Hardly any other invention has had such an important and immediate effect upon daily life as the petrol engine. This chapter describes how it works and its various applications and its various applications in motor cars, motor cycles, motor boats and aircraft

SECTION OF A 4-CYLINDER  PETROL ENGINE.

(1) Crank case; (2) Oil base; (3) Oil troughs for connecting rods; (4) Crank shaft; (5) Crank shaft bearing blocks; (6) Fly-wheel; (7) Cylinders; (8) Cylinder plugs; (9) Water outlet pipe; (10) Connecting rods; (11) Connecting rod bearings; (12) Pistons; (13) Gudgeon pins; (14) Cam shaft; (15) Oil pump driving wheel; (16) Engine chain cover; (17) Fan blades; (18) Fan centre and pulley ; (19) Water pump; (20) Magento machine; (21) Starting handle.

HARDLY any other invention has had such an important and immediate effect upon habits of life and methods of warfare as the petrol engine. For more than a century men had dreamed of a horseless carriage propelled by mechanical power, and their efforts had all fallen short of success for want of an engine at once light, reliable, and sufficiently powerful for the task. For twenty years a few daring spirits made perilous experiments in aerial flight, but lacked an engine light enough to be mounted on their machines. During several hundred years there had been isolated attempts to construct a submarine boat, but no means of mechanical propulsion were available which could be used under water. The same space of twenty years witnessed a new method of locomotion on land, and saw man acquire the power of navigating both the ocean of air and the still depths of the sea.

The early inventors of internal combustion engines did not confine their efforts to the use of gaseous fuel, though it was by this means that success was first attained. They tried various liquids and devised all sorts of contrivances to get these liquids to burn. But it was not until 1884 that the difficulties were overcome. In that year Gottlieb Daimler, who had been manager of Dr. Otto’s gas engine works in Germany, patented the engine which is the parent of the petrol motors of to-day.

Petrol, or gasolene, as it is called in America, is a constituent of petroleum, which is pumped up from wells in the United States, Canada, Mexico, the Caucasus, Rumania, Persia, and other parts of the world. When heated in retorts it gives off vapours, and the temperature at which it boils rises gradually. By collecting the materials at different temperatures the following are obtained :

(a) Gases which liquefy at about the temperature of ice.

(b) A clear colourless light oil, known as naphtha or mineral naphtha, to distinguish it from that obtained by the distillation of wood.

(c) A yellow oil used in lamps and called kerosene or paraffin.

(d) Oils useful as lubricants.

(e) Paraffin wax.

(f) Coke, pitch, or asphalt.

When the naphtha is again heated, the portion which boils away first is gasolene or petrol, and it is this substance which is used in small internal combustion engines. In spite of the source it is not oily. It is clear, colourless, easily converted into vapour on heating, and both the liquid and the vapour are highly inflammable.

In order to form an explosive mixture with air, the petrol must either be vaporised or in the form of a fine spray, and the first main difference between a petrol engine and a gas engine is the necessity, in the former case, of what is called a carburettor. A typical one is shown diagrammatically below. It consists of a small vessel into which petrol flows by gravity from a reservoir at a higher level. Inside is a float, attached to levers and a needle valve in such a way that when the float rises beyond a certain point the valve is closed. By this device the space to which air has free access, and which is warmed — at any rate, when the engine is running — by a surrounding jacket of hot water from the cylinder jackets or hot gases from the exhaust. In the cold, when starting, the petrol leaves the nozzle in the form of spray, but when running it is rapidly vaporised and mixed with the air also drawn in by the suction of the engine. Ordinarily, in the type of carburettor shown, the air needed for combustion enters the orifice at the bottom, but when running at high speed additional air is obtained through the small valve on the right.

DIAGRAMMATIC SECTION of a carburettor.

Apart from this contrivance there is no difference in principle between gas and petrol engines; but in compactness and lightness of construction they are completely unlike. Generally, too, the petrol engine is wholly enclosed in order to exclude dust and dirt. A general idea of the arrangement of parts and their interdependence will be obtained from the cross section below, which shows the position of the piston and valves at a certain stage of the Otto-cycle. It will be observed that the cylinder is water-jacketed in order to prevent the temperature rising beyond about 185° Fahr. The water for this purpose may circulate naturally by the heating effect of the cylinders, or it may be pumped through. After leaving the engine it passes through a great length of tubing called a radiator, in which it is cooled. The cooling effect is greatly increased by thin “fins” fixed to the tubes, and offering a large surface to the air.

