Transient A/F Control Characteristics of the 5 Liter Central Fuel Injection Engine

Experiments have been conducted to determine the nature and causes of A/F transients during changes in throttle angle on a 5 Liter central fuel injected dynamometer engine. Tests consisted of a series of one-second throttle ramps of various magnitudes at constant engine speed. Fuel metering calculation was adjusted to give error free metering, so that observed A/F transients were due to induction system characteristics such as manifold wall wetting, air charging, and injector phasing. The effects of throttle body and manifold temperature were investigated and a comparison of speed-density and mass-flow metering strategies was made.

A simple continuous flow model was developed to predict the effects of manifold air charging and wall wetting. Comparisons of model predictions and experimental results show the agreement for air flow to be within ± 4%.

Wall wetting is described by a linear, first-order equation with two parameters; a boiling time constant, and a percent impaction parameter. Agreement between model prediction and experiment is good if the percent impaction parameter is allowed to vary linearly with throttle angle.