Diesel Engines
The Diesel cycle uses compression
ignition: the fuel ignites upon being injected into the highly compressed
air in the combustion chamber. By contrast, petrol engines utilize the
Otto cycle, in which fuel and air are typically mixed before entering
the combustion chamber.
The mixture is then ignited by a spark plug. Compression ignition is
generally considered undesirable in Otto cycle engines. A Diesel engine
is an internal combustion engine which operates using the Diesel cycle.
German engineer Rudolf Diesel invented it in 1892, basing it on the
hot bulb engine. He received a patent for it on February 23, 1893.
In mechanical terms, the
internal construction of a Diesel engine is similar to its gasoline
counterpart—components such as pistons, connecting rods and a crankshaft
are present in both. Like a gasoline engine, a Diesel engine may operate
on a four-stroke cycle (similar to the gasoline unit's Otto cycle),
or a two-stroke cycle, albeit with significant dissimilarity to the
gasoline equivalent. In both cases, the principal differences lie in
the handling of air and fuel, and the method of ignition.
A Diesel engine relies
upon compression ignition to burn its fuel, instead of the spark plug
used in a gasoline engine. If air is compressed to a high degree, its
temperature will increase to a point where fuel will burn upon contact.
This principle is used in both four-stroke and two-stroke Diesel engines
to produce power.
Unlike a gasoline engine, which draws an air/fuel mixture into the cylinder
during the intake stroke, the Diesel aspirates air alone. Following
intake, the cylinder is sealed and the air charge is highly compressed
to heat it to the temperature required for ignition.
Because the vast majority
of diesel engines in service today use solid injection, the information
below relates to that system. Diesel engines are used in mid-sized cruisers,
trawlers, large yachts, work boats and commercial vessels. In the diesel
engine, only air is introduced into the cylinder head. The air is then
compressed to about 600 pounds per square inch (psi), compared to about
200 psi in the gasoline engine. This high compression heats the air
to about 1000 degrees Fahrenheit. At this moment, fuel is injected directly
into the compressed air.
The fuel is ignited by
the heat, causing a rapid expansion of gases that drive the piston downward,
supplying power to the crankshaft.In Diesel's manuals, he described
the supply of compressed gas into the cylinder to promote the final
burn. It is now possible to fumigate the air intake with a small quantity
of LPG/CNG.The now air-gas mixture is compressed as above, and when
the diesel ignites, the small quantity of gas ignites as well, causing
a more rappid and more complete burn of the diesel.
Most diesel engines waste
between 30 and 15% of the diesel fuel, so by burning the near total
amount of diesel injested on each stroke, the mechanical affect is to
improve the torque curve by as much as 28%. The nett outcome of applying
gas into diesel is, improved fuel economy via better torque at the driving
wheels resulting in less gear changes, and a greatly improved exhaust
emission readings.
Advantages of the diesel
engine are numerous. It burns considerably less fuel than a gasoline
engine performing the same work. It has no ignition system to attend
to. It can deliver much more of its rated horsepower on a continuous
basis than can a gasoline engine. The life of a diesel engine is generally
longer than a gasoline engine. Although Diesel fuel will burn in open
air, it will not explode.
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