Kinetic Mechanism Research Articles

Aqueous co-solvent synthesis of Zeolitic Imidazolate Frameworks: The impact of co-solvents in the crystal growth kinetics

Zeolitic Imidazolate Frameworks (ZIFs) have been widely studied in recent decades in a variety of applications. However, a fundamental understanding of crystal growth kinetics as well as their formation mechanisms has been very limited. Underpinning such mechanisms might be of key importance for the predictable synthesis of ZIFs to rationally tune the structural and morphological properties for respective applications. Herein, the crystal growth kinetics and structural evolution of ZIF-8 crystals in various aqueous co-solvent reaction environments were studied with respect to synthesis time. By tracking the nucleation, crystal growth, stabilization and ripening, three potential kinetic formation mechanisms were proposed. More specifically, with methanol, isopropanol and acetone, a fast nucleation rate and crystal growth occurred within 60 minutes (min) at room temperature. However, ethanol and n-propanol showed prolonged nucleation which resulted in the slow formation of ZIF-L/ZIF-8 mixed phases at the early stage. Phase transformation to pure ZIF-8 was observed in longer syntheses. Nitrogen-containing solvent, N, N–dimethyl formaldehyde (DMF), was found to induce both nucleation and growth, resulting in large crystals in less than 60 min of fabrication. In each case, the crystal formation follows Avrami's classical model. Hence, by understanding the effects of co-solvents in ZIF nucleation, crystallization and phase selection, one can rationally design the crystals with predictable crystallinity, size, morphology, purity and surface properties for targeted applications such as adsorption of small molecules from aqueous mixtures.

A comprehensive kinetic modeling study on NH3/H2, NH3/CO and NH3/CH4 blended fuels

Ammonia (NH3), as an ideal zero-carbon fuel, plays a positive role in mitigating global warming. By cofiring NH3 with highly reactive small molecule fuels such as hydrogen (H2), carbon monoxide (CO) and methane (CH4), the reactivity of NH3 combustion can be significantly enhanced. In this work, a detailed kinetic mechanism for NH3/CH4/H2/CO containing 146 species and 1099 reactions was developed and extensively validated with selected experimental data from the literature on laminar burning velocity (LBV), ignition delay time (IDT), and species concentrations measured in burner-stabilized flames (BSF), plug flow reactors (PFR) and jet-stirred reactors (JSR), covering temperatures of 273–2000 K, pressures of 0.053–40 atm and equivalence ratios of 0.1–2. In addition, the detailed mechanism was simplified to include 53 species and 353 reactions using three simplification methods. Kinetic modeling analysis showed that the chemical and transport effects of H2, CO and CH4 are the main factors enhancing NH3 combustion, which rising with the increasing initial temperature and decreasing ammonia blending ratio. Among the four reactants, H2 is consumed first, followed by CH4 and NH3, with CO reacting last. By modifying the Metghalchi-Kech power law equation, it was found that a clear linear relationship exists between LBV and the sum of the maximum mole fractions of O, H, OH, and NH2 radicals.

High-fidelity numerical simulation of longitudinal thermoacoustic instability in a high-pressure subscale rocket combustor

A detailed analysis of thermoacoustic combustion instability in a subscale rocket combustor at high pressure is reported in this paper using the high-fidelity large-eddy simulation (LES). Self-sustained longitudinal combustion instability is observed in the experiments for this combustor configuration. The computational setup follows the past experimental study of a rig called the Continuously Variable Resonance Combustor (CVRC). In this combustor, both stable combustion and unstable combustion dynamics have been observed by varying the oxidizer injector length. A combustor configuration with an oxidizer injector length of 12 cm is chosen for this study based on the experimental evidence of longitudinal combustion instability. An autonomous meshing using the modified cut-cell Cartesian grid generation approach, coupled with on-the-fly Adaptive Mesh Refinement (AMR) is employed in this study. Chemical reactions during turbulent combustion in this configuration are modeled by solving the species transport equations with a detailed chemistry solver using a kinetic mechanism with 21 species and 84 steps. Similar to the findings of the experiments, we observe a self-sustained combustion instability in the present study, which is characterized by a limit cycle behavior of the acoustic fluctuations. The spectral analysis of these acoustic fluctuations shows good agreement with experimental data for the frequency of the three dominant modes. We further analyze the features of time-averaged and instantaneous reacting flow to study the effects of combustion instability on the flame holding dynamics, vortex shedding, mixing, and combustion regime due to flame movement along the longitudinal direction of the combustor during a limit cycle. These phenomena are effectively captured through the integration of AMR with complex chemistry in the present study. A particular focus of the study is on understanding the role of minor species (OH, HO2, and CH2O) in the physical and state-space in sustaining the flame during the combustion instability. Additionally, the physical mechanisms responsible for the production and dissipation of enstrophy are examined to demonstrate that their contribution can create significant fluctuations in the reacting flow field, which can assist in sustaining the combustion instability.

