Chemically Research Articles

Effects of strain and pressure on entropy generation in laminar flames

The mitigation of combustion noise is crucial for preventing thermoacoustic instabilities in rocket and gas turbine engines. Entropy noise, arising from entropy fluctuations within the engine, serves as a prominent noise source. Therefore, understanding the mechanisms governing entropy generation in flames becomes imperative for identifying the roots of indirect combustion noise. While previous studies have broadly examined various pathways of entropy generation under different canonical configurations of laminar flames, surprisingly, the effect of strain and pressure has been overlooked. This aspect is analyzed in the present work. Building upon previous analysis, the entropy source term of the reacting flow is decomposed into three sub-terms: the unsteady heat release term (Se,1), the sensible enthalpy term (Se,2), and the partial entropy term (Se,3). The extent to which these three sub-terms contribute to entropy generation is thoroughly analyzed. Simultaneously, the scaling laws of the three sub-terms with respect to strain rate and pressure are investigated. The inclusion of detailed chemical kinetics as well as flame structure in the simulation dataset allows for in-depth investigation into the mechanism of the strain and pressure effects. Three canonical laminar flame configurations – the freely propagating premixed flame, the premixed counterflow flame, and the counterflow diffusion flame – are investigated. The following main conclusions are drawn: the heat release term is the leading constituent of the entropy source; the sensible enthalpy term is negligible; and the partial entropy term is secondary while non-negligible. Under strain and pressure variations, the contribution of the partial entropy term to total entropy production can greatly off-set the total entropy source or even qualitatively affect the strain/pressure response of the entropy generation, i.e., the strain response of the premixed flame and pressure response of the hydrogen non-premixed flame.Novelty and significance statement1. Conducted a systematic investigation of entropy production due to chemical reactions under the influence of strain and pressure variations.2. Revealed that the partial entropy term, often overlooked in previous studies, can surpass the heat release term in certain configurations, emerging as the leading constituent of the total entropy generation source.3. Identified dominating reactions contributing to entropy production for two different fuels of hydrogen and methane.

Development and Application of Hydrogen-Based Direct Reduction Iron Process

The conventional iron and steel industry (ISI), driven by coal utilization as its predominant feedstock, constitutes a substantial source of greenhouse gas emissions. Hydrogen metallurgy presents the opportunity to mitigate carbon emissions in ISI from the origin. Among hydrogen metallurgical approaches, the hydrogen-based direct reduction iron (H-DRI) process stands out for its substantial carbon reduction capabilities and established technological maturity. The present paper provides a comprehensive review of the development and application surrounding the H-DRI process. Firstly, the main chemical reactions of H-DRI and the relevant important parameters are introduced. Subsequently, an overview is provided of several prominent H-DRI processes, including HYL, Midrex, Midrex-H2®, HYL-III, HYL-ZR, BL, and Finmet, elucidating their characteristics through comparative analysis. Moreover, some research results of H-DRI process optimization are summarized. Leveraging insights garnered from globally representative projects exemplifying the industrial deployment of H-DRI technology in recent years, the trajectory of and prospective trends for industrial development in the field of H-DRI processes are explored. Further, prevailing challenges and impediments encountered in the adoption of H-DRI processes are identified, culminating in strategic recommendations tailored towards fostering future advancements. In the long term, the H-DRI process is expected to become a key path to achieve ISI cleaner production.

Approaching Optimal pH Enzyme Prediction with Large Language Models.

Enzymes are widely used in biotechnology due to their ability to catalyze chemical reactions: food making, laundry, pharmaceutics, textile, brewing─all these areas benefit from utilizing various enzymes. Proton concentration (pH) is one of the key factors that define the enzyme functioning and efficiency. Usually there is only a narrow range of pH values where the enzyme is active. This is a common problem in biotechnology to design an enzyme with optimal activity in a given pH range. A large part of this task can be completed in silico, by predicting the optimal pH of designed candidates. The success of such computational methods critically depends on the available data. In this study, we developed a language-model-based approach to predict the optimal pH range from the enzyme sequence. We used different splitting strategies based on sequence similarity, protein family annotation, and enzyme classification to validate the robustness of the proposed approach. The derived machine-learning models demonstrated high accuracy across proteins from different protein families and proteins with lower sequence similarities compared with the training set. The proposed method is fast enough for the high-throughput virtual exploration of protein space for the search for sequences with desired optimal pH levels.

