Exhaust aftertreatment, function

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Basic components

3 AdBlue reservoir (ARLA32)

4 Pump module

6 Tail pipe with catalyst by reduction

7 Injection nozzle (in the exhaust brake mixture controller piping )

8 Dispensing unit

9 Compressed air operating unit

8.01 Check valve

30.03 Pressure regulator valve with air output

33.01 SCR (Y128) compressed air limiting solenoid valve

33.08 SCR compressed air relay valve (Y106)

A6 Engine management control module (MR)

A95 SCR chassis control module

A113 NOx sensor with operating unit

A113a1 NOx sensor operating unit

A113b1 NOx sensor

B115 Temperature sensor before the SCR catalyst

B116 Temperature sensor after the SCR catalyst

B117 Combined sensor of AdBlue (ARLA32) SCR supply level and temperature

B128 SCR compressed air pressure sensor

B129 SCR AdBlue (ARLA32) pressure sensor

B130 SCR AdBlue (ARLA32) temperature sensor

B132 Combine sensor of SCR air humidity and temperature

M25 SCR AdBlue pump (ARLA32)

Y109 SCR AdBlue (ARLA32) dispensing valve

General

The treatment after the exhaust gas with BlueTec technology acts to reduce harmful gases emission from diesel engines combustion. This is a process called "Selective catalyst reduction" (SCR), where, through a later treatment of exhaust gas, the harmful nitrogen oxide (NOx) in it are reduced to nitrogen (N2) and water vapor (H2O) which are not harmful to health and the environment.

Vehicles equipped with Blue Tec technology have a system with special components and an engine developed for this purpose, whose combustion is maximum efficiency and low emission of particulate material.

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Reason:When optimizing the engine increasing its output, achieving a better performance with low fuel consumption (C), the result is a greater generation of nitrogen oxide (NOx). If combustion were adapted to a low nitrogen oxide (NOx) emission, fuel consumption (C) would increase together with the particulate material (PM) amount, which is nothing more than not-burnt fuel.

Therefore, an engine optimization for NOx and particulate material reduction to meet emissions legislation, would not be possible due to inverse relation. It means that the exhaust gases should go through a later treatment.

Therefore, diesel vehicles equipped with Blue Tec technology feature an engine developed with components that work to reduce nitrogen oxide (NOx) generated after combustion. These components are designed with supplementary parts.

The system can operate properly also because of an embedded subsystem which is the compressed air supply.

System general operation

After engine actuation it is check, firstly by the engine control module (MR) (A6), the BlueTec system functionality in a predefined automatic routine.

After releasing the system, the SCR system (Y128) compressed air limiting solenoid valve at the compressed air (9) operating unit is actuated and the compressed air flows through the pressure limiting valve, going through the dispensing unit (8) and to the injection nozzle (7). The compressed air supply to the pump module (4) take place similarly. At this moment, the air makes the pressure relief pneumatic valve close the AdBlue return pipe, from the pump module (4) to the AdBlue reservoir (3) so that it is possible to build up AdBlue pressure at the dispensing unit (8).

It takes place whether there is AdBlue injection or not. The continuous flow at the dispensing unit (8) and the injection piping ensures that AdBlue is always supplied by the injection nozzle (7) located on the side of the exhaust brake piping.

It also ensures that no AdBlue residue is left in the dispensing unit (8), in the injection nozzle (7) or in the injection piping.

When the engine control module (MR) (A6), based on sensor values, actuates the pump module (4), AdBlue is drawn from the reservoir (3), filtered and pumped to the dispensing unit (8).

Once in the dispensing unit (8), AdBlue will be under operational pressure and after the closed dispensing valve (Y109). When the dispensing valve opens, at intervals calculated by the engine control module (MR) (A6), AdBlue is injected and flows by the compressed air current due to the combination of pressure and flow of exhaust gases, throughout the injection piping and injection nozzle (7).

Therefore, AdBlue is directly injected in the hot current of exhaust gases.

The resulting mix of AdBlue/air decomposes into ammonia (NH3) in the hot flow of exhaust gases. The ammonia generated flows towards the tail pipewith reduction catalyst (6), together with the nitrogen molecules originated during the combustion. Inside the reduction catalyst (6) there is a core type structure covered with ceramics. Here there is a second stage of reduction.

The nitrogen oxide molecules meet the ammonia molecules releasing energy in the form of heat and, as a result of this chemical reaction, there is only nitrogen (N2) and water vapor (H2O), harmless to the environment. It is necessary a constant data exchange between Blue Tec sensors and the engine control module (MR) (A6) so that in each duty cycle the correct amount of AdBlue is injected at the correct time.

For that, the dispensing unit (8) sensors supply, for instance, continuous information about AdBlue pressure and temperature, as well as compressed air pressure. Additional sensors provide information on exhaust gas temperature at the intake and output of the reduction catalyst.

There is also the SCR (B132) combined air humidity and temperature sensor to take into account the influence of the intake air humidity and temperature on the nitrogen oxide emissions.

Chassis sensors analog data are sent to the chassis control module (A95), where they are digitized and transmitted by the CAN-Bus to the engine control module (MR) (A6).

The engine control module (MR) (A6) also receives information on the NOx content in the exhaust gas, through the NOx sensor with the control module (A113).

In the engine control module (MR) (A6) take place the calculation for the opening time for the AdBlue dispensing valve (Y109) according to the engine data and the values stored in the performance map. Calculations are carried out also in the SCR (A95) chassis control module that needs to actuate the SCR (M25) AdBlue pump and the pressure limiting (33.01/Y128) solenoid valve . After turning off the ignition, the dispensing unit (8) is vented to avoid damages caused by freezing.

