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Research Papers

Nonlinear Model Predictive Control of Integrated Diesel Engine and Selective Catalytic Reduction System for Simultaneous Fuel Economy Improvement and Emissions Reduction

[+] Author and Article Information
Pingen Chen

Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210

Junmin Wang

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

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received October 9, 2014; final manuscript received March 26, 2015; published online April 21, 2015. Assoc. Editor: Gregory Shaver.

J. Dyn. Sys., Meas., Control 137(8), 081008 (Aug 01, 2015) (13 pages) Paper No: DS-14-1405; doi: 10.1115/1.4030252 History: Received October 09, 2014; Revised March 26, 2015; Online April 21, 2015

The applications of diesel engines in ground vehicles have attracted much attention over the past decade for the reasons of outstanding fuel economy, power capability, and reliability. With the increasing demand of less greenhouse gas emissions, the current diesel engine fuel efficiency remains unsatisfactory partially due to the conflict between the engine fuel efficiency and engine-out NOx emissions. While advanced aftertreatment systems, such as selective catalytic reduction (SCR) systems or lean NOx trap, have been integrated to diesel engines for reducing the tailpipe NOx emissions, the integrated controls for coordinating diesel engine and SCR system to achieve high engine efficiency and low tailpipe emissions are still limited. The purpose of this study is to develop such an integrated diesel engine and SCR system control method using nonlinear model predictive control (NMPC) approach with both start of injection (SOI) timing and urea solution injection rate as the control inputs. Control-oriented engine models were developed to quantify the influences of SOI timing on engine efficiency and engine-out NOx emissions. Simulation results under US06 driving cycle demonstrate that, given the same catalyst size in total, the proposed controllers are capable of reducing total engine fuel consumption over the driving cycle by 9.36% and 9.50%, respectively, for lumped SCR system and two-cell SCR system, while maintaining high NOx conversion efficiencies and low tailpipe ammonia slip.

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Figures

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Fig. 1

Demonstration of typical ammonia coverage ratio control

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Fig. 2

Integrated diesel engine and aftertreatment systems

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Fig. 3

Schematic diagram of SCR mechanism

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Fig. 4

Influence of EGR valve opening on the BSFC (engine speed: 1400 rpm and pedal position: 22%)

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Fig. 5

Influence of fuel injection strategy on BSFC at engine speed of 1400 rpm

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Fig. 6

Calibration results of engine efficiency model at different engine speeds

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Fig. 7

Calibration results of NOx/NOx,MBT ratio model at different engine speeds (no EGR was applied)

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Fig. 8

Integrated diesel engine and SCR control using NMPC

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Fig. 9

Engine speed and torque profiles under US06 cycle

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Fig. 10

Exhaust flow rate and SCR temperature profile under US06 cycle

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Fig. 11

Ammonia coverage ratio profiles with MPC controller and PID controller during US06 cycle

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Fig. 12

NOx concentrations before SCR system under US06 cycle

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Fig. 13

Comparison of tailpipe NOx emissions with MPC control and PID control

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Fig. 14

Comparison of tailpipe ammonia slip with MPC control and PID control under US06 cycle

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Fig. 15

Ammonia concentration input required by MPC control under US06 cycle

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Fig. 16

Comparison of SOI angle profiles under US06 cycle

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Fig. 17

Comparison of fuel injection rates with and without integrated control under US06 cycle

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Fig. 18

Ammonia coverage ratio profile for the upstream cell under US06 cycle

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Fig. 19

Ammonia coverage ratio profile for the downstream cell under US06 cycle

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Fig. 20

Comparison of NOx concentrations across the two-cell SCR system under US06 cycle

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Fig. 21

Tailpipe ammonia slip profile for the two-cell SCR system under US06 cycle

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Fig. 22

Ammonia concentration input for the two-cell SCR system under US06 cycle

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Fig. 23

Comparison of SOI angle profile under US06 cycle

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Fig. 24

Comparison of fuel injection rates with and without integrated control under US06 cycle

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