Common rail diesel fuel systems

Welcome
to a technical overview of
Common Rail
Diesel Fuel Systems
presented by
Tony Kitchen
(AK Training)

Foreword
Tony Kitchen (AK Training) offers professional technical courses for those working in the motor industry
wanting to improve their knowledge and skills and who are serious about personal development. Courses
are based upon 25 years practical experience and extensive hands on technical knowledge of subject
matter (not possible to obtain from reading a book or watching a CD)!
A comprehensive programme of courses is available from AK Training. Courses run from regular venues in
the Milton Keynes, Northampton and Buckingham area. Courses can also be delivered on site at clients
premises anywhere in the UK. Overseas training services are also available. This presentation forms the
basis for a generic common rail diesel course which is now undergoing development and will be available
in the near future.
For further information about courses, course dates, fees, venues and all other enquiries including on site
and overseas training, please contact AK Training direct. In the meantime, please enjoy the following
presentation for your technical information.
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Aims, objectives and disclaimer:
The aim of this presentation is to give a generic technical overview of the main features and
operating principles of the common rail diesel fuel injection system. The objectives are that
by the end of this presentation, you will have gained a working knowledge and
understanding of the fundamental principles of common rail diesel fuel systems.
Please bear in mind that all facts and figures quoted are intended to show typical examples
only for explanation purposes. Always refer to manufacturer technical data for exact system
specifications and repair procedures.
Finally this slide show does not include speaker notes. If you have any comments or would
like further information, please contact AK Training directly
Common Rail Diesel Fuel Systems

Advantages of common rail:
• Fuel pressure available on demand.....
• Higher injection pressures and finer atomization of fuel.....
• Injection pressure created independent of engine speed.....
• Multiple injections per cylinder combustion are possible.
Benefits of common rail:
• Reduction of overall exhaust emissions.....
• Reduction of particulate emissions.....
• Reduction of noise emissions.....
• Improved fuel efficiency.....
• Higher performance.

Examples of typical common rail system maximum fuel pressures:
• Bosch: Generation 1: up to 1350 Bar (19845 psi). Unijet
Generation 2: up to 1600 Bar (23520 psi) EDC 16
Generation 3: up to 2000 Bar + (29400 psi)
• Denso: 1st generation: up to 1450 Bar (21315 psi) ECD-U2P
2nd generation: 1800 Bar + (26460 psi) HP3/HP4
• Delphi Multec: up to 2000 Bar
Direct acting diesel common rail system: up to 2000 Bar
Various systems differ in design, components layout and specific
functions. However, all operate in a similar way.
Bosch
EDC16
Denso
ECD-U2P

The fuel system can be divided into three basic circuits
• Low pressure supply circuit
• High pressure delivery circuit
• Fuel leak back and return
Low pressure
supply
High pressure delivery
Fuel leak back and return
Example: Bosch EDC16

Electric fuel
pump
Fuel filter
High pressure
fuel pump
Fuel metering control valve
Fuel rail pressure control valve
Fuel rail pressure sensor
Common rail
Injectors
ECM
Low pressure
High pressure
Leak back/return
Components overview (example: Bosch EDC 16)

Denso HP4
High pressure fuel pump
The High pressure pump is the interface between the low pressure
and the high pressure side of the fuel system.
Bosch CP3
Denso HP3Bosch CP1
Basic function:
To ensure that enough fuel is delivered at sufficient pressure across
the engine’s entire operating range. This includes delivery of sufficient
fuel for a rapid engine start and pressure increase in the rail.

Fuel supply inlet
Fuel metering control
valve (solenoid)
High pressure
fuel outlet
Gear type transfer
pump
Pressure valve
Suction valve
Fuel return
Polygon ring
Pump shaft with
eccentric cam
The pump has several pumping chambers
Example:
Bosch CP3

1: Pressure valve
2: Suction valve
3: Low pressure (yellow)
4: High pressure (red)
1
2 3
3
4
Fuel metering valve
Pumping
chamber
Transfer pump

Transfer pump supplies fuel from the fuel tank to the
pumping chambers of the high pressure pump.
Fuel metering valve regulates the fuel intake volume
to the pumping chambers of the high pressure pump.
Transfer pump
Fuel metering valve

