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 motor fuels, lubricating oils, anti-freeze, and petroleum distillation methods.
| Identifier | ExFiles\Box 144\1\ scan0008 | |
| Date | 8th April 1910 guessed | |
| 6 leading to the valve and carburettor, I was thus led to infer that in these cases the petrol had not been volatilized, but had been carried along the pipe in the form of atoms, as Mr. Bickford has shown by his experiments. These atoms in their journey from the carburettor to the cylinder naturally impinge upon the pipe at the bend and upon the back of the valve as they are deflected, first by the one and then by the other, towards the admission valve. Gradually the pipe at the bend and the back of the valve are covered and succeeding showers of atoms accumulate on the first layer till the engine is taken down for cleaning. Air Volume Required for Combustion. The final matter for discussion between motor engineers and oil manufacturers as regards responsibility for cylinder deposits depends, I think, upon the quantity of air required for complete combustion. The accompanying table shows the amount of oxygen required for the complete combustion of various oils and the volume of air required to yield that quantity of oxygen :— TABLE B. One lb. Requires Material. Oxygen (a). lb. Air (b). lb. Air (c). Cubic ft. Motor Spirit. Carbon = .84 x 2.66 2.24 Hydrogen = .16 x 8.00 1.28 ----------------- ------------------- --------------- 3.52 x 4⅓ = 15.84 206 Royal Daylight. Carbon = .85 x 2.66 2.26 Hydrogen = .15 x 8.00 1.20 ----------------- ------------------- --------------- 3.46 x 4⅓ = 15.57 202 Lubricating Oil. Carbon = .85 x 2.66 2.26 Hydrogen = .13 x 8.00 1.04 ----------------- 3.30 Oxygen = .02 (deduct) .02 ----------------- 3.28 x 4⅓ = 14.76 192 Fatty Oils. Carbon = .76 x 2.66 2.02 Hydrogen = .12 x 8.00 .96 ----------------- 2.98 Oxygen = .12 (deduct) .12 ----------------- 2.86 x 4⅓ = 12.87 167 Alcohol. Carbon = .52 x 2.66 1.38 Hydrogen = .13 x 8.00 1.04 ----------------- 2.42 Oxygen = .35 (deduct) .35 ----------------- 2.07 x 4⅓ = 9.31 121 (a) 1lb. carbon requires 2.66lb. oxygen } For combustion. 1lb. hydrogen „ 8.00lb. „ } (b) Air by weight = 23 oxygen + 77 nitrogen. (c) 13 cubic feet of air = 1lb. by weight. This table shows that while the quantity of oxygen and of air required for the combustion of alcohol is very low, that required for similar combustion of motor spirit and of mineral lubricating oil is much higher and practically identical. In the case of the fatty oils, the lower proportion of carbon, together with the oxygen which they contain, calls for considerably less oxygen. Hydrocarbon v.{VIENNA} Fatty Oils—Relative Lubricating Value. This subject is one to which, in years gone by, I have given considerable attention, and I have spent much time in frictional experiments with many different oils. The subject is, however, too large to enter upon here. My points are :— (1) Specific gravity has nothing to do with, and is not to be confused with, body or viscosity. (2) Body or viscosity is by itself no indication of the lubricating value of an oil. Sperm oil is one of the thinnest oils on the market, and is one of the finest lubricants. Resin oil is one of the thickest and heaviest oils and is useless as a lubricant on account of its gummy tendency. Castor oil, on the other hand, is also one of the thickest oils, and is a splendid lubricant for heavy machinery as it is entirely free from gumming tendency. (3) Body v Weight.—Oils ought to be selected with careful regard to the relation of their body to the weight of the machinery for which they are intended. If they are too thin, the lubricating film may be ruptured and metallic contact will ensue. If they are too thick the temperature of the bearing will continue to rise until the body of the oil has been reduced to normal and every degree of heat calls for power and coal to produce it. (4) Fatty oils of moderate body will do the work of mineral oil of much heavier body. Fatty oils will, therefore, run cooler and they last longer. If this is not the case, why do you use such an expensive oil as lard upon your finest automatic tools? (5) The Waste Factor.—There is good reason for using cheaper oils on ordinary tools and machinery. It was given to me many years ago by an intelligent engineer of my acquaintance, who said :—” Fatty oils are the best lubricators, and if properly used would be the cheapest in the long run, but more than half of the oil that comes into my shop, no matter whether it is sperm or mineral, goes on the floor, and I think that the cheapest oil I can get is good enough for that.” Clutch and Gear Lubrication. The only other parts in a motor car which seem to call for special consideration are the gear case and clutch, both of which present conditions which do not occur in ordinary engineering practice. Disc Clutch Lubricant.