| GAS
ENGINES
A gas engine is an internal combustion engine which uses blast
furnace gas, producer gas, natural gas and others as fuel.
As it was a German engineer, Dr. Otto who, in 1876, built the first
gas engine, his name is used to call a special cycle of operations.
'-Thus the Otto cycle, or four cycle, is a four-stroke cycle for
internal combustion engines that consists of induction stroke, compression
stroke, power stroke and exhaust stroke, two revolutions of the
crankshaft being necessary to complete the cycle of events.
Modern gas motors are of single, twin and multicylinder type.
The cylinder is equipped with two valves which are alternately
opened at the right moment by a cam operated by a camshaft.
In the suction stroke, the piston starts its downward movement
in the cylinder and by the action of a cam, the inlet valve opens
slightly before top dead centre. The mixture is drawn into the cylinder
from the carburettor and the inlet valve closes after the piston
has completed its downward stroke.
In the compression stroke, the piston ascends the cylinder and
as the inlet and outlet valves are closed, the mixture is compressed
within the cylinder. As the piston gets to the end of the upstroke
and the gases are wholly compressed, the spark is produced in the
cylinder igniting the charge.
The resulting explosion from this charge makes the gases expand
very quickly, the pressure rises, and the gases act with great force
on the top of the piston driving it down. This is the power stroke.
In the last stroke - exhaust stroke - the piston travels up the
cylinder and the burnt gases are forced out through the open exhaust
valve into the exhaust system. When the piston reaches the end of
its upstroke, the exhaust valve closes and the cycle is complete
to start again.
The first practical gas engine was built in 1860 by a Frenchman
named Lenoir, but as it was largely improved by Dr. Otto, his name
was given to its cycle of operations.
He made his first gas engine in
the year 1876. It consisted of a single cylinder, a small combustion
chamber and two ports to let the gas in and expel the products of
combustion. A water jacket surrounded the cylinder keeping it cool.
A piston, moving within the cylinder was connected to a simple crank
and shaft by a connectingrod. The forward motion thus imparted to
the piston was turned into a rotary movement by the crank. A heavy
flywheel kept the movement going and compressed the charge. The
latter was ignited by a hot tube. After the explosion took place
the exhaust port served as outlet for the burnt gases.
DIESEL
ENGINES
A Diesel engine, or compression-ignition engine, is an internal
combustion engine which requires no electric spark to ignite the
charge in the cylinder. It has neither carburettor nor ignition
system and the fuel is injected in the form of a very fine spray,
by means of a nozzle, into the combustion chamber where it is ignited
by the heat of compression of the air with which the chamber is
already charged.
A four-stroke Diesel engine resembles a gasoline engine as it works
on the four-stroke cycle, that is: admission, compression, power
and exhaust.
In the moment the piston gets down on the admission stroke, the
depression created conveys a charge of air into the cylinder through
the inlet valve which opens just before top dead centre.
Once the piston has passed the bottom dead centre and is beginning
to ascend, the admission valve closes and the movement of the piston
compresses the air charge in the cylinder causing a quick rise of
temperature.
Before the second stroke is over, the charge of fuel oil is gradually
injected into the cylinder by an injector.
The burning of the air-fuel charge makes the gases expand; they
push the piston downwards and produce the power stroke.
Before the piston has got to bottom dead centre, the exhaust valve
opens and, as the piston goes up again, the burnt gases are forced
out through the exhaust pipes and silencer.
Just before top dead centre the inlet valve opens and the cycle
begins again.
On account of the high compression required to ignite the charge,
the fuel must be injected at a very high pressure to penetrate the
dense volume of air, and therefore a special type of injection pump
is used.
A small amount of fuel is poured through a nozzle inserted in the
combustion chamber. The fuel is raised from the principal tank by
means of a pump and is taken by a pipe-line passing through some
filters to the injection system.
The injector consists of a main body with a nozzle at one end. A
spring needle keeps the nozzle closed. When the pressure from the
injection pump is enough, the needle valve is lifted off its place
and through very small holes or through an annular space, the fuel
injection takes place.
Diesel engines are widely used nowadays in heavy industry, electric
generating plants, marine and traction services, motor-trucks, airplanes
and so on.
THE
MOTOR-CAR
The motor-car, which marks the beginning of the speedy age in which
we live, is possibly one of the most complicated machines that are
mass produced.
Before a car begins to take shape, the different parts must be
collected ready for assembly, each one being built by a specialist
in his own type of work.
The main parts of a motor-car are: the engine, chassis frame, radiator,
bumper, mudguards, head-lamps, petrol pump, steeringwheel, gear-box,
clutch and brake pedals, accelerator pedals, gear lever, springs,
petrol-tank, propeller shaft, hand brake, and so on.
In mass-production factories, a mechanical conveyor system is used
for carrying the parts from one department to another.
Various metals are used in the foundry ranging from aluminum alloys
for gear-boxes and other cases to fine steels for crankshafts. Samples
of the metals are subject to test before the castings are made as
a metal may be able to resist stretching or crushing but not sudden
blows, that is, it may be strong but brittle..
Complete engine units that are either of a new design or contain
new parts , are run under-all kinds of abnormal conditions on experimental
test benches equipped with numberless special devices which record
various data such as the horse-power developed, the number of revolutions
of the engine per minute and so on.
The work of the engine begins in the foundry where such parts as
crankcases, cylinder blocks, cylinder heads, pistons, connecting-rods,
axle casings and the shells of gear boxes are made.
The exterior accessories such as the ignition coil and air cleaner
are added during assembly work. Valves are among the small but important
parts that must be made before the engine assembly can be completed.
The assembly begins with the crankshaft by which the reciprocating
or up-and-down motion of the piston is turned into a rotary or round
and round motion. The crankshaft revolves in main bearings which
are in two semicircular pieces, each being carried in each half
of the crankcase.
If the engine is fitted with side valves the camshaft will fit
into the crankcase. The rotation of the camshaft causes the cams
in their correct order to lift the tappets by which the valves are
opened for a given time according to the design of the cams.
After fitting certain small items, the lower part of the crankcase
can be attached. Then follow the timing pinions and their case,
the next step being to bolt the cylinder head into position. There
are still some important outer items - dynamo, carburetor and sparking-plugs
- to be fixed.
The clutch mechanism is keyed to the rear end of the crankshaft
and then, encased in its aluminium alloy casing. At the rear of
the clutch mechanism, the gear-box completes the engine unit. The
controls such as the gear lever and clutch pedal may be carried
on the engine unit or fitted to other parts of the chassis and linked
with control arms on the engine unit.
Once the engine is completed, a number of adjustment operations
is required before the engine can receive its running test.
The earliest predecessor of the motor-car is believed to have been
a steampropelled vehicle built about 1770 by Nicholas Cugnot but
modern motor-cars did not come into being until after the patenting
of Daimler's internal combustion engines in 1887. In 1893, Henry
Ford finished his first engine and some ten years after his work
was in the required conditions to be offered to the public. He became
the king of the motor-car industry and held the ideal that everybody
ought to have a car so as to satisfy the necessity of overcoming
time and distance.
Henry Ford, the promoter of the motor-car industry, was born near
Detroit on the 30th of July of 1863. He was the son of a farmer
and his natural liking for mechanics led him to think of new methods
for making the work on the farm lighter.
In 1893, when he was thirty years old, he finished his first engine
but devoted his next ten years in perfecting it. By 1980 some 20.000.000
cars had come out from the Ford plant.
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