In this dissertation, the operational map of a lean reacting jet-in-crossflow situation has been explored with Computational Fluid Dynamics (CFD) and an axially staged combustor experiment at pressure of five atmospheres to aid scaling to gas turbine engine conditions applied industrially. The optically accessible test section features three side windows, allowing in-house local flow and flame analysis with PIV and CH* chemiluminescence along with pressure, temperature and species measurements. The dissertation research revealed local formation of NOx emission and analyzed contribution of thermal NOx and prompt NOx pathways. The full GRI Mech 3.0 was computed with detailed chemistry and compared with models utilizing Flamelet chemistry or reduced methane mechanisms. Lean operating points with any 12.7mm or 4mm axial jet composition were characterized to be in the finite-rate regime. A nitrogen oxide benefit was proven at elevated operating pressures due to the transition from shear layer burning to jet core flame burning. Optimization of the axial fuel split to 25% utilized a lean headend with a slightly rich jet equivalence ratio. For the range of conditions analyzed, lower fuel splits with a lean headend did not maintain a sufficient axial temperature rise and higher fuel splits would require addition of reacting axial length to maintain near-complete combustion. Simulated jet trajectories were in good agreement with the data and were described by an elliptic curvature to compensate for the poor far-field prediction of existing correlations. Non-premixed fuel-air condition in the axial fuel line resulted in an ignition point further downstream and reduced reaction rates. This delay can affect a NO benefit paired with relatively rich headend equivalence ratio, reducing the residence time of the reacting axial jet without exceeding spatial limitations. Dependencies of axial NO emission on the key influence parameters temperature, pressure and residence time were proposed. For a 4mm axial jet, variation of main stage (f = 0.575 - 0.73) and jet equivalence ratio (f = 1.1 - 8) have been investigated. The premixed flames were found to be controlled by the crossflow temperature before ignition and the crossflow oxygen level during axial combustion. Analysis of the flame shape and position for the rich premixed operating points describes an upstream stabilized flame along with a highly lifted windward flame branch. Control of added jet fuel amount as well as headend temperature and coupled oxygen level were critical to attain a compact flame body and allow combustion at sufficient reaction rate. Delayed combustion event with overshooting, spatially divided flames was observed for the axial jet equivalence ratios f = 8 and f = 8 combined with at a relatively rich main stage f = 0.73 due to the lack of available oxidizer.


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Graduation Date





Ahmed, Kareem


Doctor of Philosophy (Ph.D.)


College of Engineering and Computer Science


Mechanical and Aerospace Engineering

Degree Program

Mechanical Engineering




CFE0008248; DP0023602





Release Date


Length of Campus-only Access

5 years

Access Status

Doctoral Dissertation (Campus-only Access)

Restricted to the UCF community until 8-15-2025; it will then be open access.