PAGEList of IllustrationsixPrefacexiiiCHAPTER IGeneral Principles—Explosive Mixtures1The Meaning of Suction2The Meaning of Compression3The Meaning of a Stroke3The Otto Cycle5CHAPTER IIDescription of a Typical Petrol Engine—The Cylinder8CHAPTER IIIEngine Details—The Piston17The Connecting Rod21The Crankshaft23The Flywheel25CHAPTER IVThe Valves—Poppet Valves29Sleeve Valves31The Camshafts and Eccentric Shafts33The Timing Wheels37The Crankchamber38CHAPTER VThe Carburettor and Carburation—The Float Chamber44The Petrol Jet and Choke Tube46The Mixing Chamber and Throttle Valve47Recent Improvements in Carburettors47Pressure Feed and Gravity Feed50CHAPTER VIIgnition and Ignition Devices—The Sparking Plug51The High Tension Magneto52The Ignition Coil57Wiring Diagram for Magneto Ignition System60Wiring Diagram for a Coil Ignition System60Timing the Ignition62CHAPTER VIILubrication—Properties of Oils63Splash System of Lubrication63Improved System of Splash Lubrication64Forced Lubrication65CHAPTER VIIICooling—Natural or Thermo-Syphon Circulation69Forced or Pump Circulation71CHAPTER IXThe Points of a Good Engine—Choosing the Number of Cylinders75The Question of the Valves77Economy and Durability79CHAPTER XTwo-stroke Engines—The Two-port Two-stroke Engine80The “Kean” Duplex Air Scavenging Engine85The Twin-cylinder Two-stroke Engine96CHAPTER XIHorse-power and the Indicator Diagram—Work98Power98Brake Horse-power99Rated Horse-power100Indicated Horse-power101The Indicator Diagram102CHAPTER XIILiquid Fuels—Petrol108Benzol108Alcohol109Paraffin109Thermal Efficiency110APPENDIXEngine Troubles113Timing the Ignition115INDEX117

fig.Description.page1.Diagram to explain the meaning ofSuction12.Diagram to explain the meaning ofCompression23.Otto Cycle. The Suction Stroke34.Otto Cycle. The Compression Stroke45.Otto Cycle. The Power Stroke56.Otto Cycle. The Exhaust Stroke67.General arrangement of a Modern Petrol Engine98.Sectional Drawing of aT-headed Cylinder129.Outside View of a Water-jacketed Cylinder1210.Stud1411.Bolt1412.Setscrew1413.Motor-cycle Engine with air-cooled Cylinder1414.Aeroplane Engine Cylinder1515.Cast-iron Piston1816.Method of fixing Gudgeon Pin1917.Three forms of Piston-head1918.Connecting Rod in the form of a Stamping2019.Connecting Rod turned from a solid Bar of Steel2120.Crankpin and Crankwebs2221.Four-throw Crankshaft2322.Motor-cycle Crankpin2423.Balanced Crank2524.Sketch showing the unbalanced portion of a Crank2525.Balanced Two-throw Crankshaft2626.Force acting on a Flywheel Rim2627.Built-up Steel Flywheel2728.Flywheel turned from a Steel Stamping2829.General arrangement of a Poppet Valve3030.Sectional Drawing of the Cylinder of a Sleeve-valve Engine3131.Sectional Drawing of the Cylinder of a Sleeve-valve Engine3232.Poppet Valve-head, showing Slot for Grinding-in purposes3433.Inlet and Exhaust Valve Cams3434.Eccentric Sheave and Rod for a Sleeve Valve3635.A Pair of Timing Wheels3736.A Crank Chamber, outside end view3937.A Crank Chamber, sectional view3938.General arrangement of the Carburetting Plant4339.Sectional Drawing of a Carburettor of theJetType4440.Plain Form of the Choke Tube4741.Petrol Jet foratomisingthe Petrol4842.Compensated Petrol Jet4843.Automatic Spring-controlled Extra-air Valve4944.Plan View of Automatic Extra-air Valve4945.Sectional Drawing of a Sparking Plug5146.A Sparking Plug5247.Outside View of a High-tension Magneto5248.View of High Tension Magneto showing Distributor and Contact Breaker5349.End View of High Tension Magneto5450.An Ignition Coil5651.An Ignition Coil Case5752.Low Tension Contact Breaker for Coil Ignition (Wipe Form)5853.Wiring Diagram for Four Cylinder Engine with Magneto Ignition (High Tension)6054.Wiring Diagram for Four Cylinder Engine with Trembler Coil Ignition6155.Improved System of Splash Lubrication6456.Sectional View of Connecting Rod end, showing Scoop and Oil Trough6557.Forced Lubrication System6658.Sectional View of Rotary Oil Pump6759.A Rotary Oil Pump6760.Thermo-syphon Water Cooling System6961.Forced Water Circulation by means of a Pump7062.Forms of Water Piping7463.Two-port Two-stroke Engine with Crankchamber Compression8164.Diagrammatic Sketch of a Duplex Two-stroke Air Scavenging Engine8765.General Arrangement of the “Kean” Two-stroke Engine9166.Twin-cylinder Two-stroke Engine with Crankchamber Compression9767.Petrol Engine Brake10068.Force-space or “Work” Diagram10369.Petrol Engine Indicator Diagram Four-stroke Cycle10570.Petrol Indicator Diagram for a Two-stroke Engine10671.Diagram of Valve-setting116

