Torque Modeling for Optimising Fuel Economy in Variable Compression Engines
Fuel optimal control of a variable compression engine is studied and it is
shown that a crucial component is the model for the engine torque. A model
for the produced work that captures the important effects of ignition and
compression ratio is proposed and investigated. The main task for the model
is to be a mean for determining the fuel optimal control signals, for each
requested engine torque and speed. The contribution is a model suitable for
finding this optimal combination. This model consists of well-known
components, and the novelty lies in the compilation and validation of the
control-oriented efficiency model for a variable compression engine. The
modelling and validation is performed on a multicylinder variable
compression engine using two fuels with different octane rating. Despite the
models simplicity, it describes the indicated work with good accuracy, and
suits its purpose of finding optimal control signals. In the evaluation, it
is shown that a fuel optimal controller based on the proposed model captures
the optimal IMEP to within 1.2%. This corresponds to a loss in engine
efficiency that is in the range of 0.5% units or less.
Ylva Nilsson, Lars Eriksson and Martin Gunnarsson
International Journal of Modeling, Identification and Control (IJMIC),
2008

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