Ignition Delay Time Measurements of Jet, Rocket, and Diesel Fuel

Multicomponent fuels, such as kerosene and diesel fuel, are the primary source of energy powering the engines used in the transportation sector. The study of these fuels is essential to improving engine efficiency and reduce pollutants. This efficiency improvement can be partially achieved by improving the combustion chemistry, which can potentially lead to numerous economic and environmental benefits. Several parameters affect the combustion chemistry, but one of the most important parameters is the ignition delay time of the fuel and oxidizer. The work presented in this thesis explored the ignition behavior of three fuels heavily utilized in the transportation sector. Ignition delay times were measured for gas-phase jet fuel (Jet-A), rocket propellant (RP-1), and diesel fuel (DF-2), in a heated, high-pressure shock tube. The measurements were performed behind a reflected shock wave for each fuel in air over a temperature range of 785 to 1293 K for two equivalence ratios, ϕ = 0.5 and 1.0, at two different pressures, 10 and 20 atm. Ignition delay time was determined by observing the pressure and OH* chemiluminescence (~307 nm) at the endwall location. Measured ignition delay times for Jet-A were in agreement with the available historical data from the literature. Results showed few differences in ignition delay times between any of the three fuels over the temperature range studied. High-temperature correlations were developed to accurately predict the ignition delay times of the three fuels. The experimental measurements for Jet-A and DF-2 were modeled using several chemical kinetics mechanisms utilizing different surrogate mixtures. To the author’s knowledge, this study presents the first gas-phase ignition delay time measurements for RP-1. In addition, the data presented in this thesis expand the archival data of Jet-A and DF-2 to a broader range of conditions

ADVANCES IN AMMONIA COMBUSTION CHEMISTRY AND NH3 SENSING USING LASER DIAGNOSTICS

LecturesAmmonia (NH3) is a promising alternative carbon-free fuel. For this reason and others, significant research is directed towards studying NH3 especially pertaining to its chemical kinetics. A brief review of the literature on ammonia combustion chemistry is provided in this paper, with emphasis on the studies related to fundamental reaction kinetics at elevated temperatures. Until recently, NH3 was never measured using laser absorption spectroscopy to study its chemical kinetics. This recent NH3 measurement was conducted by the authors’ group using a newly developed laser absorption diagnostic that probes the v2 fundamental band of NH3 in the mid-infrared near 10.4 μm. The present study utilized this recently developed NH3 diagnostic to highlight its capabilities and potential future use for studying ammonia combustion chemistry and also as an ammonia sensor for practical applications. The laser was operated using two methods: a scanned-wavelength method to measure the absorption spectra of NH3-containing mixtures, and a fixed-wavelength method to measure NH3 time histories behind reflected shock waves. The scanned-wavelength method was used to determine the NH3 mole fraction in multi-component gas mixtures; such a method presents future promise when the accurate determination of NH3 in a sampled gas is needed. The fixed-wavelength method, coupled with a shock tube, was used to follow NH3 time histories during the oxidation of NH3/O2 in Ar; such a method shows promise for studying the chemical kinetics of ammonia

