Conversion of Nitrogen Oxide Readings

The readings from the connected NOX sensor are converted according to VDMA 6299:2019-09 in the NOX monitor of the EasyNOₓ.

At first, the oxygen content measured in wet exhaust gas is converted to dry exhaust gas:

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In the next step, the measured nitrogen oxide value is corrected by sensor- and plant-specific NO2 correction factors:

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Following that, this NO2-corrected nitrogen oxide value measured in wet exhaust gas is converted to dry exhaust gas:

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Then the volume-based nitrogen oxide measured value is converted to a mass-based value in mg/Nm3:

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In the last step, the mass-based nitrogen oxide measured value is converted to a reference oxygen content of Or = 5 %:

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Variable

Meaning

K

NO2/NOX ratio of the exhaust gas as a constant (see section Determining the NO2/NOₓ Ratio)

KNO2

Sensor-specific NO2 correction factor as a constant (see section Sensor)

NOX,r

Nitrogen oxide measured value converted to reference oxygen content and based on mass and dry exhaust gas in mg/Nm3

NOX,w

Nitrogen oxide value of the NOX sensor measured wet in ppm

NOX,w-c

NO2-corrected nitrogen oxide measured value related to wet exhaust gas in ppm

NOX,dr

Nitrogen oxide measured value related to dry exhaust gas in ppm

NOX,dr-mg

Mass-based nitrogen oxide measured value related to dry exhaust gas in mg/Nm3

Or

Reference oxygen

O2,dr

Oxygen measured value of the NOX sensor calculated on dry exhaust gas in vol.%

O2,w

Oxygen value of the NOX sensor measured wet in vol.%