Diesel
engine
is the most efficient power plant among all known types
of internal combustion engines. Heavy trucks, urban buses,
and industrial equipment are powered almost exclusively
by diesel engines all over the world. In Europe, diesel
powered cars have been increasingly popular. The diesel
engine is a major candidate to become the power plant of
the future. Before that happens, however, further progress
in diesel emission control is needed. Diesel particulates
and nitrogen oxides, the two most troublesome components
of diesel exhaust emissions, have a dramatic, damaging impact
on the environment and on our health. The new 2004 emission
standards in the U.S. as well as the tightening regulations
in Europe and East Asia reflect the growing concern with
diesel emissions.
The way a diesel engine works is pretty much the same
as a gasoline engine. Diesel engines can be, like gasoline
engines, two or four stroke engines. Automobile diesel engines
are four stroke units, as are most gasoline engines. The
four stroke engine is also called an Otto engine. The four
stroke (Otto) engine was originally propesed by a Frenchman
called Beau de Rochas in 1862. But it was a German called
Nikolaus Otto who first succesfully incorporated De Rochas'
concept in a working engine, so the engine got named after
him.
On
a Diesel Otto engine, the engine work can be divided into
four distinguishable parts, each one called a stroke (on
a gasoline engine the strokes are pretty much the same,
with only the third stroke being substantially different).
On
the first stroke the piston is at its top and the intake
valve is open; and as the piston moves down, it sucks in
air. At the end of this stroke, the intake valve closes.
This stroke is called the INTAKE stroke.
During
the second stroke, all valves are closed. As the piston
moves back up, it compresses the air up to 25 times
its original volume. As the pressure rises up to 1000psi,
so does the temperature, up to 1500o F. This
stroke, called the COMPRESSION stroke, ends when the piston
reaches the top of its path.
The
third stroke starts with the high pressures and temperatures
from the prior stroke. A jet of fuel is injected at
a very precise time, and it almost instantly ignites in
contact with the hot air. The explosion caused by this ignition
tries to raise the cylinder pressure even more, but instead
drives the piston down, keeping the pressure almost constant.
The ignition is completed at 1/3 of the way, but its force
still drives the piston down. This is the only stroke that
makes power, so it's often called the POWER stroke (not
to be confused with the Ford Navistar Powerstroke Diesel
engine), or IGNITION or EXPLOSION stroke. It ends when the
piston reaches the bottom of its path.
The
final stroke starts when the piston is at the bottom of
its path, and the only things that remained from the poweer
stroke are the burnt gases of the fuel that ignited. As
the piston travls back up its path, the pressure rises once
more, untill the exhaust valve opens and the burnt gases
are expelled, and after the piston reaches its top the cylinder
is ready to restart the cycle, with the first stroke again.
This stroke is called the EXHAUST stroke.
The
key components that differenciate the way a gasoline engine
works from the way a diesel engine works are the following:
the fuel properties and the fuel injection pump.
The
diesel fuel has some very interesting properties.
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