Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation







Internal exhaust gas recirculation counteracts the formation of nitrogen oxides NOx. Just like external exhaust gas recirculation, the formation of NOx is based on the fact that the combustion temperature is reduced through the introduction of combustion exhaust gases. The combustion gases in the fresh air/fuel mixture cause a slight lack of oxygen, whereby the combustion does not become as hot as it would if there was surplus oxygen. Nitrogen oxides are only formed in a greater concentration at a relatively high temperature. The reduced combustion temperature in the engine and the lack of oxygen prevent the formation of NOx.

Function







Both the intake and exhaust valves are open during the exhaust stroke. The high intake manifold vacuum causes some of the combustion gases from the combustion chamber to be sucked back into the intake port and then flushed back into the combustion chamber for the next combustion with the next intake stroke.

This has the following advantages:
- Reduced consumption due to reduced gas exchange work.
- Increased part-load range with exhaust gas recirculation.
- Smoother running.
- Exhaust gas recirculation is possible even when the engine is cold.