Development of Emission Control Systems to Enable High NO
Conversion on Heavy Duty Diesel Engines
Selective Catalytic Reduction (SCR) systems have been demonstrated as effective solutions for controlling NOx emissions from Heavy Duty diesel engines. Future HD diesel engines are being designed for higher engine out NOx to improve fuel economy, while discussions are in progress for tightening NOx emissions from HD engines post 2020. This will require increasingly higher NOx 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 NOx 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 NOx conversions.
First, high performance NOx 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 NOx during cold start when system is cold for any SCR reaction and then releases when the system warms up to allow NOx reduction across the SCR-DPF filter. The SCR-DPF filter enables lower temperature NOx conversion due to its location closer to the turbo and improved SCR coating. Finally the advance SCR on high porosity substrate provides additional NOx reduction to achieve overall very high NOx control.
Second, the impact of different parameters on the system performance was studied. This included, changes in engine out NOx 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 NOx 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 NOx conversion at lower temperature. The results of this work demonstrated that such systems along with improvement in control strategies can provide >95% NOx conversion under cold FTP transient cycle and will allow diesel engines to meet future emission regulations and fuel economy.