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OIL ENGINE
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OIL See also:ENGINE . Oil engines, like See also:gas engines (q.v.), are See also:internal conbustion See also:motors in which See also:motive See also:power is produced by the See also:explosion or expansion of a mixture of inflammable material and See also:air. The inflammable fluid used, however, consists of vapour produced from oil instead of permanent gas. The thermodynamic operations are the same as in gas engines, and the structural and See also:mechanical See also:differences are due to the devices required to vaporize the oil and See also:supply the measured proportion of vapour which is to mix with the air in the cylinders. See also:Light and heavy See also:oils are used; light oils may be defined as those which are readily volatile at See also:ordinary atmospheric temperatures, while heavy oils are those which require See also:special See also:heating or spraying processes in See also:order to produce an inflammable vapour capable of forming explosive mixture to be supplied to the cylinders. Of the light oils the most important is known as petrol. It is not a definite chemical See also:compound. It is a mixture of various See also:hydrocarbons of the See also:paraffin and See also:olefine See also:series produced from the See also:distillation of See also:petroleum and paraffin oils. It consists, in fact, of the lighter fractions' which distil over first in the See also:process of purifying petroleums or paraffins. The specific gravity of the See also:standard petrels of See also:commerce generally ranges between 0.700 to about 0'740; and the See also:heat value on See also:complete See also:combustion per 1-1-d- See also:gallon burned varies from 14,240 to 14,850 See also:British thermal See also:units. The thermal value per gallon thus increases with the See also:density, but the volatility diminishes. Thus, samples of petrol examined by Mr See also:Blount C C 3'5 of from • 700 to • 739 specific gravity showed that 98% of the lighter See also:sample distilled over below 12o° C. while only 88% of the heavier came over within the same temperature range. The heavier petrol is not so easily converted into vapour. The See also:great See also:modern development of the motor See also:car gives the light oil engine a most important See also:place as one of the leading See also:sources of motive power in the See also:world. The See also:total petrol power now applied to cars on See also:land and to vessels on See also:sea amounts to at least two million H.P. The petrol engine has also enabled aeroplanes to be used in practice. The earliest proposal to use oil as a means to produce motive power was made by an See also:English inventor—See also:Street—in 1794, but the first See also:practical petroleum engine was that of See also:Julius Hock of See also:Vienna, produced in 187o. This engine, like Lenoir's gas engine, operated without See also:compression. The See also:piston took in a See also:charge of air and light petroleum spray which was ignited by a See also:flame See also:jet and produced a, See also:low-pressure explosion. Like all non-compression engines, Hock's See also:machine was very cumbrous and gave little power. In 1873, Brayton, an English engineer, who had settled in See also:America, produced a light oil engine working on the See also:constant pressure See also:system without explosion. This appears to have been the earliest compression engine to use oil See also:fuel instead of gas. Shortly after the introduction of the " See also:Otto " gas engine in 1876, a motor of this type was operated by an inflammable vapour produced by passing air on its way to the See also:cylinder through the light oil then known as gasolene. A further air supply was See also:drawn into the cylinder to See also:form the required explosive mixture, which was subsequently compressed and ignited in the usual way. The Spiel petroleum engine was the first Otto See also:cycle motor introduced into practice which dispensed with an See also:independent vaporizing apparatus. Light See also:hydrocarbon of a specific gravity of not greater than 0.725 was injected directly into the cylinder on the suction stroke by means of a See also:pump. In entering it formed spray mixed with the air, was vaporized, and on compression an explosion was obtained just as in the gas engine.
Until the See also:year 1883 the different gas and oil engines constructed were of a heavy type rotating at about 150 to 250 revolutions per See also:minute. In that year Daimler conceived the See also:idea of constructing very small engines with light moving parts, in order to enable them to be rotated at such high speeds as Boo and r000 revolutions per minute. At that See also:time See also:engineers did not consider it practicable to run engines at such speeds; it was supposed that low See also:speed was necessary to durability and smooth See also:running. Daimler showed this idea to be wrong by producing his first small engine in 1883. In 1886 he made his first experiment with a motor See also:bicycle, and on the 4th of See also: I is a diagrammatic See also:section of an See also:early Daimler motor. A is the cylinder, B the piston, C the connecting See also:rod, and D the See also:crank, which is entirely enclosed in a casing. A small See also:fly-See also:wheel is carried by the crank-See also:shaft, and it serves the See also:double purpose of a fly-wheel and a clutch, a is the combustion space, E the single See also:port, which serves both for inlet of the charge and for See also:discharge of exhaust. W is the exhaust See also:valve, F the charge inlet valve, which is automatic in its See also:action, and is held closed by a See also:spring f, G the carburettor, H the igniter See also:tube, I the igniter tube See also:lamp, K the charge inlet passage, L the air See also:filter chamber, and M an adjustable air inlet cap for regulating the air inlet See also:area. The light oil—or petrol, as it is commonly called—is supplied to the See also:float chamber N of the vaporizer by means of the valve O. So See also:long as the level of the petrol is high, the float n, acting by levers about it, holds