Date of Award

12-2025

Document Type

Thesis

Degree Name

Master of Science

Department

Mechanical Engineering

Abstract

Advanced combustion engines are trending towards high-pressure operations to increase the efficiency and power of the engines. Injecting liquid fuel at subcritical temperature into a supercritical ambient temperature and pressure environment is a key challenge in many practical combustion engines. This process involves fuel transitioning from subcritical to supercritical conditions, leading to combustion through jet atomization and droplet formation. Due to the complexity of this problem, the current research divided the process into two areas focused on the combustion of a single droplet and the fundamentals of the liquid transition in a jet stream in an inert environment at supercritical conditions. This work focused on examining how a liquid fuel jet disintegrates and transitions in an inert, supercritical ambient environment.

Engine operating pressures are rising, leading to a transition past critical points of at least one component in fuel-air mixtures. Limited knowledge exists on the behavior of multicomponent mixtures of liquid fuel and gas near critical points due to the different critical temperatures and pressures of individual components. This experiment observed the behavior of n-Heptane fuel jets injected at a high pressure of 2.8 MPa to 10 MPa, above the critical pressure of Heptane, into a supercritical Nitrogen gas chamber at ambient temperatures of 570 K to 620 K, above the critical temperatures of both Heptane and Nitrogen. The volumetric flow rate of the jet was varied from 0.5-4 mL/min to allow for a low Reynolds number.

This study utilized low to moderate Reynolds numbers to reduce turbulent effects, improving the interpretation of the experimental results. The experiment was conducted at the NASA Glenn Research Center Zero-G Facility in microgravity to minimize buoyancy effects and reduce disturbances in the fuel jet stream. Temperature variation during the experiment allowed for the observation of subcritical, supercritical, and transcritical jets. Both the subcritical and transcritical jets exhibited Rayleigh-Plateau instability, breaking into droplets. For subcritical jets, the droplets maintained sharp interfaces, while in the transcritical case, the droplets transitioned from evaporative to diffusive mixing. Supercritical jets progress from dense liquid-like cores to gas-like supercritical mixing, without forming droplets.

Index Terms– Fuel injection, high pressure, microgravity, transcritical.

Committee Chair/Advisor

Ziaul Huque

Committee Member

Uday Hegde

Committee Member

Paul Biney

Committee Member

Jianren Zhou

Committee Member

Yuhao Xu

Publisher

Prairie View A&M University

Rights

© 2021 Prairie View A & M University

Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Date of Digitization

04/13/2026

Contributing Institution

John B Coleman Library

City of Publication

Prairie View

MIME Type

Application/PDF

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