Ammonia and NOx Measurements on SCR Catalysts

Background

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Prompt NO is one of the most unwanted compounds next to sulfur in engine emission treatment, generated by the dissociations of N2 in the cylinder and reacting with O2 at high cylinder temperatures. Suppression of NOx formation as well as its reduction in aftertreatment processes is the main work of engine and catalyst developers. Whichever strategy, e.g. low temperature combustion, high EGR, post injection for generation of enough HCs for catalytic reduction or SCR technology with the decomposition of urea into ammonia molecules, these highly dynamic and very temperature dependent reactions require fast monitoring of a variety of compounds for the optimization under transient conditions.

Solution

The patented V&F IMR-technology (Ion Molecule Reaction) is capable of determining all nitrogen compounds of interest i.e. NO, NO2, NH3 etc. with the required measurement speed. In addition, other relevant molecules for monitoring DeNOx processes on nitrogen traps such as O2 can be measured. The V&F CombiSense instrument also facilitates determination of N2O at low ppm levels. Inlet pressure regulation (0 to 5 bar), filters for particulates and a heated transfer capillary are additional features prerequisite for measuring exhaust gas emissions. A variety of interface options such as AK protocol ensure easy implementation into the test bench environment.

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Figure: Breakthrough Monitoring on SCR Catalysts

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Figure: DeNOx in Lean to Rich Engine Mode

Advantage

DeNOx concepts for road vehicles require more complex strategies than the control of hydrocarbon (HC) and CO emissions. HC and CO formation is directly related to the air fuel ratio which is well determined by fuel input, air volume and lambda value. NO formation is related to air fuel ratio, flame temperature and cylinder pressure. FTIR instruments are limited in their gas response times and lower detection levels, especially in diluted gases (continuous volume sampling - CVS) applications. The IMR-Technology by V&F allows for measurements at up to 10 Hz and detection limits in the low ppb range. The robust and compact design of the V&F instruments combined with low maintenance effort make them an excellent tool for advanced applications within the field of exhaust gas measurements.

Highlights

  • Selectively measures NO, NO2 and NH3
  • N2O measurement – CombiSense
  • Fast response times

Reference customers (excerpt)

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Applicable instruments

AirSense
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CombiSense
TwinSense