.

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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Common Rail Diesel Fuel Systems

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.

Common Rail Diesel Fuel Systems

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.

Denso

Bosch

ECD-U2P

EDC16

Common Rail Diesel Fuel Systems

The fuel system can be divided into three basic circuits

High pressure delivery

• Low pressure supply circuit

• High pressure delivery circuit

• Fuel leak back and return

Low pressure

supply

Fuel leak back and return

Example: Bosch EDC16

Common Rail Diesel Fuel Systems

Components overview (example: Bosch EDC 16)

Fuel metering control valve

High pressure

Fuel rail pressure control valve

fuel pump

Fuel rail pressure sensor

Fuel filter

Common rail

Electric fuel

pump

ECM

Low pressure

High pressure

Injectors

Leak back/return

Common Rail Diesel Fuel Systems

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 HP4

Bosch CP1

Denso HP3

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.

Common Rail Diesel Fuel Systems

High pressure fuel pump

Fuel metering control

Fuel return

valve (solenoid)

Fuel supply inlet

Example:

High pressure

Bosch CP3

fuel outlet

Gear type transfer

Pump shaft with

pump

eccentric cam

Pressure valve

Polygon ring

Suction valve

The pump has several pumping chambers

Common Rail Diesel Fuel Systems

High pressure fuel pump

2

3

3

Pumping

4

chamber

1

Fuel metering valve

Transfer pump

1: Pressure valve

2: Suction valve

3: Low pressure (yellow)

4: High pressure (red)

Common Rail Diesel Fuel Systems

High pressure fuel pump

Fuel metering valve

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.

Common Rail Diesel Fuel Systems

High pressure fuel pump

Pump shaft

Polygon ring

Pumping piston

Eccentric cam

3 pumping pistons are operated by a polygon

ring on an eccentric cam on the pump shaft.

Common Rail Diesel Fuel Systems

High pressure fuel pump

Pump shaft

Polygon ring

Pumping piston

Eccentric cam

As the pump rotates, the polygon ring moves in

a circular motion to operate the pump pistons.

Common Rail Diesel Fuel Systems

Transfer pump

Fuel inlet port

Fuel outlet port

Trochoidal type (Denso HP3)

Gear type (Bosch CP3)

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.

Common Rail Diesel Fuel Systems

Fuel metering control valve

Example:

Bosch CP3

• Located at back of high pressure pump.

• Controls the fuel intake volume to the pump.

Fuel inlet

• Receives battery voltage supply from engine ECM.

• Energized by ECM via negatively triggered PWM.

Fuel outlet

• Operating frequency: approximately 180Hz.

Common Rail Diesel Fuel Systems

Fuel metering control valve

When solenoid de energized, valve is open

Fuel inlet

= LOW fuel volume intake to pump.

When solenoid energized, valve is closed

Fuel outlet

= HIGH fuel volume intake to pump.

The fuel volume intake is controlled as follows

Common Rail Diesel Fuel Systems

Fuel volume intake control

1

2

1

Pump piston

13

2

Pressure valve

3

to common rail

3

4

Suction valve

5

Return

4

6

Safety valve

12

7

Feed (from the tank)

5

8

Gear pump

11

9

Fuel metering control

7

6

valve

10

Throttle bore

11

Control piston

12

Lubricating-oil bore

8

10

13

High-pressure pump

Valve de energized OPEN

More fuel returns to tank

9

LOW fuel volume to pump

Common Rail Diesel Fuel Systems

Fuel volume intake control

1

2

1

Pump piston

13

2

Pressure valve

3

to common rail

3

4

Suction valve

5

Return

4

6

Safety valve

12

7

Feed (from the tank)

5

8

Gear pump

11

9

Fuel metering control

7

6

valve

10

Throttle bore

11

Control piston

12

Lubricating-oil bore

8

10

13

High-pressure pump

Valve energized CLOSED

Less fuel returns to tank

9

HIGH fuel volume to pump

Common Rail Diesel Fuel Systems

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

Common Rail Diesel Fuel Systems

Fuel metering control valve failure symptoms and diagnosis

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.

Mechanical faults can cause DTC’s relating to positive

or negative rail pressure deviations.

Common Rail Diesel Fuel Systems

High pressure regulator valve

System variant.

Fitted to back of HP pump.

