Doctoral Dissertations

Date of Award

5-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Mechanical Engineering

Major Professor

Peng Zhao

Committee Members

Trevor Moeller, Zhili Zhang, Montgomery Smith

Abstract

Increase in global temperatures has resulted in a rise in concerns and efforts towards lowering carbon emissions from fossil fuels due to their role in trapping heat and their negative impact on the environment. Alternative fuels are being considered due to their low/zero carbon emission nature. Most notable is ammonia as it has a mature production, transportation, and storage infrastructure due to its use as a fertilizer. However, NH3 suffers from poor combustion characteristics such as slow flame speed and long ignition delay times due to its low reactivity. As such, combustion enhancement through the addition of the reactive fuels such as hydrogen (H2) and dimethyl ether (DME) are considered. Firstly, this dissertation computationally explores the role of hydrogen addition to ammonia in improving the combustion phasing and the resulting emissions formed in a homogeneous charge compression ignition engine 0D model. A parametric investigation is conducted for initial intake thermodynamic conditions and mixture composition. Secondly, this dissertation explores the computational investigation of direct injection of ammonia spray in a constant volume chamber at engine relevant conditions using a single nozzle injector. Due to the low reactivity of ammonia, H2 and DME addition are considered to facilitate ammonia sprays through H2 added to the ambient air or as a dissolved gas in liquid ammonia, and blending liquid NH3 and DME. Finally, the thermodynamic conditions of the engine will be low temperature and high-pressure during injection of ammonia thus resulting in the condensation of the fuel. As such, this work will explore the head-on quenching and emissions of ammonia laminar flames with and without a wall film under different mixtures and engine relevant conditions. This dissertation adapts a systematic approach involving numerical simulations, data analysis, chemical kinetics examination, and practical applications. The results demonstrate the role of H2 and DME in facilitating ignition where small concentrations of H2 are sufficient to facilitate ignition. Furthermore, the role of DME low temperature is explored in the oxidation of ammonia. Finally, NOX and N2O emissions are shown in high concentrations through the fuel pathways and from thermal NOX.

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