Thermal decomposition kinetics and storage life prediction of nitramine propellants with different energetic plasticizers based on model-fitting method

The research on the thermal decomposition of propellant is critical to determining its safe storage life. The thermogravimetry (TG) testing of nitramine propellants plasticized by nitroglycerin (NG), glycidyl azide polymer (GAP), 2,2-dinitropropanol hexanoate (DNPH), and N-butyl-2-nitratoethylnitramine (BuNENA) was performed under non-isothermal circumstances. The thermal decomposition mechanism of propellant was then analyzed using the model-fitting method, and the storage life was predicted based on the mechanism. The results show that when heated to the same mass loss, the temperature of GAP-NC-RDX, BuNENA-NC-RDX, and DNPH-NC-RDX is higher than that of NG-NC-RDX. GAP-NC-RDX, BuNENA-NC-RDX, and DNPH-NC-RDX propellants have superior thermal stability to that of NG-NC-RDX. The kinetic mechanism functions and equations of the propellants were calculated, and multi-step reaction models of the thermal decomposition were built. The major thermal decomposition mechanism of nitramine propellants was discovered to be composite autocatalytic decomposition (Kamal-Sourour equation), which means that the reaction of reactants and the reaction catalyzed by products occur in tandem. The decomposition depth of propellants increases as the temperature rises during the same storage time. The storage lifetimes of GAP-NC-RDX, BuNENA-NC-RDX, DNPH-NC-RDX, and NG-NC-RDX propellants at 288 K are 28.71 years, 24.49 years, 18.34 years, and 16.33 years, respectively. The inclusion of GAP, DNPH, and BuNENA in the formulation improves the storage life of propellant more than NG. This study offers an attractive strategy for analyzing the decomposition mechanism of propellant with a multi-step decomposition reaction and forecasting its storage life.

Elucidating the Selective Mechanism of Drugs Targeting Cyclin-Dependent Kinases with Integrated MetaD-US Simulation.

Cyclin-dependent kinases (CDKs), including CDK12 and CDK13, play crucial roles in regulating the cell cycle and RNA polymerase II activity, making them vital targets for cancer therapies. SR4835 is a selective inhibitor of CDK12/13, showing significant potential for treating triple-negative breast cancer. To elucidate the selective mechanism of SR4835 among three CDKs (CDK13/12/9), we developed an innovative enhanced sampling method, integrated well-tempered metadynamics-umbrella sampling (IMUS). IMUS synergistically combines the comprehensive pathway exploration capability of well-tempered metadynamics (WT-MetaD) with the precise free energy calculation capability of umbrella sampling, enabling the efficient and accurate characterization of drug-target interactions. The accurate calculation of binding free energy and the detailed analysis of the kinetic mechanism of the drug-target interaction using IMUS successfully elucidate the drug selectivity mechanism targeting the three CDKs, showing that the selectivity is primarily arising from differences in the stability of H-bonds within the Hinge region of the kinases and the interaction patterns during the protein-ligand recognition process. These findings also underscore the utility of IMUS in efficiently and accurately capturing drug-target interaction processes with clear mechanisms.

Thermochemistry of Solid-State Formation, Structure, Optical, and Luminescent Properties of Complex Oxides Eu2MeO6 (Me-Mo, W), Eu2W2O9: A Combined Experimental and DFT Study.

