Exhaust aftertreatment, function

B14.40-0042-06

B14.40-0083-06

Generalities

The post-treatment of exhaust gases with Diesel Blue Tec technology reduce the emission of harmful gases from the exhaust system of diesel engines. The technology is based in the process nominated "Selective Catalytic Reduction" (SCR), in which, upon a subsequent treatment of the exhaust gases, the harmful nitrogen oxides (NOx) are reduced to nitrogen (N2) and water vapor (H2O).

The vehicles equipped with the Diesel Blue Tec technology have special system components and an engine developed for this purpose, whose combustion has maximum efficiency and low emission of soot particles.

W14.40-1061-71

Reason

When optimizing the engine to increase its efficiency and, thus, the best possible performance with the lowest fuel consumption (C), the result is more nitrogen oxide (NOx) produced. If the combustion were adapted to a low emission of nitrogen oxide (NOx), then, the fuel consumption (C) would increase together with the quantity of soot particles (PM), which is fuel without burnout.

Therefore, an internal engine optimization implementation for the reduction of NOx and soot, to accomplish future legal requirements won't be possible, due to this inverse relation. It means that the exhaust gases will have to go through a post-treatment.

Vehicles equipped with diesel technology have an engine developed through components that help reduce nitrogen oxides (NOx) formed after combustion. These components are designed with separate parts.

Additionally, the vehicles require an extra fluid: the NOx AdBlue, which is a solution of urea and is stored in a reservoir.

To enable the correct operation, besides the system components, the following subsystems are integrated in the general system:

 AdBlue Heating

 Compressed air supply

Complete operation of the system

After the engine start, the engine control module (10A01), through an automatic check routine, provides the Blue Tec. system service.

After a system authorization, the solenoid valve (17Y04) activates the compressed air operating unit (5) and the compressed air flows through the pressure limiting valve, passes by the dosing unit and is propelled to the injector nozzle (7), through the injection pipeline. The compressed air is also provided to the pump module inlet (2). Here, the air makes the pressure relief pneumatic valve to close the AdBlue return pipeline, from the pump module (2) up to the AdBlue reservoir (3), so that it is possible to form AdBlue pressure in the dosing unit (8). This occurs regardless if the AdBlue is injected or not. The continuous flow in the dosing unit (8) and in the injection pipeline ensures that the AdBlue is always supplied to the injector nozzle (7) located in the external side of the exhaust brake mixture controller pipeline.

This also ensures that no residue of AdBlue is left in the dosing unit (8), in the injector nozzle and in the injection pipeline.

When the engine control module (MR) activates the pump based on the sensors values, the AdBlue supplied by the pump module (2), which aspirates from the reservoir (3), is filtered and pumped to the dosing unit (8).

As such, the AdBlue gets in the dosing unit (8), the service pressure in the AdBlue SCR dosing valve (17Y03) is closed. When the valve opens with a calculated periodicity by the engine module (MR), the AdBlue is propelled through it and flows by the compressed air chain, due to the combination of pressure and the exhaust gases flow, throughout the injection pipeline and the injector nozzle (7).

As such, the AdBlue is injected directly in the hot exhaust gases chain.

The resulting mixture AdBlue/air decomposes into ammonium (NH3) in the heat exhaust gases flow. The generated ammonium flows towards the exhaust muffler with reduction catalyst (6), together with nitrogen molecules arisen from the combustion. The interior of the reduction catalyst (6) has a honeycomb-type framework, ceramic coated. Here, the second reduction stage happens.

The nitrogen oxide molecules meet the ammonia molecules. Releasing energy in the form of heat and, as a consequence of a chemical reaction, there are only nitrogen (N2) and water vapor (H2O) left, harmless to the environment. So that the correct injected quantity of AdBlue is injected in each job cycle, in the right moment, a constant data exchange is necessary between the Blue Tec sensors and the engine control module (MR).

For that, the dosing unit sensors (8) provide, for example, continuous information about the AdBlue pressure and temperature, as well as the compressed air pressure. Additional sensors supply information on exhaust gas temperature at the inlet and outlet of the reduction catalytic converter.

There is also the air temperature and humidity combined sensor (17B01) to take into consideration the influence of humidity and intake temperature over the nitrogen oxide emissions.

The analog data of the chassis sensors are sent to the chassis control module (17A01), where they are digitalized and transmitted by the CAN to the engine control module (MR).

The engine control module (MR) also receives information about the NOx concentration in the exhaust gases, through the Ox sensor with operating unit (17B08).

In the engine control module (MR), the calculations for the opening times of the AdBlue dosing valve (17Y03) occur, as well as the reservoir heating valve (4), under the inclusion of the current engine characteristics and the stored values in the performance map. The calculations are also carried out in the chassis control module (17A01) which needs to activate the pump module (17M01) and the pressure limiting solenoid valve 33.01 (17Y04). After the ignition is switched off, the dosing unit (8) is ventilated to avoid damage for freezing.

This occurs during the operation of the control module (max. 300s) by opening and closing the pressure regulating electromagnetic valve 33.01 (17Y04) and the AdBlue dosing valve (17Y03) at defined intervals. The basic influence variables for the ventilation time period are the pressure existing in the AdBlue pressure sensor (17B05) and the pressure sensor of the compressed air (17B06). Based on the sensors signals, the control module (MR) detects that the dosing unit has been properly filled with air and the ventilation is finished.

