A turbine is any motor in which a shaft is steadily rotated by
the impact of a current of steam, air, water or other fluid directed
from jets or nozzles upon the blades of a wheel.
A turbine generally consists of a series of curved blades or vanes
on a central spindle arranged to rotate, the whole being enclosed
by a casing fitted with passageways that let the fluid in and out
The most important feature of all turbines is the shape of the blades
and the angle they present because the speed may be largely affected
by an alteration in the shape of the blades or in the direction
of flow of the incoming fluid.
Turbines are primarily classified according to the fluid employed
in: water or hydraulic turbines, steam turbines, gas turbines, mercury-vapour
turbines and others.
According to the principal direction of fluid flow, they are classed
into parallel-flow turbines or axial-flow turbines, radial-flow
turbines (including the outward and inward-flow types), mixed-flow
turbines, and so forth.
Turbines are also classified considering the method of steam expansion
in: impulse turbines and reaction turbines. The former have steam
expansion only in the stationary blades or nozzles and the latter
have steam expansion both in the stationary and in the moving blades.
Finally, turbines may be classified according to the method of
subdividing the available energy in : pressure stage turbines and
velocity-stage turbines. In the pressure- stage turbines the steam
pressure drop is subdivided among two or more successive sets of
rotating blades, each set taking care of a part of the pressure
drop; while in velocity-stage turbines, the steam at constant pressure
passes through two or more successive sets of rotating blades starting
with a high steam speed and decreasing the same from set to set.
Steam turbines are high-speed prime-movers and are most efficiently
used in direct connection to electrical generators, centrifugal
pumps, centrifugal compressors and ship propellers.
If we compare turbines with the other prime movers we shall see
that they require less floor space, lighter foundation, less attention,
a lower consumption of oil and maintenance cost and excellent regulation.
They have extreme overload capacity and great reliability on account
of their simplicity of construction.
A turbine is a device in which the steam from a boiler is directed
by jets, or by guide vanes, against blades fixed to the outer surface
of a drum, the energy of the escaping steam causing the drum and
its blades to rotate.
The steam is allowed to expand in a number of separate stages.
The steam from the boiler passes first through jets or a set of
fixed blades where it expands slightly, and a fraction of its pressure
energy is used to set the steam in motion. The moving steam now
falls on a set of moving blades and in passing through them gives
up its kinetic energy to the blades.
The steam now expands passing by
another set of jets or stationary blades and is directed against
a second set of moving blades. Thus, the expansion of steam is so
controlled that its speed at all stages, is that required for efficient
An internal combustion engine is one in which the energy supplied
by a burning fuel is directly converted into mechanical energy by
the controlled burning of the fuel in an enclosed cylinder behind
The explosive fuel-air mixture may be ignited either by an electric
spark or by the resulting compression temperature. This explosion
causes the rotation of the rotary parts of the engine by driving
the piston in the cylinder, motion which is transmitted to the crankshaft
by means of the connecting-rod.
In order to aid the inlet and outlet of the charge, the cylinder
is fitted with two valves operated by their cams and a camshaft.
We say the engine is on its bottom dead
center when the piston
is at its lower position whereas it is on its top dead center when
the piston reaches its upper point.
We call stroke the motion of the piston from one end of the cylinder
to the other. The first stroke constitutes the admission of the
proper amount of explosive mixture; in the second stroke this mixture
is compressed; in the third one it burns, while the exhaust of the
burned gases takes place in the fourth and last stroke. These operations
constitute what we term cycle.
We can classify internal combustion engines according to the number
of strokes of the piston in one complete working cycle. Thus, we
speak of two-stroke-cycle engines and four-stroke-cycle engines.
The complete cycle of events of the former group, that is suction,
compression, explosion and exhaust, is accomplished in a single
revolution of the crankshaft or in two strokes of the piston, as
the compression and expansion of the charge take place during one
stroke, while the admission of a fresh charge occurs during the
other stroke simultaneously with the escape of the burnt gases.
In the four-stroke cycle engines the explosive mixture is drawn
into the cylinder on the induction stroke, compressed on the compression
stroke and ignited. It burns and performs useful work on the expansion
stroke and the products of combustion are exhausted in the exhaust
Internal combustion engines may be classified according to the
kind of fuel used in four main groups: gas engines, heavy oil engines,
light oil engines and special engines.
There is still another classification according to the process
of combustion: explosion or constant-volume combustion engines and
constant-pressure combustion or Diesel engines.
efficiency of internal combustion engines is higher than that of
external combustion engines, where loss of heat occurs during the
raising of the steam and its passage to the cylinders.
The principal fuels
used in them are petrol, as in the motor-car engine, coal-gas and
similar gases, as in the gas engine; and heavy oil as in Diesel
engines. The essential elements of all these fuels are carbon and
hydrogen and the action that takes place when they are burned, is
the combustion of their elements with atmospheric oxygen to form
carbon dioxide and water, respectively, with liberation of
In an explosion or
constant-volume-combustion engine, a mixture of volatile liquid or
gas and air, compresses to a moderate pressure during the
compression stroke of the piston, ignites usually by an electric
spark, explodes and expands with constant volume.
or Diesel engines operate on the Diesel cycle, and mixed-cycle
engines, in which the combustion is partly explosive and partly at
constant pressure, operate on what is termed Sabathe's cycle.
engines the fuel-air mixture is ignited by a flame of gas or by some
form of hot tube, hot bulb or uncooled portion of the surface of the
engines, a portion of the compressed charge is compressed to a
higher pressure than the remainder during the last steps of the
compression stroke, in this way raising this portion of mixture to a
temperature above the one of ignition.
engines have a small uncooled precombustion chamber or cup separated
from the cylinder in which a portion of the mixture is ignited, and
in turn, this portion ignites the cylinder charge.
engines are very similar to Diesel-cycle engines and are called
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