THE PETROL ENGINE
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The Petrol Engine
A Text-book dealing with the Principles
of Design and Construction, with
a Special Chapter on the
Two-stroke Engine
By
FRANCIS JOHN KEAN
B.SC. (LOND.); M.I.M.E.
First-Class Honourman in Engineering; Head of the Motor Car Engineering
Department of the Polytechnic School of Engineering, Regent Street,
London, W.; Formerly Lecturer on Experimental Engineering
at McGill University, Montreal, Canada
71 ILLUSTRATIONS
[Colophon]
London
E. & F. N. SPON, LIMITED, 57 HAYMARKET
New York
SPON & CHAMBERLAIN, 123 LIBERTY STREET
1915
CONTENTS
PAGE
LIST OF ILLUSTRATIONS ix
PREFACE xiii
CHAPTER I
GENERAL PRINCIPLES—
Explosive Mixtures 1
The Meaning of Suction 2
The Meaning of Compression 3
The Meaning of a Stroke 3
The Otto Cycle 5
CHAPTER II
DESCRIPTION OF A TYPICAL PETROL ENGINE—
The Cylinder 8
CHAPTER III
ENGINE DETAILS—
The Piston 17
The Connecting Rod 21
The Crankshaft 23
The Flywheel 25
CHAPTER IV
THE VALVES—
Poppet Valves 29
Sleeve Valves 31
The Camshafts and Eccentric Shafts 33
The Timing Wheels 37
The Crankchamber 38
CHAPTER V
THE CARBURETTOR AND CARBURATION—
The Float Chamber 44
The Petrol Jet and Choke Tube 46
The Mixing Chamber and Throttle Valve 47
Recent Improvements in Carburettors 47
Pressure Feed and Gravity Feed 50
CHAPTER VI
IGNITION AND IGNITION DEVICES—
The Sparking Plug 51
The High Tension Magneto 52
The Ignition Coil 57
Wiring Diagram for Magneto Ignition System 60
Wiring Diagram for a Coil Ignition System 60
Timing the Ignition 62
CHAPTER VII
LUBRICATION—
Properties of Oils 63
Splash System of Lubrication 63
Improved System of Splash Lubrication 64
Forced Lubrication 65
CHAPTER VIII
COOLING—
Natural or Thermo-Syphon Circulation 69
Forced or Pump Circulation 71
CHAPTER IX
THE POINTS OF A GOOD ENGINE—
Choosing the Number of Cylinders 75
The Question of the Valves 77
Economy and Durability 79
CHAPTER X
TWO-STROKE ENGINES—
The Two-port Two-stroke Engine 80
The “Kean” Duplex Air Scavenging Engine 85
The Twin-cylinder Two-stroke Engine 96
CHAPTER XI
HORSE-POWER AND THE INDICATOR DIAGRAM—
Work 98
Power 98
Brake Horse-power 99
Rated Horse-power 100
Indicated Horse-power 101
The Indicator Diagram 102
CHAPTER XII
LIQUID FUELS—
Petrol 108
Benzol 108
Alcohol 109
Paraffin 109
Thermal Efficiency 110
APPENDIX
ENGINE TROUBLES 113
TIMING THE IGNITION 115
INDEX 117
LIST OF ILLUSTRATIONS
FIG. DESCRIPTION. PAGE
1. Diagram to explain the meaning of _Suction_ 1
2. Diagram to explain the meaning of _Compression_ 2
3. Otto Cycle. The Suction Stroke 3
4. Otto Cycle. The Compression Stroke 4
5. Otto Cycle. The Power Stroke 5
6. Otto Cycle. The Exhaust Stroke 6
7. General arrangement of a Modern Petrol Engine 9
8. Sectional Drawing of a =T=-headed Cylinder 12
9. Outside View of a Water-jacketed Cylinder 13
10. Stud 14
11. Bolt 14
12. Setscrew 14
13. Motor-cycle Engine with air-cooled Cylinder 14
14. Aeroplane Engine Cylinder 15
15. Cast-iron Piston 18
16. Method of fixing Gudgeon Pin 19
17. Three forms of Piston-head 19
18. Connecting Rod in the form of a Stamping 20
19. Connecting Rod turned from a solid Bar of Steel 21
20. Crankpin and Crankwebs 22
21. Four-throw Crankshaft 23
22. Motor-cycle Crankpin 24
23. Balanced Crank 25
24. Sketch showing the unbalanced portion of a Crank 25
25. Balanced Two-throw Crankshaft 26
26. Force acting on a Flywheel Rim 26
27. Built-up Steel Flywheel 27
28. Flywheel turned from a Steel Stamping 28
29. General arrangement of a Poppet Valve 30
30. Sectional Drawing of the Cylinder of a Sleeve-valve
Engine 31
31. Sectional Drawing of the Cylinder of a Sleeve-valve
Engine 32
32. Poppet Valve-head, showing Slot for Grinding-in purposes 34
33. Inlet and Exhaust Valve Cams 34
34. Eccentric Sheave and Rod for a Sleeve Valve 36
35. A Pair of Timing Wheels 37
36. A Crank Chamber, outside end view 39
37. A Crank Chamber, sectional view 39
38. General arrangement of the Carburetting Plant 43
39. Sectional Drawing of a Carburettor of the _Jet_ Type 44
40. Plain Form of the Choke Tube 47
41. Petrol Jet for _atomising_ the Petrol 48
42. Compensated Petrol Jet 48
43. Automatic Spring-controlled Extra-air Valve 49
44. Plan View of Automatic Extra-air Valve 49
45. Sectional Drawing of a Sparking Plug 51
46. A Sparking Plug 52
47. Outside View of a High-tension Magneto 52
48. View of High Tension Magneto showing Distributor and
Contact Breaker 53
49. End View of High Tension Magneto 54
50. An Ignition Coil 56
51. An Ignition Coil Case 57
52. Low Tension Contact Breaker for Coil Ignition (Wipe
Form) 58
53. Wiring Diagram for Four Cylinder Engine with Magneto
