Engine | 900.91/92 in model 000.001 |
with BlueTec | |
Engine | 902.91/93 in model 000.001 |
with BlueTec | |
Engine | 904.94/95/96/97 in model 000.001 |
with BlueTec | |
Engine | 906.93/94/95/96/98/99 in model 000.001 |
with BlueTec | |
Engine | 924.91/93/94 in model 000.001 |
with BlueTec | |
Engine | 925.9 in model 000.001 |
with BlueTec | |
Engine | 926.91/92/93/95/97/98 in model 000.001 |
with BlueTec |
Location
The SCR catalytic converter (2) is located in the exhaust gas aftertreatment unit (6).
1 | Inlet pipe |
2 | SCR catalytic converter |
3 | Outlet chamber |
4 | Exhaust tailpipe |
5 | Inlet chamber |
6 | Exhaust aftertreatment unit |
7 | Honeycomb bodies |
B115 | Temperature sensor upstream of SCR catalytic converter |
B116 | Temperature sensor downstream of SCR catalytic converter |
W14.40-1090-06
Task
In the SCR catalytic converter (2), the poisonous nitrogen oxide (NOx) that arises during combustion is reduced to non-toxic nitrogen (N2) and water (H2O).
Structure
The SCR catalytic converter (2) has a housing made from stainless steel. Its core is formed by honeycomb bodies (7) made from ceramic; to facilitate the chemical reactions, the ceramic block has a special coating made from rare metals such as titanium, tungsten, platinum and vanadium.
The exhaust gas aftertreatment unit (6) also has a temperature sensor upstream of the SCR catalytic converter for measuring the temperature in the inlet chamber (5) and a temperature sensor downstream of the SCR catalytic converter for measuring the temperature in the outlet chamber (3).
Flow pattern in SCR catalytic converter (2) |
2 | SCR catalytic converter |
7 | Honeycomb bodies |
A | Exhaust gas from engine (input product) |
B | Hydrolysis segment |
C | AdBlue® |
D | Exhaust gas (end product) |
W14.40-1278-05
Function
The exhaust gas from the engine (A) flows through the mixing tube, the so-called hydrolysis segment (B). The calculated amount of AdBlue® (C) is injected by the exhaust aftertreatment (ACM) control unit (A60) on the basis of the sensor information.
The AdBlue® (C) is converted here initially in a first process step into ammonia (NH3) and then flows on in the direction of the SCR catalytic converter (2).
The second stage of the reduction process takes place in the honeycomb structure that it contains. The nitrous oxide molecules collide with the ammonia molecules (NH3) and energy is released in the form of heat. Only nitrogen (N2) and water vapor (H2O) are left over as products of this chemical reaction, which are not harmful to the environment.
For this process, called selective catalytic reduction, a specific operating temperature of the SCR catalytic converter (2) is required. The temperature required here is 250 °C. The aftertreatment control module (ACM) directly reads in the temperature sensor upstream of the SCR catalytic converter and the temperature sensor downstream of the SCR catalytic converter.