Volatile compounds and quality changes of lesser mealworm larvae: effect of blanching, storage temperature and time

Abstract The impact of blanching and storage temperature (−20 °C and −80 °C) on the formation of volatile organic compounds and changes in quality characteristics of lesser mealworm (Alphitobius diaperinus) larvae was examined over seven weeks. Acid and peroxide values, pH, and colour of lesser mealworm larvae were significantly affected by the studied variables. The changes in these characteristics as well as in the volatile profile indicated occurring lipid oxidation and lipid hydrolysis processes during the storage. The intensity of these reactions was mostly influenced by blanching treatment and storage time, and a lesser extent by storage temperature. It was proposed that changes in composition and intensity of volatiles can be used for rapid quality assessment of lesser mealworm larvae during frozen storage. Thus, the selection of optimum storage conditions for lesser mealworm larvae is important for the prevention of undesirable chemical reactions and preservation of the quality of insect biomass.

Cold plasma/alkaline pretreatment facilitates corn stalk fractionation and valorization towards zero-waste approach

The present study employed alkaline hydrogen peroxide pretreatment coupled with cold plasma for corn stalk’s complex biopolymers fractionation and valorization through enzymatic hydrolysis. This hurdle approach enables the prolonged generation of reactive oxidative species, initiating chemical reactions otherwise hardly possible under ambient conditions. A delignification rate between 76±1 and 86±2 % was obtained under different process parameters in a significantly shorter time compared to conventional alkaline pretreatment. Up to 94±4 % of cellulose in treated biomass was converted to glucose after enzymatic hydrolysis, achieving around 3.5 times higher glucose yield than the raw biomass. Different spectroscopic analyses confirmed specific alterations in the structure of the lignin-rich fraction caused by cold plasma. Micro- and nanoscale lignin particles obtained were rich in total phenolic content, reaching up to 140±20 and 107±12 µg gallic acid equivalents (GAE) per mg of lignin, respectively. The proposed concept of corn stalk fractionation through biorefinery can open new opportunities for valorizing different agricultural waste types.

Synthesis and Evaluation of 1,4-Dihydropyridine-Based Urea Derivatives as Polyphenol Oxidase Inhibitors

This study investigated the potential inhibitory effects of nine novel synthesized urea-substituted 1,4-dihydropyridine derivatives (DT-DEN-1-9) on polyphenol oxidase (PPO) activity. The compounds were synthesized via the Hantzsch reaction, providing a series of structurally diverse urea and thiourea-modified 1,4-dihydropyridines. Polyphenol oxidase enzyme was extracted from banana (Musa cavendishii) and purified using affinity chromatography with a Sepharose 4B-L-tyrosine-p-aminobenzoic acid affinity gel. The purified enzyme's activity was measured spectrophotometrically using catechol as the substrate, monitoring the increase in absorbance at 420 nm. The inhibitory effects of the synthesized compounds on PPO activity were evaluated through in vitro assays. Various concentrations of each compound were incorporated into the enzyme reaction mixture, and the residual PPO activity was determined. The percentage of PPO activity was calculated relative to a control reaction without inhibitors. IC50 values, representing the concentration of inhibitor required to reduce enzyme activity by 50%, were determined using Lineweaver-Burk plots. Among the tested compounds, DT-DEN-6, featuring a phenyl thiourea substituent, exhibited the most potent inhibition with an IC50 value of 100.14 μM. DT-DEN-8, containing a 2,5-dichlorophenyl thiourea moiety, also showed strong inhibitory activity with an IC50 below 150 μM. Structure-activity relationships were observed, with electron-withdrawing substituents generally enhancing inhibitory potency. Conversely, DT-DEN-5, bearing a 4-(trifluoromethyl)phenyl thiourea substituent, exhibited the weakest inhibition profile (IC50: 233.33 μM). Our findings provide valuable insights for the design of next-generation PPO inhibitors, potentially leading to the development of novel anti-browning agents for applications in food preservation and other industries where control of enzymatic browning is crucial.

