Advanced NOx Aftertreatment System And Controls For On-Highway Heavy Duty Diesel Engines

This paper describes a NO_x aftertreatment system and control strategy for heavy-duty diesel engines to achieve US EPA 2010 emissions regulations. The NO_x aftertreatment system comprises of a fuel reformer catalyst, a LNT catalyst, and a SCR catalyst. The only reductant required to operate this system is diesel fuel; hence, no urea infrastructure is required to support this approach. The fuel reformer is used to generate reformate which is a combination of hydrogen, carbon monoxide and unburned hydrocarbons. This reformate provides a more efficient feedstock to improve LNT NO_x regeneration efficiency. Engine out NO_x is reduced using a two-step process. First, NO_x is stored in the LNT catalyst during lean operation. During rich operation, portions of the stored NO_x are converted to nitrogen and ammonia. Next, the ammonia released from the LNT is captured by the downstream SCR catalyst. The stored ammonia is further used to reduce the NO_x that slips past the LNT catalyst.

System hardware was developed and evaluated in dynamometer test cells using 9L and 14L commercial-available heavy-duty diesel engines. System control strategies were developed to optimize the NO_x conversion efficiency and fuel penalty.