Date of Award

2-2010

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Mechanical Engineering

First Advisor

David P. Schmidt

Second Advisor

J. Blair Perot

Third Advisor

Dimitrios Maroudas

Subject Categories

Mechanical Engineering

Abstract

Among the many factors that effect the atomization of a fuel spray in a com- bustion chamber, the flow characteristics of the fuel inside the injector nozzle play significant roles. The enthalpy of the entering fuel can be elevated such that it is higher than the local or downstream saturation enthalpy, which will result in the flash-boiling of the liquid. The phase change process dramatically effects the flow rate and has the potential to cause subsonic two-phase choking. The timescale over which this occurs is comparable to the flow-through time of the nozzle and hence any attempt to model this phenomenon needs to be done as a finite rate process. In the past the Homogeneous Relaxation Model (HRM) has been successfully employed to model the vaporization in one dimension. Here a full three dimensional imple- mentation of the HRM model is presented. Validations have been presented with experiments using water as working fluid. For the external spray modeling, where the fuel is said to be flash boiling, the phase change process plays a role alongside the aerodynamic breakup of the liquid and must be considered for obtaining the fuel spray characteristics. In this study the HRM model is coupled with Linearized Sheet Instability Analysis (LISA) model, for primary atomization, and with Taylor Analogy Breakup (TAB) model for secondary breakup. The aerodynamic breakup model and phase change based breakup model are designed as competing processes. The mechanism which satisfies its breakup criterion first during time integration is used to predict resulting drop sizes.

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