Green Synthesis of Iron Nanoparticles Using Spinacia oleracea and Their Role in Antioxidant Defence

The green synthesis of iron oxide nanoparticles (Fe2O3) using Spinacia oleracea leaf extract is explored in this study. Iron oxide nanoparticles are noted for their unique properties, such as enhanced chemical reactivity due to their high specific surface area to volume ratios. Unlike traditional physical and chemical methods, green synthesis presents an environmental friendly alternative, leveraging biological processes for nanoparticle production. This method is particularly significant due to its potential applications in various fields, including medicine, where iron nanoparticles demonstrate antibacterial activity. However, limited research exists on their antioxidant properties. In this research, Spinacia oleracea leaf extract is utilized to synthesize iron oxide nanoparticles, followed by characterization using UV-Visible spectroscopy, FTIR, XRD, and SEM techniques. The results underscore the necessity for further investigation into the impact of nanoparticles on biological processes and the long-term effects of high nanoparticle concentrations on ecological stability. Additionally, this study includes an evaluation of antioxidant properties of the nanoparticles to address gaps in current research. Key Words Green synthesis, iron oxide, ecological stability, antioxidant, biological, nanoparticles.

Rate-potential decoupling: a biophysical perspective of electrocatalysis

Abstract In this perspective, the chemical physics of biological electron transfer are considered in relation to artificial electrocatalyst development. Nature’s ability to access a wide range of chemical reactivities through a relatively narrow set of redox-active motifs, in part by decoupling electron transport rates from reaction driving forces, are suggested as a model for the future of electrocatalyst design and testing. Theoretical rationale and experimental precedents for this concept are put forth, outlining how emulating nature’s ability to arbitrarily tune tunneling currents with respect to donor/acceptor redox potentials – reaction driving forces – may enhance our control over electrocatalyst selectivity.

Effect of chemical reactions and melting heat on the dynamics of maxwell nanofluid flow

AbstractThis study investigates the electrically conducting Maxwell fluid flow over a stretching sheet with the effects of homogeneous‐heterogeneous chemical reactions, thermal radiation, and melting heat. The nanomaterial characteristics are analyzed considering Brownian motion and thermophoresis (Buongiorno's model). Irreversibility analysis is conducted to assess entropy generation. The governing equations of the problem are transformed into dimensionless equations through appropriate similarity transformations. The graphical and tabular numerical solutions are attained through NDSolve via Mathematica. The study examines how various parameters affect the velocity, concentration, temperature, and entropy generation within the flow. This study provides insights into isothermal chemical processes which contribute to the optimization of industrial and engineering applications. It is seen that heterogeneous diffusion parameter increases molecular disorder and rate of irreversible processes, whereas homogeneous diffusion parameter shows opposite trend.

Safety Profile of Mass Administration of Albendazole Among School Children (6-19 Years): A Prospective Active Surveillance Study

