ORCID

kh173161

Keywords

Liquid fuel detonations, Detonability limits, cell size, Droplet cloud evaporation, Multiphase de

Abstract

Detonation-based propulsion systems are of significant interest owing to their high thermodynamic efficiency, rapid energy release, and favorable entropy production relative to deflagration-based systems. Liquid fuels offer practical advantages in storage and volumetric energy density, making them attractive candidates for next-generation detonation engines. This dissertation investigates the detonability characteristics of liquid hydrocarbon fuel clouds through three interconnected studies conducted in a turbulent shock-tube environment using high-speed imaging and pressure diagnostics. The first study maps the detonability limits of monodisperse n-dodecane clouds by systematically varying droplet diameter (5-50 μm) and O₂/N₂ oxidizer composition at equivalence ratios spanning ϕ = 0.8-2.0. Results show that detonability improves with decreasing droplet size, with successful propagation confined primarily to droplets between 5 and 20 μm under stoichiometric to fuel-rich conditions. Measured detonation velocities and pressures remain approximately constant up to the point of abrupt failure, and the normalized ratios P/PCJ and V/VCJ increase with nitrogen dilution, indicating that droplet evaporation timescales govern wave propagation rather than gas-phase thermochemistry. The second study extends this work through a comparative analysis of detonation cell size between n-Dodecane and Jet-a fuel clouds. Cell measurements show that Jet-a cells grow from approximately 5 mm at 5 μm to 10.3 mm at 20 μm, while n-Dodecane yields 7.3 mm at 10 μm and 10.9 mm at 20 μm. Despite their differing chemical compositions, both fuels produce nearly identical detonation cell structures, confirming that droplet size and evaporation rate control reaction zone thickness and cellular instability. The third study develops and validates a cloud evaporation model for droplet clouds in the detonation environment. An unsteady kinematic analysis of 5 μm Jet-a droplets yields a lifetime of approximately 10 μs, corresponding to a 5 mm survival length scale behind the leading shock, iii exceeding predictions from conventional breakup models. Applying group evaporation theory in the sheath vaporization regime recovers the observed timescale within 14.6%, confirming that group evaporation governs droplet persistence in liquid-fueled detonations. Together, these investigations provide a comprehensive framework for understanding how droplet size, fuel type, and evaporation dynamics govern the initiation and propagation of detonations in liquid-fueled systems, with direct implications for the design and operation of liquid-fueled detonation propulsion systems.

Completion Date

2026

Semester

Spring

Committee Chair

Kareem Ahmed

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Format

PDF

Document Type

Thesis

Identifier

DP0053288

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