Researchers: Rolf Johansson, Anders Widd in
cooperation with Assoc. Prof. Per Tunestål and Prof. Bengt
Johansson, Div. Combustion Engines.
KCFP, Closed-Loop Combustion Modeling and Control
Competence Center Combustion
Processes at Lund University focuses on
research of combustion processes between conventional HCCI (Homogeneous
Charge Compression Ignition) and classical Otto and Diesel engines.
Project aims:
System identification of combustion processes under
closed-loop
control;
Development of algorithms hardware implementation
suitable for
ASICs and FPGA;
Control-oriented modeling and simulation of
combustion processes
.
In addition to aspects of modeling related to thermodynamics, chemical
combustion kinetics, and engine operation, careful attention is
required for control-oriented combustion modeling and the interactions
among dynamics, control, thermodynamics and chemical combustion
properties. Modeling of engine-load transients as well as
thermal
transients also belong to this important domain of modeling. Progress
in this area is important and necessary for successful and robust
control such as model-predictive control.
Within the project a cycle-resolved, physics-based, model of HCCI has
been developed. The model includes a low-complexity model of the
cylinder wall temperature dynamics in order to capture the relevant
time-scales of transient HCCI when only small amounts of hot residuals
are trapped in the cylinder. The temperature evolution of the gas
charge is modeled as isentropic compression and expansion with three
heat transfer events during each cycle.
During 2008, work focused on design and evaluation of model
predictive controllers based on linearizations of the model. The
considered control signals were the inlet valve closing and the intake
temperature. Simulations were used for the initial control design and
the resulting controller was tested experimentally. The control
performance was evaluated in terms of response time to set-point
changes and the resulting output variance.
It was found that a comparable decrease in the output variance in some
operating points could be achieved either by introducing a disturbance
model or by changing linearization.
All tested set-point changes were accomplished within 20 engine cycles
or less. Only minor changes to the intake temperature were required for
moderate changes.
The closed-loop system showed good robustness towards disturbances in
engine speed, injected fuel energy, and the amount of recycled exhaust
gases.
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