Complex oxides Eu2MeO6 (Me-Mo, W), Eu2W2O9 were obtained by a solid-phase reaction between binary oxides. The thermodynamic and kinetic mechanisms of the reaction processes were established using a variety of physical-chemical methods. All compounds obtained in this work crystallize in the low-symmetry monoclinic system, forming complex framework structures, which determine a set of very valuable physical-chemical properties. Comparison of experimental Kubelka-Munk functions and DFT- calculated absorption spectra shows adequate agreement and reveals the origin of the fundamental absorption. In addition, the deficiency in DFT calculations in the part of mutual contribution of CTBs of Mo-O and W-O, from one side, and Eu-O contributions, from the other side, is reported. Calculations of absorption spectra are shown to be superior to band structure analysis in the determination of optical band gaps. Additionally, luminescent properties of Eu2MeO6 and Eu2W2O9 compounds were investigated. These studies provide a better understanding of the electronic and optical properties of the compounds Eu2MeO6 and Eu2W2O9, along with their potential applications in various areas.

Development of Detailed and Reduced Chemical Kinetic Models for Ammonia Gas Turbines

Abstract The power generation sector has been recently moving towards decarbonization and there is an increased interest in replacing conventional fossil fuels with fuels that produce reduced/zero carbon emissions. One such fuel is ammonia (NH3). However, ammonia is hard to ignite, has a low flame speed, and produces a significantly large amount of nitrogen oxide (NOx) emissions. Hence, using 100% ammonia as fuel in gas turbines requires significant modifications and the development of novel combustors. Blending hydrogen with ammonia, however, helps in having better control over the combustion properties. Before utilizing hydrogen-blended ammonia in an actual gas turbine combustor, thorough simulation studies are required to evaluate its performance, possible hazards, and emissions. The literature lacks well-validated chemical kinetic models for the combustion of hydrogen-blended ammonia for undiluted mixtures at gas turbine-relevant conditions (~20 bar). Hence, in this work, we develop a detailed chemical kinetic model for hydrogen blended ammonia combustion and validate it with a wide range of experimental data for both dilute and undiluted mixtures relevant to gas turbine operating conditions. The detailed chemical kinetic mechanism was reduced to a smaller version (32 species mechanism) without significant loss in accuracy using the direct relation graph with error propagation (DRGEP) and full species sensitivity analysis. The resultant mechanism can predict a wide range of experimental results with the least cumulative error and will be a valuable tool in CFD simulations that will enable the development of gas turbines for zero-carbon power generation.

Stage development characteristics of oxygen-lean combustion of coal in fire zone: Leap-migration mechanism, kinetic transition mechanism, and critical oxygen concentration

Effectively preventing the re-ignition of fire zones and safely unsealing enclosed fire zones are challenging. To address these issues, a thermogravimetric analysis technique was used to explore the leap-migration mechanism of the characteristic parameters (burnout index (H), comprehensive combustion performance parameters (Cb, S, and HF), and maximum combustion mass loss rate (dWmax))/temperatures (maximum pyrolysis mass loss rate point temperature (TVmax), pyrolysis endpoint temperature (Td), thermal polycondensation endpoint temperature (Tp), maximum combustion mass loss rate point temperature (TWmax), burnout temperature (Th), and combustion half-peak width (ΔT1/2)) of low-rank coal oxygen-lean combustion under different time-scale effects (TSEs). The sensitivity of characteristic parameters/temperatures to changes in oxygen concentration under coal rank transition was analyzed. Simultaneously, the kinetic real-time transformation mechanism during the oxygen-lean combustion stage progression was investigated. The results revealed that because of the competition between oxidation and pyrolysis, the leap-migration interval of characteristic parameters/temperatures for oxygen-lean combustion of low-rank coals is in the range of 5 %–3% oxygen concentration. This feature was less affected by the coal rank but is not affected by the TSE. In the low oxygen-lean range (5 %-1%), a change of oxygen concentration was more sensitive to the coal rank, and the high sensitivity of the oxygen concentration change reduced the influence of the coal rank on coal combustion performance. In addition, the apparent activation energy (Eα) curves during the early stage of combustion were relatively concentrated with the change of oxygen concentration, but relatively dispersed during the late stage of combustion. At 3 % oxygen concentration, the Eα values of different coals began to continuously decrease with increasing conversion rate, approaching the spontaneous reaction activation energy value of 40 kJ/mol. At oxygen concentration of 1 % reflected the complete limitation of the oxidation consumption reaction. Therefore, the critical oxygen concentration of typical low-rank coal oxygen-lean combustion was determined below 3 % oxygen concentration. The results of this study can provide scientific guidance for the unsealing of fire zones, and the effective prevention and control of the formation of new fire zone disasters.

