Investigation of Underbody Metal SCR Systems with Active Thermal Management: Experience Update

The Selective Catalytic Reduction (SCR) is the main after-treatment solution for high efficient diesel engines under development to cope with future lower fuel consumption and NOx emissions requirements (EU6+ legislation). Exhaust gas temperatures are decreasing too, leading to new after-treatment system developments in a close coupled position. Nevertheless before all vehicle architectures allow it, SCR systems are and will still be installed in underbody position.

The current paper deals with an underbody metal SCR after-treatment systems, which is capable of active thermal management, and an ultra-compact SCR dosing system. These technologies are described and emission results obtained on several application examples (from passenger cars to light duty commercial vehicles) are presented and discussed in conjunction with an effective active thermal management of the SCR function. It is shown that the NO₂/ NOx ratio as well as the temperature level at SCR system inlet, among all the parameters governing the SCR efficiency play an important role for the feasibility and the acceptance of an underbody SCR solution.