Keywords

flame, stability, supersonic, combustion, timescale, hypersonic

Abstract

This research focuses on advancing our understanding of flame stability in supersonic non-premixed flames by employing experimental data to develop a flame stability correlation parameter (SCP). Experimental data were acquired from a generalized supersonic cavity flameholder combustor equipped with converging-diverging (CD) nozzles, generating Mach 1.8-3 flow at the combustor inlet. The study encompassed both upstream and direct cavity fuel injection methods, considering diverse flameholder geometries, including axisymmetric and rectangular configurations, and utilizing ethylene and propane fuels. To address the flame stability challenge, the critical physical parameters impacting SCP were systematically identified, categorizing them into two distinct domains: the flow timescale and the chemical timescale, delineated by the Damköhler number. Flow timescale parameters were assessed by modifying flow rate to account for compressibility effects. These parameters were found to be significantly influenced by density variations attributed to high-speed aerodynamics. Pressure increases and velocity reductions at the flame shear layer were observed, arising from cavity geometry, upstream fuel jet dynamics, and flame presence. As the Mach number increased or pressure decreased, the flow timescale exhibited a proportional increase. The chemical timescale parameters were investigated through similarity, showing sensitivity to thermal diffusivity, flame speed, and flame shear layer thickness. These were further deconstructed into physical parameters such as pressure and temperature. It was observed that the chemical timescale decreased with rising temperature and pressure. Empirical relationships were derived for both flow and chemical timescales, enabling the consolidation of flame stability data onto a unified curve. This research significantly advances the understanding of flame stability mechanisms in supersonic combustion. All data was generously provided by the Air Force Research Lab (AFRL).

Completion Date

2023

Semester

Fall

Committee Chair

Ahmed, Kareem

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Degree Program

Aerospace Engineering

Format

application/pdf

Identifier

DP0028083

URL

https://purls.library.ucf.edu/go/DP0028083

Language

English

Release Date

December 2028

Length of Campus-only Access

5 years

Access Status

Doctoral Dissertation (Campus-only Access)

Campus Location

UCF Online

Download

Restricted to the UCF community until December 2028; it will then be open access.

Share

COinS