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:

900_Abmessungen_EasyNOx-in-Gehäuse

In this context, the NOX monitor of the EasyNOₓ does not regard oxygen readings for wet exhaust gas, which lead to oxygen contents in the dry exhaust gas of over 20 %.

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

900_Abmessungen_EasyNOx-in-Gehäuse

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

900_Abmessungen_EasyNOx-in-Gehäuse

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

900_Abmessungen_EasyNOx-in-Gehäuse

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

900_Abmessungen_EasyNOx-in-Gehäuse

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.%