Common Rail Injection System – Diesel Engines Troubleshooting

Bosch-Common Rail System – Fuel additive

Metallic catalysts, cerium and iron, are used as fuel additives. These accelerate burn-off of the diesel particulates and lower the temperature at which burn-off can occur.

Each time after the fuel tank is filled, a metered quantity of fuel additive is injected into the fuel tank where it mixes with the fuel. When combustion takes place, the cerium and iron traces mix with the particulates from the diesel exhaust gas and provide for a considerably lower burn-off temperature. As a result, the particulate matter collected in the filter can be burned off at temperatures of just over 450 °C.

The homogeneously bound cerium oxide/diesel particulate matter is then filtered out by the particulate filter, where it becomes embedded. Due to the combination of fuel additives (reduction in the burn-off temperature of the particles) and the engine management system (increase in the exhaust gas temperature) diesel particulate filters can be regenerated not only under full load conditions, but also in the partial load range at comparatively low exhaust gas temperatures typical for urban traffic.

20. August 2018 by samuel07042012
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Bosch-Common Rail System – Fuel additive Injector

The injector is connected to the fuel additive tank by means of a fuel pipe. The fuel additive pump generates pressure in the fuel pipe. The injector check valve opens and fuel additive is fed into the fuel tank.

20. August 2018 by samuel07042012
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Bosch-Common Rail System – Fuel additive pump unit

1 Connection to the fuel tank
2 Fuel additive pump
3 Piezo sensor

The fuel additive pump is designed as a displacement-type pump (piston pump). It feeds the fuel additive, metered according to the command issued by the fuel additive control unit, via a short fuel pipe to the injector where it is injected into the fuel tank.

The piezo sensor at the bottom end of the fuel additive pump unit contains two sensor elements with the following functions:
• They determine changes in the viscosity of the fuel additive as a result of changes in ambient temperature.
• They detect when the fuel additive tank is empty (measurement of the precise fuel level in the fuel additive tank is also envisaged and will be implemented at a later date).

In the event of an empty fuel additive tank, initially the engine system fault warning lamp illuminates. This means that from this point, only a residual quantity of fuel additive is available for approximately 250 liters of fuel. If the fuel additive tank is not refilled, the MIL illuminates and the fuel additive injection process is stopped.

20. August 2018 by samuel07042012
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Bosch-Common Rail System – Fuel additive tank

1 Fuel line to fuel tank
2 Overflow (when filling)
3 Fuel filler connection
4 Fuel additive tank
5 Fuel additive pump unit
6 Vent assembly

The fuel additive tank is located behind the fuel tank and is attached to the crossmember. The fuel additive tank forms a unit together with the fuel additive pump unit and can therefore only be replaced as a whole. The fuel additive tank has a capacity of 1.8 liters for an average total mileage of 60,000 km. Therefore, the fuel additive has to be topped up according to the service specifications.

Note: The fuel additive tank cannot be emptied fully. Once the quantity remaining falls below 0.3 liters, fuel additive injection ceases (the driver is informed before this occurs via the relevant warning lamps). The residual quantity prevents the fuel additive pump from drawing in air, which could result in incorrect quantities of fuel additive being metered. The maximum top-up quantity is therefore 1.5 liters.

20. August 2018 by samuel07042012
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Bosch-Common Rail System – Fuel additive system

1 Fuel tank
2 Hoses for fuel additive (top up and ventilation)
3 Fuel additive tank
4 Fuel additive pump unit
5 Fuel additive pipe to fuel injector
6 Fuel injector

The fuel additive system comprises the following components:
• a fuel additive tank with a fuel additive pump unit,
• fuel additive pipes,
• a fuel injector.

In addition, a tank flap switch and a fuel additive control unit are installed in the vehicle (not illustrated). The fuel additive is injected into the fuel tank via the fuel additive pump unit, the fuel additive pipe and the fuel injector.

The fuel additive mixes with the diesel fuel in the fuel tank. The quantity of the fuel additive to be injected is dependent on the diesel fuel quantity at each refueling.

20. August 2018 by samuel07042012
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Bosch-Common Rail System – Intercooler bypass

1 MAP sensor
2 Intake manifold flap housing
3 Intercooler bypass
4 MAF sensor with integral IAT sensor
5 Connecting piece between turbocharger and intercooler
6 Intercooler
7 Turbocharger vacuum unit
8 Intercooler bypass flap servo motor
9 Intercooler/intake manifold flap connection
10 Intake manifold flap servo motor

An intake manifold flap housing has been added to the intake system in conjunction with the particulate filter system. The intake manifold flap housing contains the following components:
• Intercooler bypass flap with servo motor,
• Intake manifold flap with servo motor,
• MAP sensor,
• IAT sensor (not illustrated).