the valve 0 closed against oil forced by air pressure along the See also:pipe P When the level falls, however, the valve opens and more petrol is admitted. When the piston B makes its suction stroke, air passes from the See also:atmosphere by thepassage K through the valve F, which it opens automatically. The pressure falls within the passage K, and a spurt of petrol passes by the jet GI, See also:separate air at the same time passing by the passage Ki See also:round the jet. The petrol breaks up into spray by impact against the walls of the passage K, and then it vaporizes and passes into the cylinder A as an inflammable mixture. When the piston B returns it compresses the charge into a, and upon compression the incandescent igniter tube H fires the charge. H is a See also:short See also:platinum tube, which is always open to the compression space, It is rendered incandescent by the burner I, fed with petrol from the pipe 'upplying the vaporizer. The open incandescent tube is found to See also:act well for small engines, and it does not ignite the charge until the compression takes place, because the inflammable mixture cannot come into contact with the hot See also:part till it is forced up the tube by the compression. The engine is started by giving the crank-shaft a See also:smart turn round by means of a detachable handle. The exhaust is alone actuated from the valve shaft. The shaft Q is operated by pinion and a See also:spur-wheel Q4 at See also:halt the See also:rate of the crank-shaft. The governing is accomplished by cutting out explosions as with the gas engine, but the See also:governor operates by preventing the exhaust valve from opening, so that no charge is discharged from the cylinder, and therefore no charge is drawn in. the See also:cam R operates the exhaust valve, the levers shown are so controlled by the governor (not shown) that the See also:knife edge S is pressed out when speed is too high, and cannot engage the See also:recess T until it falls. The engine has a See also:water jacket V, through which water is circulated. Cooling devices are used to economize water. Benz of See also:Mannheim followed See also:close on the See also:work of Daimler, and in See also:France Panhard and Levassor, Peugeot, De See also:Dion, Delahaye and Renault all contributed to the development of the petrol engine, while See also:Napier, Lanchester, Royce and See also:Austin were the most prominent among the many English designers. The modern petrol engine differs in many respects from the Daimler engine just described both as to See also:general See also:design, method of carburetting, igniting and controlling the power and speed. The carburettor now used is usually of the float and jet type shown in fig. 1, but alterations have been made t4 allow of the See also:production of See also:uniform mixture in the cylinder under widely varying conditions of speed and load. The See also:original form of carburettor was not well adapted to allow of great See also:change of See also:volume per suction stroke. Tube ignition has been abandoned, and the electric system is now supreme. The favourite type at See also:present is that of the high-tension magneto. Valves are now all mechanically operated; the automatic inlet valve has practically disappeared. Engines are no longer controlled by cutting out impulses; the governing is effected by throttling the charge, that is by diminishing the volume of charge admitted to the cylinder at one stroke. Broadly, throttling by reducing charge weight reduces pressure of compression and so allows the power of the explosion to be graduated within wide limits while maintaining continuity of impulses. The See also:object of the throttle See also:control is to keep up continuous impulses for each cycle of operation, while graduating the power produced by each impulse so as to meet the conditions of the load. Originally three types of carburettor were employed for dealing with light oil; first, the See also:surface carburettor; second, the See also:wick carburettor; and third, the jet carburettor. The surface carburettor has entirely disappeared. In it air was passed over a surface of light oil or bubbled through it; the air carried off a vapour to form explosive mixture. It was found, however, that the oil remaining in the carburettor gradually became heavier and heavier, so that ultimately no proper See also:vaporization took place. This was due to the fractional evaporation of the oil which tended to carry away the light vapours, leaving in the See also:vessel the oil, which produced heavy vapours. To avoid this fractionation the wick carburettor was introduced and here a complete portion of oil was evaporated at each operation so that no concentration of heavy oil was possible. The wick carburettor is still used in some cars, but the jet carburettor is practically universal. It has the See also:advantage of discharging separate portions of oil into the air entering the engine, each portion being carried away and evaporated with all its fractions to produce the charge in the cylinder.
The modern jet carburettor appears to have originated with See also: When, however, the speed range is great, such as in modern motors, which may vary from 300 to 1500 revolutions per minute under light and heavy loads, then it becomes impossible to secure proportionality sufficiently accurate for See also:regular ignition. This implies not only a change of engine speed but a change of volume entering the cylinder at each stroke as deter-See also:mined by the position of the throttle. This introduces further complications. Throttle control implies a change of total charge volume per stroke, which change may occur either at a low or at a high speed. To meet this change the petrol jet should See also:respond in such manner as to give a constant proportionality of petrol weight to air weight throughout all the See also:variations- -otherwise sometimes petrol will be present in excess with no See also:oxygen to See also:burn it, and at other times the mixture may be so dilute as to See also:miss firing altogether. To meet these varying conditions many carburettors have been produced which seek by various devices to maintain uniformity of quality of mixture by