Combined SCR and DPF Technology for Heavy Duty Diesel Retrofit 2005-01-1862

The retrofitting of diesel engines with oxidation catalyst and particulate filter technology for the reduction of particulate matter (PM), hydrocarbons (HC) and carbon monoxide (CO) emissions 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 a cost effective means for states to effectively meet pollution reduction goals. One of the reasons that these technologies are so widely applied is because they can be sized and fitted based on easily measurable vehicle parameters and published engine emission information. These devices generally work passively with basic temperature and back pressure monitoring devices being used to alert the operator to upset conditions. The application of an effective NOx reduction technology in similar retrofit installation, is more complicated. There are no passive NOx reduction technologies that can be retrofit onto HDD vehicles. Because of the long useful life of existing HDD vehicles, a retrofit SCR technology that could provide 80% NOx reduction will be very beneficial.

Previously, a retrofit CRDPF plus SCR technology was demonstrated for NOx reductions of 80% [1]. However, this system was primarily designed for development and demonstration purposes and there is a need for a truly commercialized retrofit product. In order to be widely acceptable, a retrofit SCR technology needs to be flexible in its control and installation, allowing it to fit on to a large cross section of vehicles. It must also be durable and cost effective.

This paper will discuss the development of a commercially available four-way (NOx, PM, CO and HC) emission reduction product for retrofit on HDD vehicles. The system combines the Johnson Matthey CRT ® filter with a urea SCR system and is known commercially as SCRT® system. This paper will discuss the development of such a system through integration of the injection system hardware, control algorithm and catalysts. The SCRT® system utilizes a urea injection system that is deployed on the vehicle as components giving the product more flexibility and lower cost. The urea injection components are: urea pump, air regulator, dosing unit and nozzle. The system utilizes a control system that allows the application engineer to customize it to the engine and catalyst size. It can also use either an engine map or NOx sensor for urea injection control. Transient and steady state test cell data demonstrating > 80% NOx reduction with this system are presented. In addition, chassis dyno emissions results and field data from Europe are reported, demonstrating successful on-road performance of the system.