Page 238 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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222 Automobile mechanical and electrical systems

Figure 2.290 Fuel fi lter
Injectors operate with a pulsing action at high pressure to break the fuel down
Key fact into fi nely atomized parts. Atomization is critical to good fuel distribution in the
compressed air charge. The air charge pressure may be in excess of 60 bar. The
Injectors operate with a pulsing
action at high pressure to break the pressure differential between the fuel injection pressure and air charge pressure
fuel down into fi nely atomized parts. must be suffi cient to overcome the resistance during injection. This will also give
good fuel atomization and a shorter injection time.
The main components of a diesel fuel system provide for either the low-pressure
or the high-pressure functions. The low-pressure components are the fuel tank,
the fuel feed and return pipes and hoses, a renewable fuel fi lter with a water trap
and drain tap, and a priming or lift pump.
The high-pressure components are the fuel injector pump, the high-pressure
pipes and the injectors. Other components provide for cold engine starting.
Key fact Electronically controlled systems include sensors, an electronic diesel control
(EDC) module and actuators in the injection pump.
The internal components of

the pump and injectors are All diesel fuel entering the injection pump and injectors must be fully fi ltered
manufactured to very fi ne tolerances. ( Fig. 2.290 ). The internal components of the pump and injectors are
manufactured to very fi ne tolerances. Even very small particles of dirt could be
damaging to these components.
The most common rotary injection pumps are axial-piston designs having a roller
ring and cam plate attached to an axial piston or plunger in the distributor head
to generate the high pressure. The latest versions have full electronic control. The
details are examined further in the next section.
The high-pressure pipes are of double-thickness steel construction and are all
of the same length. This is so that the internal pressure rise characteristics are
identical for all cylinders. The high-pressure connections are made by rolled
fl anges on the pipe ends and threaded unions securing the rolled fl anges to
convex, or occasionally concave, seats in the delivery valves and injectors.
The fuel injectors are fi tted into the cylinder head with the nozzle tip projecting
into the precombustion (indirect injection) or combustion chamber (direct
injection). The injectors for indirect combustion are of a pintle or ‘pintaux’ design
(similar to petrol injectors in many ways) and produce a conical spray pattern
on injection. The injectors for direct injection (DI) are of a pencil-type multihole
design that produces a broad distribution of fuel on injection ( Fig. 2.291 ).
Fuel injectors are held closed by a compression spring. They are opened by
hydraulic pressure when it is suffi cient to overcome the spring force on the