Convergent synthesis, kinetics and computational attributions of indole-N-phenyltriazole hybrids bearing N-(aryl)butanamides as alkaline phosphatase inhibitors

In the research delineate herein, an innovative sequence of new series of multi-functional target molecules (9a-i) having indole-N-phenyltriazole bi-heterocyclic hybrids unified with N-arylated butanamides was synthesized as alkaline phosphatase inhibitor. The structural validation of all the formulated compounds was accomplished through IR, EI-MS, 1H NMR, 13C NMR and CHN analysis data. The in vitro enzyme inhibitory investigation revealed the efficacy of these bi-heterocyclic derivatives, 9a–i, as potent inhibitors of alkaline phosphatase relative to the standard used. The compound 9h was found to be the most active compound (IC50 = 0.062 ± 0.017 μM), and its inhibitory activity is about 10 times higher than potassium dihydrogen phosphate (KH2PO4) (IC50 = 5.251 ± 0.468 μM). The kinetics mechanism was attributed by evaluating the Lineweaver–Burk plots, which revealed that compound 9h inhibited the alkaline phosphatase non-competitively to form an enzyme–inhibitor complex. The inhibition constant Ki determined from Dixon plots for this compound was 0.045 μM. The computational study was in full agreement with the experimental records and these ligands exhibited good interactions and binding energy values. These molecules also demonstrated mild cytotoxicity toward red blood cell membranes when analyzed through hemolysis. So, based on the presented results, these molecules, being the promising inhibitors of alkaline phosphatase, might be deliberated as suitable medicinal scaffolds to render normal calcification of bones and teeth.

An experimental study of surrogates of diesel from indirect coal liquefaction and the development of an improved kinetic mechanism

The increasing energy shortage and environmental pollution make the use of clean and efficient alternative fuels an effective way to solve the emission problem. Diesel from indirect coal liquefied (DICL) is a clean and efficient alternative fuel for diesel engines. The composition and chemical kinetics mechanism of DICL research contributes to a better understanding of combustion and pollutant formation process. The components of DICL were analysed by gas chromatography-mass spectrometry (GC-MS). The proportion of normal alkanes contained in DICL is particularly high, 93.82%, which proves that its reactivity is particularly good. The mixture of n-dodecane and iso-octane was selected as the surrogates of DICL. The oxidation process of DICL surrogates was examined by a jet-stirred reactor (JSR) over the temperature range of 500–890 K. A detailed kinetic mechanism of surrogates encompassing 1356 species and 6008 reactions was constructed. The critical reactions associated with the reactivity of surrogates were adjusted by the sensitivity analysis method to increase the accuracy of mechanism prediction. The predicted value of the improved mechanism is in good agreement with the experimental value. The improved mechanism can reasonably predict the oxidation process and the ignition characteristics of DICL and the improved mechanism can provide a good reference value for the subsequent analysis of combustion and emission problems of DICL. Abbreviations: C/H, C/H ratio; CN, cetane number; DDCL, direct coal liquefy diesel; DICL, Diesel from indirect coal liquefied; GC-MS, gas chromatography-mass spectrometry; HMN, 2,2,4,4,6,8,8-heptamethylnonane; HXN, n-hexadecane; IDT, ignition delay time; JSR, jet-stirred reactor; LHV, low heating value; LLNL, Lawrence Livermore National Laboratory; NSRL, National Synchrotron Radiation Laboratory; NTC, negative temperature coefficient; PICS, photoionization cross section; PRF, gasoline substitute; PSR, perfectly stirred reactor; SVUV-PIMS, Synchrotron VUV photoionization mass spectrometry; TOF-MS, time-of-flight mass spectrometer

Isoconversional Analysis of the Catalytic Pyrolysis of ABS, HIPS, PC and Their Blends with PP and PVC.

