Numerical Study of Fuel Flow Through Small Orifices

Fuel delivery in carburetors strongly depends on the flow characteristics through a small orifice whose function is to limit the flow between a constant pressure reservoir and a fuel tube. The geometry of this orifice is developed by a trial and error procedure, often without a good understanding of the underlying physics of the flow. In this work, a commercial CFD package was used to perform a numerical simulation of the flow through square edged orifices in order to study the effect of individual parameters on the discharge coefficient, the development of the boundary layer and the velocity profile at the exit of the orifice. Parameters of the study included orifice diameter, length and fuel properties. The simulation used a two-dimensional, axisymmetric, fully turbulent two-equation model in single-phase flow, and was validated by comparison with experimental discharge coefficients of orifices.