Control of Charge Dilution in Turbocharged Diesel Engines via Exhaust Valve Timing

[+] Author and Article Information
Hakan Yilmaz, Anna Stefanopoulou

Department of Mechanical Engineering,  University of Michigan, Ann Arbor, MI 48109

J. Dyn. Sys., Meas., Control 127(3), 363-373 (Aug 24, 2004) (11 pages) doi:10.1115/1.1985440 History: Received April 10, 2003; Revised August 24, 2004

In this paper we extend an existing crank angle resolved dynamic nonlinear model of a six-cylinder 12 l turbocharged (TC) Diesel engine with exhaust valve closing (EVC) variability. Early EVC achieves a high level of internal exhaust gas recirculation (iEGR) or charge dilution in Diesel engines, and thus reduces generated oxides of nitrogen (NOx). This model is validated in steady-state conventional (fixed EVC) engine operating points. It is expected to capture the transient interactions between EVC actuation, the turbocharger dynamics, and the cylinder-to-cylinder breathing characteristics, although this has not been explicitly validated due to lack of hardware implementation. A nominal low order linear multi-input multi-output model is then identified using cycle-sampled or cycle-averaged data from the higher order nonlinear simulation model. Various low-order controllers that vary EVC to maximize the steady-state iEGR under air-to-fuel ratio (AFR) constraints during transient fueling demands are suggested based on different sensor sets. The difficulty in the control tuning arises from the fact that the EVC affects both the AFR and engine torque requiring coordination of fueling and EVC. Simulation results are shown on the full order model.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Current external EGR applications: Venturi mixer, intake EGR throttle, variable geometry turbocharger, exhaust backpressure valve

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Figure 2

Notations of control volumes and gas flows

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Figure 3

Apparent fuel burn rate from experimental data and model prediction vs crank angle

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Figure 4

Quasi-static in-cylinder pressure, valve profiles, and gas flows through valves (scaled) vs crank angle (°)

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Figure 5

Steady state maps for in-cylinder burned gas fraction vs EVC

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Figure 6

Steady state air to fuel ratio vs EVC

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Figure 7

Steady state maps for mean torque vs EVC

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Figure 8

Steady state inlet manifold pressure vs EVC

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Figure 9

System identification results (Wf step up∕down, EVC step up∕down, respectively)

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Figure 10

Bode magnitude plots in dB and rad∕s of the linear identified systems at 1600 rpm, 57 lb∕h with EVC 350° (solid line) and 395° (dash line).

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Figure 11

Three control architectures based on different sensor sets

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Figure 12

Bode plot for the ideal-cancellation controller (Ccanc solid line) and reduced-cancellation controller (Cred dash line)

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Figure 13

Response of linear closed loop schemes: FFC in solid line, fbAFRdec in dash line, fbMAPred in dash-dot line, and conventional engine linear response with fixed EVC=404° in dot line. All graphs show deviations from the nominal values where linearization was performed.

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Figure 14

Nonlinear full order closed loop system response for FFC in solid line, fbAFRdec in dash line, and fbMAPred in dash-dot line




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