A Nonlinear Wall-Wetting Model for the Complete Operating Region of a Sequential Fuel Injected SI Engine

The wall-wetting dynamics represent a very important subsystem of the air/fuel path of an SI engine. The precise feedforward control of the air/fuel ratio requires a valid model of the wall-wetting dynamics over the whole operating region of the engine.

A global wall-wetting model has been developed for a production SPFI gasoline engine. This model is capable of describing the wall-wetting dynamics not only in a fixed operating point, but also for radical changes of the operating point. Its structure specifically allows for model-based compensator design and on-line parameter identification.

Earlier, related publications discussed linear model structures. Those models described the dynamics around a fixed operating point only. This paper shows how one global model for the whole operating range can be constructed from a linear model and its parameter range. New functions describe the changes of the total amount of fuel in the intake manifold during transient stages of the engine operation. Measurements conducted on a dynamic engine test bench show good results for this approach.