Using close-coupled SCR to meet ultra-low NOx requirements

John  Kasab, AVL Powertrain Engineering, Inc.

In April 2019, the California Air Resources Board (CARB) released its white paper on the ultra-low NOx standard for heavy-duty diesel engines (HDDE)¹. AVL has been conducting research on how to meet these new limits and to address the continuing challenge of cold start emissions from HDDE, including incorporating

• Advanced thermal management strategies to accelerate exhaust aftertreatment system (EAS) warm-up
• Close-coupled selective catalytic reduction (ccSCR) system upstream of the current Euro VI or EPA 2013 EAS

To date, the most of the work done has been in simulation, with the intent of evaluating control strategies.

This paper will describe the following results:

• Effect of thermal management strategies on EAS warm-up
• Control strategy for ultra-low NOx incorporating ccSCR
• Interactions between ccSCR system and on-board diagnostics (OBD) requirements

The interaction between NOx control and reduced fuel consumption or CO₂ emissions will be discussed. AVL recommendations and next steps will also be discussed.

Co-authors: Mario de Monte, Klaus Hadl, Hannes Noll, Stefan Mannsberger.

1. California Air Resources Board, “California Air Resources Board Staff Current Assessment of the Technical Feasibility of Lower NOx Standards and Associated Test Procedures for 2022 and Subsequent Model Year Medium-Duty and Heavy-Duty Diesel Engines.” California Air Resources Board Report No, 2019.

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