An Analysis of Air to Fuel Ratio Response in a Multi Point Fuel Injected Engine Under Transient Conditions

In this paper the λ response during a fast change of the throttle is studied. A mathematical model based on a manifold air flow model and a fuel film model with two deposit parameters and two time constants was used, together with a time delay between air and fuel supply to the engine during the transient, for data matching of the measurements.

It was found that a single deposit parameter (X) and one time constant (τ) together with a time delay (Δt) describe the fuel film behaviour during a transient very well.

It was also found that a large part of the λ excursion is due to the time delay effect. This applies particularly to positive transients.

The time delay is of major importance for the λ excursion peak.

The fuel film effect is dominating during negative transients.