the automatic change of throttle around the jet. Fig. 3 shows in diagrammatic section one of the simplest of these contrivances, known as the Krebs carburettor. The petrol enters from the float chamber to the jet E; and, while the engine is running slowly, the whole supply of air enters by way of the passage F, mixes with the petrol and .eaches the cylinders by way of the pipe G. The volume of charge entering the cylinder per stroke is controlled by the piston throttle valve H, operated by the rod I ; and so long as the charge volume required remains FIG. 3. small, air from the atmosphere enters only by F. When speed rises, however, and the throttle is sufficiently opened, the pressure within the apparatus falls and affects a spring-pressed See also:diaphragm K, which actuates a piston valve controlling the air passages L, so that this valve opens to the atmosphere more and more with increasing pressure reduction, and additional air thus flows into the carburettor and mixes with the air and petrol entering through F. By this device the required proportion of air to petrol is maintained through a comparatively large volume range. This 'change of air See also:admission is rendered necessary because of the difference between the See also:laws of air and petrol flow. In order to give a sufficient weight of petrol at low speeds when the pressure drop is small, it is necessary to provide a somewhat large area of petrol jet. When suction increases owing to high speed, this large area discharges too much petrol, and so necessitates a device, such as that described, which admits more air. A still simpler device is adopted in many carburettors—that of an additional air inlet valve, kept closed until wanted by a spring. Fig. 4 shows a diagrammatic section as used in the See also:Vauxhall carburettor. Here the petrol jet and See also:primary and secondary air passages are lettered as before. The same effect is produced by devices which alter the area of the petrol jet or increase or diminish the number of petrol jets exposed as required. Although engine designers have succeeded in pro-portioning mixture through a considerable range of speed and charge demand, so as to obtain effective power explosions under all these conditions, yet much remains to be done to secure constancy of mixture at all speeds. Notwithstanding much which has been said as to varying mixture, there is only one mixture of air and petrol which gives the best results—that in which there is some excess of oxygen, more than sufficient to burn all the See also:hydrogen and See also:carbon present. It is necessary to secure this mixture under all conditions, not only to obtain See also:economy in running but also to maintain purity of exhaust gases. Most engines at certain speeds discharge consider-able quantities of carbonic See also:oxide into the atmosphere with their exhaust gases, and some discharge so much as to give rise to danger in a closed garage. Carbonic oxide is an extremely poisonous gas which should be reduced to the minimum in the interests of the See also:health of our large cities. The enormous increase of motor See also:traffic makes it important to render the exhaust gases as pure and innocuous as possible. Tests were made by the Royal Automobile See also:Club some years ago which clearly showed that carbonic oxide should be kept down to 2 % and under when carburettors were properly adjusted. Subsequent experiments have been made by See also:Hopkinson, Clerk and K See also:Watson, which clearly prove; that in some cases as much as 3o% not only discharge purer exhaust gases but would work on very of the whole heat of the petrol is lost in the exhaust gases by ins- much less petrol than they do at present. Practically all modern petrol engines are controlled by throttling the whole charge. In the earlier days several methods of control; were attempted: (r) missing impulses as in fig. i of the Daimler engines; (2) altering the timing of spark; (3) throttling petrol supply, and. (4) throttling the mixture of petrol and air. The last method has proved to be the best. By maintaining the proportion of explosive mixture, but diminishing_ the total volume admitted to the cylinder per stroke, graduated impulses are obtained without any, or but few, missed ignitions. The effect of the throttling is to reduce compression by diminishing total charge weight. To a certain extent the proportion of petrol to total charge also varies, because the residual exhaust gases remain constant through a wide range. The thermal efficiency diminishes as the throttling increases; but, down to a third of the See also:brake power, the diminution is not great, because although compression is reduced the expansion remains the same. At low compressions, however, the engine works practically as a non-compression engine, and the point of maximum pressure becomes greatly delayed. The efficiency, therefore, falls markedly, but this is not of much importance at light loads. Experiments by Callendar, Hopkinson, Watson and others have proved that the thermal efficiency obtained from these small engines with the throttle full open is very high indeed; 28% of the whole heat in the petrol is often given as indicated work when the carburettor is properly adjusted. As a large gas engine for the same compression cannot do better than 35%, it appears that the loss of heat due to small dimensions is compensated by the small time of exposure of the gases of explosion. due to the high speed of rotatio:i. Throttle control is very effective, and it has the great advantage of diminishing maximum
