The selective catalytic reduction SCR is extensively used for NOx reduction of recent HD-vehicles.
There are some manufacturers and some applications of SCR as retrofit systems (mostly for the low emission zones LEZ and in combination with a DPF).
In charge of Swiss authorities AFHB investigated several SCR-systems, or (DPF+SCR)-systems on HD-vehicles and proposed a simplified quality test procedure of those systems. This procedure can especially be useful for the admission of retrofit systems but it can also be helpful for the quality check of OEM-systems.
The project name was TeVeNOx - Testing of Vehicles with NOx reduction systems.
In the present paper the test procedures will be described and some specific results will be discussed.
As general conclusions it can be stated:
The foundations for the quality verification procedures of SCR-systems are established,
The SCR-systems are not active at lower temperatures < 200°C,
SCR-testing on vehicle has more importance than DPF testing on vehicle and is a simple & low-cost tool for quality check,
The overall average NOx reduction rate depends on the operating profile of the vehicle - for low-load, for cold operation and for interrupted operation (HEV) there are lower NOx reduction efficiencies.