Thermochemical recycling of plastics in the presence of catalysts is often employed to facilitate the degradation of polymers. The choice of the catalyst is polymer-oriented, while its selection becomes more difficult in the case of polymeric blends. The present investigation studies the catalytic pyrolysis of polymers abundant in waste electric and electronic equipment (WEEE), including poly(acrylonitrile-butadiene-styrene) (ABS), high-impact polystyrene (HIPS) and poly(bisphenol-A carbonate) (PC), along with their blends with polypropylene (PP) and poly(vinyl chloride) (PVC). The aim is to study the kinetic mechanism and estimate the catalysts' effect on the activation energy of the degradation. The chosen catalysts were Fe2O3 for ABS, Al-MCM-41 for HIPS, Al2O3 for PC, CaO for Blend A (comprising ABS, HIPS, PC and PP) and silicalite for Blend B (comprising ABS, HIPS, PC, PP and PVC). Thermogravimetric experiments were performed in a N2 atmosphere at several heating rates. Information on the degradation mechanism (degradation steps, initial and final degradation temperature, etc.) was attained. It was found that for pure (co)polymers, the catalytic degradation occurred in one-step, whereas in the case of the blends, two steps were required. For the estimation of the activation energy of those degradations, isoconversional kinetic models (integral and differential) were employed. In all cases, the catalysts used were efficient in reducing the estimated Eα, compared to the values of Eα obtained from conventional pyrolysis.

MAX phases: Unexpected reactivity under impact

This study reveals that MAX phase materials can exhibit extraordinary reactivity when subjected to impact loading. This previously unknown behavior was discovered and examined in a case study of Ti3SiC2 subjected to Split Hopkinson pressure bar (SHPB) testing. The employed methodology integrated SHPB coupled with thermal measurements and ex-situ spectroscopic analysis, yielding crucial quantitative insights into MAX phase reactivity and mechanical impact response. We observed a substantial release of high energy in the form of elevated temperatures upon impact and disintegration of the MAX phase. Surprisingly, it was found that oxidation, usually the prominent contributor to reactivity, only plays a secondary role. Instead, microstructural transformation emerges as the primary source of energy release. It is postulated that the transformative kinetic mechanism involves rapid kinking, delamination, and bond breakage within the bulk material. These findings shed light on the fundamental energetics of MAX phases and highlight their potential as versatile reactive structural materials.

Effective waste management through Co-pyrolysis of EFB and tire waste: Mechanistic and synergism analysis

Driven by the need for solutions to address the global issue of waste accumulation from human activities and industries, this study investigates the thermal behaviors of empty fruit bunch (EFB), tyre waste (TW), and their blends during co-pyrolysis, exploring a potential method to convert waste into useable products. The kinetics mechanism and thermodynamics properties of EFB and TW co-pyrolysis were analysed through thermogravimetric analysis (TGA). The rate of mass loss for the blend of EFB:TW at a 1:3 mass ratio shows an increase of around 20% due to synergism. However, the blend's average activation energy is higher (298.64 kJ/mol) when compared with single feedstock pyrolysis (EFB = 257.29 kJ/mol and TW = 252.92 kJ/mol). The combination of EFB:TW at a 3:1 ratio does not result in synergistic effects on mass loss. However, a lower activation energy is reported, indicating the decomposition process can be initiated at a lower energy requirement. The reaction model that best describes the pyrolysis of EFB, TW and their blends can be categorised into the diffusion and power model categories. An equal mixture of EFB and TW was the preferred combination for co-management because of the synergistic effect, which significantly impacts the co-pyrolysis process. The mass loss rate experiences an inhibitive effect at an earlier stage (320 °C), followed by a promotional impact at the later stage (380 °C). The activation energy needed for a balanced mixture is the least compared to all tested feedstocks, even lower than the pyrolysis of a single feedstock. The study revealed the potential for increasing decomposition rates using lower energy input through the co-pyrolysis of both feedstocks. These findings evidenced that co-pyrolysis is a promising waste management and valorisation pathway to deal with overwhelming waste accumulation. Future works can be conducted at a larger scale to affirm the feasibility of EFB and TW co-management.

Influence of Temperature on the Nucleation and Adsorption Kinetic Mechanisms for Copper Corrosion

