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TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels

A High-Pressure Droplet Model for Spray Simulations

[+] Author and Article Information
Changlin Yan

Department of Mechanical Engineering, University of Illinois at Chicago, 842 West Taylor Street, MC 251, Chicago, IL 60607-7022

Suresh K. Aggarwal1

Department of Mechanical Engineering, University of Illinois at Chicago, 842 West Taylor Street, MC 251, Chicago, IL 60607-7022ska@uic.edu

1

To whom correspondence should be addressed.

J. Eng. Gas Turbines Power 128(3), 482-492 (May 05, 2004) (11 pages) doi:10.1115/1.1915390 History: Received August 04, 2003; Revised May 05, 2004

Droplet vaporization models that are currently employed in simulating sprays are based on a quasisteady, low-pressure formulation. These models do not adequately represent many high-pressure effects, such as nonideal gas behavior, solubility of gases into liquid, pressure dependence of gas- and liquid-phase thermophysical properties, and transient liquid transport in the droplet interior. In the present study, a high-pressure quasisteady droplet vaporization model is developed for use in comprehensive spray simulations for which more rigorous vaporization models, such as those based on unsteady formulations, are beyond the present computational capabilities. Except for the gas-phase quasisteady assumption that is retained in the model, the model incorporates all high-pressure effects. The applicability of the model for predicting droplet vaporization in diesel and gas turbine combustion environments is evaluated by comparing its predictions with the available experimental data and with those from a more comprehensive transient model. Results indicate a fairly good agreement between the quasisteady (QS) and transient (TS) models for a wide range of pressures at low ambient temperatures, and for pressure up to the fuel critical pressure at high ambient temperatures. The QS model generally underpredicts the vaporization rate during the earlier part of droplet lifetime and overpredicts during the later part of lifetime compared to those using the TS model, and the difference becomes increasingly more significant at higher ambient pressure and temperature. The differences can be attributed to the quasisteady gas-phase average temperature and composition assumption for the QS model that reduces and increases the gas-phase heat and mass fluxes at the droplet surface during the earlier and later part of lifetime, respectively. The applicability of the QS model is quantified in terms of the maximum pressure as a function of ambient temperature.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Comparison of predicted thermophysical and transport properties with measured data; (a) gas (nitrogen) properties and (b) liquid (n-heptane) properties

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Figure 2

Comparison of predicted mole fraction of nitrogen with measured data at two different temperatures for an n-heptane-nitrogen binary system

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Figure 3

Temporal variation of nondimensional surface area for two different ambient conditions; comparison of predictions using the transient (TS) and quasisteady (QS) models with experimental data from Ref. 35

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Figure 4

Temporal histories of nondimensional surface area and temperature predicted using the QS models at different ambient pressures for Ta=500K; (a) surface area and (b) surface temperature. The initial droplet diameter (d0) is 0.05 mm and temperature (T0) is 300 K.

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Figure 5

Temporal histories of nondimensional surface area and temperature predicted using the QS models at different ambient pressures for Ta=1000K; (a) surface area and (b) surface temperature

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Figure 6

Temporal histories of nondimensional surface area and temperature predicted using the QS models at different ambient pressures for Ta=1500K; (a) surface area and (b) surface temperature

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Figure 7

Droplet lifetime versus pressure at different ambient temperatures

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Figure 8

Final droplet surface temperature plotted as a function of pressure for different ambient temperatures. The boiling line and critical mixing line are shown in the figure.

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Figure 9

Comparison of temporal histories of nondimensional surface area and temperature predicted using the QS and TS models at three different ambient pressures. (a) Surface area and (b) surface temperature. Ta=500K. The initial droplet diameter (d0) is 0.05 mm and temperature (T0) is 300 K.

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Figure 10

Comparison of temporal histories of nondimensional surface area and temperature predicted using the QS and TS models at three different ambient pressures. (a) Surface area and (b) surface temperature. Ta=1000K. The initial droplet diameter (d0) is 0.05 mm and temperature (T0) is 300 K.

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Figure 11

Minimum pressure required for an n-heptane fuel droplet to attain the critical mixing state, plotted as a function of ambient temperature

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Figure 12

Variation of droplet lifetime, resulting from an increase of a given property by 20%, plotted versus pressure for Ta=1000K

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Figure 13

Temporal variation of the ratio of gas density (at the droplet surface) to liquid density plotted versus pressure. (a) Ta=500K, (b) Ta=1500K.

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Figure 14

The final ratio of gas density (at the droplet surface) to liquid density plotted versus pressure at different ambient temperatures

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Figure 15

The range of applicability of the QS model in terms of the limiting pressure plotted as a function of ambient temperature

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