—As regards disc clutches, the conditions include the possibility of violent rubbing at the instant of engagement. The oil must therefore be sufficient to prevent damage to the surfaces while that action lasts, but must also be of such a nature that it will present no obstacle to quick and prompt disengagement when wanted. These conditions can be met by its body or adhesiveness resist complete and prompt disengagement when wanted. These conditions can be met with a light and rich oil, which should consist of a fine mineral oil of low viscosity enriched by the addition of a suitable percentage of refined sperm or similar oil. For the gear case it is fortunate that the two conditions—reduction of friction and noise—are not antagonistic and may both be attained by using a thick oil or a semi-fluid grease. I recommend the latter, having about the consistency of Devonshire cream, as combining efficient lubrication and tenacity to overcome the scraping action of the teeth with a capacity to reduce sound. Such a material offers the further advantage that it is not liable to escape through the end bearings in the gear case. Anti-Freezing Mixtures. There is one other matter in connection with motors which annually, on the approach of winter, arouses interest among motorists and engineers, and is periodically discussed in the motor press. I refer to the question of anti-freezing mixtures. I have, therefore, thought it desirable to obtain from our chemists reports upon the questions of (a) materials available for lowering the freezing point of water; (b) the percentage of each required to produce certain results, and (c) the effect the various agents might have upon metal and joints. If you refer to any chemical or engineering hand book you will find fifty agents enumerated for reducing the freezing point of water, but many of these are unsuitable for motorists. The simplest is the addition of common salt (sodium chloride) to the water, to form brine, the freezing point of which is in the neighbourhood of zero (Fahr.) for saturated solution. The two agents most commonly used are glycerine and calcium-chloride. From tests which have been made in the Belmont works it has been found that sodium chloride (common salt) acts destructively upon iron, but shows little effect upon brass or copper. Glycerine of good quality has little action on iron. Calcium-chloride has a slight action on iron—See Table E in Appendix. 3 cost of the light of the people by imposing a duty on petroleum, or even indirectly to encourage home industries by raising the legal minimum flash point which would have given a monopoly to British over foreign oils. I have already referred to the different conditions which obtain in the production of petroleum and shale oils, the former being obtained as a natural oil, while, to produce shale oil, the shale has to be hewn or wrought, to be conveyed to the surface and passed through retorts to arrive at the stage at which the petroleum refiner starts. It is fair to say that there is some sort of compensation for the disadvantages, under which they labour; the Scotch shale oil manufacturers obtain two valuable products which are either wholly absent or present only in small quantities in petroleum. These are paraffin wax, for while American petroleum contains only about 2 per cent. to 3 per cent. of wax, while Russian contains none, and ammonia, which is not found so far as my knowledge goes, in any petroleum. The business of the Scotch shale oil manufacturer was, therefore, to reduce the cost of manufacture and to increase the yield of the two products to which I have referred. These two objects were effected in a remarkable manner. I have already explained that in the earlier days of the trade the process of gas manufacture was closely followed. This involved the idea that the charge of shale had been exhausted of its volatile contents, the spent shale, still in a state of incandescence and capable of giving out much heat, was withdrawn from the retorts and quenched with water. It seemed to some of the leading minds in the trade that this involved a clear loss of energy. The first to introduce a method by which the latent heat of the spent shale could be utilized was Mr. Norman Henderson, who designed a vertical retort, with a tilting valve or door at the bottom, through which the exhausted shale was dropped into the furnace which heated the retort and distilled the next charge. By the earlier methods it had required 4cwt. to 5cwt. of coal to distil one ton of shale, and when it was found possible to dispense with this fuel and its cost it almost seemed as if something akin to finality had been obtained. But Beilby, one of the pioneers in the improved system of distilling shale, and others, were not satisfied that in merely using the spent shale as fuel they were getting all that was valuable out of it. They argued that if it were possible to subject it to a higher temperature after the finer oils had been extracted, they might increase the yield of paraffin and gas, while securing in the shape of incondensable gas the value of the residue of carbon which it still contained. The problem, therefore, was to design a retort in which the low temperature required for the production of oil should be combined with the high temperature of a gas retort. Various schemes to give effect to this purpose were propounded and tried. The aim in view was ultimately accomplished by greatly extending the height of the retort and the adoption of arrangements which rendered it possible to regulate the heat in such a manner that three zones of temperature were provided; low or moderate at the top, where the fresh shale is introduced and the higher spirit and oils are extracted, higher in the middle where the heavier oil and paraffin are extracted, and highest at the bottom where gas is produced. The shale, entering the relatively cool zone at the top of the retort, encounters the lowest temperature which is about 800 deg. to 1,000 deg. Fahr., and gives off the lighter products viz., spirit and light oil. Passing downward to the central section, it is exposed to a temperature of 1,400 deg. to 1,500 deg. Fahr., and gives off lamp oil, lubricating oil, and paraffin wax. Continuing its