Pump shaft
Eccentric cam
Polygon ring
3 pumping pistons are operated by a polygon
ring on an eccentric cam on the pump shaft.
Pumping piston

Pump shaft
Eccentric cam
Polygon ring
As the pump rotates, the polygon ring moves in
a circular motion to operate the pump pistons.
Pumping piston

Transfer pump
Fuel inlet port
Fuel outlet port
An electric pre supply pump in fuel tank may be used
instead of a transfer pump. Some systems may use a
combination of electric pump and transfer pump.
Gear type (Bosch CP3)
Trochoidal type (Denso HP3)

• Located at back of high pressure pump.
• Controls the fuel intake volume to the pump.
• Receives battery voltage supply from engine ECM.
• Energized by ECM via negatively triggered PWM.
• Operating frequency: approximately 180Hz.
Fuel inlet
Fuel outlet
Example:
Bosch CP3

Fuel inlet
Fuel outlet
When solenoid de energized, valve is open
= LOW fuel volume intake to pump.
When solenoid energized, valve is closed
= HIGH fuel volume intake to pump.
The fuel volume intake is controlled as follows.....

Valve de energized OPEN
More fuel returns to tank
LOW fuel volume to pump
1 2
6
5
4
3
7
8
9
10
11
12
13
Fuel volume intake control
1 Pump piston
2 Pressure valve
3 to common rail
4 Suction valve
5 Return
6 Safety valve
7 Feed (from the tank)
8 Gear pump
9 Fuel metering control
valve
10 Throttle bore
11 Control piston
12 Lubricating-oil bore
13 High-pressure pump

1 2
6
5
4
3
7
8
9
10
12
13
11
Fuel volume intake control
1 Pump piston
2 Pressure valve
3 to common rail
4 Suction valve
5 Return
6 Safety valve
7 Feed (from the tank)
8 Gear pump
9 Fuel metering control
valve
10 Throttle bore
11 Control piston
12 Lubricating-oil bore
13 High-pressure pump
Valve energized CLOSED
Less fuel returns to tank
HIGH fuel volume to pump

Advantages of fuel intake volume regulation:
• Only the required volume of fuel is supplied to the common rail from
the high pressure pump.....
• Reduced fuel flow around system results in lower fuel return flow
temperature.....
• Reduced parasitic load on engine from high pressure pump contributes
towards further reductions in exhaust emissions.
Low volume High volume

Solenoid circuit monitored by engine ECM.
If an open or short circuit is detected:
Engine stops or will not start.
DTC stored and MIL illuminated.
Mechanical failure of the metering
control valve does not necessarily
prevent the engine from starting.
Fuel metering control valve failure symptoms and diagnosis
Mechanical faults can cause DTC’s relating to positive
or negative rail pressure deviations.

High pressure
regulator valve
Fuel return
(to fuel tank)
Low pressure fuel inlet
(from fuel tank)
High pressure fuel
delivery to common tail
High pressure regulator valve
System variant.
Fitted to back of HP pump.
Controls high pressure fuel
delivery to common rail.
Excess fuel returns to
tank.
Fuel cooler required to cool
return fuel flow.

It also damps pressure vibrations caused by the high pressure pump
and injection processes.
Typical volume of fuel held in common rail: 16 – 20cm³.
Fuel is supplied to the common rail at high pressure from the high
pressure pump.
The rail stores the fuel and distributes it to the individual injectors.
High pressure accumulator (common rail)

Typical fuel rail pressure with engine idling and at running temperature:
approximately between 300 – 400 Bar (4410 – 5880 psi)
Typical maximum possible fuel rail pressure:

Typical fuel rail pressure with engine idling and at running temperature:
Typical maximum possible fuel rail pressure:
Health and safety
Due to the extremely high working fuel pressures in the common
rail fuel system, NEVER slacken fuel or injector pipes or try to
disconnect components of the fuel system whilst the engine is
running and high pressure is present in the system!

Fuel pressure sensor
A fuel rail pressure sensor is located on the fuel rail.

Monitors the fuel pressure in the common rail.
Typically a piezo resistive type sensor.
Three wires:
• 5 Volt supply from engine ECM.
• Sensor ground via engine ECM.
• Linear signal voltage output to ECM.
Signal utilization:
To enable the engine ECM to determine the fuel rail pressure.....
Used by the ECM as part of the calculation for the % duty cycle applied
to the rail pressure control solenoid and fuel metering solenoid.

