Page 38 - Introduction to Marine Engineering

Diesel engines 25

Adjustment for
Injection timing regulation each fuel pump

Fuel setting
Regulating shaft
Plunger Fuel quality
adjustment
Control air output
Position sensor
•*— Air inlet

Figure 2.13 Variable injection timing (VIT) pump

spill valve will control the end of injection by releasing fuel pressure. No
helix is therefore present on the pump plunger.

Common rail system
The common rail system has one high-pressure multiple plunger fuel
pump (Figure 2.14). The fuel is discharged into a manifold or rail which
is maintained at high pressure. From this common rail fuel is supplied to
all the injectors in the various cylinders. Between the rail and the injector
or injectors for a particular cylinder is a timing valve which determines
the timing and extent of fuel delivery. Spill valves are connected to the
manifold or rail to release excess pressure and accumulator bottles
which dampen out pump pressure pulses. The injectors in a common
rail system are often referred to as fuel valves.