Ammonia is a promising green fuel with several favorable attributes that could make it a replacement for current nonrenewable aviation fuels. The feasibility of using an NH3-H2 blend as the fuel in terms of the NOx emitted has been explored in this work, consisting of residence times of 10 ms and 5 ms which represent the residence times in modern aviation gas turbine combustors. Chemical reactor network (CRN) models have been simulated using the Ansys Chemkin-Pro software, implementing air-staging techniques like RQL (Rich-Quench-Lean) to efficiently combust the fuel and bring down the NOx while also minimizing ammonia slip. Various CRN configurations have been investigated for operating conditions reflecting take-off, while varying crucial parameters such as equivalence ratio, NH3-H2 fuel fraction, inlet temperature, and pressure. This exploration aims to understand the trends in NOx emissions and ammonia slip while ensuring that the reactor exit temperature remains within the cycle requirements to prevent any material damage to the components post combustion. The effect of varying the residence times in the individual CRN components on the NOx and ammonia slip was also investigated and discussed. The minimal NOx possible while varying the parameters was about 20 ppm for the 10 ms overall residence time simulations, and about 30 ppm for the 5 ms overall residence time simulations. The trends obtained from the parametric variations along with the understanding of the different CRN models explored can help in optimizing the NOx minimization further and assist in obtaining the optimal conditions for the NH3-H2 blend used, not just for take-off, but additionally for other flight operating conditions as well. Understanding the parametric trends for minimizing NOx emissions and controlling the NH3 slip from this study can help establish an understanding of using ammonia as aviation combustor fuel, serving as a basis for further computational and experimental research.

Soot is a by-product formed from the incomplete combustion of hydrocarbon-based fuels. As a result, the detonation of common highly explosive (HE) compounds produces some level of soot particulate. These particulates are of interest due to their effect on the formation of the resultant fireball via changes in fluid dynamics and internal radiative heating. In the case of a fireball initiated by a nuclear event, soot particles can act as nucleation sites for radionuclides through absorption and adsorption. Soot particles also contribute to the fallout in the form of a propagating ash cloud or by acting as sites for water or ice condensation, producing additional cloud cover and precipitation that may spread radioactive material more readily. These aspects make soot an important target to track in the case of long-term fallout analysis. However, predictive uncertainties related to particle size distributions, inception, growth, and chemical composition can make fallout modeling difficult, especially at fireball conditions. In this work, high-temperature experiments were conducted using shock tube and laser absorption to measure soot time-histories, volume fraction, and induction times for fireball intermediates. A comparative baseline is established between a Lawrence Livermore National Laboratory mechanism developed for n-C-12 and i-C-12 fuels and a University of Central Florida mechanism initially created for studying soot production from biofuels. The current research provides insights into the deficiencies of nuclear fallout models.

This study demonstrates the implementation of a backlight particle image velocimetry technique for visualizing and quantifying the flow field of high-pressure liquid CO2 in a channel. High-speed imaging and advanced cross-correlation processing within a micro-PIV 2D2C (two-directional two-component) framework were employed to extract velocity vectors from the flow field. Silver-coated hollow glass microspheres with diameters ranging from 5 to 30 microns were used as tracer particles to enable flow visualization. The experimental setup comprises a CO2 flow manifold, a K-type thermocouple for temperature measurement, digital pressure transducers, and a backlight illumination arrangement for PIV imaging. The implementation of the backlight PIV technique provides high-resolution velocity measurements while minimizing laser-induced heating effects, making it a suitable approach for studying CO2 flow dynamics under near-critical and supercritical thermodynamic conditions. This work serves as a crucial step in advancing the understanding of CO2 flow characteristics and heat transfer mechanisms.

Ammonia (NH3) has been shown to serve as an effective hydrogen (H2) carrier in both power and transportation applications, as its similar properties to existing fuels like propane (C3H8) allow for relatively easier storage and transportation operations (Veziro and Barbir, 1992, "Hydrogen: The Wonder Fuel," Int. J. Hydrogen Energy, 17(6), pp. 391-404). Hence, applied turbine-combustion research on NH3 and H2 fuels has been conducted to identify combustion performance parameters to facilitate the development of high-pressure, sustainable turbomachinery and identify the conditions for efficient burning and nitric oxide (NOx) reduction (Chai et al., 2021, "A Review on Ammonia, Ammonia-Hydrogen and Ammonia-Methane Fuels," Renew. Sustain. Energy Rev., 147, p. 111254). One key combustion parameter is the laminar burning speed (LBS), which provides gas turbine design engineers with knowledge of combustion physiochemistry, flashback propensity, and efficiency. While abundant literature exists on the combustion of NH3 and H2 fuels at lower pressures, there is not sufficient evidence in elevated-pressure environments to provide a comprehensive understanding of NH3 and H2 combustion phenomena and NH3 conversion for practical engine conditions. Therefore, to advance the state of knowledge, NH3 and H2 mixtures were ignited in this work at an initial temperature and pressure of 323 K and 10 atm to understand their performance properties and LBS, which was calculated using a multizone, constant volume combustion model. The effect of H2 dilution on NH3 was studied by comparing the LBS across a range of fuel mixtures and equivalence ratios. Peak LBS values for NH3 and NH3-H2 were located at stoichiometry. Pressure-dependent LBS suppression effects were observed to be stronger in H2-diluted NH3 mixtures relative to pure NH3. Sensitivity analyses revealed the strongest LBS-suppressing reactions were mainly the radical termination reactions [O + H+M <-> OH+M] and [H+O2+M <-> HO2+M]. Current work provides the crucial knowledge needed to advance the chemical kinetic models for ammonia-hydrogen mixtures at high pressure.

