07-02-2013, 03:25 PM
Diesel distributor fuel-injection pumps
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The diesel engine
Diesel combustion principle
The diesel engine is a compressionignition
(CI) engine which draws in air
and compresses it to a very high level.
With its overall efficiency figure, the diesel
engine rates as the most efficient combustion
engine (CE). Large, slow-running
models can have efficiency figures of as
much as 50% or even more.
The resulting low fuel consumption,
coupled with the low level of pollutants in
the exhaust gas, all serve to underline
the diesel engine’s significance.
The diesel engine can utilise either the
4- or 2-stroke principle. In automotive
applications though, diesels are practically
always of the 4-stroke type (Figs. 1
and 2).
Working cycle (4-stroke)
In the case of 4-stroke diesel engines,
gas-exchange valves are used to control
the gas exchange process by opening
and closing the inlet and exhaust ports.
Induction stroke
During the first stroke, the downward
movement of the piston draws in unthrottled
air through the open intake valve.
Compression stroke
During the second stroke, the so-called
compression stroke, the air trapped in the
cylinder is compressed by the piston
which is now moving upwards. Compression
ratios are between 14:1 and
24:1. In the process, the air heats up to
temperatures around 900°C. At the end
of the compression stroke the nozzle injects
fuel into the heated air at pressures
of up to 2,000 bar.
Power stroke
Following the ignition delay, at the beginning
of the third stroke the finely atomized
fuel ignites as a result of auto-ignition
and burns almost completely. The
cylinder charge heats up even further
and the cylinder pressure increases
again. The energy released by the ignition
is applied to the piston.
The piston is forced downwards and the
combustion energy is transformed into
mechanical energy.
Exhaust stroke
In the fourth stroke, the piston moves up
again and drives out the burnt gases
through the open exhaust valve.
A fresh charge of air is then drawn in
again and the working cycle repeated.
Fields of application
Diesel engines are characterized by their
high levels of economic efficiency. This is
of particular importance in commercial
applications. Diesel engines are employed
in a wide range of different versions
(Fig. 1 and Table 1), for example as:
– The drive for mobile electric generators
(up to approx. 10 kW/cylinder),
– High-speed engines for passenger
cars and light commercial vehicles (up
to approx. 50 kW/cylinder),
– Engines for construction, agricultural,
and forestry machinery (up to approx.
50 kW/cylinder),
– Engines for heavy trucks, buses, and
tractors (up to approx. 80 kW/cylinder),
– Stationary engines, for instance as
used in emergency generating sets (up
to approx. 160 kW/cylinder),
– Engines for locomotives and ships (up
to approx. 1,000 kW/cylinder).
Fuel-injection systems
Assignments
The fuel-injection system is responsible
for supplying the diesel engine with fuel.
To do so, the injection pump generates
the pressure required for fuel injection.
The fuel under pressure is forced through
the high-pressure fuel-injection tubing to
the injection nozzle which then injects it
into the combustion chamber.
The fuel-injection system (Fig. 1) includes
the following components and
assemblies: The fuel tank, the fuel filter,
the fuel-supply pump, the injection
nozzles, the high-pressure injection
tubing, the governor, and the timing
device (if required).