EGR controller: Notes

The exhaust-gas recirculation is a measure to reduce the formation of nitrogen oxide (NO_X ). Nitrogen oxides are created in great quantities when combustion runs with an excess air and at very high temperature. Here, the oxygen combines with the nitrogen of the combustion air to form nitrogen monoxide (NO) and nitrogen dioxide (NO₂ ). On the diesel engine, exhaust-gas recirculation is sometime required at idle speed and always in the partial load range, because a particularly high excess air is used there. The recirculated exhaust gas, to which fresh air is added and which has the same properties as inert gas, achieves the following:

• Lower residual oxygen content in the cylinder
• Lowering of the maximum combustion temperature by up to 500 °C. This effect is enhanced further if the recirculated exhaust gases are cooled.