perfect combustion. This opens a wide See also: I.—Water Uptake. Q.—Throttle and Automatic Air J.—Crank Chamber. R.—See also:Main Mixture Pipe. [Valve. 1, —Under See also:Cover to Crank Chbr. S.—Carburetter. .—See also:Distribution See also:Gear See also:Case. U.—Magneto. L.—Oil Sump. V.—Inlet Valve. M.—Oil Pump. W.—Inlet See also:Trunk. pressures to which the piston and cylinders are exposed While the engine is running at the See also:lower loads. This is important both for smooth running and See also:good wearing qualities. Theoretically, better results could be obtained from the point of view of economy by retaining a constant compression pressure, constant charge of air, and producing ignition, somewhat in the manner of the Diesel engine. Such a method, however, would have the disadvantage of producing practically the same maximum pressure for all loads, and this would'tend to give an engine which would not run smoothly at slow speeds. As has been said, tube ignition was speedily abandoned for electric ignition by See also:accumulator, See also:induction coil distributor and sparking plug. This in its turn was largely displaced by the low-tension magneto, system, in which the spark was formed between contacts which were mechanically separated within the cylinders. The separable contacts gave rise to complications, and at present the most popular system of ignition is undoubtedly that of the high-tension magneto. In this system the ordinary high-tension sparking plugs are used, and the high-tension current is generated in a secondary winding on the See also:armature of the magneto, and reaches the sparking plugs by way of a rotary distributor. In many cases the high-tension magneto system is used for the ordinary running of the engine, combined with an accumulator or See also:battery and induction coil for starting the engine from See also:rest. Such systems are called dual ignition systems. Sometimes the same ignition plugs are adapted to spark from either source, and in other cases separate plugs are used. The magneto systems have the great advantage of generating current without battery, and by their use See also:noise is reduced to a minimum. Allelectrical systems are now arranged to allow of advancing and retarding the spark from the steering wheel. In modern magneto methods, however, the spark is automatically retarded when the engine slows and advanced when the speed rises, so that less change is required from the wheel than is necessary with battery and coil. See also:Sir See also:Oliver See also:Lodge has invented a most interesting system of , electric ignition, depending upon the production of an extra oscillatory current of enormous tension produced by the combined use of spark See also:gap and See also:condenser. This extra spark passes freely even under water, and it is impossible to stop it by any ordinary sooting or fouling of the ignition plug. The most popular engines are now of the four and six cylinder types. Fig. 5 shows a modern four-cylinder engine in See also:longitudinal and transverse sections as made by the See also:Wolseley See also:Company. A, A are the cylinders; B, B, water jackets; G', oil scoops on the large ends of the connecting-rods. These scoops take up oil from the crank chamber. Forced See also:lubrication is used. The oil pump M is of the toothed wheel type, and it is driven by skew gearing. An oil sump is arranged at L, and the oil is pumped from this sump by the pump described. The overflow from the main See also:bearings supplies the channels in the crank case from which the oil scoops take their charge. It will be seen that the two inside pistons are attached to cranks of co-incident centres, and this is true of the two outside pistons also. This is the usual arrangement in four-cylinder engines. By.this device the primary forces are balanced; but a small secondary unbalanced force remains, due to the difference in See also:motion of the pistons at the up and down portions of their stroke. A six-cylinder engine has the advantage of getting rid of this secondary unbalanced force; but it requires a longer and more rigid crank chamber. In this engine the inlet and exhaust valves of each cylinder are placed in the same See also:pocket and are driven from one cam-shaft. This is a very favourite arrangement; but many engines are constructed in which the inlet and exhaust valves operate on opposite sides of the cylinder in separate ports and are driven from separate cam-shafts. Dual ignition is applied to this engine; that is, an ignition composed of high-tension magneto and also battery and coil for starting. U is the high-tension magneto. Under the figure there is' shown a See also:list of parts which sufficiently indicate the nature of the engine. An interesting and novel form of engine is shown at fig. 6. This is a well-known engine designed by Mr See also:Knight, an See also:American inventor, and now made by the Daimler and other companies. It will be observed in the figure that the ordinary lift valves are 'entirely dispensed with, and slide valves are used of the cylindrical See also:shell type. The engine operates on the ordinary. Otto cycle, and all the valve actions necessary to admit charge and discharge exhaust gases are accomplished by means of two sleeves sliding one within the other. The -See also:outer See also:sleeve slides in the main cylinder and the inner sleeve slides within the outer sleeve. The piston fits within the inner sleeve. Tha sleeves receive separate motions front short connecting links C and E, driven by eccentrics carried on a shaft W. This shaft is driven from the main crank-shaft by a strong See also:chain so as to make See also:half the revolutions of the crank-shaft in the usual manner of the Otto cycle. The inlet port is formed on one See also:side of the cylinder and is marked I. The exhaust port is arranged on the other side and marked J. These ports are segmental. A., water-jacketed cylinder See also:head carries stationary rings L, K, which See also:press outwards. These are clearly shown in the See also:drawing. The inner sleeve ports run past the lower broad See also:ring L when compression is to be accomplished, and the contents of the cylinder are retained within the cylinder and compression space by the piston rings and the fixed rings referred to. Fro. 6. The outer sleeve does not require rings at all. Its See also:function is simply to distribute the gases so that the exhaust port is closed by the outer sleeve when the inlet port is open. The outer sleeve acts really as a distributor; the inner sleeve supplies the pressure tightness required to resist compression and explosion. The idea of working exhaust and inlet by two sleeves within which the main piston operates is very daring and ingenious; and for these small engines the sleeve valve system works admirably. There are many advantages; the shape of the compression space is a