General
The exhaust gas recirculation (EGR) primarily serves to reduce the amount of nitrogen oxides (NOx) to comply with the emissions limit values even before the exhaust gas aftertreatment.
The suctioned in or supercharged fresh air is mixed with exhaust so that the concentration of oxygen in the fuel/air mixture reduces.
If the concentration of oxygen reduces the combustion temperature drops which leads to reduced output of nitrogen oxides (NOx).
The fact that exhaust gas recirculation (EGR) is active over the whole rotational speed range means that the ratio between recycled exhaust gas masses and suctioned in or supercharged fresh air mass must be matched exactly and thus exactly regulated. For a fuel/air mixture with an excessively high proportion of exhaust gas, the combustion deteriorates and emission of soot particles, carbon monoxide (CO), and hydrocarbon (HC) increases. On the other hand, the emission of nitrogen oxides (NOx) increases if the portion of fresh or supercharged air is too high.
System components, shown on engine 471.9 |
1 | Exhaust gas recirculation cooler |
2 | Turbocharger |
3 | Exhaust manifold center part |
4 | Control lever |
5 | Throttle valve |
6 | EGR line (cold) |
7 | Charge air pipe (mixer housing) |
8 | Charge air distributor |
9 | EGR line (hot) |
10 | Exhaust pipe |
Y621 | Exhaust gas recirculation positioner |
A | Intake air from air filter |
B | Charge air to charge air cooler (hot) |
C | Charge air to charge air cooler (cold) |
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Networking of the electrical components |
A4 | Engine management control unit (MCM) |
B608 | Charge air pressure and temperature sensor in charge air pipe |
B617 | Charge air temperature sensor in charge air distributor |
B621 | Exhaust gas recirculation (AGR) differential pressure sensor |
Y621 | Exhaust gas recirculation positioner |
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Function
The EGR rate describes the relationship of recycled quantity of exhaust to the quantity of fresh air. It is determined over the engine management (MCM) control unit (A4) that the mass of actually suctioned in or supercharged fresh air and the mass of actually recycled exhaust are correlated with one another.
Regulation of the EGR rate takes place via the exhaust gas recirculation positioner (Y621), which opens or closes the throttle valve (5) in the exhaust gas recirculation line (6) via the adjustment lever (4) and therefore regulates which amount of exhaust gas is mixed with it.
The branched off exhaust initially flows through the exhaust gas recirculation cooler (1) attached to the coolant circuit. Here, it is cooled from approx. 650 °C to approx. 170 °C.
The EGR rate can be increased by the cooling since the density and therefore the mass of the recycled exhaust is increased.
Furthermore, the added quantity of cooled exhaust causes a reduction in the NOx emissions by the lowering of the combustion temperature.
Once the exhaust has passed through the exhaust gas recirculation cooler (1), it passes through the EGR line (6) into the charge air pipe (7). It is mixed here with the fresh air coming out of the charge air cooler and then led to the individual cylinders for combustion.
Engine management (MCM) control unit, component description | A4 | ||
Charge air pressure and temperature sensor in charge air pipe, component description | B608 | ||
Charge air temperature sensor in charge air distributor, component description | B617 | ||
Exhaust gas recirculation differential pressure sensor, component description | B621 | ||
Component description for exhaust gas recirculation actuator | Y621 | ||
Component description for exhaust gas recirculation cooler | |||
Overview of system components for exhaust gas recirculation |