Controls high pressure fuel

High pressure fuel

delivery to common rail.

delivery to common tail

Excess fuel returns to

tank.

High pressure

Fuel cooler required to cool

regulator valve

Fuel return

return fuel flow.

(to fuel tank)

Low pressure fuel inlet

(from fuel tank)

Common Rail Diesel Fuel Systems

High pressure accumulator (common rail)

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.

It also damps pressure vibrations caused by the high pressure pump

and injection processes.

Typical volume of fuel held in common rail: 16 - 20cm³.

Common Rail Diesel Fuel Systems

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:

approximately between 1600 - 2000 Bar (23520 - 28400 psi)

Common Rail Diesel Fuel Systems

High pressure accumulator (common rail)

Typical fuel rail pressure with engine idling and at running temperature:

approximately between 300 - 400 Bar (4410 - 5880 psi)

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!

Typical maximum possible fuel rail pressure:

approximately between 1600 - 2000 Bar (23520 - 28400 psi)

Common Rail Diesel Fuel Systems

Fuel rail pressure sensor

Fuel pressure sensor

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

Common Rail Diesel Fuel Systems

Fuel rail pressure sensor

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.

Common Rail Diesel Fuel Systems

Fuel rail pressure sensor

Signal voltage

(0 - 5V)

5 Volts supply

Sensor ground

from ECM

(<0.2 Volts

Piezo crystal

sensor

Pressure

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.

Common Rail Diesel Fuel Systems

Fuel rail pressure sensor

Signal voltage

(0 - 5V)

5 Volts supply

Sensor ground

from ECM

(<0.2 Volts

Piezo crystal

sensor

Pressure

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).

Common Rail Diesel Fuel Systems

Rail pressure limiter valve

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.

Rail pressure limiter

valve (mechanical)

Common Rail Diesel Fuel Systems

Rail pressure limiter valve

If excessive fuel pressure is generated, the valve opens

a fuel return port.

Fuel return

Excess fuel is relieved back to the fuel tank.

Rail pressure limiter

valve (mechanical)

Common Rail Diesel Fuel Systems

Rail pressure limiter valve

Fuel return to 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)

Common Rail Diesel Fuel Systems

Fuel rail pressure control valve solenoid

A rail pressure control valve solenoid is fitted to the common rail on

some systems.

Fuel return

Rail pressure control

valve (solenoid)

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.

Common Rail Diesel Fuel Systems

Rail pressure control valve solenoid

Receives battery voltage supply from engine ECM.

Energized by engine ECM via a negatively

triggered PWM.

Operating frequency: approximately 1000Hz

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.

Common Rail Diesel Fuel Systems

Rail pressure control valve de energized

0

max.

More fuel is returned to fuel tank

A

via return port.

Rail pressure

600

900

300

1200

Decreases.

Engine ECM

0

1500

Rail pressure

Fuel return port

Common Rail Diesel Fuel Systems

Rail pressure control valve energized

0

max.

Less fuel is returned to fuel tank

A

via return port.

Rail pressure

600

900

300

1200

Increases.

Engine ECM

0

1500

Rail pressure

Fuel return port

Common Rail Diesel Fuel Systems

Rail pressure control valve failure symptoms and diagnosis

Most likely consequence:

Engine stops or will not start.

Solenoid circuit monitored by engine ECM.

Open or short circuit detected:

DTC stored and MIL illuminated.

(Engine stops or will not start).

Mechanical failure:

A minimum amount of fuel rail pressure is

required to enable the engine to start.

Typical value:

approximately between 200 - 300 Bar

Common Rail Diesel Fuel Systems

Rail pressure control valve failure symptoms and diagnosis

Most likely consequence:

Engine stops or will not start.

Solenoid circuit monitored by engine ECM.

Open or short circuit detected:

DTC stored and MIL illuminated.

(Engine stops or will not start).

Mechanical failure:

Valve stuck open = Low rail pressure.

Engine stops or will not start.

Valve stuck closed = High rail pressure.

Engine stops or will not start.

Common Rail Diesel Fuel Systems

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.

Common Rail Diesel Fuel Systems

Pressure control valve waveform: engine idling

Green = % duty cycle

Blue = rail pressure

Red = current draw

Common Rail Diesel Fuel Systems

Pressure control valve waveform: snap acceleration

Green = % duty cycle

Blue = rail pressure

Red = current draw

Common Rail Diesel Fuel Systems

Pressure control valve waveform

Remember:

The engine stops or will not

start if the fuel rail pressure

control valve fails!

