Development of Emission Control Systems to Enable High NO_x Conversion on Heavy Duty Diesel Engines

Abstract

To meet NO x emission requirements and regulations for heavy duty diesel engines, selective catalytic reduction (SCR) has been demonstrated to be an effective solution. With increasing demand for improved fuel economy there is a desire to improve the NO x emission reduction of the SCR system, thus allowing for higher engine out NO x emissions. Such requirements will challenge the current aftertreatment designs, which consist of DOC, catalyzed soot filter (CSF) and SCR units. One approach is to replace the CSF with a diesel particulate filter coated with SCR (SCR-DPF) while keeping the flow-through SCR downstream. The downstream SCR can also be improved by using a highly porous flow-through substrate coated with higher washcoat loadings than those typically used on standard substrates today. This design will not only allow for improvement of NO x conversion at low temperature since the SCR-DPF unit will be closer to turbo out, but also an increased number of SCR active sites can be placed in the overall system without increasing the packing size in a typical 2010/13 system and thus provide high NO x conversion. For the SCR-DPF technology, high porosity filters are needed to enable the use of the higher catalytic loadings necessary to get good performance and durability. These highly porous filters need to have very good thermo mechanical properties to enable them to survive the active regeneration events over the life of the system. Also, a novel catalyst known as diesel Cold Start Concept (dCSC™) ABSTRACT Selective Catalytic Reduction (SCR) systems have been demonstrated as effective solutions for controlling NO x emissions from Heavy Duty diesel engines. Future HD diesel engines are being designed for higher engine out NO x to improve fuel economy, while discussions are in progress for tightening NO x emissions from HD engines post 2020. This will require increasingly higher NO x conversions across the emission control system and will challenge the current aftertreatment designs. Typical 2010/2013 Heavy Duty systems include a diesel oxidation catalyst (DOC) along with a catalyzed diesel particulate filter (CDPF) in addition to the SCR sub-assembly. For future aftertreatment designs, advanced technologies such as cold start concept (dCSC™) catalyst, SCR coated on filter (SCRF ® hereafter referred to as SCR-DPF) and SCR coated on high porous flow through substrates can be utilized to achieve high NO x conversions, in combination with improved control strategies.The objective of this work is to evaluate different advanced emission control system options in order to meet future high NO x conversions.First, high performance NO x control system architecture was designed by using a combination of dCSC catalyst, SCR-DPF filter system and high performance SCR on high porosity substrates. In this architecture, dCSC technology stores NO x during cold start when system is cold for any SCR reaction and then releases when the system warms up to allow NO x reduction across the SCR-DPF filter. The SCR-DPF filter enables lower t...

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