Pressure
5 Volts supply
from ECM
Piezo crystal
sensor
Sensor ground
(<0.2 Volts
Signal voltage
(0 - 5V)
The engine ECM applies a stabilized 5 Volts supply to the signal wire
of the fuel pressure sensor.....
The resistive value of the sensor creates a change in the voltage on the
signal wire relative to the fuel rail pressure.

Pressure
5 Volts supply
from ECM
Piezo crystal
sensor
Sensor ground
(<0.2 Volts
Signal voltage
(0 - 5V)
Typical signal voltages from rail pressure sensor:
Engine stationary: approximately 0.5 volts.
Engine idling: approximately 1.32 volts.
Snap acceleration: approximately 3.77 volts +
(Example figures Bosch EDC16).

Rail pressure limiter valve
Rail pressure limiter
valve (mechanical)
A mechanical pressure limiter valve is fitted to some
systems. It is located at the end of the fuel rail.
Its function is to relieve rail pressure if abnormally
high system pressure is generated.

If excessive fuel pressure is generated, the valve opens
a fuel return port.
Fuel return
Rail pressure limiter
valve (mechanical)
Excess fuel is relieved back to the fuel tank.

Example operating pressure of rail pressure
limiter valve (Denso HP3 system):
valve opens at 230 MPa (2300 Bar)
valve closes at 50 MPa (500 Bar)
Fuel return to fuel tank

Fuel rail pressure control valve solenoid
Rail pressure control
valve (solenoid)
Fuel return
The valve controls fuel pressure by opening and closing a return port
in the rail.
Excess fuel returns to the fuel tank via the fuel return.
A rail pressure control valve solenoid is fitted to the common rail on
some systems.

Rail pressure control valve solenoid
Operating frequency: approximately 1000Hz
Receives battery voltage supply from engine ECM.
Energized by engine ECM via a negatively
triggered PWM.
Used in conjunction with fuel metering solenoid, the rail pressure solenoid
provides more accurate and faster control of pressure, particularly when
reducing rail pressure during overrun.

Rail pressure control valve de energized
A
0 max.
300
600 900
1200
15000
Engine ECM
Rail pressure
Fuel return port
More fuel is returned to fuel tank
via return port.
Rail pressure
Decreases.

Rail pressure control valve energized
300
600 900
1200
15000
A
0 max.
Engine ECM
Rail pressure
Fuel return port
Less fuel is returned to fuel tank
via return port.
Rail pressure
Increases.

Rail pressure control valve failure symptoms and diagnosis
Most likely consequence:
Open or short circuit detected:
(Engine stops or will not start).
Mechanical failure:
Valve stuck open = Low rail pressure.
Valve stuck closed = High rail pressure.
A minimum amount of fuel rail pressure is
required to enable the engine to start.
Typical value:
approximately between 200 - 300 Bar

Rail pressure control valve failure symptoms and diagnosis
Most likely consequence:
Open or short circuit detected:
(Engine stops or will not start).
Mechanical failure:
Valve stuck open = Low rail pressure.
Valve stuck closed = High rail pressure.

Testing rail pressure control valve
Multimeter:
Test internal resistance of valve solenoid winding.
Typical value: approximately 3.6 Ohms.
Diagnostic scan tool:
DTC’s and monitoring of rail pressure values.
Oscilloscope:
Test supply voltage and earth switching signal from
engine ECM.
Test stability of waveform.

Pressure control valve waveform: engine idling
Green = % duty cycle
Blue = rail pressure
Red = current draw

Pressure control valve waveform: snap acceleration
Green = % duty cycle
Blue = rail pressure
Red = current draw

Pressure control valve waveform
Remember:
The engine stops or will not
start if the fuel rail pressure
control valve fails!

Fuel injectors
The fuel injectors are controlled by either a solenoid or piezo actuator.
They are energized sequentially by the engine ECM.
The ECM simultaneously switches a live voltage supply and an earth for
each injector.
Multiple injection processes per cylinder combustion are possible.

