Computational Analysis of After-Treatment Systems to Obtain High NOx Conv. in Future Diesel Engines

Balaji  Sukumar, Johnson Matthey

As diesel engine technologies change to improve fuel economy, new challenges to after-treatment systems are introduced. One such challenge is significantly increased NOx reduction over both steady state and transient cycles in order to meet the regulation limits and deliver the expected benefits in real-world NOx emissions. This has led to the question of what after-treatment system configurations would be suitable for future advanced diesel engines.

In this work, computational modeling has been used to investigate various options and determine the best way to meet the NOx limits. The goal is to obtain a suitable combination of system configuration, substrate and coating properties and operating conditions to reduce the tail pipe NOx to <0.1 g/kwh from a very high engine out NOx (~8 g/kwh). With SCR (Selective Catalytic Reduction) as the base technology, in addition to the typical system configuration for diesel engines (Diesel Oxidation Catalyst (DOC) – Catalyzed Soot Filter (CSF) – SCR – Ammonia Slip Catalyst (ASC)), simulations were carried out for a system that replaces the CSF with an SCR coated filter (SCRF®) and/or replaces the DOC with a Cold Start Concept Catalyst (dCSC(TM)). Substrate properties (porosity) and coating properties (washcoat loading) were also changed to determine the benefits of these properties on high NOx reduction. Other operating variables or engine control variables like urea dosing strategy and fuel injection (thermal management) were also examined. In order to reach high NOx reduction, simulation results show that dCSC(TM)-SCRF®-SCR-ASC configuration with optimal urea dosage and thermal management will be able to obtain the required NOx reduction for high NOx future diesel engines.