SUPPLEMENTAL AMMONIA STORAGE AND DELIVERY SYSTEM

摘要

An exhaust after-treatment system is described. Generally speaking, the system includes separate primary and secondary NOx reducing systems for delivering reductant (e.g. urea and ammonia) to an exhaust stream, a sensor system for determining relevant operating conditions and an electronic control module for activating the reducing systems. The two NOx reducing systems include flow control modules coupled to the electronic control module. Methods for reducing NOx in an exhaust stream are also described. Generally speaking, the methods include the steps of determining a need for NOx reduction in an exhaust stream, determining temperature of exhaust stream, and injecting at least one of a primary reductant and a secondary reductant into the exhaust stream based on the determined temperature of the exhaust stream. Typically, the primary reductant comprises urea and the secondary reductant comprises ammonia.