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Technical Briefs

Robust Filtering for Ammonia Coverage Estimation in Diesel Engine Selective Catalytic Reduction Systems

[+] Author and Article Information
Hui Zhang

e-mail: huizhang285@gmail.com

Junmin Wang

e-mail: wang.1381@osu.edu
Department of Mechanical and Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210

Yue-Yun Wang

Propulsion Systems Research Lab,
GM Global Research and Development,
Warren, MI 48090
e-mail: yue-yun.wang@gm.com

1Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received January 15, 2013; final manuscript received June 10, 2013; published online August 23, 2013. Assoc. Editor: Gregory Shaver.

J. Dyn. Sys., Meas., Control 135(6), 064504 (Aug 23, 2013) (7 pages) Paper No: DS-13-1024; doi: 10.1115/1.4024890 History: Received January 15, 2013; Revised June 10, 2013

In this paper, we investigate the nonlinear observer designs to estimate the ammonia coverage ratio in the diesel engine selective catalytic reduction (SCR) systems. The ammonia coverage ratio is an important variable due to its critical role in the SCR NOx conversion and the ammonia slip. However, the ammonia coverage ratio cannot be directly measured by onboard sensors. Therefore, it is necessary to develop effective observers to estimate the ammonia coverage ratio online. Based on a three-state SCR model, we develop two nonlinear observers. The first one only employs the dynamics of the ammonia concentration. The structure and the algorithm are simple. But it is sensitive to the measurement noises and the uncertainties in the system parameters. The second one is a discrete-time smooth variable structure estimator which is robust to the measurement noises, the approximation error, and the system uncertainties. Both estimators are implemented on a full-vehicle simulation of the FTP75 test cycle. The simulation results have verified the theoretical analysis.

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Figures

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Fig. 1

Schematic of the control-oriented urea-based SCR aftertreatment system and the corresponding sensors

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Fig. 2

Schematic of the urea-based SCR reactions in the diesel aftertreatment system

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Fig. 5

Observer performance with measurement noises

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Fig. 4

Observer performance with perfect measurements

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Fig. 3

Main varying parameter values in the FTP75 test cycle simulation

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Fig. 6

Estimation performance of the smooth variable structure observer with measurement noises

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Fig. 7

Estimation performance of the smooth variable structure observer with measurement noises in the range [0 0.002]

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Fig. 8

Estimation performance of the smooth variable structure observer with uncertainties, approximation errors, and measurement noises

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Fig. 9

Estimation performance of the smooth variable structure observer with sensor faults (ρ is time-varying within [0.8 1.2]), uncertainties, approximation errors, and measurement noises

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