Copper is a valuable catalyst that is widely used in electrochemical devices, particularly in the generation of clean, renewable energy and the CO2 reduction reaction (CO2RR). Gaining insight into the fundamentals of corrosion/deposition of Cu in an electrochemical cell can aid in the design of more durable and efficient devices. To take advantage of the capabilities of Cu and comprehend the broader impacts, it is crucial to understand the kinetics of nucleation and adsorption mechanisms and conduct a thorough investigation of the underlying principles. Here, we utilize a model system with Cu underpotential deposition (UPD) on an Au(111) electrode surface in sulfuric acid electrolyte and investigate the impact of temperature change on the kinetics of Cu corrosion/deposition. The Transient technique, chronoamperometry, is employed to differentiate and illustrate the effects of the nucleation process and adsorption of ions. At temperatures below 20°C, peaks indicate the nucleation and adsorption processes can be identified individually. At temperatures 20°C and above, more adsorption characteristics are seen which may be due to the interactions between less-ordered monolayers at the interface, further demonstrated by the loss of nucleation characteristics. Electrochemical devices operate across a wider temperature range in practical uses. The aim of this study is to examine and quantify the influence of temperature on the nucleation and adsorption mechanisms for the kinetics of Cu in order to optimize the durability of Cu-containing electrochemical devices.

(Industrial Electrochemistry and Electrochemical Engineering Division H. H. Dow Memorial Student Achievement Award) Tailoring Electrode-Electrolyte Interfaces through Non-Covalent Interactions for Electrochemical Energy Storage and Conversion

Li-ion batteries and fuel cells play essential roles in electrifying transportation. Central to the electrochemical systems is the electrode-electrolyte interface, where (electro)chemical surface reactions or intercalation occur, and its thermodynamic and kinetic properties determine the energy density, power density, and lifetime of the electrochemical devices. However, the molecular structures at the electrical double layer and reaction mechanisms remain poorly understood, hindering the rational material design for more efficient electrochemical devices. This talk focuses on the mechanisms of (electro)chemical reactions and charges transfer kinetics at the electrode-electrolyte interface, providing design principles based on non-covalent interactions in electrolytes.First, an in situ Fourier-transform infrared spectroscopy (FTIR) method was developed for Li-ion batteries, which revealed unique evidence for dehydrogenation of carbonate electrolytes on Ni-rich lithium nickel, manganese and cobalt oxides (NMC), accounting for interface impedance build-up and battery capacity fading. Based on the proposed mechanism, strategies on suppressing electrode and electrolyte reactivity were demonstrated to improve battery cycling. Next, the kinetic mechanism for ion intercalation at the electrode-electrolyte interface will be discussed. Li-ion concentration-dependent intercalation kinetics was demonstrated from charge-adjusted electrochemical experiments and fit into a coupled ion-electron transfer mechanism, which governed the current-dependent maximum capacity and power density of intercalation batteries. Finally, for electrocatalytic reactions central to fuel cell technologies, we demonstrated tuning interfacial hydrogen bonding through protic ionic liquids with different acid dissociation constants and organic solvents with different donor numbers to tailor oxygen-reduction reaction (ORR) and hydrogen evolution reaction (HER). Strengthening hydrogen bonding between ORR products and ionic liquids, or between interfacial water molecules facilitated proton-coupled electron transfer kinetics, revealed by in situ surface-enhanced infrared absorption spectroscopy and density functional theory (DFT) calculations. The study can pave the way for the electrolyte and electrode design of electrochemical storage devices with improved energy and power density and cycle life.

Optimization of kinetic mechanism for hydrogen combustion based on machine learning

Optimization of kinetic mechanism for hydrogen combustion based on machine learning

4D printing of Pickering emulsion: Temperature-driven color changes

Pickering emulsion inks were employed to demonstrate the temperature-driven 4D printing method. The Pickering emulsion consisted of water phase containing NaHCO3 and oil phase containing curcumin. Upon heating, the movement of pigment molecules was induced, resulting in color changes. The formation mechanism, rheological properties, printing properties and color changes of Pickering emulsion as well as the release kinetic mechanism of curcumin were investigated. The results indicated that relationships were also established between quantified color values (L*, a*, b*) and heating time. Moreover, the release of the curcumin in the Pickering emulsion, which was designated as a swelling process, followed the non-Fickian mechanism due to the occurrence of diffusion and erosion. The Hixson-Crowell model exhibited the highest linearity (R2: 0.9430 to 0.9825) of Pickering emulsions. In conclusion, the research offers a new perspective for the development of personalized Pickering emulsion food with bright colors.