most favourable one for reducing loss by cooling. All the valve ports required in ordinary lift valve engines are entirely dispensed with; that is, the surface exposed to the explosion causing loss of heat is reduced to a minimum. The engines are found in use to be very flexible and economical. The petrol engines hitherto described, although light compared to the old stationary gas engines, are heavy when compared with See also:recent motors See also:developed for the purpose of aeroplanes. Many of these motors have been produced, but two only will be noticed here—the Anaani, because Bleriot's great See also:flight b across the Channel was accomplished by means of an Anzani engine, and the See also:Gnome engine, because it was used in the aeroplane with which Paulhan flew from See also:London to See also:Manchester. Fig. 7 shows transverse and longitudinal sections through the Anzani motor. Looking at the longitudinal section it will be observed that the cylinders are of the air-cooled type; the exhaust valves alone are positively operated, and the inlet valves are of the automatic lift See also:kind. The transverse section shows that three radially arranged cylinders are used and three pistons act upon one crank-See also:pin. The Otto cycle is followed so that three impulses are obtained for every two revolutions. The cylinders are spaced apart 6o° and project from the upper side of the crank chamber. Although not shown in the drawing, the pistons overrun a See also:row of holes at the out end of the stroke and the exhaust first discharges through these holes. This is a very See also:common device in aeroplane engines, and it greatly increases the rapidity of the exhaust discharged and reduces the work falling upon the exhaust valve. The pistons and cylinders are of See also:cast See also:iron; the rings are of cast iron; the ignition is electric, and the petrol is fed by gravity. The engine used by Bleriot in his See also:Cross-Channel flight was 25 H.P., cylinders 105 mm. boreX 130 mm. stroke; revolutions, 1600 per minute; total weight, 145 lb. The engine, it will be seen, is exceedingly See also:simple, although air-cooling seems somewhat See also:primitive for anything except short flights. The larger Anzani motors are water-cooled.
A diagrammatic transverse section of the Gnome motor is shown at fig. 8. In this interesting engine there are seven cylinders disposedradially round a fixed crank-shaft. The seven pistons are all connected to the same crank-shaft, one piston being rigidly connected to a big end of See also:peculiar construction by a connecting-rod, while the other connecting-rods are linked on to the same big end by pins; that is, a hollow fixed crank-shaft-has a single throw to which only one connecting-rod is attached; all the other connecting-rods work on pins let into the big end of that connecting-rod. The cylinders revolve round the fixed crank in the manner of the well-known engines first introdued to practice by Mr See also: The total weight of the engine complete is 18o lb, or just over 5 lb per brake See also:horse-power. The subject of aeroplane petrol engines is a most interesting one, and rapid progress is being made. So far, only 4-cycle engines have been described, and they are almost universal for use in motor-cars and aeroplanes. Some motor cars, however, use 2-cycle engines. Several types follow the "Clerk" cycle (see Gas ENGINE) and others the "See also:Day" cycle. In America the Day cycle is very popular for motor _FIG. 8. launches, as the engine is of a very simple, easily managed kind. At present, however, the two-cycle engine has made but little way in motor car or aeroplane work. It is capable of great development and the See also:attention given to it is increasing. So far, petrol has been alluded to as the main liquid fuel for these motors. Other hydrocarbons have also been used; benzol, for example, obtained from gas See also:tar is used to some extent, and See also:alcohol has been applied to a considerable extent both for stationary and See also:locomotive engines. Alcohol, however, has not been entirely successful. The amount of heat obtained for a given monetary See also:expenditure is only about half that obtained by means of petrol. On the See also:continent of See also:Europe, however, alcohol motors have been considerably used for public vehicles. The See also:majority of petrol motors are provided with water jackets arohnd their cylinders and combustion spaces. As only a small quantity of water can be carried, it is necessary to cool the water as fast as it becomes hot. For this purpose radiators of various constructions are applied. Generally a pump is used to produce a forced circulation, discharging the hot water from the engine jackets through the radiator and returning the cooled water to the jackets at another place. The radiators consist in some cases of See also:fine tubes covered with projecting fins or gills; the motion of the car forces air over the exterior of those surfaces and is assisted by the operation of a powerful See also:fan driven from the engine. A favourite form of radiator consists of numerous small tubes set into a casing and arranged somewhat like a See also:steam-engine condenser. Water is forced by the pump round these tubes, and air passes from the atmosphere through them. This type of radiator is sometimes known as the " See also:honeycomb " radiator. A very large cooling surface is provided, so that the same water is used over and over again. In a day's run with a modern petrol engine very little water is lost from the system. Some engines dispense with a pump and depend on what is called the thermo-syphon. This is the old gas-engine system of circulation, depending on the different density of water when hot and cool. The engine shown at fig. 5 is provided with a water-circulation system of this kind. For the smaller engines the thermo-syphon works extremely well. Heavy oil engines are those which consume oil having a flashing-point above 730 F.