CROSS SECTION through a petrol engine.

The piston is of the trunk type. The connecting rod is of steel, and is of such a form as to give the requisite strength with maximum lightness, and the valves are of the mushroom type, held down on their seats by springs and lifted by cams fixed on a rotating shaft or shafts as shown in the diagram below. The tappet lifter, between the cam and the valve rod, can be altered in position as the end of the valve rod wears. The cam shaft is driven from the main shaft by toothed wheels or by a chain, and turns at half the rate. Originally the inlet valve was not operated by a cam, but was held down by a rather weak spring and opened by suction of the engine. The cylinder is bolted directly to the crank case, which may be of thin malleable iron or aluminium alloy. Oil is supplied to the rubbing surfaces by a pump and flows into crank case.

In the early engines the explosive mixture was fired by a hot tube, but with the improvement of electrical apparatus this has been completely replaced by the electric spark. This is produced between the ends of a rod and one or two wires of nickel, nickel-steel, or platinum, fixed in a plug which is screwed into the end of the cylinder. The rod down the centre is insulated from the metal body by mica washers. Sometimes, for high speeds, two sparking plugs are used to ignite the explosive mixture at two points and secure a more rapid explosion. If, for example, an engine is running at a thousand revolutions a minute, then, since there are two strokes to a revolution, each stroke takes only three-hundredths, or ·03 of a second. The explosion, therefore, must be extremely rapid if it is to have any effect upon the piston, which, immediately it has passed the end of the stroke, will move away at an average rate of a thousand feet a minute, or nearly 17 feet a second.

DIAGRAM SHOWING an adjustable valve tappet.

The spark is produced either by an induction coil and accumulator or by a magneto, which is really a small dynamo having permanent magnets instead of electro-magnets for the field magnets. The armature is wound to give a high-tension current, and the magneto is driven from the main shaft. The spark is produced by a metal stud on a rotating ebonite disc making contact with a fixed stud, and in view of the high speed of the piston it must be accurately timed. For if the explosion takes place before the piston has finished its stroke a “back fire” occurs and the engine reverses. Usually the “timing” can be varied. In order to avoid a “back fire” when starting, it should be retarded; but when the engine is running at full speed an increase of power is obtained by advancing the spark.

With all single-cylinder engines and with some arrangements of doublecylinder engines, a flywheel is necessary to carry on in the intervals between the successive impulses. But, as a rule, no governor is required, since the petrol engine is rarely used for any purpose in which the load is suddenly reduced at a time when there is no one with his hand on the throttle valve or the brake.

While the foregoing description covers the majority of petrol engines there are a few variations from general practice to which reference must be made. First as to valves. The poppet or mushroom type has the disadvantage of being noisy, especially if the “lift” is large, and there is a tendency for them to knock their heads off. In order to secure silence some engines have rotary valves, not unlike the Corliss valves; others have piston valves; and in others there is a sliding, or sliding and turning, sleeve between the piston and cylinder, provided with holes which at the right moment coincide with ports in the cylinder itself. Thus the Itala and Daracq are rotary valve engines, and the Argyll and Daimler companies make sleeve engines. There is, further, an engine open at both ends with two pistons between which the explosion takes place.

DIAGRAM OF A two-stroke petrol motor.

But the most important departure in principle is the substitution of the two-stroke for the four-stroke cycle. The plan adopted is the same as in the two-stroke gas engine to which reference has already been made in the chapter on “The Gas Engine”, except that the crank case is employed as a sort of receiver. In the diagrammatic view (above) it will be seen that the admission and exhaust ports are in the side of the cylinder and are opened and closed by the movement of the piston itself. As the crank case is air-tight the upward movement of the piston draws in the explosive mixture from the carburettor. The downward movement first compresses this charge, and then, when the port is exposed, forces it into the upper half of the cylinder, where it displaces the waste gases from the previous explosion. The return of the piston closes both ports and compresses the mixture. Explosion then takes place and the whole process is repeated, the piston thus receiving an impulse for every revolution of the crank. We can now leave the general principles and proceed shortly to examine engines for motor-cars, motor-boats, and aeroplanes.

