Browse Publications Technical Papers 2004-01-1461

An Easily Tunable Wall-Wetting Model for PFI Engines 2004-01-1461

In modern spark-ignited engines the accurate estimation of the amount of fuel to be injected is an important issue, in particular if a specific air-to-fuel ratio is required. The knowledge of the events occurring between the intake duct (injectors) and the exhaust duct (λ-sensor) is thus very important. Among all the systems that play a role, the best studied are the wall-wetting dynamics.
Nowadays, the wall-wetting effects are compensated on the basis of simple linear models that are tuned with the help of a large number of measurements. These models are quite effective but they cannot be used universally.Their extrapolation for a non-measured operating point can lead to unsatisfactory results. Other problems arise at operating points where direct measurements are difficult, e.g., at cold start.
Complex models already exist, but usually they require a lot of work in the parameterization phase. This paper introduces a wall-wetting model based on first physical principles which has all the properties of the simple model, but is able to extrapolate the behavior of the film dynamics when needed, and it is suitable for control purposes.
The results of this paper show that by applying such a model on an SI engine the number of measurements can be even further reduced, because of an increased understanding of the physics of the wall-wetting.


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