The heating of the AdBlue consists of a reservoir heating valve (17Y02), which is located in the engine's right side, and a cooling pipeline system, from the engine to the AdBlue reservoir

B14.40-0031-11

The individual Blue Tec components, such as the pump module (4), flow directly through ducts and/or pipelines with engine coolant.
The heat supply of the AdBlue pipelines is carried out through a package of pipelines and isolating flexible hoses

B14.40-0043-76

Function - AdBlue heating

The heating of the AdBlue is in charge that the frozen AdBlue, during the vehicle stop, is fluidized once again and also avoiding it to freeze while driving in low temperature environments.

The heating valve of the tank (17Y02) is driven by the control module (MR). The temperature of the AdBlue is recognized by the sensor combined of level and temperature AdBlue (17B02) integrated in the AdBlue tank (3), if the temperature is close to the limit value defined of approx.  8 °C. As soon as the liquid reaches a temperature of  65 ° C, the reservoir heating solenoid valve (17Y02) receives the signal from the engine control module (MR) to open, so that the coolant is directed towards the circuit.

As soon as the liquid reaches a temperature of 65°C, the tank heater unit SCR solenoid valve (17Y02) receives an open signal from the engine control (MR control unit) (10A01), so that the coolant branches to the engine coolant circuit.

After the opening, the coolant flows through the pipes towards the pump module (2). In the pump module (2) and in the AdBlue reservoir (3) there is a duct, through which the engine coolant flows directly to these components. Then, the engine coolant returns towards the engine.

Compressed air supply

The compressed air is supplied by the compressed air operating unit (5), (set in the interior part of the chassis board next to the exhaust muffler) through pipelines from the pump module (2) up to the dosing unit (8)

B14.40-0044-76

B14.40-0013-02

Compressed air supply function

The compressed air provides transportation to the AdBlue from the dosing unit (8) up to the injector nozzle (7) and the return of the AdBlue from the pump module (2) up to the AdBlue reservoir (3).

After the engine start, the engine control module (MR) activates the pressure limiting solenoid valve (17A01) through the chassis module (17Y04).

When opened, the compressed air is derived from the secondary consumer circuit. The compressed air flows through the pressure limiting solenoid valve 33.01(17Y04), fills up the reservoir (5.01) with 8.5 bar. On the pressure limiting valve with quick discharge (30.03), the pressure is limited to 5.5 bar. The compressed air flows by the compressed air contactor valve (33.08) which doesn't receive a signal and, thus, allows the compressed air to pass through any equipment which has been switched on.

When the engine is running, the compressed air flows continuously during this period. The role of the check valve (8.01) is to protect the compressed air circuit from the engine's exhaust gases.

the compressed air, coming from the secondary consumption circuit, flows through the dosing unit (8) to the injector nozzle (7) by a compressed air pipeline. Compressed air is also propelled up to the pump module connector (4). Here, the compressed air is in charge that the pneumatic change-over switch valve closes the return of AdBlue, from the pump module (2) up to the AdBlue reservoir (3). This valve is closed when submitted to compressed air.

Air outlet and pressure reduction of individual Blue Tec components

After the ignition is switched off, the dosing unit (8) is ventilated to avoid damage for freezing. This occurs during the operation of the control module (max. 30 seconds) when activated the compressed air relay valve (33.08). During this period, the pressure limiting solenoid valve 33.01 (17Y04) is not activated because the supply of compressed air in the circuit doesn't empty unnecessarily. After the compressed air relay valve (33.08) is applied for 5 times, the pressure reservoir is totally emptied. It ensures that the circuit gets clearly ventilated.

If the pressure limiting solenoid valve 33.01 closes, the pressure relief pneumatic valve opens in the pump module (2), because there is no compressed air there. The consequence of it is that the return channel to the AdBlue reservoir (3) in the pump module (2) is released.

The main influences for the ventilation time of the dosing unit (8) are the pressure existing in the AdBlue pressure sensor (17B05) and the pressure in the pressure sensor of the compressed air (17B06).

Firstly, the pressure in the AdBlue pressure sensor (17B05) and the pressure in the compressed air pressure sensor (17B06) are calculated

If the pressure difference is situated above a defined limit and/or being the measured AdBlue pressure higher than the measured compressed air pressure, the pressure limiting solenoid valve (33,01) is immediately shut and the pressure reservoir is completely emptied by the compressed air relay valve (33.08) through the supply line.

The compressed air of the secondary consumption circuit 4 flows to the dosing unit (8) and then, against the AdBlue dosing valve (17Y03) flow direction, through the dosing unit (8) and propels the residual AdBlue back into the pipeline between the dosing unit (8) and the pump module (2).

The AdBlue dosing valve (17Y03) is closed, there can't be AdBlue flow. The pressure formed in the AdBlue pipeline is reduced by the open return line up to the AdBlue reservoir (3), since the pneumatic control valve in the pump module (2) is not submitted to the compressed air pressure anymore.

Thus, the AdBlue can flow back to the AdBlue reservoir (3) and the pressure in the ADBlue pipeline system is reduced in the approximate atmospheric pressure.

The AdBlue pipeline, between the pump module (2) and the dosing unit (8), is an elastic hose. It is able to transport additional volumes that may arise due to the freezing of residual AdBlue in line.

The intermittent processes of opening and closing of the concerned valves are carried out until the pressure in the AdBlue pressure sensor (17B05) gets lower than the pressure in the compressed air pressure sensor (17B06)

The AdBlue line between the pump module (2) and the measurement device (8) is a line of elastic hoses. This hose line can transport additional volumes that may arise due to the freezing of residual AdBlue in line.

If the engine control module (MR), based on sensor signals, recognizes that the dosing unit (8) is sufficiently filled with air and the pressure in the AdBlue pipeline system is sufficiently reduced, the ventilation is finished.

The ventilation of the dosing unit (8) and the pump module (2) can be heard until the end of the ventilation process, after the engine shut-off.