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The diesel engine is a type of internal
combustion engine that was invented by Rudolf Diesel in 1892.
Diesel intended the engine to use a variety of fuels including
coal dust. He demonstrated it in the 1900 World's Fair using
peanut oil. Diesel engines are know as compression ignition
engines.
Diesel Engines don't use spark plugs, the compression of the fuel
in the engine is what ignites the fuel because when a gas is
compressed, its temperature rises. Air is drawn into the cylinder
of a diesel engine and compressed by the rising piston, at a much
higher compression ratio than for a spark-ignition engine. At the
top of the piston stroke, diesel fuel is injected into the
combustion chamber at high pressure, through an atomising nozzle,
mixing with the hot, high-pressure air. The resulting mixture
ignites and burns very rapidly. This contained explosion causes
the gas in the chamber to expand, driving the piston down with
considerable force and creating power in a vertical direction. The
connecting rod transmits this motion to the crankshaft which is
forced to turn, delivering rotary power at the output end of the
crankshaft. Scavenging (pushing the exhausted gas-charge out of
the cylinder, and drawing in a fresh draught of air) of the engine
is done either by ports or valves.
A vital component of any diesel engine system is the governor,
which limits the speed of the engine by controlling the rate of
fuel delivery.
In very cold weather, the compression itself is insufficient to
heat the air enough to ignite the fuel. Glow plugs are electrical
heaters inside the cylinder to help warm the air. Once the engine
is started and warmed up, the glow plugs are no longer needed and
may be turned off.
Diesel engines are more massive than gasoline/petrol engine of the
same power because of the higher combustion pressures needed for
ignition.
Diesel engines can produce black soot from their exhaust. This
consists of unburnt carbon compounds. Other problems associated
with the exhaust gases (high particulates, nitrogen oxide,
sulfurous fumes) can be mitigated with further investment and
equipment.
The addition of a turbocharger or supercharger to the engine
greatly assists in increasing fuel economy and power output. The
higher compression ratio allows a diesel engine to be more
efficient than a comparable spark ignition engine, although the
calorific value of the fuel is slightly lower at 45.3 megajoules/kilogram
to gasoline at 45.8 megajoules/kilogram.
The lack of an electrical ignition system greatly improves the
reliability. Unfortunately due to the greater compression force
required and the increased weight of the stronger components,
starting a diesel engine is a harder task. More torque is required
to push the engine through compression. Either an electrical
starter or an air start system are used to start the engine
turning. On large engines pre-lubrication and slow turning of an
engine as well as heating are required to minimise the possibility
of damaging the engine during initial start-up and running. Some
smaller military diesels are started with an explosive cartridge
that provides the extra power required to get the machine turning.
Diesel fuel is a product of crude oil, although other oils can be
burned inside an adapted engine. Good quality diesel fuel can be
synthesised from vegetable fat and alcohol, these fuels are very
clean with low emissions and are known as bio-diesel.
The manufacturers of diesel engines have improved them to a point
where they are almost equal in performance to that of a normal
Otto Cycle engine. As cleaner fuels become more popular and people
begin to realise the advantages of the economical and reliable
diesel cars, The diesel engine may be seen in more and more
passenger cars.
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