The demand for low cost, high efficiency and clean burning gas turbine has increased in past years to meet consumer demands and governmental emission policies. The direct relationship between the production of NOx, temperature, and residence time has shown difficulty in obtaining higher efficiency without elevating emission level. Modern Dry Low NOx (DLN) combustors are reaching their limits for effectively operating at low NOx levels. As such, research for further improvements in current combustors has increased in recent years. The work in this dissertation further investigates axial stage combustion, one of the novel technologies aiming to reach desirable firing temperatures and emission levels. Real time gas turbine can operate at elevated pressures, making it difficult to scale the results in literature to operational load conditions. Multiple studies were conducted to isolate the effects of the various parameters on the reacting jet. The current work experimentally investigated premixed reacting jets in vitiated crossflow under various pressure, mixture composition and stoichiometric conditions to further understand their influence on flame characteristics and emission. Recent literature investigating jet in crossflow, conduct the experiments at ambient conditions. The goal of this work was to provide more insight in the jet in crossflow interaction at relevant operating conditions found in a gas turbine. The first part of this work focus on understanding the influence of pressure on the jet in crossflow mechanism as well as and the effect on NOx levels. Jet conditions such equivalence ratio and momentum flux ratios were held constant throughout the study with the pressure of the system ranging from 1atm to 5atm. The flow structure and flame stabilization of the jets at different pressures were characterized using particle image velocimetry (PIV) and CH* chemiluminescence. The results of this study demonstrated variation in jet trajectory, flame stabilization and NOx level, demonstrating the underpredictions of studies at atmospheric conditions. The second part of this work studied the influence of the axial jet mixture composition by introducing diluents such as CO2 and N2. Flame stabilization and NOx emission are driven by both the fluid dynamics and chemical kinetics of the system. By adding diluents to the axial jet, the chemical kinetics are altered allowing for further investigation on the relationship between the axial jet chemical kinetics, flame stabilization and NOx emissions. CH* chemiluminescence was utilized to analyze the flame behavior such as liftoff height, flame attachment, and dispersion as a result to the addition of diluents. Emissions were obtained to study the direct relationship between emissions and axial jet composition. The results of this work demonstrate the important effect of pressure and axial jet composition on the flame dynamics and emissions of reacting jets in crossflow.


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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

Aerospace Engineering




CFE0008363; DP0023800





Release Date

December 2025

Length of Campus-only Access

5 years

Access Status

Doctoral Dissertation (Campus-only Access)

Restricted to the UCF community until December 2025; it will then be open access.