Ph.D. Thesis Proposal

Ari Jain

(Faculty Advisor: Professor Adam Steinberg)

"Flame Structure, Operability, and Diagnostic Development in Lean Premixed Prevaporized Gas Turbine Combustors"

Friday, May 15

2:00 p.m.

Montgomery Knight Room 317

Virtual

Join: 

https://teams.microsoft.com/meet/242880409726980?p=PWrxWMphslubt5dWgL

Meeting ID: 242 880 409 726 980

Passcode: p6Cf3g8D

Abstract:

This proposal investigates flame structure, operability, and diagnostic development in lean premixed prevaporized (LPP) gas turbine combustors across operating regimes relevant to future low-emissions aircraft engines. LPP combustion offers a pathway to reduced NOx and non-volatile particulate matter emissions by burning globally lean. However, practical implementation is limited by competing operability challenges, including fuel-dependent mixing and vaporization effects, lean blowoff, and high-power failure modes such as flashback and upstream flame holding. This work addresses these challenges through three coordinated experimental campaigns using advanced optical diagnostics in both industrially relevant and laboratory-scale combustors.

The first campaign examines how conventional Jet-A, hydroprocessed esters and fatty acids (HEFA) sustainable aviation fuel, and a 50/50 Jet-A–HEFA blend influence spray behavior, flame structure, and lean operability in a multi-element LPP combustor. Measurements using OH planar laser-induced fluorescence (PLIF), OH* chemiluminescence (CL), Mie scattering, and phase Doppler particle analysis are used to connect fuel physical properties to droplet penetration, vaporization, flame topology, and blowoff behavior. Preliminary results show that HEFA produces shorter liquid-fuel penetration depths than Jet-A and the blend, consistent with its lower density, viscosity, surface tension, and distillation characteristics. These results provide a basis for determining whether fuel-dependent spray and mixing differences significantly alter global lean blowoff behavior or primarily affect local flame structure and intermittency.

The second campaign investigates pilot–main flame interactions in a practical multi-element LPP combustor by independently varying pilot and global equivalence ratios while acquiring measurements across multiple radial planes. OH/kerosene PLIF, Mie scattering, and high-speed OH* or CH* CL are used to identify how the central pilot modifies the surrounding bluff-body-stabilized main flames. This campaign is designed to determine whether the pilot primarily stabilizes the mains by supplying hot products and chemically active species to the main-flame recirculation zones, and whether global lean blowoff limits are more strongly controlled by main-flame conditions than by pilot equivalence ratio within the pilot’s own stability limits.

The third campaign develops laser-induced phosphor thermometry (LIPT) for spatially and temporally resolved wall-temperature measurements under high-power takeoff conditions. Candidate phosphor coatings will be selected, calibrated, and evaluated for lifetime-based thermometry in a medium-pressure burner. LIPT measurements, combined with chemiluminescence imaging, will be used to identify localized wall-temperature signatures associated with abnormal flame–wall interactions and potential upstream flame holding. Although the medium-pressure burner cannot fully reproduce the thermal and optical environment of high-power testing, it provides a controlled platform for developing diagnostic capability that can later be extended to more severe gas-turbine operating conditions.

Together, these campaigns aim to clarify how fuel properties, pilot–main coupling, and wall thermal response influence LPP combustor operability. The expected outcome is an improved physical understanding of flame stabilization and failure mechanisms in practical lean-burn combustors, along with diagnostic tools needed to characterize these processes across operating regimes.

Committee:

Dr. Adam Steinberg (advisor), School of Aerospace Engineering
Dr. Ellen Mazumdar, School of Mechanical Engineering
Dr. Benjamin Emerson, School of Aerospace Engineering