Farnesane is an isoprenoid that has been identified as a sustainable jet fuel candidate. In this work, fuel-rich oxidation of pure ethylene and farnesane blended with ethylene was conducted behind reflected shock waves at 3-4.5 atm and 1700-2100 K. Simultaneous measurements for ethylene decay, carbon monoxide formation, and soot volume fraction were reported. The addition of farnesane to ethylene resulted in a slower decomposition of ethylene and a slower formation rate of CO and soot. However, more soot was observed at higher temperatures for the farnesane blend, indicating a shift in peak temperature for soot formation. A model was developed to predict ethylene and CO concentration time histories based on the mechanism of Yu et al. (Energy & Fuels, Vol. 34, No. 2, 2020, pp. 2366-2375). For predicting the growth and destruction of polycyclic aromatic hydrocarbons, reactions were adopted from Sinha et al. (Physical Chemistry Chemical Physics, Vol. 19, No. 29, 2017, pp. 19,262-19,278). The new model captured ethylene and CO concentration time histories for rich oxidation of pure ethylene and farnesane-blended ethylene mixtures. The model was also able to predict soot volume fraction qualitatively. The prediction for soot volume fractions captured the general trend in soot growth and inhibition with temperature. However, further studies are required to predict soot quantitatively and improve our understanding of soot nucleation, growth, and condensation reactions.

This experimental study investigated the thermal decomposition kinetics of 4,6-diamino-5,7-dinitro-benzo-furazan (referred to as F1 hereafter)-an important decomposition product of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB-a prototypical insensitive high explosive). Simultaneous differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and mass spectrometry (MS) measurements were employed to determine the decomposition kinetics of F1 and to track the evolution of product gases. The DSC profiles were measured at 10 different heating rates between 0.025 degrees C/min and 10 degrees C/min. The measured exotherms were influenced by F1 melting at heating rates above 0.25 degrees C/min, and corresponding changes in decomposition enthalpy and TGA mass-loss-rate profiles indicated a transition from solid-to-gas decomposition to an increasing contribution from liquid-to-gas decomposition. Analysis of low-heating-rate DSC data between 0.025 degrees C/min and 0.17 degrees C/min with the extended Prout-Tompkins model yielded an activation energy of 305 kJ/mol for solid-to-gas F1 decomposition, higher than previous values inferred from TATB decomposition models involving F1. This study provides the first direct experimental determination of the energy barrier for F1 decomposition. MS measurements showed that the major gaseous products matched species previously reported for TATB decomposition (e.g., CO2, HCN, C2N2, etc.), with water identified as the dominant product. These results provide important experimental constraints for improving chemical kinetics models of TATB decomposition and for predicting the reactivity, stability, and safety of TATB-based high explosives under long-term aging conditions and abnormal thermal environments.

This paper aims to investigate the design benefits of including a dump tank as a relief system in a detonation tube facility. This study aims to investigate initial recorded attempts at quenching effects occurring inside the dump tank. Three unique initial pressure experiments are covered at 0.6 bar, 1 bar, and 1.6 bar for stoichiometric hydrogen-oxygen detonations. Additionally, comparisons were made between lower-pressure and higherpressure tests to identify trends and validate the performance of the design.

Aluminum (Al) is a crucial additive in propellant and explosive applications, enhancing combustion when introduced in powder form to liquid or solid fuels. Understanding its combustion characteristics is pivotal for refining reactive computational fluid dynamics (CFD) models. This report discusses the challenges faced in researching aluminum powders at the University of Central Florida and presents a design for a component to introduce powders into the detonation tube. The new detonation tube facility allows the production detonation conditions near Chapman-Jouguet (CJ) conditions. The proposed component employs the knife edge method for powder introduction. It is designed to hold at most 100 mg of aluminum powder and facilitate easy servicing. This component aims to enhance the detonation tube facility's capabilities, enabling diverse experiments with improved repeatability and data collection for future research.

