<b>Injection Systems</b>
The injection quantities can be controlled electrically or mechanically. For a good mixture formation in the cylinder, which is a prerequisite for good fuel utilization, an intensive swirling of the air and the injected fuel must be effected. This can be achieved through a suitable design of the combustion chamber. The most common types of construction are briefly presented below:
In the prechamber process, an injection process for diesel engines that was widespread until the 1990s, a small part of the combustion chamber (the so-called prechamber) is separated from the main chamber by a narrowing (the firing channel). The fuel is injected into the prechamber at moderate pressure (around 100 bar), ignites and some of it burns there; the resulting momentary overpressure blows the burning mixture through the firing channel into the air-rich main combustion chamber. Today, this process has largely been replaced by direct injection and is only used in smaller diesel generators.
In the swirl chamber engine, the air flow in the swirl chamber results in a good mixture formation. The fuel is injected tangentially in the direction of the swirl. The time of fuel supply, ignition and the combustion process take place in the same way as for the pre-chamber engine.
In the case of the air storage motor, the fuel jet is directed onto the inlet cone of the air nozzle of the storage unit, so that the injected fuel is carried away by the air flowing into the antechamber. The ignition starts in the prechamber, partial combustion takes place and the overflow with strong turbulence into the cylinder chamber takes place. In modern designs, the air storage volume is around 20-25% of the total compression chamber, the injection pressure is around 10-12 MPa.
In direct injection, where the combustion chamber can be partially or completely in the piston crown, the fuel is injected directly into the compression chamber through an injection nozzle that contains one or more small holes. The injection pressures are 400 bar and more in order to achieve the finest distribution and atomization of the fuel in the combustion air. A suitable shape of the piston supports the effect of the nozzle arrangement.
The MAN-M process is characterized by the typical design of the piston with the recessed combustion chamber in the form of a sphere. The special design of the inlet channel creates an air vortex in the ball by injecting the fuel tangentially through a single-hole nozzle into the spherical recess in the piston. About 95% of it is distributed as a film on the wall surface; it only evaporates during combustion and is also carried away by the air vortex. Ignition takes place with the small residual proportion of fuel that has already formed a mixture directly with the air. Now the fuel sprayed onto the hot combustion chamber surface evaporates and continuously mixes with the air vortex. A very soft and relatively complete combustion takes place.
Various pump systems are used to build up the injection pressures in the processes mentioned:
for engines with prechamber or vortex chamber injection:
- Single injection pump
- Distributor injection pump
- In-line injection pump
for engines with direct injection:
- Single injection pump, etc. in the design as a single piston pump, colloquially often called a unit pump,
- In-line injection pump
- Distributor injection pump
- Pump-nozzle injection systems
- Common rail injection
Injection Systems
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