New Star Software Collection/NSS_Collection.iso/3-251 oo2 english program/1.ima/RR.ZIP/PTHEINTE.SEQ

Text File | 1991-06-30 | 4.6 KB | 83 lines

The idea for the internal combustion engine was conceived long
before the means were available to build one. The major obstacle
to its development was the lack of a suitable fuel. In the 17th
century various fuels, such as gunpowder and hydrogen gas, were
ignited under compression in engines designed to harness the
force of the resulting explosions. None of these experiments met
with any success, however. It was not until the second half of
the 1 9th century that petroleum products were first developed.
Even then, for many years, the primary product of petroleum
refining was kerosene, used for lamps and stoves, while gasoline
was considered a dangerous byproduct. It was a German named
Nikolaus August Otto who first used petrol successfully to power
an engine.

Otto's engine was a four stroke internal combustion engine,
basically no different from those still used in modern cars. It
was mass produced and widely used in industry for many years
before anyone succeeded in adapting it for use in powering a
vehicle. Gottlieb Daimler, another German, was the first
engineer to fit an engine of this type onto a four-wheeled
carriage, though Karl Benz had, a year earlier, made a
three-wheeled car, fitted with a simpler petrol engine. By the
year 1900, automobiles had become quite common in Europe and the
United States. Soon thereafter, in 1903, the first successful
flight in an aircraft powered by an internal combustion was made
by two Americans, Wilbur and Orville Wright. They put a gasoline
engine into a glider and flew it for twelve seconds.

The basic principle of operation of the internal combustion
engine is very simple. If we mix air and gasoline and then
compress the mixture, a tiny spark will cause it to explode. The
force of this explosion can be used to power an engine. Like
Newcomen's famous steam engine, the internal combustion engine
uses pistons which move up and down inside cylinders. However,
fuel combustion for Newcomen's engine was external to the
cylinder, while for Otto's it was internal.

The design of an internal combustion engine must allow four
different operations to occur within each cylinder: (1)
induction of the gas and air mixture from the carburettor, (2)
compression of the mixture, (3) combustion, and (4) exhaust of
the burnt gases. The piston moves either up or down for each of
these operations, and each of its movements is called a stroke.
There are two upward strokes (one each for compression and
exhaust) and two downward ones (one each for induction and
combustion). The combustion chamber has two valves, an inlet
valve and an exhaust valve, which open and shut very rapidly.
The first of these admits the air and gas mixture into the
chamber, while the other one allows the burnt gases to escape.

Combustion causes the piston to move downward in the chamber,
but what force moves the piston during the other three strokes?
The answer is that combustion is occurring in only one of the
four cylinders at any given moment, while exhaust, induction and
compression are occurring in the other three. The force of that
single explosion is sufficient to move the other three pistons
upward or downward. The pistons can affect each other in this
way because they are connected by means of a rotating crankshaft
and four pivoting rods, called connecting rods. Thus, the
up-and-down movement of the pistons both causes and is caused by
the circular movement of the crankshaft. In addition, a heavy
flywheel attached to the crankshaft helps to keep the crankshaft
rotating after each combustion stroke. The rotary power of the
crankshaft is then transmitted to the wheels of a car or the
propellers of an aircraft or boat.

The internal combustion engine is one of the most significant
inventions of all time. It is used to power almost every kind of
vehicle, including aeroplanes and small boats, and after a
century of development it has become extremely efficient and
reliable. Recently, though, it has become a target of criticism
from environmentalists, who complain that it is the major
consumer of precious oil reserves as well as one of the major
sources of air pollution. However, engineers have managed to
improve the internal combustion engine's performance in these
areas. As a result, modern internal combustion engines cause
much less pollution and are much more fuel efficient than those
of the 1960s and 1970s. As new technologies develop in the years
ahead, the internal combustion engine may assume less importance
than it has had during most of this century. However, for the
present it is still considered a key element in modern
transportation systems.