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Development and Validation of a Two-Site Kinetic Model for NH3-SCR over Cu-SSZ-13—Part 2: Full-Scale Model Validation, ASC Model Development, and SCR-ASC Model Application

  • Rohil Daya
  • Chintan Desai
  • Bruce Vernham
Special Issue: 2017 CLEERS October 3 - 5, Ann Arbor, MI, USA

Abstract

We present herein the final part in the development and validation of a two-site kinetic model for NH3-SCR over Cu-SSZ-13. To predict tailpipe emissions accurately, it was necessary to combine the kinetic model of the SCR catalyst developed in part I (Daya et al. 2018), with a reaction-diffusion model of the dual-layer ammonia slip catalyst (ASC). This dual-layer ASC model was developed following a three-step process, including development of the kinetic models of the individual layers, followed by parameterization of a parallel pore diffusion model of the dual-layer ASC. Reactor-scale validation of the dual-layer ASC model confirmed the kinetic model accuracy and highlighted the significance of intra-porous diffusion. Following this, the SCR model developed in part I of this paper was validated on an engine dynamometer through comprehensive steady-state experiments with inlet NH3 to NOx ratio (ANR) sweeps. The final SCR and ASC models were then evaluated on cold and hot heavy-duty transient (HDT) cycles, to examine the capability of predicting tailpipe NOx, NH3 slip as well as storage-based dynamics. Overall cycle-averaged NOx conversion was predicted within 3% using these models. Validated models have significant application in model-based control as well as improving catalyst design through improved functional understanding. The present Cu-SSZ-13 SCR model was simulated using the four-step SCR protocol Kamasamudram et al. (Catal. Today 151(3):212–222) to calculate the intra-catalyst dynamic capacity. These numerical experiments showed that the dynamic capacity decreases upon hydrothermal aging but leads to higher NOx conversion under standard and fast SCR conditions at 250 °C. This increase in NOx conversion is due to more uniform NH3 storage along the length of the catalyst, leading to higher NH3 utilization near the rear of the aged catalyst. Similar numerical experiments on the dual-layer ASC model demonstrated intra-layer washcoat distributions causing NO slip during transient drive cycles for both hydrothermal aging conditions.

Keywords

Global Kinetic Model Dual-Layer ASC Model Intra-Porous Diffusion Drive Cycle Validation Hydrothermal Ageing 

Nomenclature

Deff

effective diffusivity m2/s

Dgas

species bulk diffusivity m2/s

DKn

Knudsen diffusivity m2/s

dp

washcoat pore diameter m

τ

washcoat tortuosity

ε

washcoat porosity

Notes

Acknowledgments

The authors would like to acknowledge Cormetech Inc. for executing the test protocol, supplying the reactor data, and assisting with the reactor setup description. Furthermore, the Gamma Technologies Aftertreatment support team helped us with useful discussions and continuous assistance with modeling work.

Supplementary material

40825_2018_94_MOESM1_ESM.docx (2.5 mb)
ESM1 (DOCX 2596 kb)

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Copyright information

© Springer Nature Switzerland AG 2018

Authors and Affiliations

  1. 1.Isuzu Technical Center of AmericaPlymouthUSA

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