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Abstract |
Cylinder Air Charge Estimator in Turbocharged SI-Engines
Mean value cylinder air charge (CAC) estimation models for control and
diagnosis are investigated on turbocharged SI-engines. Two topics are
studied; Firstly CAC changes due to fuel enrichment and
secondly CAC sensitivity to exhaust manifold pressure changes. The
objective is to find a CAC model suitable for control and diagnosis. Measurements show that CAC models based on volumetric efficiency
gives up to 10% error during fuel enrichment. The error is
caused by the cooling effect that the fuel has as it evaporates and
thus increases the charge density. To better describe the CAC during
fuel enrichment a simple one parameter model is proposed which
reduces the CAC estimation error on experimental data from 10% to
3%. With active wastegate control, the pressure changes in the exhaust
manifold influences the CAC. The magnitude of this influence is
investigated using sensitivity analysis on an exhaust manifold
pressure dependent CAC-model. From the sensitivity analysis it can be
concluded, that the CAC is most sensitive to exhaust manifold pressure
changes for low intake manifold pressures (part load). Without taking
the exhaust manifold pressure into account the CAC error is
approximately 5% when the wastegate is opened at part load. The exhaust manifold pressure dependent CAC model is then augmented
with the charge cooling model and the total model gives precise
agreement on experimental data. The resulting model is thus highly
suitable for CAC estimation for control and diagnosis of turbocharged
SI-engines.
Per Andersson and Lars Eriksson
SAE Technical paper series SP-1822, 2004
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Last updated: 2021-11-10
