The combined exhaust gas aftertreatment systems (DPF+SCR) are the most efficient way and the best available technology (BAT) to radically reduce the critical Diesel emission components particles (PM&NP) and nitric oxides (NOx). SCR (selective catalytic reduction) is regarded as the most efficient deNOx-system, diesel particle filters are most efficient for soot abatement. Today, several suppliers offer combined systems for retrofitting of HD vehicles.
Quality standards for those quite complex systems and especially for retrofit systems are needed to enable decisions of several authorities and to estimate the potentials of improvements of the air quality in highly populated agglomerations.
The present paper informs about the VERTdePN *) quality test procedures, which were developed in an international network project with the same name 2007-2011 (VERT … Verification of Emission Reduction Technologies; dePN … decontamination, disposal of PM / NP and of NOx). Some interesting results of research on the engine dynamometer from the last test period 2011-2013 are given as a complement of the already published results.
The most important statements are:
the procedures for the quality verification of SCR-, or (DPF+SCR) - systems are developed and confirmed,
engine dynamometer testing enables the deepest insight in the investigated system concerning: secondary- and non- legislated emissions, variations of feed factor, analysis on different sampling positions and at specific engine operating conditions (like legal test procedures),
testing of SCR-systems on vehicle (chassis dynamometer, or road) is important, because of urea dosing, urea mixing and electronic control,
the filtration efficiency of a DPF is independent of the operating condition (except of regeneration period, or passing over the maximum space velocity),
the NOx reduction efficiency of SCR-systems is dependent on the operating conditions, because of the optimal temperature window of the SCR-catalysis; at the conditions with exhaust temperature below 200°C the urea dosing is stopped.
There is an intense further development of those aftertreatment systems and their electronic control, which opens further potentials of improvements.