Keywords

Ammonia Cracking, Kinetics, Heat Transfer, Radiation, Hydrogen, Aviation

Abstract

Ammonia is a promising carbon-free fuel for commercial aviation and represents a viable pathway toward net-zero emissions. However, direct ammonia combustion is inefficient, creating the need for onboard cracking to generate hydrogen for improved combustion characteristics. One pathway for onboard cracking is to have the hardware live around the combustor liner where heat generated from the combustion process can be used to sustain the reaction. This study aims to develop a design tool for the ammonia cracking reactor hardware. A simplified, single-step surface reaction mechanism was implemented using ANSYS FLUENT and CHEMKIN PRO R1, demonstrating strong agreement with experimental data from the literature. Compared to a volumetric reaction model, the surface reaction significantly reduced computational cost by eliminating the need to resolve the small length scale of the catalyst layer. This study also quantifies the radiative and convective heat loads by the combustion flame through a one-dimensional thermal energy balance model and extended to CFD using the Discrete Ordinate (DO) radiation model with weighted sum of gray gas (WSGG) model. Results indicate that the radiative and convective liner heat-load predictions from the one-dimensional model and the CFD simulation agree within ~14%, providing a reasonable baseline for validating the CFD approach in the absence of experimental data. This consistency supports moving to higher-fidelity simulations, including combustion modeling and representative swirler geometries, which are expected to influence the convective heat load. Under the predicted heat-flux levels by the one-dimensional model, roughly 3% of the ammonia can be cracked at cruise, showing that endothermic decomposition is fundamentally governed by the heat flux entering the liner from the flame side.

Completion Date

2025

Semester

Fall

Committee Chair

Jayanta Kapat

Degree

Master of Science in Mechanical Engineering (M.S.M.E.)

College

College of Engineering and Computer Science

Department

Thermofluids

Format

PDF

Identifier

DP0029752

Document Type

Thesis

Campus Location

Orlando (Main) Campus

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