Potential of inertial instabilities for fuel film separation in port fuel injection engine conditions

Abstract

In port fuel injection engines, the liquid fuel film accumulated in the vicinity of intake valves is torn away and goes into the cylinder during the intake phase. In order to predict the fuel mixture preparation inside the cylinder, a model for the fuel film separation near the sharp edges of the intake valves has been developed. A separation criterion is set up using an analogy with Rayleigh-Taylor instabilities driven by the inertial forces of the film.

The critical value for the separation criterion is adjusted using experimental data obtained in a two-dimensional wind tunnel fitted with different steps shaped as the valve seat and reproducing the main characteristics of the intake of a spark ignition engine. Computational fluid dynamics simulations are performed using the KMB code, a modified version of KIVA-2 already including a film model and a stochastic Lagrangian description of the spray. Computation for the intake stroke on a four-cylinder 1.9 litre port fuel injection engine confirms that the fuel droplets are not completely vaporized at the end of the intake stroke.