Aside from sulfur, NO is one of the most undesirable substances in exhaust gas after-treatment. It is formed by the splitting of NO₂ in the cylinder and a chemical reaction with O₂ at high cylinder temperatures. Suppression of NO_x formation, like reduction in exhaust after-treatment, is the main task of engine and catalyst developers. Whatever the strategy, be it, for example, low-temperature combustion, exhaust gas recirculation (EGR), post-injection to form enough HC for catalytic reduction, or SCR technology with decomposition of urea into ammonium molecules, to achieve optimization under volatile conditions these highly dynamic and heavily temperature-dependent reactions require the rapid measurement of a wide range of components.

DeNOx concepts for on-road vehicles require a strategy that is more complex than simply controlling hydrocarbon (HC) and CO emissions. HC and CO formation is directly related to the air-fuel ratio, which is clearly determined by fuel inlet, air volume, and lambda value. NO formation is related to the air-fuel ratio, flame temperature, and cylinder pressure. FTIR instruments are limited in their gas response times and low determination levels, especially in diluted gases (CVS = continuous volumetric sampling). V&F's IMR technology allows measurement speeds of up to 10 Hz and limits of quantitation (LOQ) in the low ppb range. The robust and compact design of the V&Finstruments combined with low maintenance makes them an excellent tool for more demanding applications in the field of exhaust gas measurements.