Exhaust Gas RECIRCULATION, Function - GF14.20-D-3000TSA
Engine 651 in model 907
Block diagram
Function requirements for exhaust gas recirculation (EGR), general points
- Circuit 87M (Engine management ON)
- Engine running.
- Engine in load range from neutral to the upper partial-load range
Exhaust gas recirculation, general
Exhaust gas recirculation reduces the nitrogen oxide (NOx) portion in the exhaust gas. This takes place via the following 3 processes:
- Reduction of oxygen (O 2) concentration in combustion chamber
- Reduction of the combustion temperature through reduction of the combustion speed
- Reduction of the combustion temperature through a higher heat capacity of the recirculated exhaust compared to the intake air
Heat capacity
The heat capacity is a material property and indicates how much heat a substance can store per temperature change.
Function sequence for exhaust gas recirculation
The EGR is active from neutral through to the upper partial-load range. Determination of the exhaust gas recirculation rate takes place depending on the following variables:
- Engine temperature, engine load and engine RPM
- Ambient conditions such as the air intake or the charge air temperature
- Exhaust temperature
- Diesel particulate filter status
- Exhaust pressure
- Time limitation (in idle)
- Boost pressure
- Coolant temperature
For this purpose, the CDI control unit reads in signals from the following components:
- Engine oil temperature sensor
- Hot film mass air flow sensor
- Boost pressure sensor
- Coolant temperature sensor
- Charge air temperature sensor
- Temperature sensor upstream of SCR catalytic converter
- Temperature sensor upstream of diesel particulate filter
- Temperature sensor downstream of exhaust gas recirculation cooler
- Temperature sensor upstream of turbocharger
- Diesel particulate filter differential pressure sensor
- Exhaust back pressure sensor
- Crankshaft position sensor
After evaluating the input signals, the CDI control unit uses the stored characteristics map to actuate the exhaust gas recirculation actuator with a pulse width modulated signal. The exhaust gas recirculation actuator increases or decreases the quantity of recycled exhaust according to actuation which is led over a mixing tube to the throttle valve actuator in the charge air distributor.
To increase the effect of EGR, the exhaust gas is led to the exhaust gas recirculation cooler where it is cooled.
If the temperature of the recirculated exhaust gas is too low, the recirculated exhaust gas can be guided past the exhaust gas recirculation cooler via a bypass duct.
The exhaust temperature calculated by the temperature sensor after exhaust gas recirculation is used by the CDI control unit to monitor the cooling function of the exhaust gas recirculation cooler.
| Overview of system components for common rail diesel injection (CDI) | GF07.16-D-9997TSA |