NOx and PM reduction using combined SCR and DPF technology in heavy duty diesel applications

The application of oxidation catalyst and particulate filter technology for the reduction of particulate matter (PM), hydrocarbons (HC) and carbon monoxide (CO) emissions from heavy duty diesel engines has become an established practice. The design and performance of such systems have been commercially proven to the point that the application of these technologies is cost effective and durable. The application of an effective NOx reduction technology in heavy duty diesel applications is more complicated since there are no passive NOx reduction technologies that can be fit onto HDD vehicles. However, Selective Catalytic Reduction (SCR) systems using Urea injection to achieve NOx reduction have become the technology of choice in Europe and have been applied to achieve Euro IV emissions levels on new HDD vehicles. In addition, retrofit SCR emission control systems have also been developed that can provide high NOx reduction when applied on existing HDD vehicles. This paper will discuss the development of a commercially available four-way (NOx, PM, CO and HC) emission reduction product for HDD vehicles. The system combines the Johnson Matthey CRT® diesel particulate filter system with a urea SCR system and is known commercially as SCRT® system. This paper will discuss the development and application of such a system for OE and retrofit applications. SCRT product development included optimization of the SCR catalyst performance, integration of the urea injection system hardware, development of a control algorithm and detailed alarm systems. Transient and steady state test cell data demonstrating 70 - 90% NOx reduction with this system are presented. In addition, chassis dyno emissions results and field operational data on SCRT equipped vehicles is also reported.