AQME: Automated quantum mechanical environments for researchers and educators

AQME, automated quantum mechanical environments, is a free and open-source Python package for the rapid deployment of automated workflows using cheminformatics and quantum chemistry. AQME workflows integrate tasks performed across multiple computational chemistry packages and data formats, preserving all computational protocols, data, and metadata for machine and human users to access and reuse. AQME has a modular structure of independent modules that can be implemented in any sequence, allowing the users to use all or only the desired parts of the program. The code has been developed for researchers with basic familiarity with the Python programming language. The CSEARCH module interfaces to molecular mechanics and semi-empirical QM (SQM) conformer generation tools (e.g., RDKit and Conformer–Rotamer Ensemble Sampling Tool, CREST) starting from various initial structure formats. The CMIN module enables geometry refinement with SQM and neural network potentials, such as ANI. The QPREP module interfaces with multiple QM programs, such as Gaussian, ORCA, and PySCF. The QCORR module processes QM results, storing structural, energetic, and property data while also enabling automated error handling (i.e., convergence errors, wrong number of imaginary frequencies, isomerization, etc.) and job resubmission. The QDESCP module provides easy access to QM ensemble-averaged molecular descriptors and computed properties, such as NMR spectra. Overall, AQME provides automated, transparent, and reproducible workflows to produce, analyze and archive computational chemistry results. SMILES inputs can be used, and many aspects of tedious human manipulation can be avoided. Installation and execution on Windows, macOS, and Linux platforms have been tested, and the code has been developed to support access through Jupyter Notebooks, the command line, and job submission (e.g., Slurm) scripts. Examples of pre-configured workflows are available in various formats, and hands-on video tutorials illustrate their use

Computational Study of the Impacts of Directing Group and Ligand Flexibility in Directed Alkene Functionalization

This computational study investigates the roles of flexible ligands and directing groups in Ni- and Pd-catalyzed alkene functionalization reactions. Many hemilabile and conformationally flexible ligands and directing groups have been employed in these catalytic transformations, where the ligands (e.g., bioxazolines and quinones) may adopt different binding modes and the chelating directing groups may have different ring-flip conformations. However, the effects of flexibility on reactivity and selectivity are still not well understood. Here, we examine the flexibility effects in three catalytic reactions, including the binding modes of quinone-type ligands in Ni-catalyzed 1,2-carbosulfenylation of unactivated alkenes, the coordination modes of bioxazoline-based ligands in Ni-catalyzed asymmetric 1,2-diarylation of unactivated alkenes, and the effectiveness of L-tert-leucine as a transient directing group (TDG) in controlling enantioselectivity in Heck-reductive hydrofunctionalization. We show that the duroquinone (DQ) ligand adopts different binding modes in different elementary steps of the Ni-catalyzed 1,2-carbosulfenylation—it binds as an X-type redox-active durosemiquinone (DSQ) radical anion to promote alkene migratory insertion with a less distorted square planar Ni(II) center, whereas it binds as an L-type ligand to promote oxidative addition at a more electron-rich Ni(I) center. We found that in different elementary steps of the catalytic cycle of the Ni-catalyzed alkene diarylation, the bioxazoline ligand can be bidentate, monodentate, or completely dissociated depending on the steric and electronic properties of the transition state. The enantioselectivity-determining step involves a square planar Ni(II) migratory insertion transition state, stabilized by non-covalent interactions with a dissociated arm of the bioxazoline ligand. Finally, we show how the rigidity of the bidentately bounded chiral amino acid TDGs, induced by their α-substituent, promote binding of the TDG and induce high levels of enantioselectivity in alkene insertion with a variety of migrating groups in the reductive-Heck hydrofunctionalization