Background: Infections with Soil-transmitted Helminths (STHs) impact about 24% of the global population. A disproportionate number of individuals, particularly those from low socioeconomic backgrounds, live in emerging nations. In India, between the ages of one and fourteen, almost 220 million children are susceptible to intestinal worm infestations caused by parasites. The National Deworming Day (NDD) initiative was started by the Indian government in February 2015 as a part of the National Health Mission to address this problem. Though the adverse effects of albendazole in routine therapy are known, the mass administration of the medicine in children as part of a public health program has not been adequately studied. Objective: This study aimed to determine the occurrence, type, and severity of adverse drug reactions resulting from mass administration of albendazole in school children aged 6-19 years in a district of northern India. Methods: Twenty specified clusters were randomly chosen from a total of 94 clusters in the state to participate in this prospective, descriptive, observational study that was carried out in Karnal, Haryana. Both a passive approach and an active adverse drug reaction reporting system were used in the study. The six-step process known as Deb’s Active Surveillance & Assisted Reporting System was employed in our study. Adverse drug reactions were recorded using the suspected Adverse Drug Reaction (ADR) reporting form of the Pharmacovigilance Programme of India (PvPI). Results: Twenty clusters with a combined total of 94 schools and 12,751 students were observed during the study. In this study, there were more female participants (N = 8,060; 63.21%) than male participants (N = 4,691; 36.78%). A total of 29 ADRs were reported. All reported ADRs were mild in nature. It was discovered that there were 1.37 incidences for every 1000 individuals. As illustrated in Fig. (1), the most frequently reported Adverse Drug Reactions (ADRs) were vomiting (N = 10), nausea (N = 4), abdominal pain (N = 2), and headache (N = 1). The majority of ADRs were categorized as probable (N=18; 62.06%), followed by possible (N=11; 37.93%). result: Twenty clusters with a combined total of 94 schools and 12,751 students were observed during the study. In this study, there were more female participants (N = 8,060; 63.21%) than male participants (N = 4,691; 36.78%). A total of 29 ADRs were reported. All reported ADRs were mild in nature. It was discovered that there were 1.37 incidences for every 1000 individuals. As illustrated in figure 1, the most frequently reported adverse drug reactions (ADRs) were vomiting (N = 10), nausea (N = 4), abdominal pain (N = 2), and headache (N = 1). The majority of ADRs were categorized as probable (N=18; 62.06%), followed by possible (N=11; 37.93%). Conclusion: An active surveillance system alongside voluntary passive reporting during the mass administration of medicines can help evaluate the safety profile of the medicinal products. The occurrence of ADRs following mass administration of albendazole in school children was found to be only 1.37 incidences for every 1000 recipients, being mild in nature, with vomiting being the most common.

Integrated attrition model of mechanical-thermal-reaction for CaCO3/CaO thermochemical energy storage

Fluidized bed reactors have become a pivotal trend in the future development of thermochemical energy storage. However, high temperatures and chemical reactions exacerbate particle attrition in fluidized bed reactors, affecting particle cyclic stability and reducing energy storage efficiency. This study conducted experiments under three different temperature conditions to compare and investigate the attrition mechanisms of CaCO3/CaO particles. The contributions of mechanical forces from collisions, thermal stress due to uneven cooling and heating, and chemical stress from cyclic reactions to particle attrition are analyzed. The edge effects caused by sphericity dominate the attrition behavior during the initial period of fluidization. High-temperature thermal stress significantly weakens the attrition resistance of the particles, while repeated chemical cycling degrades the internal skeletal structure of the particles, lowering the fracture threshold. Based on fitting experimental data, a comprehensive numerical model for predicting particle attrition has been developed and improved by incorporating factors such as edge effects from sphericity, thermally induced stress, and chemically driven fragmentation. Through validation, the model effectively predicts particle attrition behavior in thermochemical storage process, providing a simulation tool for in-depth research on particle stability in thermochemical energy storage field.

Simultaneous quantification of alkanolamines and their dehydrogenation products in aqueous samples using high-performance liquid chromatography with pre-column derivatization with 2,4-dinitrofluorobenzene

