Exhaust Gas Recirculation (EGR)

The use of EGR can reduce NO_X emissions up to a certain degree without increasing particle emissions. The accumulator injection system, the common rail, has a positive effect on the EGR mode.

With exhaust gas recirculation, a part of the exhaust gas under partial-load conditions is taken from the exhaust manifold and directed through the exhaust gas recirculation cooler and the exhaust gas recirculation positioner into the intake manifold.

This reduces various important values:

• Oxygen level
• Combustion rate
• Peak temperature at the ignition flame-front (and thereby NO_X emissions)

However, if the recirculated exhaust quantity is too high, fuel consumption rises due to lack of oxygen and the following emission levels increase:

• Soot
• Carbon monoxide
• Hydrocarbon

EGR is controlled by the CDI control module according to a performance map.

The EGR positioner is actuated by the CDI control module. The CDI control module calculates the air mass on the basis of the input signals of the MAF sensor and regulates the corresponding EGR volume for the applicable operating condition.

 

 

EGR 1 Left/right intake air line 2 Left/right damper filter 3 Left/right clean-air line 4 Left/right hot film mass air flow sensor 5 Crankcase vent line 6 Turbocharger 7 Charge air pipe 8 Pulsation damper 9 Hose to charge air cooler 10 Intercooler 11 Hose from charge air cooler 12 Coupling flange 13 Intake air throttle 14 Charge air cross pipe 15 Left/right intake manifold

16 Intake port shutoff 17 Left/right cylinder head 18 Left/right exhaust manifold 19 Left/right compensator 20 Left/right exhaust pipe 21 Exhaust collector 22 Rear EGR pipe 23 EGR valve 24 EGR cooler 25 Front EGR pipe 26 Vent line 27 Radiator 28 Engine thermostat 29 Coolant feed line 30 Exhaust pipe downstream of turbocharger

 

Diesel Particulate Filter Regeneration

The CDI control module initiates DPF regeneration by periodically increasing the exhaust gas temperature to in excess of 550 °C, e.g. the soot particles stored in the DPF are burned to form predominantly CO2. The ash produced remains in the DPF. The temperature sensor upstream of the catalytic converter and the temperature sensor upstream of the DPF monitor the exhaust gas temperature during regeneration. The pressure differential sensor uses the exhaust gas pressure lines upstream and downstream of the DPF to measure the difference in pressure between the exhaust gas upstream and downstream of the diesel particulate filter. The ash and soot load in the diesel particulate filter is detected by way of a performance map on the basis of the difference in pressure and the exhaust gas mass calculated by the CDI control module. If the soot load exceeds a value governed by the performance map, the CDI control module initiates the regeneration phase only if the regeneration conditions are fulfilled.

 

NO_X and SO_X regeneration

If the maximum fill level of the
catalytic converter is reached, and if the engine is in a suitable operating range, the regeneration phase for the catalytic converter is started.

During exhaust gas reduction conditions (λ< 1), the nitrates and sulfates stored in the catalytic converter are broken down into nitrogen oxides or sulfur oxides and are then reduced to nitrogen, carbon dioxide and water or sulfur dioxide and hydrogen sulfide by the reducing agents present in the enriched exhaust gas such as hydrocarbons, carbon monoxides and hydrogen. This process is called NO_X or SO_X regeneration. An exhaust temperature of 200 °C - 450 °C is used to regenerate the NO_X storage catalytic converter. SO_X regeneration is made at temperatures starting at 650 °C in the NOX storage catalytic converter. An oxygen sensor downstream of the catalytic converter measures the concentration of oxygen in the exhaust gases and then indicates when the regeneration process is complete by changing its voltage from lean to enriched (λ - change over).

For the short term enrichment of the exhaust gasses, the efficiency of the engine is intentionally reduced by changing the amount of air and fuel. One way of doing this is by reducing the air mass of the intake air by throttling it. This also reduces the boost pressure. Another way is by increasing the amount of fuel injected using an additional secondary injection and by adjusting the quantity injected, the starting point of injection and the pressure in the rail. Enriched operation is performed with no EGR.

 

Regeneration times and intervals

The regeneration times are dependent on temperature and decrease significantly as the exhaust gas temperature rises.

NO_X regeneration (λ < 1):

• About every 3 km
• About 3-5 secs.
• 200 °C - 450 °C

SO_X regeneration (λ < 1):

• About every 800 - 1,600 km
• About 1 - 2 min. total duration (in single phases with max. 20 secs.)
• Starting at 650 °C in NO_X storage catalytic converter

DPF regeneration (λ < 1):

• About every 1,000 km
• For about 10-20 min.
• Starting at approx. 560 °C upstream of DPF

 

Measures to increase the exhaust temperature for DPF regeneration

• Secondary injection
• Exhaust gas recirculation with intake air throttling in overrun mode
• DPF regeneration glowing

Following the regeneration phase, the CDI control module registers the calculated differences in pressure and compares this value with a reference value. From this the CDI control module determines the ash load of the diesel particulate filter.

 

 

Exhaust after treatment with DPF (model series 164 and 251 - BIN 10)
114 Diesel particulate filter (DPF) A1 Instrument cluster B19 TWC temperature sensor B19/9 Temperature sensor upstream of DPF B28/8 Pressure differential sensor (DPF) B60 Exhaust back pressure sensor G3/2 O2 sensor upstream of TWC	M16/6 Throttle valve actuator N3/9 CDI control module Y27/9 Left EGR positioner Y76 Fuel injector Y77/1 Boost pressure positioner   CAN CAN bus (Controller Area Network)