—the minimum at present allowed by act of See also:parliament in Great See also:Britain for oils to be consumed in ordinary See also:illuminating lamps. Such oils are American and See also:Russian petroleums and Scottish paraffins. They vary in specific gravity from •78 to •825, and in flashing-point from 750 to 152° F. Engines burning such oils may be divided into three distinct classes: (1) Engines in which the oil is subjected to a spraying operation before vaporization; (2) Engines in, which the oil is injected into the cylinder and vaporized within the cylinder; (3) Engines in which the oil is vaporized in a device See also:external to the cylinder and introduced into the cylinder in the See also:state of vapour. The method of ignition might also be used to See also:divide the engines into those igniting by the electric spark, by an incandescent tube, by compression, or by the heat of the internal surfaces of the combustion space. Spiel's engine was ignited by a flame igniting device similar to that used in Clerk's gas engine, and it was the only one introduced into Great Britain in which this method was adopted, though on the continent flame igniters were not uncommon. Electrically-operated igniters have come into extensive use throughout the world. The engines first used in Great Britain which See also:fell under the first head were the Priestman and Samuelson, the oil being sprayed before being vaporized in both. The principle of the spray pro- ducer used is that so well and so widely known in connexion with the See also:atom- izers or spray producers used by perfumers. Fig. 9 shows such a spray pro- ducer in section. An air blast passing from the small jet A crosses the See also:top of the tube B and creates within it a partial vacuum. The liquid contained in C flows up the tube B and issuing at the top of the tube through a small orifice is at once blown into very fine spray by the action of the air jet. If such a See also:scent distributor be filled with petroleum oil, such as Royal Daylight or Russoline, the oil will be blown into fine spray, which can be ignited by a flame and will burn, if the jets be properly proportioned, with an intense See also:blue non- luminous flame. The earlier inventors often expressed the idea that an explosive mixture could be prepared without any vaporization whatever, by simply producing an atmosphere containing inflammable liquid in extremely small particles dis- tributed throughout the air in such proportion as to allow of complete combustion. The See also:familiar explosive combustion of See also:lycopodium, and the disastrous explosions caused in the exhaus- tion rooms of See also:flour-See also:mills by the presence of finely divided flour in the air, have also suggested to inventors the idea of producing explosions for power purposes from combustible solids. Al- though, doubtless, explosions could be produced in that way, yet in oil engines the production of spray is only a preliminary to the vaporization of the oil. If a sample of oil is sprayed in the manner just described, and injected in a hot chamber also filled with hot air, it at once passes into a state of vapour within that chamber, even though the air be at a temperature far below the boiling-point of the oil; the spray producer, in fact, furnishes a ready means of saturating any volume of air with heavy petroleum oil to the full extent possible from the vapour tension of the oil at that particular temperature. The oil engines described below are in reality explosion gas engines of the ordinary Otto type, with special arrangements to enable them to vaporize the oil to be used. Only such parts of them as are necessary for the treatment and ignition will therefore be described. Fig. to is a See also:vertical section through the cylinder and vaporizer of a Priestman engine, and fig. I t is a section on a larger scale, showing the vaporizing jet and the air admission and regulation valve m / P leading to the vaporizer. Oil is forced by means of air pressure from a See also:reservoir through a pipe to the spraying nozzle a, and air passes from an air-pump by way of the See also:annular channel b into the sprayer c, and there meets the oil jet issuingi from a. The oil is thus broken up into spray, and the air charged with spray flows into the vaporizer E, which is heated up in the first place on starting the engine by means of a lamp. In the vaporizer the oil spray becomes oil vapour, saturating the air within the hot walls. On the out-charging stroke of the piston the mixture passes by way of the inlet valve H into the cylinder, air flowing into the vaporizer to replace it through the valve 1 (fig. II). The cylinder K is thus charged with a mixture of air and hydrocarbon vapour, some of which may exist in the form of very fine spray. The piston L then returns and compresses the mixture, and when the compression is quite complete an electric spark is passed between the points M, and a compression explosion is obtained precisely similar to that obtained in the gas engine. The piston moves out, and on its return stroke the exhaust valve N is opened and the exhaust gases discharged by way of the pipe 0, round the jacket P, enclosing the vaporizing chamber. The e latter is thus kept hot by the exhaust gases when the engine is at work, and it remains sufficiently hot with-out the use of the lamp provided for starting. To obtain the electric spark a bichromate battery with an induction coil is used. The spark is timed by contact pieces operated by an See also:eccentric rod, used to actuate the exhaust valve and the air-pump for supplying the oil chamber and the spraying jet. To start the engine a See also:hand pump is worked until the pressure is sufficient to force the oil through the spraying. nozzle, and oil spray is formed in the starting lamp; the spray and air mixed produce a blue flame which heats the vaporizer. The fly-wheel is then rotated by hand and the engine moves away. The eccentric shaft is driven from the crank-shaft by means of toothed wheels, which reduce the speed to one-half the revolutions of the crank-shaft. The charging inlet valve is automatic. Governing is effected by throttling the oil and air supply. The governor operates on the butterfly valve T (fig. II), and on the plug-See also:cock t connected to it, by means of the spindle t'. The air and oil are thus simultaneously reduced, and the See also:attempt is made to maintain the charge entering the cylinder at a constant proportion by