Student Name: Samuel Wonfor

Advisor: Dr. Adam Steinberg

Milestone: PhD Thesis Final Examination (Defense)

Degree Program: Aerospace Engineering

Title: Effects of Reactant Inhomogeneity on Lean-Premixed-Prevaporized Gas Turbine Combustor Performance

Abstract: With the growing interest in lean-burn combustors for aviation gas turbine engines, further understanding of the connections between combustor stability and pollutant emissions is required to achieve reliable and sustainable combustor designs. An important parameter that remains to be systematically studied in regard to lean-premixed-prevaporized (LPP) combustion is the level of fuel-air prevaporization and premixedness. Deviations from perfect premixing, henceforth referred to as reactant inhomogeneities, have been shown to enhance both laminar and turbulent flame stability through partial premixing and stratification phenomena. Unfortunately, this comes at the cost of increased pollutant emissions, such as nitrogen oxides (NOx), due to poorly mixed “hot spots” which produce disproportionate amounts of pollutants compared to the combustion of a homogeneous mixture. Studies of reactant inhomogeneity phenomena have been conducted on benchtop burners with canonical geometries operating with gaseous fuels at atmospheric pressures. This dissertation explores when and how reactant inhomogeneity effects influence a liquid-fueled LPP combustor operating at flight relevant conditions. A multi-element, high pressure LPP test facility was constructed featuring a variable premixer, enabling fuel injection at one of four locations, each a different axial distance from the combustor inlet. This premixer enabled the systematic study of the effects of reactant inhomogeneity on LPP combustor performance. NOx emissions were shown to increase with increased reactant inhomogeneity, demonstrating the significant effect of hot spots on pollutant production. However, the effect of reactant inhomogeneity on lean blowoff limits showed conflicting trends, with results suggesting that optimal stability in the LPP combustor was not achieved with perfect premixing. Through the development and deployment of advanced laser diagnostic techniques, the mechanisms through which reactant inhomogeneity influenced combustor performance were studied, the results of which further supported the hypothesis that an optimal level or reactant inhomogeneity exits for LPP combustor performance.

Date and time: 2025-12-03, 1:00 pm

Location: Food Processing Technology Building, Auditorium 102

Committee:
Dr. Adam Steinberg (advisor), School of Aerospace Engineering
Dr. Jerry Seitzman, School of Aerospace Engineering
Dr. Wenting Sun, School of Aerospace Engineering
Dr. Ellen Mazumdar, School of Mechanical Engineering
Dr. Benjamin Emerson, School of Aerospace Engineering