The enormous extension of motor traffic during the last fifteen years has made heavy demands upon the world’s supply of petrol, and the price of this fuel rose from 8d. to 1s. gd. a gallon even before the First World War. It was natural, therefore, for owners of petrol engines to look around for a cheaper fuel, and among those most easily obtainable were paraffin, benzol or benzene, and alcohol. Paraffin is ordinary illuminating oil, such as is used in lamps. Benzol is produced when coal is distilled, in the manufacture of coal gas, and alcohol is obtained when vegetable matter ferments. All are inflammable, but do not vaporise so easily as petrol, while there is such a heavy duty on alcohol that the price is prohibitive. Before the war benzol, which was only two-thirds the price of illuminating oil, and paraffin, which was still cheaper, were both used. The only disadvantage is that the engine will not start with them. Once, however, the carburettor has become warmed up they work very well.

Many engines are made to start on petrol and then work with paraffin or benzol. Other engines are made to work with paraffin or benzol altogether, and are provided with a vaporising chamber which can be heated up by a lamp. This is surrounded by a jacket through which the exhaust gases pass, so that when once it has been heated it remains hot enough to vaporise the fuel as long as the engine is working.

There is also a form of mechanical vaporiser, in which the spray produced is so fine that it forms a mixture with air which is easily ignited. Engines fitted with a vaporiser of one form or another are intermediate between the petrol engine proper and the oil engines to be described in the next chapter. They differ from petrol engines only in the means for converting a less volatile liquid fuel into vapour.

Engines for Motor-cars

The number of makes of motor-car engines is so great that if details were discussed it would be difficult to know where to stop. We shall, therefore, confine attention in this section to one well-known type, selecting for that purpose the engine made by Wolseley Motors, Limited, of Birmingham. The illustration at the top pf this page shows a view, half in section, of the 16-20 horse-power four-cylinder Wolseley engine, as seen from the water pump and magneto side. Each important part is marked on the drawing with a figure, and the index to parts will enable the construction and mode of operation to be understood without difficulty. The illustration (shown below) shows a similar view from the carburettor and oil-pump side. For the sake of the reader who wishes to examine the construction a little more closely a line drawing of the complete section is given further down this page. In this drawing three pistons are shown in outside view, and one — that on the left — in section.

SECTION OF A 4-CYLINDER PETROL ENGINE, showing carburettor and oil pump.

It will be noticed that the crank case carrying the bearings is in two parts, bolted together and provided with a well in the lower portion in which the lubricating oil collects, and whence it is pumped to other parts of the engine. Below each crank is an oil trough. A small dipper on the connecting rod end enters this oil when the crank is at its lowest point and lubricates the pistons by “splashing”. No lubricating oil should be allowed to enter the cylinder itself if it can be avoided. Under the high temperature of the explosion it would char, leaving a deposit of soot on the ends of the pistons and the inside of the cylinders, and if a particle of this remained red hot from a previous explosion it would cause pre-ignition. Almost invariably a small amount creeps past the piston rings, and the interior has to be cleaned out by an oxy-acetylene blow-pipe flame.

LONGITUDINAL SECTION of a 16-20 horse-power engine.

The valves work in a small combustion chamber on the far side of the drawing, and not, therefore, shown in the figures. They and the method of operating them are shown separately in the diagram shown below.

The adjustment for wear is made by turning a nut, which lengthens the spindle, and differs, therefore, from that shown above depicting an adjustable valve tappet. The valve plunger also has a small piece of compressed fibre inserted to reduce the noise. The valves are ground into their seats with jeweller’s rouge in order to obtain a perfect fit, and occasionally they need to be reground. The sparking plugs are fixed just above the valves, and the order of firing in the four-cylinder engine is 1, 3, 4, 2, this being the order in which the cylinders compress their charges.

The water is caused to circulate by a small centrifugal pump on the same spindle as the magneto. After passing round the cylinder jackets it flows by means of the pipe leading into the top of the radiator, which is fixed just in front of the fan at the very front of the car. This fan draws air through the nest of tubes and aids the cooling. Nevertheless the water in the radiator becomes very hot in warm weather.

TRANSVERSE SECTION OF A 24-30 HORSE-POWER ENGINE.