It takes place during the later operation of the control module (up to 300 seconds) due to the opening and closing of the pressure limiting (33.01/Y128) solenoid valve and the AdBlue (Y109) dispensing valve at predefined intervals. Basic variables that influence the duration of the ventilation are the pressures in the AdBlue (B129) pressure sensor and in the SCR (B128) compressed air pressure sensor . Based on the sensors signals, the engine control module (MR) (A6) senses that the dispensing unit was properly supplied with air and the ventilation finishes.

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Compressed air supply

5 Compressed air operating unit

8.01 Check valve

30.03 Pressure regulator valve

33.01 SCR (Y128) compressed air limiting solenoid valve

33.08 SCR compressed air relay valve (Y106)

The compressed air supply takes place through the compressed air (5) operating unit, which is fixed in the inside of the chassis left side member at the tail pipe height and to a pump module piping system up to the AdBlue dispensing unit.

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Compressed air supply operation diagram

3 AdBlue reservoir (ARLA32)

4 Pump module

5 Compressed air operating unit

7 Injection nozzle

8 dispensing unit

8.01 Check valve

33.01 SCR compressed air limiting solenoid valve

30.03 Pressure regulator valve with air output

33.08 SCR compressed air relay valve

A Compressed air

M25 SCR AdBlue pump (ARLA32)

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Compressed air supply function (vehicle with general key)

The compressed air provides AdBlue transportation from the dispensing unit (8) to the injection nozzle (7) and the AdBlue return from the pump module (4) to the AdBlue reservoir (3).

After engine start-up, the engine control module (MR) (A6) is enabled, through the chassis module (A95), the SCR (33.01/Y128)compressed air limiting solenoid valve .

When open, the compressed air is derived from the secondary consumer circuit. The compressed air flows through the SCR (Y128) compressed air limiting solenoid valve, fills up the reservoir (5.01) with 8.5 bar, goes through the SCR compressed air relay valve (33.08/Y106), which will be off and, consequently open, after the check valve (8.01) and through the pressure regulator valve with air output (30.03). In the pressure regulator valve with air output (30.03), the original pressure of 8 bar is reduced to the operation pressure of the compressed air supply at  5.5 bar.

The compressed air from the secondary consumption circuit flows then through the compressed air piping and the dispensing unit (8) and the injection nozzle (7). Compressed air is also transported to the pump module (4) pneumatic connection. At this point, compressed air is responsible for a pneumatic switch valve to close the AdBlue return, from the pump module (4) to the AdBlue reservoir (3). This valve is closed when subjected to the compressed air pressure.

Air output and reduction of pressure at the Blue Tec individual components

After turning off the ignition, the dispensing unit (8) is vented to avoid damages caused by freezing. It takes place during the control module operation (up to 300 seconds ) when opening and closing the SCR (33.08/Y106) compressed air relay valve and the AdBlue SCR (Y109) dispensing valve in the dispensing unit (8) at predefined and adjusted intervals .

If the SCR (33.01/Y128) compressed air limiting solenoid valve closes, the pressure relief pneumatic valve will open in the pump module (4), because there is no compressed air actuation there. The consequence of this is that the return channel to the AdBlue reservoir (3), in the pump module (4), is released.

The main figures that influence the duration of the dispensing unit (8) ventilation are the pressures in the SCR AdBlue (B129) pressure sensor and in the SCR (B128) compressed air pressure sensor .

Firstly, the pressure is measured at the SCR (B128) compressed air pressure sensor and the AdBlue pressure sensor (B129).

If the pressure difference is above a defined threshold and/or if the AdBlue measured pressure is higher than the one measured at the compressed air, the pressure limiting solenoid valve (33.01/Y128) is immediately closed and the pressure reservoir is completely emptied by the compressed air (33.08/Y106) relay valve through the supply line.

The compressed air in the secondary consumption flows to the dispensing unit (8) and then, against the AdBlue (Y109) dispensing valve flow direction, pushes the remaining AdBlue back to the piping between the dispensing unit (8) and the pump module (2).

In the next interval, the SCR (33.01/Y128) compressed air limiting solenoid valve closes. Therefore, there will be no compressed air flowing by the dispensing unit (8) and by the pump module (4) pneumatic control valve.

The AdBlue SCR (Y109) dispensing valve is closed, and there is no AdBlue flow back. The AdBlue pressure built up in the piping is reduced through the return channel, now open, to the AdBlue reservoir (3), since the pneumatic control valve in the pump module (4) is no longer subjected to the compressed air pressure.

The AdBlue can then flow back to the AdBlue reservoir (3) and the pressure in the AdBlue piping system is reduced approximately to the atmosphere pressure.

The AdBlue piping between the pump module (4) and the dispensing unit (8) is comprised of an elastic hose. It is capable of compensating the eventual additional volume generated by frozen AdBlue remaining in the piping.

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Compressed air supply function (vehicle without general key)

In vehicles without power supply general key, the operation of compressed air supply to the AdBlue injection system is similar to the one in vehicles with general key. The difference is in the pressure limiting unit (30.09/Y106.1) that includes, in a single component, compressed air pressure settings functions, opening and closing of air flow and one-way direction of air flow through an internal retention. This system is also different because it is constantly being controlled by the engine control module (MR) (A6), through the electrical solenoid (Y106.1), both during engine operation and after turning ignition off.

When starting the engine, the engine control module (MR) (A6) manages the pressure (30.09/Y106.1) limiting unit operation according to the engine conditions. After turning off the ignition, the engine control module (MR) (A6) will coordinate the compressed air emission (cycles) from the pressure limiting unit (30.09/Y106.1), for up to 300 seconds, to ensure AdBlue piping and dispensing unit (8) are clean.

The pressure limiting unit (30.09/Y106.1) only works if it is connected to the power supply system. Because of that, it is only installed in vehicles without a power supply general key.