Page 348 - Mechanic Diesel - TT
P. 348
MECHANIC DIESEL - CITS
MODULE 17 : CRDI System
LESSON 108 - 113: Description of CRDI systems and
its components. Precautions to be
observed before removing the CRDI
fuel system-study about the low and
high pressure fuel supply circuits
Objectives
At the end of this lesson you shall be able to
• describe the CRDI system and its components
• demonstrate precaution to be observed while servicing fuel supply system
• study about low and hight pressure circuits in fuel supply system.
Description of CRDI systems and its components
Common Rail Diesel Injection (CRDI) System: In this system, single injection pump and injector are used for
each cylinder. These are in the form of a unit; hence they are also called unit injectors. The action of the unit
injector is via a rocker arm and spring, similar to the engine valves. Fuel is drawn from the fuel tank by the feed
pump and supplied to the unit injectors through a filter at low pressure and excess fuel is returned to the fuel tank
through the relief valve. It has a manifold with the help of which the engine is fed with pressure in the drive pump.
As shown in the following picture. The injector pump is fed by pipes connected to the rail.
In this type of system, a low pressure electric fuel pump draws diesel from the fuel tank and sends the diesel
through a filter to a high pressure pump. This high pressure pump creates high pressure in the common rail
through a pressure regulator valve.
The electronic control unit controls this pressure regulator valve through a pressure sensor. In this way the diesel
pressure created in the common rail is free from the influence of engine speed. The flow limiters installed in
the system protect against the consequences of any diesel leakage from the injector. In this system, pressure
control valve (pressure limiter valve) works to prevent excess diesel pressure. Diesel is injected into the engine
combustion chamber through the injection nozzle of an injector controlled by a solenoid valve. In this system,
the amount of diesel injected depends on the diesel pressure, injection duration, size and shape of the injection
nozzle.
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