BackgroundDiethanolamine, monoethanolamine, iminodiacetic acid, and glycine are important fine chemical intermediates, often requiring simultaneous quantitative analysis in various applications. This presents the challenge of accurately quantifying multiple substances within a single sample. The catalytic dehydrogenation of diethanolamine and monoethanolamine has garnered significant research interest, yet no analytical method has been reported for the simultaneous quantification of reactants and products in the dehydrogenation reaction mixtures of different alkanolamines. ResultsA high-performance liquid chromatography (HPLC) method has been developed for the simultaneous quantification of diethanolamine (DEA), iminodiacetic acid (IDA), glycine (Gly), and monoethanolamine (MEA) in aqueous solutions using 2,4-dinitrofluorobenzene (DNFB) for pre-column derivatization. The method demonstrated excellent linearity, with correlation coefficients (R2) of 0.9999, 0.9997, and 0.9998 for IDA, DEA, and Gly, respectively. The detection limits (LODs) were 0.02, 0.08, and 0.01 mg L−1, respectively. The quantification limits (LOQs) were 0.06, 0.24, and 0.03 mg L−1, respectively. Spiked recovery rates ranged from 96.99 % to 104.32 %, with relative standard deviations (RSDs) between 0.70 % and 3.03 %. For MEA and Gly, the R2 values were 0.9970 and 0.9990, the LODs were 0.12 and 0.01 mg L−1, the LOQs were 0.36 and 0.03 mg L−1, and spiked recoveries ranged from 96.24 % to 104.82 %, with RSDs between 1.22 % and 3.68 %. Compared to other methods, this HPLC approach offers superior sensitivity, accuracy, and precision. SignificanceThis method provides a robust reference for the individual or simultaneous quantification of alkanolamines, glycine, and iminodiacetic acid in aqueous matrices. It offers new insights into the simultaneous analysis of alkanolamines with multiple organic acids in complex matrices. Additionally, the method can guide the optimization of catalytic dehydrogenation processes for alkanolamines, potentially extending the advantages of dehydrogenation catalysts to other reactions.

Coupling kinetic modeling with artificial neural networks to predict the kinetic parameters of pine needle pyrolysis

The pyrolysis behavior of biomass is critical for industrial process design, yet the complexity of pyrolysis models makes this task challenging. This paper introduces an innovative hybrid model to quantify the pyrolysis potential of pine needles, predicting the entire process of their pyrolysis behavior. Through experimental analyses and kinetic parameter calculations of pine needle pyrolysis, the study employs a kinetic model with a chemical reaction mechanism. Additionally, it introduces an improved dung beetle optimization algorithm to accurately capture the primary trends in pine needle pyrolysis. The developed artificial neural network model incorporates meta-heuristic algorithms to address process error factors. Validation is based on experimental data from TG at three different heating rates. The results demonstrate that the hybrid model exhibits strong predictive performance compared to the standalone model, with coefficients of determination (R²) of 0.9999 and 0.999 for predicting the conversion degree and conversion rate of untrained data, respectively. Additionally, the standard errors of prediction (SEP) are 0.249% and 0.449% for predicting the conversion degree and conversion rate of untrained data, respectively.

Dissolution of denim waste in N-methyl morpholine-N-oxide monohydrate for fabrication of regenerated cellulosic film: Experimental and simulation study

Despite the significant amount of denim waste and its potential as a cellulose source, its use has been neglected. This study uses N-methyl morpholine-N-oxide, an eco-friendly solvent, to dissolve denim (including 100 % cotton) and create a denim film. Achieving a 10 % denim record solubility, a cellulosic film was also fabricated for comparison. Characterisation techniques were applied, and molecular dynamics simulations explored intramolecular interactions and the influence of indigo dye on dissolution process. FTIR spectra indicated no chemical reactions during dissolution and regeneration, though a shift in OH stretching suggested a change in crystallinity, confirmed by XRD results showing decreased crystallinity and a structural shift from cellulose I to cellulose II. 13C NMR analysis revealed disruptions in interchain hydrogen bonds after regeneration. TGA results showed lower decomposition temperatures for both films compared to the powders. Testing mechanical properties showed the denim film had higher elongation at break but lower tensile strength than the cellulose film. MD simulations indicated indigo dye did not significantly affect fundamental interactions but decreased denim solubility by reducing the diffusion coefficient. Rheological tests supported the simulation results, showing higher viscosity and molecular weight for the denim solution compared to cellulose.

