Coolant temperature sensor before low temperature exhaust-gas recirculation cooler: Notes

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The coolant temperature sensor is installed at the end of the exhaust-gas recirculation cooler. The coolant temperature sensor is required for the exact control of the exhaust-gas recirculation.

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 oxygen content and nitrogen 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.

A low temperature EGR cooler is used to cool the exhaust gas. The EGR cooler is integrated on the cold side after the radiator. As a result, the routed back exhaust gas can be further cooled down.