Author ORCID Identifier

https://orcid.org/0009-0009-4905-8098

Semester

Spring

Date of Graduation

2024

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Omid Askari

Committee Member

Cosmin Dumitrescu

Committee Member

V’yacheslav Akkerman

Committee Member

Fabien Goulay

Committee Member

Hailin Li

Abstract

The next generation of advanced combustion devices is being developed to operate under ultra-high-pressure conditions, to improve combustion efficiency and reduce pollutant emissions. However, at such extreme conditions, flame tends to become unstable, and measurement of fundamental properties becomes challenging. The laminar burning speed ( ) is among those properties, as it is required for the validation of kinetic models and the modeling of turbulent combustion. One potential method to resolve this issue and achieve measurement at very high pressures (i.e., 20-50 atm), is focusing on ignition affected region. The flame kernel in this region is more resistant to perturbations and remains smooth due to the high stretch rates (i.e., small radii). Therefore, the principal aim of this work is to provide detailed time-resolved information for a deep understanding of the ignition process at high pressures. In addition, the measurement methodologies and developed computational models will have a broad and valuable impact on combustion and plasma communities by enabling predictive capabilities for designing and optimizing advanced combustion devices operating under high-pressure conditions.

The result of this work is a novel framework/method to measure in the ignition-affected region using a spherically expanding flame (SEF) under ultra-high pressures. The complication with this region is that the kernel growth rate does not only depend on the chemical reaction but also on other terms such as energy discharge, as well as radiative and conductive energy losses. None of these terms has been adequately assessed, due to the generation of ionized gas (i.e., plasma). This research will fill this broad knowledge gap via combined experimental and modeling studies focused on two specific aims: (1) using a well-defined and well-controlled high-pressure experimental configuration and (2) developing a self-consistent theoretical framework to explain the influence of energy discharge on the plasma formation and initial flame propagation. On the experimental side, the project will utilize high-speed imaging of the plasma kernel propagation in conjunction with electronic ignition power. The plasma properties were calculated using statistical thermodynamics and a presently developed thermodynamic model.

Experiments presented in this work examine methane and air combustion up to 50 atm initial pressure. Flame propagation is observed via high-speed camera for radii up to 20 mm at 45kfps. Flame propagation is modeled for the purpose of laminar burning speed extraction utilizing ignition affected flame down to ~0.5 mm radius. Modeling work is supported by several measurements including plasma temperature, electrical power, and potential drop across plasma sheath formations. The electrical power was measured via the voltage and current across the electrode gap while the sheath formation was extracted via a modified zero length extrapolation. Plasma temperature was measured using optical emission spectroscopy.

The model interpretation of the ignition propagation was found to accurately account for symmetric, steady, normal glow, and arc discharge. Inaccuracies up to ~15% were found for the present ignition propagation because of the transit behavior. This behavior (because of the current waveform) results in a time varying sheath formation and bulk plasma temperature.

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