Laser Absorption Diagnostic for Chemical Kinetics Studies of Ammonia

Avoiding global warming necessitates using alternative fuels on a large scale to decarbonize the power generation sector. Ammonia (NH₃), the second-most produced chemical globally, is a carbon-free fuel that has the potential to be the primary driver of this sector. However, the combustion chemistry of NH₃ is not well understood, limiting its large-scale application. In particular, the species-specific kinetics interactions during NH₃ combustion have been seldom studied, and new measurements of this kind provide optimization targets for the enhanced understanding of NH₃ combustion chemistry. In this study, a new NH₃ laser absorption diagnostic, intended for chemical kinetics measurements, was developed to access twelve NH₃ transitions in the v₂ fundamental band near 10.4 μm. Spectroscopic characterization of these transitions, located between 957.5 and 963.0 cm⁻¹, was conducted via scanning-wavelength absorption experiments to measure the line strength and broadening coefficients due to collisions of Ar, He, O₂, N₂, and NH₃. Using this new and other diagnostics, laser absorption experiments were performed to study NH₃ chemical kinetics at high temperatures and near-atmospheric pressures in a shock tube. First, experiments were performed to monitor NH₃ time histories during the thermal decomposition of ~ 0.5% NH₃/Ar and ~ 0.42% NH₃/2% H₂/Ar over a temperature range of 2096–3007 K. Using these data, along with literature data, a detailed NH₃ thermal decomposition kinetics mechanism was proposed and validated. Second, experiments were conducted to monitor N₂O time histories during NH₃/O₂/Ar oxidation between 1829 and 2198 K for equivalence ratios of 0.54, 1.03, and 1.84. These equivalence ratios were determined accurately by measuring the NH3 concentration in the mixtures using the new diagnostic. Third, simultaneous measurements of NH₃ and H₂O time histories were obtained during the oxidation of several NH₃/O₂/Ar and NH₃/H₂/O₂/Ar over a temperature range of 1474–2307 K, equivalence ratios varying from 0.56 to 2.07, and NH₃:H₂ ratios of 100:0, 80:20, and 50:50. These large time-history datasets were used to investigate the literature NH₃ kinetics mechanisms and illustrate several improvements. The reported time-history data offer stringent constraints for the accurate assessment and validation of future NH₃ kinetics mechanisms

Teachers of Students with Learning Disabilities Viewpoints of the Predictive Validity of Using Evidence-Based Practices

Abstract The purpose of the study was to examine predictive ability in the importance of using teachers of students with learning disabilities for evidence-based practices, from their perspectives. The differences among participants were measured based on gender, teaching experience, and the number of training programs. The study used a descriptive survey design. The survey was distributed to all elementary teachers of students with learning disabilities in the Qassim region. The participants consisted of 85 teachers. The study found that teachers use evidence-based practices to a great extent when teaching students with learning disabilities. The most used practices were ‘read naturally, repeated reading, explicit instruction, and spelling mastery’. The level of teachers’ perspectives regarding the importance of using these practices was high, and the most important practices were repeated reading, spelling mastery, explicit instruction, and direct instruction. There were significant statistical differences between the average scores for using evidence-based practices based on gender, in favor of female teachers. There were no statistically significant differences, between the average scores for using of evidence-based practices based on years of teaching experience or number of training programs. The study revealed the teachers’ perspectives regarding the importance of using evidence-based practices predicted their use of these practices. In addition, the study recommended educating teachers about the importance of using evidence-based practices when teaching students with learning disabilities and training them on the right way to use these practices. Keywords: Predictive ability, evidence-based practices, teachers of students with learning disabilities

Hemilabile Quinone Ligands Enable Nickel-Catalyzed C−S(Alkyl) Bond Formation in the Carbosulfenylation of Unactivated Alkenes

A three-component coupling approach towards structurally complex dialkylsulfides is described via the nickel-catalyzed 1,2-carbosulfenylation of unactivated alkenes with organoboron nucleophiles and alkylsulfenamide (N–S) electrophiles. Efficient catalytic turnover is facilitated using a tailored N–S electrophile containing an N-methyl methanesulfonamide leaving group, allowing catalyst loadings as low as 1 mol%. Regioselectivity is controlled by a collection of monodentate, weakly coordinating native directing groups, including sulfonamides, amides, sulfinamides, phosphoramides, and carbamates. Key to the development of this transformation is the identification of quinones as a family of hemilabile and redox-active ligands that tune the steric and electron properties of the metal throughout the catalytic cycle. DFT results show that the duroquinone (DQ) ligand adopts different coordination modes in different elementary steps of the Ni-catalyzed 1,2-carbosulfenylation—binding as an X-type redox-active durosemiquinone radical anion to promote alkene migratory insertion with a less distorted square planar Ni(II) center, while binding as an L-type ligand to promote N–S oxidative addition at a more electron-rich Ni(I) center