This book deals withprinciples. There are many books which give a descriptive account of existing types of engines, but my object in writing this volume has been to assist the reader to obtain thoroughly sound notions of theprinciplesof design and construction which underlie all current practice. If a man understands, for example, the construction of theelementsof a carburettor and how they ought to perform their several functions, he should have no difficulty in understanding any special type of carburettor placed upon the market. In dealing with the subject of ignition I have purposely avoided any detailed explanation of the manner in which the spark discharge is produced, because I felt that it introduces new ideas and probably causes the reader to lose sight of the fact that the magneto is only, after all, anaccessory, although of course a most important one. I hope that the accounts of my experiments with thetwo-strokewill be of some service to inventors and others; the many extraordinary breakdowns, defects and adventures encountered during this period of my career have not been inserted because they would undoubtedly cause the reader to forget, for the time being, his fundamentalprinciples.

My colleague, Mr. Oliver Mitchell, who lectures at the Polytechnic on “Motor Car Management and Inspection,” has read through the proofs for me and very kindly suggested several small additions to the text, which I have incorporated; he also suggested the insertion of the valve-setting diagram in the Appendix. My thanks are due to Mr. Mitchell for his services and also to my wife for her assistance in the preparation of the Index.

FRANCIS JOHN KEAN.

The Polytechnic School of Engineering,Regent Street, London, W.July, 1915.

THE PETROL ENGINE

Fig. 1.—Diagram to Explain theMeaning of “Suction.”

Explosive Mixtures.—If a small quantity of liquid petrol or benzol be placed in an open vessel and exposed to a current of air it will quickly disappear orevaporate. We say that the liquid petrol has been vaporized or turned intopetrol vapour. A mixture of air and petrol vapour can be ignited and burnt, the rate of burning being affected by thestrengthof the mixture. The strength of the mixture is determined by measuring the respective volumes of air and petrol vapour present in a known volume of the mixture. It is possible to form a mixture of air and petrol vapour in such proportions that when ignited by an electric spark it will be completely burntat such a rate that the combustion is almost instantaneous, i.e., it willexplode. This mixture of air and petrol vapour would then be referred to as anexplosive mixtureand would be suitable for supplying to the cylinder of a petrol engine.

Fig. 2.—Diagram to Explain theMeaning of “Compression.”

The Meaning of Suction.—Imagine an iron cylinder A (Fig.1) held down on a rigid base C and fitted with a gas-tight piston B. If we pull the piston down sharply to the position shown in Fig.2we will realize that there is apparently some force inside the cylinder which is trying tosuckthe piston up again. The fact that the piston is being withdrawn and no more air or gas admitted above it to fill up the volume it has displaced on its descent causes a partial vacuum in the cylinder. Now if by means of a tap or valve of some kind we could put the cylinder in communication with the atmosphere, air would rush in and fill up the cylinder until the pressure of the gasesin it became equal to atmospheric pressure, when no more air could enter, because there would be noexcess of pressureto force it in. In technical language we would say, “the piston hassucked in a chargeof air” through the tap or valve.

Fig. 3.—Otto Cycle.The Suction Stroke.

The Meaning of Compression.—Close the tap or valve and push the piston up again sharply to its original position of Fig.1. You will now encounter considerable resistance and experience a force pushing down against you because you are reducing the volume of the gas and thereby increasing its pressure; that is to say, you arecompressingthe gas, because you are now making an amount of gas that recently occupied the whole cylinder fit itself into the small space between the top of the cylinder and the crown of the piston. In technical language you would say, “the piston has nowcompressed the charge” of gas within the cylinder.

Fig. 4.—Otto Cycle.The Compression Stroke.

