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It has become evident that almost all diesel aftertreatment devices dealing with NOx and particulate matter (PM) controls require the addition of one or more reducing agents (reductants), such as diesel fuel, ammonia, or aqueous urea to enhance their efficiency and durability. These reductants can be used to catalytically convert NOx to N2, to enrich the air fuel ratio (A/F), or to increase temperatures for regenerating PM filters or for de-sulfating NOx traps. A number of injection methods have been developed recently to provide easy reductant addition. However, many of them may be cumbersome, costly, or ineffective. This paper describes a new reductant delivery system, which appears to minimize these shortcomings. To be effective, the manner of reductant injection into the exhaust is critical. First, the reductant must be added quickly to accommodate the fast transient operations.