ike 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
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 upward.
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:
- 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 in-line injection pumps a camshaft actuates one plunger and barrel assembly per engine cylinder.
In the case of the distributor injection pump—used primarily for high-speed diesel engines for cars and light trucks—a central camplate-driven plunger generates pressure and distributes the fuel to the individual cylinders.
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 engine’s 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:
- the high-pressure pump with attached solenoid valve
- a short high-pressure line and
- the nozzle holder assembly.
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).
A sampling of key terms:
Charles Heidenberg's email: [email protected]
|Absteuerbohrung||spill port |
|Angleichung||torque control |
|Ansaugrohr||intake manifold |
|Beschleunigungsanreicherung||acceleration enrichment |
|Direkteinspritzer||direct injection (DI) engine |
|Dralldüse||swirl nozzle |
|Druckstufe||valve-to-seat ratio |
|Druckzapfen||pressure spindle |
|Düsenhalterkombination||nozzle and holder assembly |
|Einspritzelement||plunger and barrel assembly |
|Einspritzmenge||injected fuel quantity |
|Entlastungsvolumen||retraction volume |
|Falltankbetrieb||gravity-feed fuel tank operation |
|Federraum||spring chamber |
|Fixierstift||locating pin |
|Fliehgewichtsweg||flyweight travel |
|Förderbeginn||port closing |
|Glühstiftkerze||sheathed-element glow plug |
|Hub (Kolben)||lift (plunger) |
|Luftzahl||excess-air factor |
|Magnetventil||solenoid-operated valve |
|Nachspritzer||secondary injection |
|P-Grad||speed droop |
|Prüfstand||test bench |
|Pumpe-Düse-Einheit (PDE)||unit injector |
|Pumpe-Leitung-Düse (PLD)||unit pump |
|Regelstange||control rack |
|Reihenpumpe||in-line pump |
|Ruckeldämpfung||anti-bucking device|| |
|Rückströmventil||snubber valve |
|Saugraum|| fuel gallery |
|schnarren (Düse)||chatter |
|Verteilerpumpe||distributor pump |
|Vorhub|| plunger lift to port closing |
|Zapfendüse|| pintle nozzle |
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