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TECHNICAL PAPERS

Steady and Dynamic Models of Fuel and Air Flow in Carburetors for Small Engines

[+] Author and Article Information
Diego A. Arias

Multiphase Flow Visualization and Analysis Laboratory, Department of Mechanical Engineering,  University of Wisconsin-Madison Madison, 53706daarias@wisc.edu

Timothy A. Shedd1

Multiphase Flow Visualization and Analysis Laboratory, Department of Mechanical Engineering,  University of Wisconsin-Madison Madison, 53706shedd@engr.wisc.edu

1

Author to whom correspondence should be addressed.

J. Fluids Eng 127(4), 778-786 (Mar 22, 2005) (9 pages) doi:10.1115/1.1949644 History: Received June 21, 2004; Revised March 22, 2005

This work presents the mathematical model of a complex flow network containing short metering orifices, compressible flow, and two-phase flow in small diameter pipes. It has been developed to study the steady and dynamic flows in a carburetor for small engines. It extends the previously published models by incorporating a detailed review of two-phase flow pressure drop, the effect of the fuel well on the control of air-bleed flow, and dynamic flow. The homogeneous two-phase flow model, which is commonly used in previous models, was compared to an empirical correlation derived from experiments in small pipes and found to be in poor agreement. In order to assess dynamic flow conditions, the model was extended by solving instantaneous one-dimensional Navier-Stokes equations in single-phase pipes. This strategy proved successful in explaining the mixture enrichment seen under pulsating flow conditions. The model was also used to derive a sensitivity analysis of geometries and physical properties of air and fuel.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Main systems in carburetor for small engines

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Figure 2

Schematic of carburetor as flow network

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Figure 3

Two-phase flow regimes in a small pipe

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Figure 4

Lines of constant gravitational and frictional pressure change for a short pipe, using the homogeneous model plotted versus airflow and fuel flow

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Figure 5

Experimental setup for emulsion tube measurements

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Figure 6

Pressure contours derived from experiments for two-hole emulsion tube

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Figure 7

Comparison of predicted and correlated data using the empirical correlation derived from data in this study

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Figure 8

Fuel flow versus airflow

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Figure 9

Experimental setup for carburetor fuel flow and airflow

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Figure 10

Experimental validation of carburetor model under steady-state flow

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Figure 11

Fuel height in fuel well versus airflow

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Figure 12

Airflow in emulsion tube versus venturi airflow, for an emulsion tube with three levels of holes

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Figure 13

Relative sensitivity analysis of fuel flow for different geometric and physical parameters

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Figure 14

Quasi-steady-state model; (a) Idealized pressure at venturi throat and air velocity at venturi inlet and (b) Instantaneous fuel flow and airflow

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Figure 15

Instantaneous fuel flow for changing venturi pressure at 900, 1800, and 3600 rpm

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Figure 16

Instantaneous fuel level in fuel well for changing venturi pressure at 900, 1800, and 3600 rpm

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Figure 17

Air-fuel ratio for changing venturi pressure at 900, 1800, and 3600 rpm

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