downward progress it enters the lowest section, which is maintained at a temperature of 1,800 deg. to 2,000 deg. Fahr. approaching that attained in gas making, as a result of the process the results sought for are akin to those attained in gas production. At this latter stage an interesting chemical and economic action occurs. In operating these retorts it is customary to introduce a continuous current of steam, part of which passes upward unchanged through the retort and promotes the removal of the gases as soon as they are formed, while part is decomposed into its elements, oxygen and hydrogen. The oxygen unites with the residue of carbon which is still present in the shale and forms carbonic oxide gas, while the hydrogen combines with the nitrogen of the shale and forms ammonia. The temperatures given from various authorities, it may be noted, are only approximate, inasmuch that different retorts call for different treatment in this respect. Each of the Henderson retorts contains a charge of 15 tons, which passes slowly downwards through the different zones of temperature at the rate of about 4 tons to 4½ tons per diem, which is replaced at the same rate. After leaving the retorts, all the gaseous products pass through stands of vertical iron pipes in which the heavier oils and steam and ammonia gases are condensed and drawn off, while the lighter gases are conveyed to coke towers in which they meet a continually descending shower of water and oil, which condenses the remainder of the ammonia and the naphtha, from which petrol is produced, the remaining incondensable portion being conveyed by huge pipes to the combustion chambers under the retorts, where it is used for heating the retorts. Methods of Distillation. The lightest spirits are refined by distillation by steam heat and by washing with sulphuric acid and soda to remove the smell. The heavier portion of the oil containing lamp oil, lubricating oil, and paraffin, is transferred to a battery of boiler-shaped stills. The battery comprises:— (a) A central still to receive the crude oil; (b) On each side a heavier oil still; and (c) Beyond these two coking stills for the heaviest oils. The crude oil enters the central still and is subjected to a current of steam and moderate heat sufficient to volatilize and carry off the lighter fractions, including a small percentage of spirit and the burning oils, while the heavier oil is conveyed by pipes to the two adjoining stills from which, by higher temperature, the intermediate oils are distilled off, the residue being carried by pipes to the coking stills which are maintained at a temperature sufficiently high to carry off the lubricating oil and the paraffin wax, while the final residue is reduced to coke. The various distillates are collected in separate tanks from which they are transferred to washing vessels allotted to each. In the first of these the oils are agitated with sulphuric acid to remove the tarry matter which they contain, and thence to other washing vessels in which they are agitated with caustic soda solution to neutralize the trace of sulphuric acid which remains after the first process and to remove other tars. The operations of distillation and washing may have to be repeated several times. Lubricating Oil and Paraffin Wax.—The heavy oil from the last distillation, which contains the lubricating oil and paraffin, is exposed to cold which causes the paraffin to crystallize. The mass is then forced through filter presses which separate the oil from the wax. The oil is refined by treatment with sulphuric acid and soda, as already described, and the wax is placed in huge shallow trays, tier above tier, or in large vertical cylinders in a house specially constructed for their reception and subjected to moderate heat, which causes the remaining oil to drain off and leaves the refined paraffin ready for candle making. The ammonia water is placed in suitable stills to which heat is applied, the ammonia gas (which is distilled from the water) being conducted by pipes to lead-lined tanks containing sulphuric acid, in the surface of which the gas is discharged through perforated lead pipes. The ammonia gas combines with the sulphuric acid and forms a solution of sulphate of ammonia which is allowed to settle. This is then transferred to evaporating tanks, in which the water is removed, and commercial sulphate of ammonia, which forms a valuable manure, is produced. Petroleum Motor Spirit. In approaching this view on the subject, the important thing for the motor engineer to consider is that the compact little steam engine, with which he deals, takes the place not only of the steam engine, or the gas engine, as a power unit, but in itself embraces the sources of power from which these engines derive their energy, i.e., the boiler and furnace required for the steam engine, and the retorts, gas holders, and purifiers, and other paraphernalia of a gas works. Evidently, therefore, a material must be found which, under the easiest conditions, will give the largest volume of useful gas or vapour and the least incidental trouble from the formation of such by-products as the non-volatile residue, pitch or carbon. By common consent petroleum spirit has been accepted as fulfilling these conditions. There are spirits and spirits. Spirit which is too light, and which may be too readily volatilized, gives gas deficient in energy, and spirit which is too heavy, and can only be partially and imperfectly volatilized, and exists in combining the disadvantages of both. See table C in Appendix. | ||