NH3-SCR currently represents the leading technology for NOx abatement from lean burn and Diesel engines. NOx emission limits from mobile sources have become more stringent with the current legislations. Accurate model predictions and on-board controls of the engine after-treatment systems are required in order to comply with the NOx emissions limits. In this thesis work, Control Oriented Models (COM) for Selective Catalytic Reduction (SCR) have been studied as a strategy to provide accurate simulations with low computational costs which are suitable for on-board control purposes. In the first part of this work a new type of Control Oriented Model of SCR converters will be developed. In order to reduce the computational costs, a combination of explicit and implicit Euler methods will be implemented, using an original approach to calculate the region of stability of the explicit method. In the second part of this work, a detailed comparison in terms of models accuracy and computational costs between a reference complete SCR monolith converter model and the reduced COM will be performed both for simple tests and for a World Harmonized Transient Cycle (WHTC) with cold start for heavy-duty diesel engines. In these tests, a large decrease in computational time (expecially in WHTC) of COM will be demonstrated with respect to the full model, with comparable accuracy.
La Riduzione Catalitica Selettiva (NH3-SCR) al momento rappresenta la tecnologia leader per l’abbattimento dei NOx da motori a combustione magra e Diesel. Risulta necessario l’uso di Modelli Predittivi on board per il controllo del sistema di post-trattamento dei gas di scarico in modo da ridurre le emissioni di NOx. In questo lavoro di tesi, l’uso di modelli predittivi di controllo è stato studiato come strategia per ottenere simulazioni accurate con ridotti tempi di calcolo. Nella prima parte di questo lavoro un nuovo tipo di COM per convertitori SCR verrà discusso. Al fine di ridurre i tempi di calcolo è stata implementata una combinazione di metodi di Eulero impliciti ed espliciti, derivando ed implementando un metodo originale ed efficiente per individuare la regione di stabilità dei metodi espliciti. Nella seconda parte della tesi, invece, sono stati svolti confronti dettagliati (test semplici e World Harmonized Transient Cycle (WHTC) with cold start for heavy-duty diesel engines) tra il modello COM e un modello completo di riferimento, in modo da evidenziarne differenze in termini di accuratezza e costi computazionali. Il modello COM ha evidenziato generalmente una buona accuratezza ed un ottimo incremento nella velocità di calcolo (soprattutto nella simulazione WHTC).
Improved control oriented model for SCR technology applied to the automotive industry
ROCCAMENA, STEFANO
2016/2017
Abstract
NH3-SCR currently represents the leading technology for NOx abatement from lean burn and Diesel engines. NOx emission limits from mobile sources have become more stringent with the current legislations. Accurate model predictions and on-board controls of the engine after-treatment systems are required in order to comply with the NOx emissions limits. In this thesis work, Control Oriented Models (COM) for Selective Catalytic Reduction (SCR) have been studied as a strategy to provide accurate simulations with low computational costs which are suitable for on-board control purposes. In the first part of this work a new type of Control Oriented Model of SCR converters will be developed. In order to reduce the computational costs, a combination of explicit and implicit Euler methods will be implemented, using an original approach to calculate the region of stability of the explicit method. In the second part of this work, a detailed comparison in terms of models accuracy and computational costs between a reference complete SCR monolith converter model and the reduced COM will be performed both for simple tests and for a World Harmonized Transient Cycle (WHTC) with cold start for heavy-duty diesel engines. In these tests, a large decrease in computational time (expecially in WHTC) of COM will be demonstrated with respect to the full model, with comparable accuracy.File | Dimensione | Formato | |
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2017_04_Roccamena.pdf
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https://hdl.handle.net/10589/134447