Keywords

Hypersonics, Scramjet Combustion, Unstart, Flame Compressibility

Abstract

Viable forms of propulsion for practical hypersonic flight are of great interest in modern times, of which supersonic combustion ramjets(scramjets) are a very advantageous option. Compared to ramjets, which are severely limited by increasing total pressure loss and dissociation effects, scramjets offer a much more efficient form of propulsion in the Mach 6 – 8 regime. Despite this, a common and unmitigated issue facing scramjet technology is scramjet unstart.

Prior investigations researching scramjet unstart have elucidated global heat release considerations in relation to total fueling or combustion modes as a result of global heat release . Minimal work has been conducted regarding fueling configuration and localized heating in relation to compressibility of flames in scramjet unstart.

This work seeks to progress the understanding of compressibility of flames in onset of scramjet unstart. Through experimental validation in University of Central Florida’s high-speed vitiated blowdown facility; high speed schlieren imaging, broadband chemiluminescence imaging, and pressure diagnostics; and an accurate one-dimensional theoretical calculation; this current effort expands upon on the role of flame compressibility in scramjet unstart. Initially, a validation of a 1D theoretical model is presented that captures local choking effects in supersonic reacting flow. Secondly, the effects of distributed fueling and equivalence ratio on pressure rise, coupled heat release, and combustor unstart in Mach 3 flow is explored. The extent to which distributed fueling’s benefits are demonstrated without thermal choking are defined. Furthermore, the effect of equivalence ratio, localized heating, and compressible flames on the onset of scramjet unstart Mach 4 flow is also studied through the delineation of a local choking mechanism. Insights into the dynamics of compressibility of flames in scramjet unstart are made. Lastly, prospective considerations for scramjet combustor operating regimes are also presented.

Completion Date

2026

Semester

Spring

Committee Chair

Ahmed, Kareem

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Format

PDF

Document Type

Dissertation

Identifier

DP0053177

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