(A ) Carburettor; (B) Exhaust valve; (C ) Admission valve; (D) Magneto; (E) Sparking plug; (F) Pipe for cooling water; (G) Cam shaft.

The cylinders of this engine are 3 9/16 inches or 90 millimetres bore, and 4¾ inches or 121 millimetres stroke. The speed is 1,200 revolutions a minute, and the speed of the car can be varied from 7 to 28 miles per hour. For higher powers six cylinders rather larger in size are necessary. The power is communicated to the rear axle by various mechanisms which it would be out of place to describe here, but which are, nevertheless, of first-rate importance in considering the car as a whole. It is in this sphere, perhaps, that the greatest difference between a good and a bad car is to be found. So far as engines are concerned, the chief variations occur in the general arrangement. Thus the cylinders may be cast singly or in pairs or in fours. The valves may be in the ends of the cylinders or in combustion chambers at the side. In the Lanchester engine, for example, they are operated by flat “leaf” springs which press upon the ends of the valve spindles just as one might do with the end of the finger; and this engine also has a wick carburettor in which the petrol vapour is drawn through wicks dipping into a reservoir. In some cases the water circulates naturally, and in others it is driven round by a pump. Where extreme lightness is required the crank case may be made of aluminium alloy, and the pistons, instead of being made of cast iron, may be of steel, or even of aluminium alloy. Apart from excellence of material, accuracy of workmanship, and perfect fit, the most essential condition of satisfactory working — and this is true of any kind of high-speed engine — is that all rubbing surfaces should be flooded with oil. It must never be forgotten that in a space of, say 2 feet by 2 feet by 1 foot, energy is being liberated at the rate of 20 horse-power — that is to say, work is being done at the rate of 660,000 ft.-lb. per minute. And if, in this confined space, something goes wrong, so that this energy is not exerted through its proper channels, serious damage will be done.

The Motor-cycle Engine

The motor-cycle engine differs in no important respect from those which have been described save that water cooling is unnecessary. The cylinder is provided with fins, and is exposed freely to the air. The rapid motion of the machine has the same effect as a strong current of air blowing over the surface and carrying away heat as fast as it is produced. Not only is the cylinder lighter than one provided with water jackets, but tank, radiator, and a not inconsiderable amount of piping are rendered unnecessary, reducing both weight and cost of the machine.

A HUMBER MOTOR-CYCLE ENGINE of 3½ horse-power.

The more powerful machines are provided with double-cylinder engines, and these are arranged either opposite to one another or in the form of a V. The latter form is more economical of space and is the most frequently adopted. Two-stroke engines are very popular because of their simplicity, and the reduction of weight which results from the absence of admission and exhaust valves, tappets, and cam shaft.

A TYPICAL V-SHAPED motor-cycle engine of 6 horse-power.

All single-cylinder engines have a crank consisting of a crankpin fixed between two solid flywheels, this, again, economising weight and space. The tank for fuel and lubricating oil is carried under the top bar, so that both can flow to the engine by the action of gravity. The carburettor is fixed in such a position that the supply of oil to the jet is not affected by the inclination of the jet when going up hill, but it does not differ in construction or principle from those used on other types of petrol engine. Similarly the explosive mixture is fired by a spark from either a coil or a magneto, the latter being, perhaps, more frequently fitted.

Engines for Motor-boats

The earliest internal combustion engines used on boats were simply motor-car engines — extremely light, quick-running engines which gave wonderful speeds and led to a great development of racing. For most purposes, however, a heavier, slow-speed engine is to be preferred, and during the last fifteen years engines have been specially designed for the purpose. As these were less economical, there has also been a tendency to use paraffin instead of petrol. The typical motor-boat engine of to-day is, therefore, a small marine engine, using paraffin as fuel, strongly built, and running at a moderate speed. Generally, the cylinders are in a row, because this arrangement takes up the least space transversely, and if the V form is adopted the angle between each cylinder of a pair is, for the same reason, a very small one.