Common Rail Diesel Fuel Systems

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.

Common Rail Diesel Fuel Systems

Fuel injectors

Fuel leak back (return)

Solenoid actuator

Injector valve

Electrical

connection

Valve piston

High pressure fuel inlet

(from common rail)

Nozzle spring

Thrust piece

Valve needle

Common Rail Diesel Fuel Systems

Fuel leak back (return) port

Operation of fuel injectors

Fuel pressure is supplied to the injector

High pressure

needle seat area

fuel inlet

Injector piston

Injector valve

Inlet port

Injector needle

and also to a small chamber above the

injector piston via a calibrated inlet port.

Common Rail Diesel Fuel Systems

Fuel leak back (return) port

Operation of fuel injectors

When the solenoid is energized,

High pressure

the injector valve opens.

fuel inlet

Injector valve

Injector piston

opens

Injector needle

Fuel pressure is relieved above the injector

piston and returns to the fuel tank via the

injector leak back (return) ports.

Common Rail Diesel Fuel Systems

Fuel leak back (return) port

Operation of fuel injectors

This creates a pressure difference above

High pressure

and below the injector piston.

fuel inlet

Injector piston

Injector needle

Fuel pressure below the injector needle lifts

the needle.

Common Rail Diesel Fuel Systems

Fuel leak back (return) port

Operation of fuel injectors

Fuel is now injected into the

High pressure

cylinder.

fuel inlet

Injector piston

Injector needle

Maximum stroke of solenoid valve:

approximately 50 micrometers (0.05 mm).

Common Rail Diesel Fuel Systems

Piezo injector

Fuel supply

Primary advantage:

Quicker response time (up to four times

Leak back

faster than solenoid controlled injector).

Features

Piezo stack

Piezo stack has several hundred wafer

thin slices of Piezo crystal material.

Injector piston

When voltage is applied, the piezo

Injector valve

stack expands and opens the injector

valve.

Mechanical principle of operation is

Injector needle

similar to the solenoid injector.

Common Rail Diesel Fuel Systems

Injector codes

Most injectors have a code that must be programmed into the engine

ECM.

Bosch injector generation 2

Denso injector

IMA code for injector flow adjustment

QR (Quick Response) code

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.

Common Rail Diesel Fuel Systems

Oscilloscope waveform: Solenoid injector de energized

Blue

= switched +

Red

= switched -

Green = current draw

Common Rail Diesel Fuel Systems

Oscilloscope waveform: Solenoid injector energized

Blue

= switched +

Red

= switched -

Green = current draw

Common Rail Diesel Fuel Systems

Oscilloscope waveform: Piezo injector de energized

Blue

= switched +

Red

= switched -

Green = current draw

Common Rail Diesel Fuel Systems

Oscilloscope waveform: Piezo injector energized

Blue

= switched +

Red

= switched -

Green = current draw

Common Rail Diesel Fuel Systems

Engine management closed loop control functions:

Rail pressure

Rail pressure calculation

calculation

(pre set values)

Engine Stationary

Engine Start

Example:

% duty cycle:

Comparison:

Fuel metering and

Bosch EDC16

Actual value

rail pressure

with set value

(2 point control)

control solenoids

Actual fuel rail

Closed loop control

pressure value

Common Rail Diesel Fuel Systems

Engine management closed loop control functions:

Rail pressure calculation

Example:

Bosch EDC16

APP

(2 point control)

CKP

ECM

ECT

B+

DPF

Common Rail Diesel Fuel Systems

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.

Common Rail Diesel Fuel Systems

Fuel system diagnosis

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?

Common Rail Diesel Fuel Systems

Fuel system diagnosis

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.

Common Rail Diesel Fuel Systems

Fuel system diagnosis

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)

Common Rail Diesel Fuel Systems

Fuel system diagnosis

Maximum fuel pressure

Snap acceleration

(approx 1519 Bar)

Engine idling

(approx 362 Bar)

Engine cranking

(approx 500 Bar)

Thank you

for attending a technical overview of

Common Rail

Diesel Fuel Systems

presented by

Tony Kitchen

(AK Training)