weight of oil and air, while reducing the total weight, and therefore volume, of the charge entering. The Priestman engine thus gives an explosion on every second revolution in all circumstances, whether the engine be running light or loaded. =C. 2 a The compression pressure of the mixture before admission is, however, steadily reduced as the load is reduced, and at very light loads the engine is running practically as a non-compression engine. A test by See also:Professor Unwin of a 41 nominal horse-power Priestman engine, cylinder 8.5 in. See also:diameter, 12 in. stroke, normal speed t8o revolutions per minute, showed the See also:consumption of oil, per indicated horse-power See also:hour to be 1•o66 lb and per brake horse-power hour 1.243 lb. The oil used was that known as Broxburn Lighthouse, a Scottish paraffin oil produced by the destructive distillation of shale, having a density of •81 and a flashing-point about 152° F. With a 5 H.P. engine of the same dimensions, the volume swept by the piston per stroke being •395 cub. ft. and the clearance space in the cylinder at the end of the stroke •210 cub. ft., the See also:principal results were light Russoline ght, Oil. il. Indicated horse-power 9.369 7.408 Brake horse-power . 7.722 6;765 Mean speed (revolutions per minute) . 204.33 207`73 Mean available pressure (revolutions per 53.2 ; 41.38 minute) . . . Oil consumed per indicated horse-power *694 lb •864 lb per hour . . . . Oil consumed per brake horse-power per •8421b •9461b hour With daylight oil the explosion pressure was 151.4 lb per square See also:inch above atmosphere, and with Russoline 134.3 lb. The terminal pressure at the moment of opening the exhaust valve with daylight oil was 35.4 lb and with Russoline 33.7 per square inch. The compression pressure with daylight oil was 35 it, and with Russoline 27.6 lb pressure above atmosphere. Professor Unwin calculated the amount of heat accounted for by the See also:indicator as 18.8 % in the case of daylight oil and 15.2 in the case of Russoline oil. The Hornsby-Ackroyd engine is an example of the class in which the oil is injected into the cylinder and there vaporized. Fig. 12 Engine (section through Engine (section through valves,, vaporizer and cylinder). vaporizer and cylinder). is a section through the vaporizer and cylinder of this engine, and fig. 13 shows the inlet and exhaust valves also in section placed in front of the vaporizer and cylinder section. Vaporizing is conducted in the interior of the combustion chamber, which is so arranged that the heat of each explosion maintains it at a temperature sufficiently high to enable the oil to be vaporized by See also:mere injection upon the hot surfaces. The vaporizer A is heated up by a separate lamp, the oil is injected at the oil inlet B, and the engine is rotated by hand. The piston then takes in a charge of air by the air inlet valve into the cylinder, the air passing by the port directly into the cylinder without passing through the vaporizer chamber. While the piston is moving forward, taking in the charge of air, the oil thrown into the vaporizer is vaporizing and diffusing itself through the vaporizer chamber, mixing, how-ever, only with the hot products of combustion See also:left by the preceding explosion. During the charging stroke the air enters through the cylinder, and the vapour formed from the oil is almost entirely confined to the combustion chamber. On the return stroke of the piston air is forced through the somewhat narrow See also:neck a into the'combustion chamber, and is there mixed with the vapour contained in it. At first, however, the mixture is too See also:rich in inflammable vapour to be capable of ignition. As the compression proceeds, however, more and more air is forced into the vaporizer chamber, and just as compression is completed the mixture attains proper explosive proportions. The sides of the chamber are sufficiently hot to cause explosion, under the pressure of which the piston moves forward. As the vaporizer A is not water-jacketed, and is connected to the See also:metal of the back cover only by the small section or area of cast-iron forming the metal neck a, the heat given to the surface by each explosion is sufficient to keep its temperature at about 700-800° C. Oil vapour mixed with air will explode by contact with a metal surface at a comparatively low temperature; this accounts for the explosion of the compressed mixture in the combustion chamber A, which is never really raised to a red heat. It has long been known that under certain conditions of internal surface a gas engine may be made to run with very great regularity, without incandescent tube or any other form of igniter, if some portion of the interior surfaces of the cylinder or combustion space be so arranged that the temperature can rise moderately; then, although the temperature may be too low to ignite the mixture at atmospheric temperature, yet when compression is completed the mixture will often ignite in a perfectly regular manner. It is a curious fact that with heavy oils ignition is more easily accomplished at a low temperature than with light oils. The explanation seems to be that, while in the case of light oils the hydrocarbon vapours formed are tolerably See also:stable from a chemical point of view, the heavy oils very easily decompose by heat, and separate out their. carbons, liberating the combined hydrogen: and at the moment of liberation the hydrogen, being in what chemists know as the nascent state; very readily enters into See also:combination with the oxygen beside it. To start the engine the vaporizer is heated by a separate heating lamp, which is supplied with an air blast by means of a hand-operated fan. This 'operation should take about nine minutes. The engine is' then moved round by hand, and starts in the usual manner. The oil tank is placed in the See also:bed See also:plate of the engine. The air and exhaust valves are driven by cams on a valve shaft. The governing is effected by a centrifugal governor which operates a by-pass valve, opening it when the speed is too high, and causes the oil pump to return the oil to the oil tank. At a test of one of these engines, which weighed 40 cwt. and was given as of 8 brake