chapter 2 (common rail diesel)

8/9/2019 CHAPTER 2 (Common Rail Diesel)

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DIESEL COMMON RAIL SYSTEM


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CHAPTER OBJECTIVE

2.1Understand the function, construction and operation of Diesel

Common Rail system

2.1.1 Explain the application of common rail

2.1.2 Identify and explain functions of common rail components

2.1.3 Explain the injection characteristics with common rail

2.1.4 Explain the application of electronic diesel control

2.1.5 Describe trouble shooting using diagnostic tool


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Demand On Modern Diesel Engine

Development

Low fuel consumption

Low pollutant emissions

Quiet running enginesImproved engine performance

Improving the diesel engine

capabilities


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Application of Common Rail

Concern for the environment

Strict limits on particle emissions lead to

increasingly higher injection pressures

Makes available provides better fuel

atomization

Optimizing injection timing and quantity forvariations in fuel quality


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Convent ional

Common Rai l Diesel


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COMPONENT OF CRD


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BASIC CONCEPT COMMON RAIL

SYSTEM


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ACCUMULATOR (RAIL)

Used to create a common reservoir of fuel

under a consistent controlled pressure That separate from the fuel injection points

Also damps pressure vibrations caused by high

pressure pump & injection processes


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FUEL RAIL PRESSURE SENSOR

A fuel rail pressure sensor is located on the fuel rail

Monitors the fuel pressure in the common rail Inputs the information to the ECU

3 wires:

- 5 volt supply from engine- Sensor ground via engine

- Linear signal voltage output to ECM


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FUEL RAIL PRESSURE CONTROL VALVE

Controls fuel pressure by opening & closing a

return port in the rail

Excess fuel returns to the fuel tank via the fuel

return


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PRESSURE LIMITER VALVE

Located at the end of the fuel rail To relieve rail pressure if abnormally high

system pressure is generated


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HIGH PRESSURE PUMP

Interface between low pressure & high

pressure side of fuel system Ensure that enough fuel is delivered at

sufficient pressure across the engines entire

operating range The pressure is set by ECU


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FUEL METERING CONTROL VALVE

Located at back of high pressurepump

Controls the fuel intake volume to

pump Receives battery voltage supply from

engine


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INJECTOR

used in Common Rail systems are triggered

externally by an Electronic Diesel Control(EDC) unit

controls all the engine injection parameters

including the pressure in the fuel rail and thetiming and duration of injection


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Injector Sizes


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Components of Injector


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Operation

(Diesel Common Rail System)


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How does a CR system operation?

Sub functions of a CRFI system

Low pressure circuit High pressure circuit ECU with sensors

COMMON RAIL FUEL INJECTION SYSTEM


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The Common Rail Sub functions (LOW PRESSURE)

The lowpressure circuit is responsible for

transporting the fuel to the highpressure circuit

Lowpressure circuit comprises of:

Fuel tank ,Pre-supply pump, Fuel filter & therespective connection lines


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The Common Rail Sub functions (HIGH PRESSURE)

Responsibility of the high pressure circuit to generate a constant

unvarying high pressure

Inject the fuel through the injectors into the engines combustion

chambers

Highpressure circuit comprises:

Highpressure pump with pressurecontrol valve

The highpressure accumulator (Rail )with the railpressure sensor Injectors

The respective highpressure connection lines


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Sensor- responsible for measuring important

physical quantities

ECU- calculates injected fuel quantity, start of

injection, duration of injection, and rate of

discharge curve, as well supervises the correct

functioning of the injection system

The Common Rail Sub functions (ECU & SENSOR)


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The Common Rail Sub functions

ECU and sensors

The common rail ECU evaluates the signals from thefollowing sensors

Crankshaft - speed sensor, Camshaft sensor

Accelerator - pedal travel sensor

Boostpressure sensor, air temperature sensor

Airmass meter & rail pressure sensor


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EDCElectronic Diesel Control

APPLICATION

Advances in fuel delivery and engine

management systems

Injectors controlled by the engine computer

Sensitive controls

Ability to process additional parameters Tighter tolerances & increased accuracy even

over very long periods of operation


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EDCElectronic Diesel Control

SENSOR

- Control collar in the injection pump by angle sensors

- detect the start of injection by sensing the needle movement

ECU- Employs digital technology

- Function of parameters : load, e/g speed coolant temp, air

quantity

- Protective circuitry & mechanical shielding provide a highlevel of EMC (electro-magnetic compatibility)

TROUBLESHOOTING


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TROUBLESHOOTING

Low Compression

not enough heat being produced to

ignite the diesel fuel and cause

hard starting

compression readings average

approximately (275-400 psi)

Low Fuel Pressure

diesel injector rail not holding the fuel within the system andpoor fuel supply

Check pressure supply from the fuel tank to the high pressure

pump

Low Cranking Speed


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Low Cranking Speed

vehicle is turning over slowly

diesel pump can't generate enough fuel pressure

to initialize fuel injection causing hard starting

problems

During the colder periods of the year low

cranking speed is more common due the battery

being flat or faulty

Diesel Injector/s Faulty

injector failure is due to excessive back leak or return flow

Cause by internal worn parts (pilot valve, nozzles or seals)

The outcome of excessive leakage is a drop in rail pressure

Injector Wiring Harness

Faults occur with injector wiring harness with vehicles that have cam

driven injectors ( Unit Injectors ) under the rocker cover which allow

engine oil to come into contact with the electrical connectors


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ADVANTAGES USING COMMON RAIL DIESEL

Delivers a more controlled quantity : -

Atomized fuel, which leads to better fuel economy

A reduction in exhaust emissions

Significant decrease in engine noise during

operation

chapter 2 (common rail diesel)

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