Like all specialized fields, the translation of materials relating to diesel engines and fuel injection
pumps poses special terminology problems. In the diesel field, terms are not translated the way
one might assume at first glance. For example, when used in the context of injection pumps,
Kolben and Zylinder are not pistons and cylinders, but plungers and barrels. If Hub appears in
connection with these plungers, the correct translation would be lift and not stroke as one might
assume. Another term is Angleichung which translates as torque control; and Förderbeginn is
called port closing. As these last examples indicate, diesel terminology is very much driven by the
function of the elements involved. On occasion, the terminology seems whimsical, as when
nozzles chatter (schnarren).
The diesel field is very complex and due to space limitations I can only give the bare outlines here.
In contrast to spark-ignition engines, diesel engines are autoignition engines. Autoignition engines
only draw in air which is then highly compressed. In this manner, a much higher compression ratio
can be achieved than in the case of gasoline engines which are susceptible to knocking and use an
air-fuel mixture coupled with externally supplied ignition. This makes diesel engines the most
efficient among internal combustion engines. Even though two-stroke cycle designs are possible,
four-stroke cycles are used almost exclusively in motor vehicles.
During the downward movement of the piston, the engine draws in air through the open intake
valve during the intake stroke. During the compression stroke, the air is compressed by the
upward movement of the piston. In the process the air heats up to temperatures of up to 800°C.
At the end of the compression stroke, the injection nozzle injects fuel into the hot air under high
pressure (up to 1,500 bar). At the beginning of the power stroke the atomized fuel combusts
almost completely as a result of autoignition. The cylinder charge heats up further and the
pressure in the cylinder increases again. The energy released by the combustion process is applied
to the piston. As a result the piston moves downward again. In the course of the exhaust stroke,
the combusted cylinder charge is expelled through the open exhaust valve as the piston moves
Diesel engines can have divided and undivided combustion chambers (indirect and direct injection
engines). Direct injection engines have a greater efficiency and operate more economically than
indirect injection engines using a pre- or swirl chamber. Direct injection engines are used for all
commercial vehicle applications. Because of lower engine noise, indirect injection engines are
more suitable for cars. In addition, they are significantly less polluting (HC and NOx) and cheaper
to produce. For these reasons their higher fuel consumption in comparison with direct injection engines is generally accepted as a compromise.
With the pre-chamber method for car diesel engines, fuel is injected into a hot pre-chamber in
which pre-combustion initiates a good mixture preparation for the main combustion. Fuel is
injected by means of a throttling pintle nozzle at relatively low pressure (up to 300 bar). The
partially combusted air-fuel mixture then passes to the main combustion chamber. A variation of
this method is the swirl chamber method. With a direct injection method used primarily for
commercial vehicles and stationary engines, fuel is injected directly into the combustion chamber
without the use of a pre-chamber.
The fuel injection system supplies the fuel to diesel engines. The injection pump generates the
pressure required for injection. The fuel is delivered to the injection nozzles via the high-pressure
lines and injected into the combustion chamber. The main types of injection pumps are in-line
injection pumps, distributor pumps, unit pumps and unit injectors.
Standard in-line injection pumps have their own camshaft as well as a plunger and barrel assembly
for each engine cylinder. The complete injection system consists of the following components:
In the case of in-line injection pumps a camshaft actuates one plunger and barrel assembly per
engine cylinder. In the case of the distributor injection pumpused primarily for high-speed
diesel engines for cars and light trucksa central camplate-driven plunger generates pressure and
distributes the fuel to the individual cylinders.
- the injection pump
- a mechanical or electronic governor to control the engine speed and the injected fuel quantity
- a timing device to adjust the port closing
- a supply pump to deliver fuel from the fuel tank to the injection pump
- high-pressure lines from the injection pump to the injection nozzle corresponding to the
number of cylinders, and
- the injection nozzles.
In the case of unit injectors, the pump and nozzle form a single unit which can be directly installed
in the cylinder head. The unit is driven by the engines camshaft. Another design is the unit pump,
a modular high-pressure injection system. It is closely related to the unit injector. Like the unit
injector, the unit pump has one injection pump per engine cylinder driven by the camshaft of the
engine via an additional injection cam.
The unit pump consists of the following modules:
Injection pumps use a variety of governors such as minimum-maximum speed governors and
variable-speed governors based on flyweights. These are increasingly being replaced by electronic
governors (EDC = Electronic Diesel Control).
- the high-pressure pump with attached solenoid valve
- a short high-pressure line and
- the nozzle holder assembly.
Source: Dieseleinspritztechnik (VDI Verlag)
A sampling of key terms:
|Direkteinspritzer||direct injection (DI) engine
|Düsenhalterkombination||nozzle and holder assembly
|Einspritzelement||plunger and barrel assembly
|Einspritzmenge||injected fuel quantity
|Falltankbetrieb||gravity-feed fuel tank operation
|Glühstiftkerze||sheathed-element glow plug
|Hub (Kolben)||lift (plunger)
|Pumpe-Düse-Einheit (PDE)||unit injector
|Pumpe-Leitung-Düse (PLD)||unit pump
|Saugraum|| fuel gallery
|Vorhub|| plunger lift to port closing
|Zapfendüse|| pintle nozzle