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Exhaust treatment function - GF14.00-P-3000OM

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ENGINE 651.9 in MODEL 204 (except 204.9), 204.9 up to 5/31/12 

ENGINE 651.9 in MODEL 207, 212 (except 212.098/298) up to model year 2014 

ENGINE 651.9 in MODEL 218 up to model year 2014 

Function requirements for exhaust treatment, general points 

Exhaust treatment, general 

The task of exhaust treatment is to reduce the exhaust emissions:

Pollutant reduction is supported by the following subfunctions:

The CDI control unit (N3/9) reads in the following sensors:

Function sequence for exhaust treatment 

The following subsystems are involved in exhaust treatment:

Function sequence for oxidation catalytic converter 

The oxidation catalytic converter serves to reduce the amount of hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx), and, on vehicles with code (474) Particulate filter, generates the required thermal energy for the DPF regeneration phase through afterburning.

Function sequence for diesel particulate filter (DPF) 

The diesel particulate filter consists of a ceramic honeycomb filter body made out of silicon carbide, which is coated with platinum. The passages of the diesel particulate filter are opened alternately at the front and rear and are separated from each other through the porous filter walls of the honeycomb filter body.

The precleaned exhaust which has passed though the oxidation catalytic converter flows into the ducts of the DPF which are open to the front and passes through the porous filter walls of the honeycomb filter body into the ducts which are open to the rear. After this, the cleaned and filtered exhaust is dissipated through the exhaust system. The soot particles are retained in the honeycomb filter body of the DPF.

If the soot particle content exceeds a map-based value, the CDI control unit will start the regeneration phase provided the prerequisites for regeneration are given. The CDI control unit receives the soot particle content in the DPF via the DPF differential pressure sensor (with code (474) Particulate filter).

Regeneration takes place by means of a periodical increase of the exhaust temperature. For this purpose, the following functions are initiated by the CDI control unit:

The soot particles retained in the DPF are mostly burnt off to produce carbon dioxide (CO2) by increasing the exhaust temperature. The ash produced remains in the DPF. On vehicles with code (474) Particulate filter, the exhaust temperature is monitored during regeneration by the temperature sensor upstream of the turbocharger and by the temperature sensor upstream of the diesel particulate filter.

On vehicles with code (474) Particulate filter, the DPF pressure differential sensor detects the pressure differential between the exhaust gas pressures upstream and downstream of the DPF. The soot particle content in the DPF is determined using a characteristic map on the basis of the pressure differential and the exhaust mass calculated by the CDI control unit. Necessary service/maintenance of the DPF is signaled by the engine diagnosis indicator lamp (A1e58) in the IC (A1). The soot particulate sensor measures the soot particulate concentration downstream of the DPF and thus monitors the whole exhaust treatment.

IMPORTANT On short trips, regeneration is interrupted and distributed over several driving cycles. This means that more heating-up phases up to the required regeneration temperature will occur. Regeneration occurs unnoticeably by the customer.

Function sequence for SCR catalytic converter (with code (U42) BlueTec (SCR) diesel exhaust treatment) (except model 204.0/2/3, 207, 212, 218) 

The exhaust gases expelled from the engine are cleaned in an oxidation catalytic converter, a diesel particulate filter (DPF) and a reduction catalytic converter (Selective Catalytic Reduction (SCR) catalytic converter). Oxidation in the oxidation catalytic converter converts the CO and HC to CO2 and water (H2 O). The diesel particulate filter consists of a ceramic honeycomb filter body made out of silicon carbide, which is coated with platinum.

The passages of the diesel particulate filter are opened alternately at the front and rear and are separated from each other through the porous filter walls of the honeycomb filter body.

The precleaned exhaust which has passed though the oxidation catalytic converter flows into the ducts of the DPF which are open to the front and passes through the porous filter walls of the honeycomb filter body into the ducts which are open to the rear. The soot particles are retained in the honeycomb filter body of the DPF. During the DPF regeneration phase, the exhaust temperature is raised to burn off the retained soot particles.

The AdBlue® reduction agent is injected upstream of the SCR catalytic converter and is converted to ammonia (NH3 ) through thermal decomposition (heat-induced chemical reaction) and hydrolysis (water-induced chemical reaction).

There is a mixing element between the AdBlue® metering valve (Y129) and the SCR catalytic converter. This improves the hydrolysis of the AdBlue® reducing agent and ensures more uniform distribution of the AdBlue® upstream of the SCR catalytic converter.

The NOx in the exhaust is converted in the SCR catalytic converter together with the NH3 into molecular nitrogen (N2) and H2O.

The CDI control unit calculates the quantity of reduction agent required based on a characteristics map and sends it via drive train sensor CAN to the AdBlue® control unit (N118/5). This control unit then initiates map-based injection of the calculated quantity of AdBlue® reducing agent through the AdBlue® metering valve.

IMPORTANT The conversion rate of the NOx portion in the exhaust is dependent on the temperature and can be up 80%. Soot content is reduced by approx. 99%.

The CDI control unit receives the load condition of the DPF over the DPF differential pressure sensor (with code (474) Particulate filter). If the soot load exceeds the map-based value, the CDI control unit will start the regeneration phase provided the prerequisites for regeneration are given. Regeneration is performed by periodically raising the exhaust temperature with another post injection.

Raising the exhaust temperature causes most of the soot particles stored in the DPF to be burnt off to CO2.

The noncombustible ash remains in the DPF. During the regeneration, the exhaust temperature is monitored by the temperature sensor upstream of the turbocharger and the temperature sensor upstream of the diesel particulate filter. Necessary maintenance of the DPF is signaled by the engine diagnosis indicator lamp in the instrument cluster.

IMPORTANT If the "Reserve" fill level in the AdBlue® tank is reached, the driver is informed parallel to an audible signal over the multifunction display (A1p13) that he must find a workshop and have the required maintenance work done. If the "empty" level is reached in the AdBlue® container, the plausibility of the "empty" level is checked through a computer model. If the plausibility check also results in an "empty" fill level, an audible signal is given, an entry is made in the fault memory of the control unit (CDI), and the engine diagnosis indicator lamp is lit on the instrument cluster. The driver then has up to 20 engine starts available, with an assumed trip distance of 32 kilometers in each case. The number of remaining starts is displayed in the instrument cluster. The vehicle can no longer be started after the last remaining "Start".

Function sequence for intake port shutoff 

The intake port shutoff (EKAS) achieves the best possible relation between air swirl and air mass in all load conditions of the engine.

The CDI control unit additionally reads the following sensors for intake port shutoff:

After evaluating the input signals, the CDI control unit actuates the intake port shutoff actuator motor (M55) by means of a pulse width modulated (PWM) signal.

Half of the intake ports (2 intake ports per cylinder) are closed over flaps for intake port shutoff in the lower engine speed and engine load range. In the open intake ports, the flow rate is thus increased. This leads to a higher swirl which creates a better vortex. This improves combustion and also contributes to reducing the soot particles in the exhaust gas.

As the engine speed and engine load increase, the closed intake ports are continuously opened so that the best possible relationship between air swirl and air mass is available for every operating phase of the engine. In this way, the exhaust characteristics and the engine performance are optimized.

IMPORTANT If there is a fault or discontinuity in the supply voltage, the flaps are opened by spring force.

  Model 204, electrical function schematic for exhaust treatment   PE14.00-P-2051-97FAE
  MODEL 207   PE14.00-P-2051-97EAE
  MODEL 212   PE14.00-P-2051-97DAE
  Model 218   PE14.00-P-2051-97XAD
  Overview of system components for common rail diesel injection (CDI)   GF07.16-P-9997OM
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