The common rail fuel injection system is finding increasing use engines as it has the potential to drastically cut emissions and fuel consumption. This system provides control of many important parameters linked to the injection system. It has a wide range of applications, From small to heavy-duty engines.

1. Common Rail Injection System
• The common rail fuel injection system is finding increasing use
engines as it has the potential to drastically cut emissions and
fuel consumption. This system provides control of many
important parameters linked to the injection system. It has a wide
range of application, From small to heavy duty engines.
• The common rail injection system has a high pressure pump
which operates continuously and charges a high pressure rail or
reservoir or accumulator. Fuel is led from this rail to the injector
mounted on the cylinder head through lines. The injector is
solenoid operated. It received pulses from the ECU to open the
same.
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3. Important features
• Some important features are:
• Very high injection pressures of the order of 1500 bar.
• Complete control over start, and end of injection
• Injection pressure is independent of engine speed
• Ability to have pilot, main and post injection
• Variable injection pressure.
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5. Common Rail Injection System
• The engine directly drives the pump of the common rail system. It is
generally of the multi-cylinder radial piston type. The generated
pressure is independent of the injection process unlike conventional
injection systems.
• The rail pressure pump is generally much smaller that conventional
pumps and also is subjected to lesser pressure pulsations. The injection
occurs when the solenoid is energized. The quantity of fuel injected is
directly dependent on the duration of the pulse when the injection
pressure is constant. Sensors on the crankshaft indicate its position and
speed and so the timing of injection and its frequency can be controlled.
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6. 1 High pressure pump 7
High pressure
accumulator
13 Accelerator pedal sensor
2 Element shutoff valve 8 Rail pressure sensor 14 Injector
3 Pressure control valve 9 ECU 15 Camshaft speed sensor
4 Fuel filter 10 Turbocharger 16 Intake air temperature sensor
5 Fuel temperature sensor 11
Coolant temperature
sensor
17 Boost pressure sensor
6 Battery 12 Crankshaft speed 18 Air mass meter
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7. • Fuel from the tank is lifted by a low pressure pump and passed
through a filter. The pump is generally run by an electric motor
independent of the engine speed. The main pumping element can
be a conventional gear pump or of the roller cell type. The roller
cell pump has a rotor with radial slots. These slots house rollers
which are always in contact with the inner surface of the housing
due to fuel pressure and centrifugal forces. The space between
rotor and the housing varies as the rotor turns and this is
responsible for the suction and delivery.
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8. • This pump has a cam which is stationary and a rotating hydraulic
head which houses two plungers. These plungers touch the cam
and are pushed in four times a rotation.
• Thus fuel is pumped four times per rotation. A non return valve
is used to send the fuel to the rail. The inlet of the Pump is
controlled to maintain the needed delivery. It may he noted that
any excess delivery is ultimately returned back from the rail
pressure regulator after it is throttled down to tank pressure.
• This amounts to fuel heating and also loss of work takes place to
pump the fuel. Hence, controlling the delivery at the pump is a
good idea.
• A high pressure regulator is also used. Both these valves are
solenoid operated and are controlled by the ECU.
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10. • In the rail-pressure regulator the spring force and the
electromagnetic force generated by the coil regulate the pressure.
The pressure is controlled by the ECU.
• The electromagnet receives a pulse at a frequency of 1 kHz
whose width is modulated to change the effective current through
the electromagnet.
• The common rail system also has a pressure sensor and a
pressure limiter attached to the rail. There is also a flow limiter to
prevent continuous injection if one of the injectors mal functions.
• Thus, it is seen that engine management is gradually turning into
electronic control thereby better combustion and economy as
well as low emissions can be achieved.
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