The intake manifold flap creates the connection between the cooled air from the intercooler and the intake ports of the engine via the intake manifold flap housing.

The intercooler bypass valve creates a direct connection between the compressor side of the turbocharger and the intake ports of the engine via the intake manifold flap housing. The intercooler is bypassed.

The intercooler bypass flap is adjusted via a servo motor during the regeneration phase of the diesel particulate filter.

During the regeneration phase the air mass flowing through the intercooler (regulated by the intake manifold flap) is reduced. At the same time, the flow of uncooled air mass via the intercooler bypass (regulated by the intercooler bypass flap) is increased. This reduces the engine’s cylinder charge while keeping the intake air temperatures constant to prevent variations in exhaust gas temperatures during regeneration. The position of both valves is dependent on the intake air temperature. For this reason, there is an additional IAT sensor in the intake manifold flap housing, downstream of the intake manifold flap and intercooler bypass flap (not illustrated).

20. August 2018 by samuel07042012
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Bosch-Common Rail System – Diesel particulate filter

1 Connection – exhaust gas temperature sensor – diesel particulate filter
2 Pipes to diesel particulate filter differential pressure sensor
3 Diesel particulate filter and catalytic converter housing

The diesel particulate filter of the 1.6L Duratorq-TDCi (DV) engine is downstream of the catalytic converter in the flow direction of the exhaust gases. Oxidation catalytic converter and diesel particulate filter are combined in one housing. The particulate matter contained in the exhaust gas is deposited in the diesel particulate filter. The pressure drop across the particulate filter (measured via the diesel particulate filter differential pressure sensor) is an indicator for the soot load of the filter. The soot load capacity of the diesel particulate filter is limited, however, so that it has to be regenerated at regular intervals (burning/oxidation of the diesel particulates).

After regeneration, ash residues that have formed from the fuel additive, engine oil and fuel remain in the diesel particulate filter. These constituents cannot be further converted and can only be deposited in the diesel particulate filter up to a certain degree. This means that the diesel particulate filter must be replaced at prescribed service intervals.

1 Exhaust gas from engine
2 Oxidation catalytic converter
3 Diesel particulate filter
4 Cleaned exhaust gas

The diesel particulate filter is a honeycomb structure, the walls of which are made of porous silicon carbide In addition, the individual ducts are sealed at one side and offset to each other.

After combustion has occurred, some diesel particulates may still be present in the exhaust gas. As part of the filtration process, the exhaust gases loaded with diesel particulate matter flow into the diesel particulate filter
and are then forced to flow through the porous walls as a result of the offset position of the sealed channels.

The build up of diesel particulate matter in the intermediate chambers of the porous walls increases the filtration effect still further.

20. August 2018 by samuel07042012
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Bosch-Common Rail System – Controlling the fuel pressure

1 PCM
2 High pressure pump
3 High pressure chambers for high pressure generation
4 Fuel feed
5 Fuel metering valve
6 Fuel pressure sensor
7 Fuel rail
8 Solenoid valve
9 Injector needle

The engine management system on the common rail injection system is capable of providing the optimum injection pressure for each operating condition.Via the high pressure chambers of the common rail high-pressure pump, fuel is compressed and fed to the fuel rail. In the process, the delivery quantity is regulated by the fuel metering valve by varying the opening cross section of the fuel metering valve accordingly. The fuel pressure is regulated in such a way that the optimum pressure is available for each operating condition. On the one hand, this reduces the noise emission during fuel combustion.

On the other hand, the engine management system can meter the fuel very precisely, which has a positive effect on exhaust emissions and fuel consumption. The fuel pressure sensor continuously informs the PCM about the current fuel pressure. Pressure is regulated via the fuel metering valve by reducing the cross section of this valve accordingly. As a result, the high-pressure pump delivers a smaller quantity of fuel (or no fuel at all, depending on the requirements) until the desired fuel pressure is reached. Fuel pressure is dependent on engine speed and engine load.

Switching off the engine

Because of the way the diesel engine works, the engine can only be switched off by interrupting the fuel supply. In the case of fully electronic engine management this is achieved by the PCM specifying an injected quantity of 0. The solenoids for fuel injection are therefore no longer energized and the engine is switched off.

Pressure drop after engine is switched off

After the engine has been switched off, pressure is reduced through leakage past the fuel injectors. The rate of pressure reduction depends on how high the fuel pressure and fuel temperature are. For safety reasons, a certain period of time has to elapse before the high-pressure system is opened after the engine is stopped.