The Meaning, of a Stroke.—In an engine such as isshown diagrammatically in Figs.3and4, when the piston P moves from its topmost position in the cylinder down to its very lowest position we say it has completed adownstroke, and when it moves upwards from its lowest to its highest position we say the piston has completed anupstroke. The length of the piston’s stroke is equal to twice the length of the crank radius R, and is measured by observing the distance moved by the piston in travelling from its highest position in the cylinder to its lowest or vice versa. The space existing above the piston between it and the cylinder head when the piston has reached its highest position in the cylinder is called theclearance space. It is also referred to as thecombustion chamber, or chamber in which the petrol gas is exploded. When the piston is either at the top or bottom of its stroke the crank radius R and connecting rod T are in one and the same straight line; under these conditions we say the crank is on its inner or outerdead-centre.

The Otto Cycle.—Most petrol engines operate on what is known as the “Otto” cycle, in which the cycle of events is completed once in every four strokes (ortworevolutions) made by the engine. The “Otto” cycle is therefore usually referred to as thefour-strokecycle. In the accompanying diagrams (Figs.3,4,5, and6) we show in diagrammatic form the interior of a petrol engine cylinder fitted with mushroom type valves.

Fig. 5.—Otto Cycle.The Power Stroke.

In studying the figures we assume the engine is being cranked round by hand in the direction of the arrow while we view it from the “flywheel” end (i.e. the end adjacent to the driver’s seat), then A is the pipe which leads the mixture of air and petrol vapour from thecarburettorto the cylinder and is called theinduction pipe. C is the cylinder, P the piston, I the inlet valve, E the exhaust valve, T the connecting rod, R the crank, and S the sparking plug. The pipe B which leads the burnt gases from theexhaust valve to thesilenceris called theexhaust pipe. The cycle of operations is as follows:—

Fig. 6.—Otto Cycle.The Exhaust Stroke.

(1)On the first downstrokemade by the piston a suction effect or partial vacuum is produced in the cylinder; the air and petrol vapour in the induction pipe being at atmospheric pressure, which is in excess of that now existing in the cylinder, flow into the cylinder as soon as the inlet valve I is opened by the engine mechanism. At the end of this,the suction stroke, the inlet valve closes and traps the charge of explosive mixture in the engine cylinder. This is shown in Fig.3.

(2)On the first upstrokemade by the piston the charge of explosive mixture is compressed ready for firing. Both valves are shut. This is shown in Fig.4.

(3)On the second downstrokemade by the piston the sparking plug S passes a spark which explodes the charge at the very commencement of the downward movement of the piston. The force of the explosion drives the piston downwards, doing useful work. Both valves are shut. This is thepower stroke, and sufficient power must be developed on this stroke not only to do the work required from the engine but also to tide it over the other threeidlestrokes. On this stroke the piston drives the crank by means of the connecting rod, but on the other three strokes of the cycle the crank has to drive the piston by means of the power or energy stored in the engine flywheel on the power stroke. Towards the end of the power stroke (or explosion stroke) the engine mechanism opens the exhaust valve E and allows part of the burnt gases to escape to the silencer along the exhaust pipe. This is shown in Fig.5.

(4)On the second upstrokeof the cycle the piston pushes the remaining burnt gases out of the cylinder through the exhaust valve. When the piston reaches the top of its stroke the exhaust valve closes. This is shown in Fig. 6. The cycle of operations then begins again, giving one power stroke and three idle strokes each time as already described.

For the purpose of explaining the cycle of operations we have considered only a diagrammatic sketch of an imaginary motor-car engine, but in Fig.7we illustrate an up-to-date motor-car engine. In the first place we note the position and arrangement of the four water-cooled cylinders, A1, A2, A3, A4, containing their pistons and mushroom type valves. These are conveniently placed in a vertical position and mounted on top of the crankchamber C, to the bottom of which is attached the oil-base B. At the front of the engine are shown the timing wheels in their casing E, and at the rear end the flywheel F. The starting-handle connexion is at S, the fan pulley being shown at M. The high tension magneto which supplies the current to the sparking plugs is shown at H, and I is the induction pipe connected to the carburettor K. The water circulating pump is on the off side of the engine and does not appear in the illustration, but L1is the inlet water pipe leading from the radiator (not shown) to the water pump, and L2is the delivery pipe from the pump to the respective cylinder jackets, L3being the outlet water pipe. The exhaust pipe is shown at D, and the oil pump at P. The valve springs, valve tappets and guides can also be clearly seen. In examining the several parts of the engine in detail we must not lose sight of their respective positions in the general arrangement view of Fig.7.