Ignition (High Tension) 60
54. Wiring Diagram for Four Cylinder Engine with Trembler
Coil Ignition 61
55. Improved System of Splash Lubrication 64
56. Sectional View of Connecting Rod end, showing Scoop
and Oil Trough 65
57. Forced Lubrication System 66
58. Sectional View of Rotary Oil Pump 67
59. A Rotary Oil Pump 67
60. Thermo-syphon Water Cooling System 69
61. Forced Water Circulation by means of a Pump 70
62. Forms of Water Piping 74
63. Two-port Two-stroke Engine with Crankchamber Compression 81
64. Diagrammatic Sketch of a Duplex Two-stroke Air
Scavenging Engine 87
65. General Arrangement of the “Kean” Two-stroke
Engine 91
66. Twin-cylinder Two-stroke Engine with Crankchamber
Compression 97
67. Petrol Engine Brake 100
68. Force-space or “Work” Diagram 103
69. Petrol Engine Indicator Diagram Four-stroke Cycle 105
70. Petrol Indicator Diagram for a Two-stroke Engine 106
71. Diagram of Valve-setting 116
PREFACE
This book deals with _principles_. 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 the _principles_ of design and construction which
underlie all current practice. If a man understands, for example, the
construction of the _elements_ of 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, an _accessory_, although of course a most important one. I
hope that the accounts of my experiments with the _two-stroke_ will
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 fundamental _principles_.
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
CHAPTER I
GENERAL PRINCIPLES
[Illustration: FIG. 1.—DIAGRAM TO EXPLAIN THE MEANING 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 or _evaporate_. We say that the liquid petrol has
been vaporized or turned into _petrol vapour_. A mixture of air and
petrol vapour can be ignited and burnt, the rate of burning being
affected by the _strength_ of 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 burnt at such
a rate that the combustion is almost instantaneous, i.e., it will
_explode_. This mixture of air and petrol vapour would then be referred
to as an _explosive mixture_ and would be suitable for supplying to the
cylinder of a petrol engine.
[Illustration: FIG. 2.—DIAGRAM TO EXPLAIN THE MEANING 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. 2 we will
realize that there is apparently some force inside the cylinder which
is trying to _suck_ the 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 gases in it became
equal to atmospheric pressure, when no more air could enter, because
there would be no _excess of pressure_ to force it in. In technical
language we would say, “the piston has =sucked in a charge= of air”
through the tap or valve.
[Illustration: 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 are _compressing_
the 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 now =compressed the charge=” of gas
within the cylinder.
[Illustration: FIG. 4.—OTTO CYCLE. THE COMPRESSION STROKE.]
=The Meaning, of a Stroke.=—In an engine such as is shown
diagrammatically in Figs. 3 and 4, when the piston P moves from its
topmost position in the cylinder down to its very lowest position we
say it has completed a _downstroke_, and when it moves upwards from
its lowest to its highest position we say the piston has completed an
_upstroke_. 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 the _clearance space_. It is
also referred to as the _combustion 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 outer _dead-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 (or _two_ revolutions) made by the engine. The
“Otto” cycle is therefore usually referred to as the _four-stroke_
cycle. In the accompanying diagrams (Figs. 3, 4, 5, and 6) we show in
diagrammatic form the interior of a petrol engine cylinder fitted with
mushroom type valves.
[Illustration: 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 the _carburettor_
to the cylinder and is called the _induction 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 the exhaust valve to the _silencer_ is called the
_exhaust pipe_. The cycle of operations is as follows:—
[Illustration: FIG. 6.—OTTO CYCLE. THE EXHAUST STROKE.]
(1) =On the first downstroke= made 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 upstroke= made 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 downstroke= made 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 the _power 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 three _idle_ strokes. 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 upstroke= of 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.