Student Name: Jeremiah C. Juergensmeyer

Advisor: Dr. Adam Steinberg

Milestone: PhD Thesis Proposal

Degree Program: Aerospace Engineering

Title: Optimization of Lean Premixed Prevaporized Combustion Through Pilot-Main Interaction

Abstract: Lean-burn engines have demonstrated significant reductions in major pollutants, particularly nitrogen oxides (NOx) and non-volatile particulate matter (nvPM). Lean premixed prevaporized (LPP) combustors have seen growing interest in aeronautical combustion as the increased combustor inlet temperatures associated with future compact core and potential civil supersonic engines can improve vaporization of liquid fuels and reduce emissions. However, a drawback of LPP combustion is the susceptibility to lean blowoff. To improve stability of the combustor, a multi-element configuration featuring a richer, more stable pilot flame is often employed. Yet further understanding of the interaction between the pilot and leaner-burning main flames, along with the stability-emission tradeoff of that interaction, is not well understood. This work aims to advance understanding of pilot-main interactions through both a fundamental and a practical perspective, including optimization of a supersonic LPP combustor operating a flight relevant conditions. To conduct this research, an LPP combustor featuring a central partially-premixed pilot flame surrounded by four LPP main flames has been developed and fabricated within the Georgia Tech Combustion Lab. Initial testing of the combustor demonstrated reductions in NOx and nvPM over conventional aeronautical combustors. In-depth analysis revealed the blowoff propensity of the LPP main flames at a given global fuel-air ratio was insensitive to the pilot flame equivalence ratio; the added stability of the slightly richer main flames appeared to offset any reduced effectiveness of a leaner, potentially less stabilizing pilot flame. Reduction of the pilot flame equivalence ratio resulted in a decrease in NOx emissions, however with diminishing returns. Thus, this configuration of an LPP combustor can achieve reduced emissions with no impact to stability by operating with a leaner pilot. However, the overall stability limits of the combustor, particularly with respect to lean blowoff, were worse than similar geometries in literature. It is expected that these stability limits can be improved with further optimization of the pilot-main interaction. For fundamental study of pilot-main interactions, along with advancement of CH PLIF, a second simplified geometry combustor has been developed. The combustor features identical dome face geometry to the LPP combustor, with the exception of containing only a single main flame. Modification to the pilot design allows for variation of critical parameters, such as the geometric swirl number and swirler divergence angle. Future research includes a preliminary test campaign on the single main combustor. CH PLIF will be used to quantify the impact of critical pilot parameters on the stability of the main flame, along with providing insight into the driving physics of the interaction. Blowoff data is to be collected at atmospheric and elevated pressures to provide a robust test matrix for characterizing the impact of a pilot flame while enabling CH PLIF for future testing in the LPP combustor. Following the single main combustor testing, the full LPP combustor will again be operated at conditions akin to cruise of a civil supersonic combustor. CH PLIF will be leveraged to characterize turbulent flame structure and local extinction. Direct gaseous emission sampling will provide metrics for characterizing combustor performance and emissions. Blowoff limits will be identified through OH and CH PLIF. Multiple pilot configurations will be explored, and the impact on stability and emissions will be studied. Ultimately, understanding of pilot-main interactions will be advanced, enabling optimization of an LPP combustor.

Date and time: 2026-04-27, 1:00 PM

Location: MK-317

Committee:
Dr. Adam Steinberg (advisor), School of Aerospace Engineering
Dr. Jerry Seitzman, School of Aerospace Engineering
Dr. Benjamin Emerson, School of Aerospace Engineering
Dr. Conner Godbold, School of Aerospace Engineering
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