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

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

ENGINE 651.9 in MODEL 218 as of 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 sensor signals:

Function sequence for exhaust treatment 

The following subsystems are involved in exhaust treatment:

Function sequence for oxidation catalytic converter 

The oxidation catalytic converter reduces 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 by 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 rare metal 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 content exceeds a characteristics map-based value, the CDI control unit will start the regeneration phase provided the prerequisites for regeneration are given. The soot content in DPF is received by the CDI control unit over the DPF differential pressure sensor (with code 474 (Particulate filter)). The soot content of the exhaust are also determined by the soot particulate sensor and transmitted to the soot particulate sensor control unit (with code U77 (BlueTEC (SCR) diesel exhaust treatment) and (with code 494 (USA version) as of 01.09.13 (except model 207, 218). The CDI control unit receives the signal about the soot content from the soot particulate sensor control unit.

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.

The DPF differential pressure sensor (with code 474 (Particulate filter) detects the pressure differential between the exhaust gas pressures upstream and downstream of the DPF, over the exhaust pressure lines upstream and downstream of the DPF. The soot content in the DPF is determined using a characteristics 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) via chassis CAN 2 (CAN E2).

IMPORTANT

An interrupted regeneration is distributed for short stretches over a number of 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 207, 218) or (with code U77 (BlueTEC (SCR) diesel exhaust treatment)) and (with code 494 (USA version)) as of 01.09.13 (except model 207, 218) or (with code U77 (BlueTEC (SCR) diesel exhaust treatment)) as of 01.09.14 

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 rare metal 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 higher exhaust temperature burns 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® reduction agent and ensures more uniform distribution of the AdBlue® upstream of the SCR catalytic converter.

In the SCR catalytic converter, the NOx contained in the exhaust is converted together with the NH3 to molecular nitrogen (N2 ) and H2 O.

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. The AdBlue® container temperature sensor (A103/1b1) detects the temperature of the AdBlue® reduction agent in AdBlue® container in order to determine the status of the aggregate of the AdBlue® reduction agent and to send this to the AdBlue® control unit. The quantity of AdBlue® reduction agent is detected by the AdBlue® fill level sensor (A103/1b5) or by the Full fill level sensor (A103/1b2), Reserve fill level sensor (103/1b3) and Empty fill level sensor (103/1b4). The AdBlue® pressure sensor (A103/2b1) detects the system pressure in the AdBlue® container and the AdBlue® control unit receives this information.

IMPORTANT

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

The CDI control unit determines the load condition of the DPF via the DPF differential pressure sensor (with code (474) Particulate filter). If the soot content exceeds a characteristics 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 regeneration, the exhaust temperature is monitored by the temperature sensor upstream of the exhaust gas turbocharger and by 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® container 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.

IMPORTANT

If the "empty" fill level is reached in the AdBlue® container, the plausibility of the "empty" fill level is checked using a computer model. If the plausibility check also results in an "empty" fill level, an acoustic signal is given in parallel, an entry is made in the fault memory of the control unit (CDI), and the engine diagnosis indicator lamp is actuated 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 standing 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 eddy and air mass in all load conditions of the engine.

The CDI control unit additionally reads the following sensors and signals 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 engine speed and load increases, the closed intake ports open continuously, so that the best possible relation between air eddying and air mass is provided for each 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.

  Electrical function schematic for exhaust treatment MODEL 207 PE14.00-P-2051-97EAN
MODEL 212 PE14.00-P-2051-97DAR
MODEL 218 PE14.00-P-2051-97XAH
  Overview of system components for common rail diesel injection (CDI)   GF07.16-P-9997OM
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