horse-power, with cylinder to in. in diameter and 15 in. stroke, according to Professor Capper's See also:report, the revolutions were very constant, and the power developed did not vary one See also:quarter of a brake horse-power from day to day. The oil consumed, reckoned on the See also:average of the three days over which, the trial extended, was .919 lb per brake horse-power per hour, the mean power exerted being 8.35 brake horse. At another full-power trial of the same engine a brake, horse-power of 8.57 was obtained, the mean speed being 239.66 revolutions per minute and the test lasting for two See also:hours; the indicated power was 10.3 horse, the explosions per minute 119.83, the mean effective pressure 28.9, per sq. in., the oil used per indicated horse-power per hour was .81 it, and per brake horse-power per hour —•977 lb. In a test at half power, the brake horse-power developed was 4.57 at 2J5.9 revolutions per minute, and the oil used per brake horse-power was. 1.48 lb. On a four hours' test, without a load, at 240 revolutions per minute, the consumption of oil was 4.23 lb per hours ' Engines of this class are those manufactured by Messrs Crossley Bros., Ltd., and the See also:National Gas Engine Co., Ltd. See also:Figs. 14 and 15 show a longitudinal section and detail views of the operative parts of the Crossley oil engine. On the suction stroke, air is drawn into the cylinder by the piston A through the automatic inlet valve D, and oil is then pumped into the heated vaporizer C through the oil sprayer G, as seen in section at fig. 1,5. The vaporizer C is bolted to the water-jacketed part B; and, like the Hornsby, this vaporizer is first heated by lamp and then the heat of the ex-plosions keeps up its temperature to a sufficiently high point to vaporize the oil when sprayed against it. On the compression stroke of the piston A the charge of air is forced into the combustion chamber B and the vaporizer chamber C, where it mixes with the oil vapour, and the mixture is ignited at the termination of the stroke by the ignition tube H. This tube is isolated to some extent from the vaporizer chamber C, and so it becomes hotter than the chamber C and is relied upon to ignite the mixture when formed at times when C would be too See also:cold for the purpose. E is the exhaust valve, which A° 04 tCeem.±zfet,-.L.--._ See also:INE operates in the usual way The water circulation passes through the jacket by way of the pipes J and K. When the engine is running at heavy loads with full charges of oil delivered by the oil pump through the sprayer G, a second pump is caused to come into action, which discharges a very small quantity of water through the water sprayer valve F. This water passes into the vaporizer and combustion chamber, together with a little air, which enters by the automatic inlet valve, which serves as sprayer. This contrivance is found useful to prevent the vaporizer from overheating at heavy loads. The principal difference between this engine and the Hornsby engine already described lies in the use of the separate ignition tube H and in the water sprayer F, which acts as a sniffing valve, taking in a little air and water when the engine becomes hot. Messrs Crossley inform the writer that the consumption of either crude or refined oil is about .63 of a See also:pint per horse-power on full load. They also give a test of a small engine developing 7 B.H.P., which consumed •6oi pint per B.H.P. per hour of See also:Rock Light refined lamp oil and only .603 pint per B.H.P. per hour of crude See also:Borneo petroleum oil. Engines in which the oil is vaporized in a device external to the cylinder have almost disappeared, because of the great success of the Hornsby-Ackroyd type, where oil is injected into, and vaporized within, the cylinder. It has been found, however, that many petrol engines having jet carburettors will operate with the heavier oils if the jet carburettor is suitably heated by means of the exhaust gases. In some engines it is customary to start with petrol, and then when the parts have become sufficiently heated to substitute paraffin or heavy petroleum oil, putting the heavy oil through the same spraying process as the petrol and evaporating the spray by hot walls before entering the cylinder. Mr Diesel has produced a very interesting engine which departs considerably from other types. In it air alone is drawn into the cylinder on the charging stroke; the air is compressed on the return stroke to a very high pressure generally to over 400 lb per sq. in. This compression raises the air to incandescence, and then heavy oil is injected into the incandescent air by a small portion of air compressed to a still higher point. The oil ignites at once as it enters the combustion space, and so a power impulse is obtained, but with-out explosion. The pressure does not rise above the pressure of air and oil injection. The Diesel engine thus embodies two very original features; it operates at compression pressures very much higher than those used in any other internal combustion engines, and it dispenses with the usual igniting devices by rendering the air charge incandescent by compression. The engine operates generally on the Otto cycle, but it is also built giving an impulse at every revolution. Mr Diesel has shown great determination and perseverance, and the engine has now attained a position of considerable commercial importance. It is made on the continent, in See also:England and in America in sizes up to moo H.P., and it has been applied to many purposes on land and also to the propulsion of small vessels. The engine gives a very high thermal efficiency. The present writer has calculated the following values from a test of a Soo B.H.P. Diesel oil engine made by Mr See also:Michael Longridge, M.Inst.C.E. The engine had three cylinders, each of 22.05 in. diameter and stroke 29.52 in., each cylinder operating on the " Otto " cycle. The main results were as follows: Indicated power . • 595 horse Brake power . . • 459 , Mechanical efficiency . . 77 % Indicated thermal efficiency . 41 % Brake thermal efficiency. . 31.7 % (D. Additional information and CommentsThere are no comments yet for this article.
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