A NOx Reduction Solution for Retrofit Applications: A Simple Urea SCR Technology 2005-01-1857

This paper presents the development and performance of a Selective Catalytic Reduction (SCR) aftertreatment system designed for diesel retrofit applications. It has been proven that Urea SCR represents a convenient and very efficient solution for NO_x reduction that can be used for stationary and mobile powerplants with NO_x reduction efficiencies that can exceed 95%. The cooperative efforts between ServoTech Engineering, Ford Motor Company, KleenAir Systems, Tenneco, and the City of Dearborn have led to the development of a simple aftertreatment system for NO_x reduction. This system consists of a catalyzed diesel particulate filter (CDPF), a SCR catalyst system, and a diesel oxidation catalyst. As part of the system, an effective and compact air-assisted dosing unit developed by ServoTech Engineering in collaboration with Ford Motor Company was used for effective urea delivery and atomization.

The system utilizes an open-loop predictive controller that dictates the amount of urea to be injected, with exhaust gas temperature the only sensor input used. The system controller requires no communication with the engine CAN bus, and this, combined with the straightforward packaging of the dosing unit, makes the entire system suitable for a wide range of diesel powered retrofit applications. A series of chassis dynamometer FTP, US06, and UDDS tests were conducted on a Ford F550 City of Dearborn dump truck in an attempt to evaluate the system performance as accurately as possible. Since the system does not incorporate a NO_x sensor, the system was calibrated to provide the maximum NO_x reduction efficiency while avoiding any ammonia slip.

The test results proved the NO_x reduction effectiveness of the aftertreatment system, with an overall NO_x reduction around 70 %.