The chief disadvantage that attends the use of an internal combustion engine on a boat is its non-reversibility. It is very important to be able to go ahead or astern at will when manoeuvring in a crowded waterway, and in the ordinary sense the four-stroke engine is non-reversible. On a motor-car there is a complicated system of gearing for which room is provided underneath the car, but in a boat this takes up floor space which cannot well be spared. One method of avoiding it is to use a reversible propeller. In this ingenious device, by merely pulling a lever, the blades of the propeller are twisted round so that, while it still rotates in the same direction, it will propel the boat either ahead or astern as desired. Failing this, the gear box is essential for all four-stroke engines. A two-stroke engine will run equally well in either direction, and to reverse it is only necessary so to advance the spark that a back fire occurs. Generally, this sets the engine running in the opposite direction, but it is not absolutely certain, and, in any case, it entails rather rough usage.

EVINRUDE OUT-BOARD MOTOR.

For very small boats there are several very ingenious arrangements whereby a small motor is fixed to the stern, and a screw propeller driven from it by means of a vertical shaft and bevel wheels. The cylinder is fixed horizontally with a flywheel above and the shaft projecting below. They work on the two-stroke principle because the absence of valves and valve gear simplifies the engine, enables them to be produced at a low cost, and facilitates reversing. Lubrication is effected generally by mixing lubricating oil with the petrol in the proportion of 1 to 20.

One of the best-known “outboard” motors is the Evinrude motor, illustrated above. With a single cylinder this can be made to give from 1½ to 4 horse-power. No rudder is required, the boat being steered by turning the engine about the vertical shaft by means of a short tiller. When the engine is running this gives a very powerful effect; but, of course, it has no influence when the engine is at rest.

Another method which has been developed for the propulsion of barges, and of small boats required to navigate very shallow or weed-choked waters, is the use of an aerial propeller. That is to say, the boat is propelled by a screw working in the air and driven

usually by a two-cylinder two-stroke engine. As the air flung back by the propeller passes over the engine the cylinders do not need to be water-jacketed, but they are provided with fins to increase the cooling surface.

Engines for Aeroplanes

The aeroplane engine is nothing more or less than a motor-car engine in which the highest quality of material and workmanship is combined with the lightest possible construction. When Professor Samuel Pierpont Langley, of the Smithsonian Institution, Washington, made his memorable experiment on mechanical flight in 1896, the lightest steam engine he could construct contained sufficient fuel and water for a journey of one and a half minutes. At the end of that period the model aeroplane sank slowly on the waters of the Potomac, where the experiment was tried. In 1897 Clement Ader, a Frenchman, succeeded in flying about 300 yards, but this remained unnoticed until flying became almost an everyday matter. The brothers Wright flew 200 yards in 1903 and from eleven to thirty miles in 1906. From that year flying on machines heavier than air passed out of the region of occasional experiments into that of regular practice, though apart from the achievements of the Wrights the distances were never more than a few hundred yards.

In these early days, as now, nearly everything depended upon the motor. The Wrights made their own, and so did Glenn Curtiss, who won the speed competition at the Aviation Meeting at Reims in 1909. In that year Hubert Lathom failed to cross the Channel owing to a defect in the motor, while Louis Bleriot was successful because the Anzani engine was reliable. None of these early motors were of more than 25 horse-power. They had three or four cylinders arranged to work on one crank, and in many cases more time was spent in getting the engine to work than in actual flying.

DIAGRAMMATIC TRANSVERSE SECTION of Gnome engine.

In 1910 a great impetus was given to flying by the invention of the Gnome engine, which was not only more reliable, but also more powerful than any which had been used before. The smallest size was of 50 horse-power, and had seven cylinders driving one crank. The cylinders were bolted to a ring fitting over the main shaft, which was fixed, and as the cylinders themselves rotated round the shaft the pistons moved in and out. Remembering that the crank is fixed and that the cylinders alone can move, fix the attention on any one cylinder with its piston and connecting rod as the cylinders rotate. Obviously the piston will move up and down in the cylinder, and if a charge of petrol and air is introduced at the proper moment and exploded the motion will be kept up.

The mode of operation was as follows: the crank case was enclosed and supplied with air and petrol from the carburettor. As each piston (by the motion of the cylinders) was withdrawn, the air and petrol passed through a valve in the head of the piston into the cylinder. On the return of the piston (again by the motion of the cylinders) the mixture was compressed, and since more room for the expanding gases could only be provided by the rotation of the cylinders, that motion was encouraged. As the piston again approached the closed end of the cylinder the exhaust valve in that end opened and the waste gases were swept out. The cycle was, therefore, a four-stroke one.

DIAGRAMMATIC LONGITUDINAL SECTION of a Gnome engine.

