a large new engine on the bench. The job was one to occupy several days, the engine was a large one and the piston heavy, so that in starting in the morning they had to use power from a travelling crane to start it from the position in which it had stuck overnight. The young gentlemen who were attending to this engine wanted to save their muscles in the morning and, drawing a bow at a venture, poured a can of oil, picked up at random in the shop, upon the piston one night before stopping the engine. Next day the engine started without the aid of the crane. Night and morning, while the engine was tested, the operation of applying oil and the freely starting was repeated, until the young gentleman’s satisfaction was tempered by the thought that they might have done wrong, and they made a confession to the foreman regarding their operations. After a private commission of enquiry it was resolved that for such engines in future the lubricant should be either the pure lard oil, which the apprentices had used, or some liberal mixture of that with gas engine oil. Carburettor or Induced Deposit. Now and then my attention has been called to deposits on the carburettor side of the induction valve and in the pipes leading from the carburettor, but, although I have a good friend—one of the pioneers in the motor trade in this country—who seems to hold me personally responsible for these, I regard such deposits, as entirely distinct and apart from those that occur in the cylinder, and I am glad to say that few opportunities have I had of examining induction valves and pipes, on which deposits have been found, seem to justify my refusal to accept responsibility. My argument against the possibility of these deposits being due to lubricating oil depends upon the fact that the induction valve opens only once in the Otto cycle, and that while it is open a strong current of gas and air is rushing inwards and would effectually prevent the escape of oleaginous matter from the cylinder. I observed, moreover, that on the induction pipe the deposit was greatest on the bend. | ||