Session: 03-01 Ammonia as Fuel and Hydrogen Carrier – Combustion, Storage, and Safety

Submission Number: 179120

Ignition Delay Time Measurements of Natural Gas/Ammonia Mixtures at Gas Turbine Operating Conditions 

With global energy demands and fossil fuel usage on the rise each year, increasing greenhouse gas emissions in the atmosphere has become a growing concern. Research into alternative fuels has gained a significant amount of attention due to the global effort to reduce carbon emissions while still providing a sustainable energy source for power generation. In recent years, hydrogen (H₂) has emerged as a promising clean energy fuel source, but it has several drawbacks due to its chemical characteristics. Some of the major limitations of hydrogen as a potential fuel are concerns regarding its transportation, storage, and safety. Due to its low boiling point and high flammability, hydrogen requires high-pressure or cryogenic storage techniques, which both raise concerns regarding leaks, container stability, and energy requirements. Many of the challenges related to the storage and transportation of hydrogen due to its low density can be overcome by the use of hydrogen energy carriers. Ammonia (NH₃) is an excellent hydrogen carrier with high energy efficiency, and its combustion does not produce carbon dioxide. Ammonia also does not suffer the same storage limitations as hydrogen, being able to be stored at room temperature and relatively low pressures. However, ammonia also has its own challenges, such as toxicity and low reactivity stemming from high ignition energy requirements and low flame speed. The biggest drawback of using ammonia as a fuel is its formation of nitrogen oxides (NOx) during combustion. During the oxidation process of ammonia, nitrogen splits and combines with oxygen from the air to form various NOx, including nitric oxide (NO), nitrous oxide (N₂O), and nitrogen dioxide (NO₂). These compounds have been linked to significant adverse environmental and health effects, thus the control and mitigation of their emissions in ammonia combustion systems is essential.

               To overcome the high ignition energy required, low flame speed, low flammability, and to offset NOx production during the combustion of ammonia, it can be blended with natural gas (NG) for use in power generation gas turbine operation. This provides a stable and efficient flame with lowered carbon and NOx emissions without completely overhauling the existing natural gas turbine infrastructure. To predict these enhanced flame properties, Fundamental chemical kinetics must be understood. Accurate chemical kinetic mechanisms are essential in understanding, predicting, and optimizing combustion processes as they provide detailed information about the chemical reactions that occur during combustion, including reaction rates, intermediate species, and reaction pathways. While recent research exists to study and improve the kinetic validation of NG/NH₃ mixtures, much of it only explores combustion at relatively low pressures below 5 bar. This study aims to validate and refine current nitrogen-based chemical kinetic mechanisms using ignition delay times (IDTs), as well as to address a gap in ammonia combustion research at very high pressures.

               Ignition delay times are a fundamental time scale in combustion and reflect the time it takes for a chemical mixture to ignite and react after being exposed to elevated pressure and temperature conditions. Accurate chemical kinetic mechanisms can predict IDTs that closely match experimental measurements. By utilizing an idealized device called a shock tube, IDTs can be replicated at exact gas turbine conditions (5-25 bar, 1400-2100 K) with the pressure and temperature behind a generated high-speed shock wave. The experiments were performed at the University of Central Florida’s High-Pressure Extended Range Shock Tube for Advanced Research (HiPER-STAR) and MSB shock tube facilities, which are designed to collect IDT measurements at high pressures. IDT data was collected utilizing the maximum slope in the emission of hydroxl radicals (OH*) at ~307 nm during NG/NH₃ mixture combustion at 5, 10 and 25 bar. A variety of blended NG/NH₃ mixtures were explored, varying the NH₃ component from 0-100% at stoichiometric (ϕ = 1.0) and fuel-rich (ϕ = 1.2, 1.4) conditions which are relevant to rich quench lean type combustors.

Presenting Author: Zachary Morris University of Central Florida

Presenting Author Biography: Zachary Morris is a graduate student at the University of Central Florida, pursuing a master’s in aerospace engineering. He is also a graduate research assistant at Vasu Labs within the Center for Advanced Turbomachinery and Energy Research (CATER) at UCF. His research includes combustion and laser diagnostics in high-pressure shock tube studies, focusing on the chemical kinetics of alternative low and zero-carbon fuel mixtures for gas turbines and power generation. Additionally, Morris has a combined three years of industry experience from several internship roles prior to joining the lab, including manufacturing, quality, and systems integration & test engineering.

Authors:

Zachary Morris University of Central Florida
Bright Katey University of Central Florida
Louis Vest University of Central Florida
Diego Ruiz Pena University of Central Florida
Lucas Pitts University of Central Florida
Jonathan Mcgaunn University of Central Florida
Esteban Diaz Rodriguez University of Central Florida
Farhan Arafin University of Central Florida
Michael Pierro University of Central Florida
Justin Urso University of Central Florida
Ramees Rahman University of Central Florida
Subith Vasu University of Central Florida
Gregory Vogel Power Systems Manufacturing, LLC