The chief advantage of this engine was its extreme lightness — a little over 2 lb. per horse-power. In fact, the weight of a 100 horse-power engine was only 220 lb. The cylinders were not water-jacketed, as the rapid motion through the air kept them sufficiently cool. They were of steel, turned and bored out of solid cylinders so that the sides were only ⅛inch in thickness, with “fins” on the outer surface, to increase the cooling effect. The rotating cylinders themselves served as a flywheel, giving a remarkably steady effect. It occupied a very small space, the 80 horse-power seven-cylinder type being only about 2 feet 6 inches in diameter and less than 1 foot from back to front at the thickest part.

Against these advantages there were certain objections. The lubricating oil in the crank chamber was flung outwards by centrifugal force, and passed through the valve in the piston with the air and petrol. Some of it was flung out through the exhaust valve while that which remained was liable to be charred by the temperature of explosion. This caused premature ignition, interfered with regular sparking by depositing soot on the sparking plug, and choked up the exhaust valve. In spite of these defects it was by far the most popular aeroplane engine in 1912, when the makers introduced several important improvements. The valve in the piston was abolished, ports were provided in the cylinder at a point where they were covered and uncovered by the piston. The exhaust valve remains open for a short time after the waste gases have been expelled, and a certain amount of air enters the cylinder. The valve then closes, the ports in the cylinder are uncovered, and a rich mixture of petrol and air is forced in by a pump. With these alterations the speed can be varied by means of a throttle valve from 1,000 to 200 revolutions a minute, and though powerful rivals have arisen the engine is still used on aeroplanes to-day.

At the military trials in England in 1912 the prize for speed was won by Samuel F. Cody on a biplane of his own construction, driven by a 120 horse-power Austro-Daimler motor. The following year, in the War Office reliability trials of aeroplane engines, only one succeeded in passing the test — a continuous run of twenty-four hours — and that was the Green engine. All the wonderful progress made during the war was under the stress of military necessity, and the details were known only to those immediately concerned in their production and use. It may be said, however, that in addition to the Gnome and the Green engines, and the R.A.F. designed at the Royal Aircraft Factory, nearly every well-known type of motor-car engine has been adapted for aeroplanes. The Rolls-Royce is popular on account of its reliability; the improved form of the Austro-Daimler, known as the Beardmore, is being made in large numbers; the Sunbeam, and several others are also used.

The Gnome remains the only radial, the only rotary, and the only air-cooled motor. So long as the number of cylinders does not exceed six, the ordinary vertical type is preferred; but for any number beyond cylinders are so arranged that each pair forms a V and works on the same cranks as shown at the bottom of this page.

In most of them the valves are situated in the tops of the cylinder, rendering a combustion chamber unnecessary and economising weight and space. They are opened by rocking levers operated from a cam shaft in the usual way. Every possible device is employed to reduce weight. The crank cases are of aluminium alloy, and so are the pistons. The water jackets are of thin copper or aluminium. The connecting rods are of steel, “drop-forged” in the shape of an H-girder, tapering towards the upper end, giving the maximum strength with the minimum weight. Wherever metal is not needed it is cut away or scooped out, involving the most minute and exact calculations and requiring the most skilful workmanship. In war time cost is of no consequence; men are not content to proceed a step at a time; they are rarely satisfied with a small improvement; if there is any advantage to be gained beyond that possessed at the moment, it must be pursued without a moment’s delay.

What wonderful things these aeroplane engines are! Here is one with six cylinders, which two men can lift, capable of giving 120 horse-power. There is another, V-pattern, with twelve cylinders arranged in six pairs, not beyond the capacity of four men to lift, and yet capable of being coaxed up to 300 horsepower, or of performing work at the rate of 9,900,000 ft.-lb. per minute. The crank shaft rotates 1,000 times a minute. Six times in every revolution does an explosion speed the shaft on its way. There are, therefore, 6,000 explosions every minute, every one timed exactly, so that they occur at equal intervals and with a regularity which is astounding.

DIAGRAM SHOWING a V-type of aeroplane engine.

You can read more on “Aircraft Engines”, “Marine Engines and Steamships” and “Story of the Motor Car” on this website.

You can read more on “Aero Engines of the Great War” and “Evolution of the Aero Engine” in Wonders of World Aviation