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

摘要

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 temperature NO_x conversion due to its location closer to the turbo and improved SCR coating. Finally the advance SCR on high porosity substrate provides additional NO_x reduction to achieve overall very high NO_x control. Second, the impact of different parameters on the system performance was studied. This included, changes in engine out NO_x concentration, early availability of ammonia, different dosing strategies and rapid catalyst warm up during cold start. Tests were carried out on a HD engine under transient test cycles. The results indicated that NO_x conversion can be significantly improved using the proposed design in combination with early availability of ammonia in the system. In addition, implementation of thermal management improved the NO_x conversion at lower temperature. The results of this work demonstrated that such systems along with improvement in control strategies can provide >95% NO_x conversion under cold FTP transient cycle and will allow diesel engines to meet future emission regulations and fuel economy.