46 Figure 3.4.5 NO
2
mode of MEXA-1170NX analyser
3.5 ETAS Lambda Meter
In this investigation, the ETAS LA4 lambda meter was use to measure O
2
at any of the instrumentation modules along the SCR exhaust system. In most cases it was used to measure O
2
across the SCR catalysts. The attributes of the LA4 Lambda Meter are described in the operating
manual [ETAS LA4 User’s Guide, 2005]. The manual describes the LA4 lambda meter as a high-
precision measuring device for emission levels. It allows determining lambda values, oxygen content, and AirFuel ratio, as well as the internal resistance, pump current, and heater voltage of the LSU
lambda sensor. The LA4 is designed for exhaust gas measurements on gasoline, diesel and gas engines.
Based on the output signals from Bosch LSU broadband lambda probes, the measurement results can be calculated either by means of an analytical method that considers fuel properties and
ambient conditions or by characteristic curves. The measured value was continuously displayed on the built-in LCD and periodically recorded manually as required. The device conducts a self-test after
being powered on using an internal reference. An optimized heater control ensures that the sensor quickly reaches its operating temperature while preventing overheating damages, even at highly
fluctuating exhaust gas temperatures and different supply voltages. The advantages of using this device is that it provides a wide measurement range of lambda, oxygen content and airfuel ratio. In
this investigation, two units of LA4 Lambda meter were used as a standalone unit but the data were
NOx to NO Converter
NO
2
MODE – NH
3
passes through unchanged
Oxidation Catalyst
NH
3
+ NO + NO
2
CLD detects
NO NOx to NO
NO NOx
NO
2
NOx to NO Converter
bypassed CLD
detects NO
Analyser Display
NO
2
= NOx –NO
47 logged to the Froude Texcel program. The LA4 lambda meters used in the experiment are shown in
figure 3.5. The LA4 wiring configuration is shown in appendix 3.5.
Figure 3.5 ETAS LA4 Lambda meter used to measure O
2
before and after the SCR catalysts
3.6 Urea Spray Setup
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