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Research Papers

NO and NO2 Concentration Modeling and Observer-Based Estimation Across a Diesel Engine Aftertreatment System

[+] Author and Article Information
Ming-Feng Hsieh

Department of Mechanical and Aerospace Engineering, Ohio State University, Columbus, OH 43210hsieh.122@osu.edu

Junmin Wang1

Department of Mechanical and Aerospace Engineering, Ohio State University, Columbus, OH 43210wang.1381@osu.edu

1

Corresponding author.

J. Dyn. Sys., Meas., Control 133(4), 041005 (Apr 07, 2011) (13 pages) doi:10.1115/1.4003380 History: Received February 14, 2010; Revised November 24, 2010; Published April 07, 2011; Online April 07, 2011

This paper presents an experimentally validated control-oriented model and an observer for diesel oxidation catalyst (DOC)-diesel particulate filter (DPF) system in the context of exhaust gas NO and NO2 concentration estimations. NO and NO2 have different reaction characteristics within DPF and selective catalytic reduction (SCR) systems, two most promising diesel engine aftertreatment systems. Although the majority of diesel engine-out NOx emissions is NO, the commonly used DOC located upstream of a DPF and a SCR can convert a considerable amount of NO to NO2. Knowledge of the NO/NO2 ratio in exhaust gas is thus meaningful for the control and diagnosis of DPF and SCR systems. Existing onboard NOx sensors cannot differentiate NO and NO2, and such a sensory deficiency makes separate considerations of NO and NO2 in SCR control design challenging. To tackle this problem, a control-oriented dynamic model, which can capture the main NO and NO2 dynamics from engine-out, through DOC, and to DPF, was developed. Due to the computational limitation concerns, DOC and DPF are assumed to be standard continuously stirred tank reactors in order to obtain a 0D ordinary differential equation model. Based on the model, an observer, with the measurement from a commercially available NOx sensor, was designed to estimate the NO and NO2 concentrations in the exhaust gas along the aftertreatment systems. The stability of the observer was shown through a Lyapunov analysis assisted by insight into the system characteristics. The control-oriented model and the observer were validated with engine experimental data and the measured NO/NO2 concentrations by a Horiba gas analyzer. Experimental results show that the model can accurately predict the main engine-out/DOC/DPF NO/NO2 dynamics very well in semisteady-state tests. For the proposed observer, the predictions converge to the model values and estimate the NO and NO2 concentrations in the aftertreatment system well.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

A commonly used diesel engine aftertreatment setup

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Figure 2

Diesel engine and aftertreatment system test bench setup

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Figure 3

Schematic presentation of the setup

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Figure 4

Experiment results of NO2 and NOx relation

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Figure 5

CSTR model of DOC

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Figure 6

Simplified model of PM contact area inside DPF

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Figure 7

CSTR model of DPF

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Figure 8

Measurements of Horiba gas analyzer and NOx sensors from test 1

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Figure 9

Engine speed and torque profile of Fig. 8

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Figure 10

Comparison of tests 3 and 4 engine-out NOx emissions

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Figure 11

Comparison of exhaust variables of tests 3 and 4 at high speed

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Figure 12

NO and NOx measurements of test 2 and comparisons to engine model predicted NO

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Figure 13

Comparisons of engine exhaust NO concentrations measured by Horiba gas analyzer and estimated by engine model

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Figure 14

Comparison of engine-out exhaust NO and NO2 measurements and model predicted values during transient operations at a higher engine speed

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Figure 15

Steady-state NO and NOx measurements from test 4 and model predicted engine exhaust NO

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Figure 16

Comparisons of NO and NO2 measurements after DOC and model simulation

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Figure 17

Validation of DOC model by experimental data

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Figure 18

Comparisons of engine exhaust NOx, downstream DOC NO, and downstream DPF NO

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Figure 19

CO and CO2 concentrations after DOC (before DPF)

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Figure 20

Comparisons of experimental data from Test 3 and DPF model simulation

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Figure 21

Validation of DPF model estimation with experimental data from test 3

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Figure 22

Comparisons of model values observer estimations

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Figure 23

Zoom-in of the initial part of Fig. 2

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Figure 24

Comparisons of measurements and observer estimations (after DOC)

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Figure 25

Comparisons of measurements and observer estimations at higher speeds (after DOC)

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Figure 26

Comparisons of measurements and observer estimations (after DPF)

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Figure 27

Comparisons of measurements and observer estimations at higher speeds (after DPF)

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