A successful transition to global clean energy hinges on meeting the world's growing demand for power, while at the same time reducing greenhouse gas emissions. Achieving this will require significant growth in electricity generation from clean and carbon-free energy sources. Several energy providers (Acar and Dincer, 2019, "Review and Evaluation of Hydrogen Production Options for Better Environment," J. Cleaner Prod., 218, pp. 835-849 and Nagashima, M., 2024, "Japan's Hydrogen Strategy and Its Economic and Geopolitical Implications," Afficher la page d'accueil du site) have already begun the transition from traditional carbon-based fuels to cleaner alternatives, such as hydrogen (H2) and hydrogen- enriched natural gas (HENG). However, there are still many technical questions/challenges that must be addressed when applying these fuels in gas turbines. The application of H-2 or H2/natural gas (NG) blends to advanced-class gas turbines, which have higher operating pressures and temperatures, has raised concerns about the potential for leakages or fuel sequencing operations where flammable mixtures of fuel and air could auto-ignite. Public information on the auto-ignition of H-2 in the air at atmospheric pressure shows an auto-ignition temperature (AIT) between 520 and 585 degrees C (U.S. Department of Energy, 2024, "U.S. Department of Energy Hydrogen Program Plan," U.S. Department of Energy, Washington, DC; Georgia Power, 2022, "Georgia Power, Mitsubishi Power, EPRI Complete World's Largest Hydrogen Fuel Blending at Plant McDonough-Atkinson," Georgia Power, Atlanta, GA; and gepower-v2, 2024, "New York Power Authority: GE Vernova," gepower-v2, Cambridge, MA). Such data show AIT of H2 is similar to 100 degrees C lower than that of methane (CH4) which has a minimum AIT of around 600 degrees C (Huth, M., and Heilos, A., 2013, "Fuel Flexibility in Gas Turbine Systems: Impact on Burner Design and Performance," Modern Gas Turbine Systems, Sawston, UK, pp. 635-684). Studies also show that as pressure increases, methane's AIT decreases significantly to around 390 degrees C (Loving, C., Mastantuono, G., Terracciano, A. C., Vasu, S. S., Pigon, T., Hernandez, A., and Cloyd, S., 2023, "Auto-Ignition Test Results of Hydrogen and Natural Gas Fuels at Atmospheric and Elevated Pressures for Gas Turbine Safety," ASME Paper No. GT2023-102674). However, there was insufficient information in the published literature to characterize the influence of pressure on the AIT of H2 and HENG fuels. At atmospheric conditions, H2 has a wider flammability range of equivalence ratios that ignition can occur compared to methane. H2's flammability ranges from 4% to 75% molar (volume) fuel concentration, which is an equivalence ratio range of 0.137-2.57. Methane's flammability limit ranges from 5% to 15% molar (volume) or an equivalence ratio between 0.53 and 1.58 (National Aeronautics and Space Administration, 1997, Safety Standard for Hydrogen and Hydrogen Systems: Guidelines for Hydrogen System Design, Materials Selection, Operations, Storage, and Transportation, National Aeronautics and Space Administration, Office of Safety and Mission Assurance; National Technical Information Service, Distributor, Washington, DC, Springfield, VA). Previous research has also been done to determine the effect of longer hydrocarbons present in natural gas mixtures. The presence of ethane (C2H6) and propane (C3H8) has been shown to reduce the AIT of natural gas, especially at elevated pressures (The Association, 1994, NFPA 49: Hazardous Chemicals Data, The Association, Quincy, MA). These longer hydrocarbons also tend to promote ignition in richer conditions, whereas methane tends to ignite easier in slightly lean conditions (National Aeronautics and Space Administration, 1997, Safety Standard for Hydrogen and Hydrogen Systems: Guidelines for Hydrogen System Design, Materials Selection, Operations, Storage, and Transportation, National Aeronautics and Space Administration, Office of Safety and Mission Assurance; National Technical Information Service, Distributor, Washington, DC, Springfield, VA). Numerous variables besides the pressure, fuel, and equivalence ratio can affect the AIT including chamber volume size, chamber materials, presence of diluents, and other factors (Standards Australia International, 2000, Electrical Apparatus for Explosive Gas Atmospheres. Part 20, Data for Flammable Gases and Vapours, Relating to the Use of Electrical Apparatus, Standards Australia International; Standards New Zealand, Strathfield, NSW, Wellington, NZ). This study describes the test methodology used to evaluate conditions where auto-ignition occurs for various fuel-air mixtures operating at different pressures (1-30 atm) and temperatures. Testing was completed with 100% H-2 and multiple H-2/NG blends at various equivalence ratios (ER) between 0.2 and 2.5. Testing was similarly performed for 100% NG to validate the test and data collection methods cited in prior published literature. Results indicate that, at atmospheric pressures, an increase in H-2 concentration results in a reduced AIT. However, at 30 atm, the increased presence of H-2 increased the AIT. At elevated pressures above 10 atm, increased equivalence ratio resulted in reduced AIT for all mixtures with NG having the greatest sensitivity to equivalence ratio. Variations of auto-ignition delay times (AIDT) were also observed during the testing and are compared to modeling predictions, providing insight into auto-ignition characteristics.