Study on Chemical Kinetic Mechanism and Autoignition Characteristics of Isopentanol/Gasoline Surrogate Fuel

Abstract In this article, the detailed mechanism of isopentanol was simplified by direct relationship graph error propagation (DRGEP), generation rate analysis, reaction path optimization, and sensitivity analysis, and a comprehensive simplified mechanism of isopentanol/gasoline alternative fuels was obtained. Isopentanol/gasoline-characterized fuels with different blending ratios were investigated, and the results showed that blending of isopentanol promoted the autoignition of gasoline. It was found that blending isopentanol does not significantly affect the low-temperature reaction path of alkanes, but increases the reaction path flux from toluene to benzene. During combustion of isopentanol/gasoline alternative fuels, the isopentanol component exhibits a unique two-stage combustion phenomenon.

Atmospheric photo-oxidation of acetic anhydride: Kinetic study and reaction mechanism. Products distribution and fate of CH3C(O)OC(O)CH2O· radical

The rate coefficient for the gas-phase reaction of acetic anhydride (Ac2O) with chlorine atoms at 298 K and atmospheric pressure was experimentally determined (kAc2O+Cl= (1.3 ± 0.4) × 10-12 cm3molec−1s−1), while the rate coefficient for the reaction with the hydroxyl radical was estimated (kAc2O+OH=1.9 x 10-13 cm3molec−1s−1). For the Structure-Activity Relationship method, a value of 0.02 was determined for the −C(O)OC(O) group. The mechanism of photo-oxidation of acetic anhydride initiated by chlorine atoms was determined and CO, CO2, CH3C(O)OH (32 %), CH3C(O)OC(O)C(O)H, and 3-hydroxy-1,4-dioxane-2,6-dione (20 %) were identified as products by infrared spectroscopy. Here we determined for the first time the relative energies of the primary reaction pathways for the CH3C(O)OC(O)CH2O· radical using computational methods, which confirmed our experimental data. Finally, the environmental implications of acetic anhydride emissions were calculated, showing an atmospheric lifetime between 31 and 220 days for the reaction with atmospheric radicals, while its wet deposition lifetime is 1.5 years.

Development of laminar burning velocity prediction model and correlation of iso-octane air mixtures using artificial neural network

Surrogate fuels provide an economical alternative for forecasting the combustion properties of transportation fuels like diesel, gasoline, and kerosene. Iso-octane (2,2,4-trimethylpentane), a primary reference fuel for gasoline, is extensively used as a surrogate component. This study utilizes a Feed-Forward Artificial Neural Network (FFANN) with back-propagation (BP) to predict the laminar burning velocity (LBV) of iso-octane/air mixtures. The ANN model was developed using a dataset of 6339 data points, including 3788 experimental data points from literature since 2004 and 2551 simulation data points from reduced kinetic reaction mechanism (RKM) CHEMKIN simulations. The grid search cross-validation (CV) method was employed to optimize the ANN hyperparameters. Implemented in Python using Keras, the ANN model addresses research gaps by forecasting LBV for hydrocarbons beyond n-heptane and modelling LBV under conditions reflective of actual engine operations. Unlike prior studies, we optimized various ML models, their complexity, size, and hyperparameters to achieve high prediction accuracy. We also integrated a hybrid model combining Particle Swarm Optimization (PSO) with Genetic Algorithms (GA) for hyperparameter optimization, ensuring efficient configuration of the ANN. The constructed ANN model was compared to other ML models, including generalized linear regression (GLR), support vector machine (SVM), random forest (RF), and XGBoost regression. For the testing set (20 % of the total dataset), the ANN model outperformed all other ML models and empirical correlations, achieving a coefficient of determination (R2) of 0.9903, root mean square error (RMSE) of 1.911, and mean absolute error (MAE) of 1.206. Optimizing the ANN model with PSO further enhanced prediction accuracy, achieving a correlation coefficient of 0.9973 and a reduced mean absolute error of 0.753. To evaluate the ANN model's predictive ability, a reduced mechanism from the Lawrence Livermore National Laboratory (LLNL) was used. Compared to the LLNL RKM, the ANN predicted values showed lower percentage deviation from experimental data. Additionally, computation cost comparisons revealed that while RKM simulations in CHEMKIN took 244.2 s per case, the PSO-optimized ANN model required only 900 s for 150 cases. A 16-term correlation for laminar burning velocity (LBV) was derived from ANN predictions, serving as a practical tool to predict LBV based on pressure, temperature, and equivalence ratio. Unlike existing literature correlations, this newly developed correlation is valid across a wide range of operating conditions, offering a fundamental database for real-time combustion applications.