Fig. 7.—General Arrangement of a Modern Petrol Engine.

The Cylinder.—Probably one of the most important parts of an engine is the cylinder. As we have already seen, it is inside the cylinder that the charge of petrolvapour and air is exploded and completely burnt. The heat energy of the petrol mixture which is liberated by the explosion is immediately transformed into mechanical work and propels the piston forward like a projectile from a gun. But we must also notice that our present-day arrangements (clever as they are) are by no means perfect, and we cannot, even under the most favourable circumstances, convert more than aboutone-thirdof the heat energy of the petrol mixture into the mechanical energy of the moving piston. Of the remaining two-thirds of the heat, part is used up in heating the cylinder walls, the piston and the valves, and the remainder goes out with the exhaust gases to the silencer, finally escaping to the outside air. Thus two important facts are brought to our notice:—

(1) The reason why we use petrol to drive our motor-cars is because petrol (and certain other liquid fuels such as benzol, etc.) contains within itself a store of energy which can be liberated as heat when the fuel is burnt or exploded in the presence of air in the engine cylinder.

(2) At the present day, even with our most up-to-date contrivances, we cannot make use of two-thirds of the available heat in our petrol. Instead of being able to turn this heat into useful mechanical work, we are compelled to throw it away—to waste it. Further than that, we have to make special provision to ensure that it shall be wasted as quickly as possible and as easily as possible. We take out the greatest amount that we can possibly turn into work and then hasten to dissipate the remaining two-thirds. We cast hollow chambers on the outside of our cylinders through which we circulate cold water to keep down the heat in the cylinder walls; if our cylinder walls and piston get too hot our engine may seize up, therefore we must cool them to ensure satisfactory running. Again we make large exhaust valves and provide a free escape through the silencer for the exhaust gases, so that when we have snatched our useful one-third of the heat supply we may throw the remainder away into the atmosphere as rapidly as possible.—this part is of no use to us, we cannot turn it into work, then why let it stay here and heat our cylinder walls and piston still further?

It is a good plan to extend this hollow chamber, containing the water in circulation, at least round the whole of the combustion chamber and all round the inlet and exhaust valve passages and down the barrel of the cylinder as far as the walls are likely to come into contact with the hot gases from the explosions. We refer to this hollow chamber, with its circulating water, as thewater-jacketof the cylinder. It is not absolutelyessentialto have our cylinder water-jacketed, especially with small engines for motor-cycles and engines for aeroplanes which have revolving cylinders,but it is practically essential in nearly all other cases. Even in the special cases mentioned it is found necessary to form special heat radiating fins on the outside of the heated walls to assist in dissipating or getting rid of the surplus heat and preventing seizure of the piston within the cylinder. These fins are clearly seen on the cylinder of the motor-cycle engine shown in Fig.13.

Thus we may say that motor-car engine cylinders are bound to be water-jacketed, i.e., to have a hollow space round them containing water in circulation. The cylinders themselves are nearly always made in the form of iron castings and the jacket spaces form part of thecylinder castingas a general rule, but occasionally the water-jacket space is formed by attaching plates or tubes to the cylinder casting by means of bolts or screws—not an easy thing to arrange successfully, as it requires water-tight joints.

The procedure for manufacturing a motor-car cylinder is first of all to design and calculate the proportions of the various parts and get out a set of working drawings. From these drawings we getpatternsandcore-boxesmade in wood. The patterns are the exact shape of the finished cylinder on theoutside, and the core-boxes are the exact shape of theinsideof the finished cylinder (except in so far as allowance has to be made for parts which must afterwards be machined).

The patterns are pushed down into the moulding sand in the foundry, and when withdrawn leave their impression, thus formingmoulds. The core-boxes are filled with sand, which when withdrawn furnishes us with masses of sand that are the counterpart of the interior of the cylinder in shape. Thesecoresare supported centrally in the mould (which is usually in halves, ormorethan two parts), while the molten iron is poured into the intervening space to form the ironcasting. When the casting has cooled down the sand can be cleaned off quite easily. One set of patterns and core-boxes will thus produce quite a number of cylinder castings, each being similar in every respect to the other, the processbeing a quick and fairly cheap method of reproduction. Later on the cylinder barrel has to be machined and bored out true to very fine limits by the use of boring tools and some kind of boring machine or lathe. The flanges or flat faces have to be planed true in a planing machine and the valve stem guides and valve seatings must be carefully and truly machined to correct size and shape.

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