CFD Characterization of Fuel Flow in Small Metering Orifices Used In Carburetors

Although each carburetor design is slightly different, it is possible to define some basic elements that can be used as building blocks to describe many carburetor designs. All carburetors designs use small metering orifices to constrain fuel and air flow through different circuits. This paper presents the CFD analysis of fuel flow across small metering orifices typically found in small engine carburetors. The analysis was divided into three parts: first, CFD simulations of liquid flow in square-edged orifices were performed. These simulations indicated the appropriate turbulent model and numerical parameters to be used in the study of orifices with more complex geometries. Second, inlet and outlet chamfers were added to the square-edged orifices, which allowed for understanding their effect on the characteristics of the flow.

Finally, the simulations were performed on geometries that represented metering orifices found in real carburetors. The verification of the CFD predictions with experimental results showed a good agreement. The information obtained from the CFD simulations were used to develop correlations for the real orifices. These correlations are simple enough so they can be incorporated into a flow network model of carburetor fuel flow.