The Development and Performance of the Compact SCR-Trap System: A 4-Way Diesel Emission Control System

The tightening of Heavy Duty Diesel (HDD) emissions legislation throughout the world is leading to the development of emission control devices to enable HDD engines to meet the new standards. NOx and Particulate Matter (PM) are the key pollutants which these emission control systems need to address. Diesel Particulate Filters (DPFs) are already in use in significant numbers to control PM emissions from HDD vehicles, and Selective Catalytic Reduction (SCR) is a very promising technology to control NOx emissions. This paper describes the development and performance of the Compact SCR-Trap system - a pollution control device comprising a DPF-based system (the Continuously Regenerating Trap system) upstream of an SCR system. The system has been designed to be as easy to package as possible, by minimising the total volume of the system and by incorporating the SCR catalysts on annular substrates placed around the outside of the DPF-based system. This novel design gives rise to an easy-to-package emission control device capable of providing very high conversions of all four major pollutants, NOx, PM, CO and HC. The design details are discussed, and the performance of the system over both steady state and transient cycles is presented. NOx conversions of up to 92% have been demonstrated, and the system's emissions of all four pollutants are well inside the Euro V, and probably also the US 2007 limits (subject to verification of PM).