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

Abstract

<div class="htmlview paragraph">This paper describes a NO<sub>x</sub> aftertreatment system and control strategy for heavy-duty diesel engines to achieve US EPA 2010 emissions regulations. The NO<sub>x</sub> 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<sub>x</sub> regeneration efficiency. Engine out NO<sub>x</sub> is reduced using a two-step process. First, NO<sub>x</sub> is stored in the LNT catalyst during lean operation. During rich operation, portions of the stored NO<sub>x</sub> 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<sub>x</sub> that slips past the LNT catalyst.</div> <div class="htmlview paragraph">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<sub>x</sub> conversion efficiency and fuel penalty.</div>