Fuel injectors
Valve piston
Valve needle
Thrust piece
Nozzle spring
High pressure fuel inlet
(from common rail)
Fuel leak back (return)
Electrical
connection
Solenoid actuator
Injector valve

Operation of fuel injectors
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Injector valve
High pressure
fuel inlet
Fuel pressure is supplied to the injector
needle seat area.....
Injector piston
and also to a small chamber above the
injector piston via a calibrated inlet port.
Inlet port
Injector needle
Fuel leak back (return) port

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High pressure
fuel inlet
Injector piston
Injector needle
When the solenoid is energized,
the injector valve opens.
Injector valve
opens
Fuel pressure is relieved above the injector
piston and returns to the fuel tank via the
injector leak back (return) ports.

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High pressure
fuel inlet
Injector piston
Injector needle
Fuel pressure below the injector needle lifts
the needle.
This creates a pressure difference above
and below the injector piston.

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High pressure
fuel inlet
Injector piston
Injector needle
Maximum stroke of solenoid valve:
approximately 50 micrometers (0.05 mm).
Fuel is now injected into the
cylinder.

Piezo injector
Primary advantage:
Quicker response time (up to four times
faster than solenoid controlled injector).
Features
Piezo stack has several hundred wafer
thin slices of Piezo crystal material.
When voltage is applied, the piezo
stack expands and opens the injector
valve.
Mechanical principle of operation is
similar to the solenoid injector.
Piezo stack
Injector piston
Leak back
Injector valve
Injector needle
Fuel supply

Injector codes
Most injectors have a code that must be programmed into the engine
ECM.
The code relates to the calibrated flow rate of the injector.
It enables the ECM to correct the injection quantity to compensate
for manufacturing tolerances.
Bosch injector generation 2
IMA code for injector flow adjustment
Denso injector
QR (Quick Response) code

Oscilloscope waveform: Solenoid injector de energized
Blue = switched +
Red = switched -
Green = current draw

Oscilloscope waveform: Solenoid injector energized
Blue = switched +
Red = switched -

Oscilloscope waveform: Piezo injector de energized
Blue = switched +
Red = switched -

Oscilloscope waveform: Piezo injector energized
Blue = switched +
Red = switched -

Engine management closed loop control functions:
Closed loop control
Rail pressure
calculation
(pre set values)
% duty cycle:
Fuel metering and
rail pressure
control solenoids
Actual fuel rail
pressure value
Comparison:
Actual value
with set value
Engine StartEngine Stationary
Rail pressure calculation
Example:
Bosch EDC16
(2 point control)

Engine management closed loop control functions:
APP
CKP
ECT
B+
DPF
ECM
Example:
Bosch EDC16
(2 point control)
Rail pressure calculation

Fuel system diagnosis
Common rail diesel fuel systems operate on a closed loop basis.
The system carries out a great many complex calculations to precisely
control fuel quantity and injection timing.
A range of tools and test equipment is commercially available to assist
with diagnosis of the system.
The following is a brief overview to highlight some of the basic tests that
can be carried out to diagnose faults with the system.

Basics first!
• Sufficient diesel in the fuel tank?
• Fuel contamination (eg from petrol).
• Fuel leaks and damage to components.
• Battery state of charge?
• Adequate low pressure fuel supply from fuel tank?
• Does engine start or crank and try to start?
• Is white smoke emitted from exhaust during engine cranking?
(not always easy to see but indicates some fuel is entering cylinders).
• Are any DTC’s stored in fault memory of engine ECM?

Is the system capable of generating sufficient fuel pressure?
Typical minimum ‘manufacturer specified’ value during engine cranking:
approximately between 200 – 300 Bar
In practice, the figure is usually higher for a good system. Above example
shows fuel pressure during engine cranking.

Injector leak back test
There should not normally be any fuel collected in receptacles during
engine cranking.
Example of acceptable leak back value with engine idling:
approximately 20ml per injector over a 2 minute period.
(Always refer to manufacturer data for exact specifications)

Maximum fuel pressure
Engine cranking
(approx 500 Bar)
Engine idling
(approx 362 Bar)
Snap acceleration
(approx 1519 Bar)

Thank you
for attending a technical overview of
Common Rail
Diesel Fuel Systems
presented by
Tony Kitchen
(AK Training)

Common rail diesel fuel systems

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