20. August 2018 by samuel07042012
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Bosch-Common Rail System – Boost pressure control

1 Boost pressure solenoid valve
2 MAP sensor
3 Intercooler
4 Vacuum unit for variable turbine geometry
5 Turbocharger(s)
6 PCM
7 Vacuum pump

On a variable turbocharger, the boost pressure is regulated by adjusting the guide vanes. This means that optimum boost pressure can be set for any operating condition.

The boost pressure actual value is measured via the MAP sensor. The set value depends on the speed and injected fuel quantity as well as the BARO.

When a control deviation occurs, the guide vanes of the variable-geometry turbocharger are adjusted via the boost pressure control solenoid valve.

In the event of a malfunction of the boost pressure control system, engine power is reduced via the fuel metering system.

Within the framework of EOBD, all the components of the boost pressure control system are monitored individually as is their interaction (during system monitoring).

Turbocharger diagnosis

Boost pressure control works as a system. The interaction of individual components (including the turbocharger) is monitored.

Malfunctions of the turbocharger and faults of the boost pressure control solenoid valve or the vacuum system for the turbocharger actuation result in increased exhaust emissions which exceed the EOBD limits. Certain faults also lead to the EGR system being switched off. Therefore, this is a MIL active system.

Malfunctions in the boost pressure control system are detected by the MAP sensor.

In the event of a fault, the PCM limits the injected fuel quantity (power output reduction) and sets a diagnostic trouble code.

Possible diagnostic trouble codes:
• MIL active: P0045, P0046, P0047, P0048
• Non MIL active: P0234, P0299

20. August 2018 by samuel07042012
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Bosch-Common Rail System – EGR system

1 MAF sensor
2 PCM
3 Oxidation catalytic converter
4 Turbocharger(s)
5 EGR valve servo motor
6 Position sensor (integrated in servo motor)
7 Intercooler
8 EGR cooler
9 Intake manifold flap with servo motor (only in emission standard IV)

By using turbochargers, the temperatures in the combustion chamber rise together with the compression and combustion performance.

In addition, the combustion temperatures are increased by using the direct fuel injection method. Both result in the increased formation of NOX in the exhaust gas. In order to keep this NOX content in the exhaust gas within required limits, the EGR system is becoming increasingly important.

In the part load range, exhaust gas recirculation is achieved by mixing the exhaust gases with the intake air. This reduces the oxygen concentration in the intake air. In addition, exhaust gas has a higher specific heat capacity than air and the proportion of water in the recirculated exhaust gas also reduces the combustion temperatures.

These effects lower the combustion temperatures (and thereby the proportion of NOX) and also reduce the amount of exhaust gas emitted. The quantity of exhaust gas to be recirculated is precisely determined by the PCM. An excessive exhaust gas recirculation rate would lead to an increase in diesel particulate, CO and HC emissions due to lack of air.

For this reason, the PCM requires feedback on the amount of recirculated exhaust gases. This works via the MAF sensor and a position sensor which is integrated into the servo motor of the EGR valve. The servo motor itself is activated by the PCM depending on requirements.

MAF sensor

The quantity of exhaust gas recirculated when the EGR valve opens has a direct influence on the MAF sensor measurement. During exhaust gas recirculation, the reduced air mass measured by the MAF sensor corresponds exactly to the value of the recirculated exhaust gases. If the quantity of recirculated exhaust gas is too high, the intake air mass drops to a specific limit. The PCM then reduces the proportion of recirculated exhaust gas, thus forming a closed control loop.

Position sensor

In the face of increasingly stringent emission standards, EGR control via the MAF sensor alone is reaching its limits. For this reason, a position sensor, which is integrated into the EGR valve servo motor, is used in addition to the MAF sensor.

Intake manifold flap

A further step towards minimizing NOX is the restriction of intake air via the intake manifold flap. By partial closing of the intake manifold flap a vacuum is generated behind the intake manifold flap. The vacuum results in the exhaust gases being drawn in more efficiently by the engine via the EGR valve, enabling the EGR rate to be metered more effectively. This combination (MAF sensor, position sensor and intake manifold flap control) allows even more precise metering of the recirculated quantity of exhaust gas. This way, it is possible to get even closer to the operating limit with a greater quantity of exhaust gas. The NOX emissions are thereby reduced to a minimum.

Diagnosis

The EGR control works as a system. The interaction of individual components is monitored. Malfunctions lead to increased exhaust emissions which exceed the EOBD limits. Certain faults also lead to the EGR system being switched off. Therefore, this is a MIL active system. Malfunctions in the EGR system are detected by the MAF sensor. In case of a fault, the EGR system is switched off. In the event of specific faults, the PCM limits the injected fuel quantity (power output reduction).

14. August 2018 by samuel07042012
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