טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentEvgeny Kushnir
SubjectInvestigation of the Structure of an Edge-Flame in a Mixing
Layer with a Fuel Spray
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Greenberg Jerrold
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Under some operating conditions, when fuel spray and oxidizer are supplied separately, a tribrachial edge flame arises, located downstream of the mixing layer. Little work has been performed to study the influence of spray characteristics on the dynamic behavior of such flames. The only theoretical work that appeared in 2009 described the flame structure using a diffusional-thermal model with the constant density approximation. Even this simple model provides evidence of unsteady flame behavior because of the presence of spray evaporation and supplied an explanation for spray flame oscillatory behavior that was observed in some experiments.

In order to understand the aforementioned phenomena, a mathematical/numerical model of an edge flame with fuel spray was implemented. In the current work we examined the impact of previously made assumptions on the results with more realistic cases and a first attempt was made to investigate spray flame dynamics with full coupling between gas flow, energy and reactants conservation equations.

For coupled two phase-flows modified vorticity-stream function (incompressible flow) and modified vorticity-like stream and potential functions (compressible flow) approaches were presented, using the sectional approach with a mono-sectional model adaptation for the sprays.

The conclusions that were presented in the previous work were checked under more realistic conditions and it was shown that they provide good explanations for the flame behavior. Additional physical explanations were provided for those parameters which were investigated for the first time and quantitative differences between different assumptions were shown.

All the cases that are presented in this work successfully capture flame oscillations and provide excellent qualitative agreement with experimental evidence. The operating conditions which lead to oscillatory behavior for the unsteady state were found to be different for the various levels of fluid interphase coupling. Also, it was shown that the spray characteristics, such as initial spray angle of injection, can contribute to edge flame stability under conditions for which spray motion parallel to the gas flow induces visible oscillations.

The compressible case with full coupling between all the physical processes provides qualitatively similar flame behavior to that found in simplified cases. However, the quantitative results are different and show the relative inaccuracy of the predictions under the different assumptions.

This work provides a basis for a complicated full coupled investigation of the edge flame with spray, based on the modified coupled two-phase model.