Kinetics of kaolinite dissolution and hydrosodalite precipitation during alkali leaching of diasporic bauxite

Alkali leaching is an effective desilication method for improving the alumina-silica mass ratio (A/S) of bauxite. The paper aims to study the kinetics of kaolinite dissolution and hydrosodalite precipitation during alkali leaching of kaolinite-rich diasporic bauxite. Alkali leaching of bauxite in NaOH solutions was studied at Na2O concentrations of 200–260 g/L, temperatures of 90–105 °C, and times of 30–150 min. The leached bauxites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) techniques. The rate equations describing kaolinite dissolution and hydrosodalite precipitation were derived by fitting the Avrami model. The results show that kaolinite with finer particle sizes was preferentially dissolved during alkali leaching, providing a material basis for the precipitation of hydrosodalite. Hydrosodalite was heterogeneously nucleated on the dissolved edges of some kaolinite and grew in both one- and two-dimensions, presenting acicular and lamellar morphology. The dissolution rate of kaolinite and the crystallization mechanism of hydrosodalite were primarily influenced by Na2O concentration and temperature. Both kaolinite dissolution and hydrosodalite precipitation were controlled by chemical reactions with activation energies of 70.152 (± 1.429) kJ/mol and 289.089 (± 2.063) kJ/mol, respectively, and the orders of reaction with respect to Na2O of 0.733 (± 0.070) and 7.165 (± 0.047), respectively. The kinetic equations describing kaolinite dissolution, hydrosodalite precipitation and even the leaching of SiO2 were eventually modeled with Na2O concentration, temperature and time as variables.

Intramolecular charge transfer dynamics of anthraquinone derivatives in the confined environments of reverse micelles

Reverse micelles (RMs) are considered important model systems for molecular dynamics and chemical reactions, where the nanopools of aqueous and nonaqueous polar cores are separated from the surrounding organic phase via a monolayer of surfactant molecules. Here, we report the intramolecular charge transfer (ICT) dynamics of anthraquinone derivatives in the methanol-in-oil RMs composed of nonionic surfactants Igepal by femtosecond transient absorption and fluorescence upconversion spectroscopy. The ICT dynamics slow down inside the RMs due to abnormally diminished solvent motions and restricted internal rotations of the (methyl)amino group during the ICT in the excited states. The micelle size-dependent dynamics of anthraquinone derivatives inside the RMs were compared with the results in bulk aliphatic alcohols and understood as the changes in the microenvironment properties such as microviscosity.

Thermodynamic properties of MnV2O6 and Mn2V2O7 at high temperatures

MnV2O6 and Mn2V2O7 are the key compounds during the manganese salt roasting for extracting vanadium from vanadium bearing slag. Thermodynamic properties of MnV2O6 and Mn2V2O7 are dispensable to get insight into the multi-phase reaction mechanism and clarify the phase evolution. In this study, the MnV2O6 and Mn2V2O7 compounds were synthesized through solid-state roasting routes under a nitrogen gas atmosphere, and their crystal structure and thermodynamic properties were determined using X-ray powder diffraction, differential scanning calorimetry, and drop calorimetry. The enthalpy increments of MnV2O6 and Mn2V2O7 were experimentally measured for temperatures ranging from 573 K to 1023 K and 573 K to 1173 K, respectively, using drop calorimetry for the first time. Based on the experimentally measured enthalpy increments, the temperature dependence of the molar heat capacity of MnV2O6 and Mn2V2O7 was then derived. Furthermore, thermodynamic properties such as enthalpy, entropy, and Gibbs free energy were also calculated. Finally, the Gibbs free energy of the chemical reactions during the roasting of vanadium slag was evaluated, and compared with other roasting techniques.

Fabrication of N-halamine/MWPPy-ZnO hybrids based cellulose nanofibril composite films with improved UV-protective, antibacterial, and biofilm control functions

The design and fabrication of synergistic hybrid antibacterial materials is a promising approach for achieving effective sterilization while compensating for the deficiency of a single component. Despite being highly effective biocidal components, the poor UV light stability of some N-halamines limits their applications. This study was conducted to address this issue by the rational integration of cyclic N-halamine precursor (PGHAPA) with microwaved zinc oxide (MWPPy-ZnO) nanoparticles via covalent bonds and the preparation of cellulose nanofibrils based antibacterial composite films after chlorination (CNF/MWPPy-ZnO-PGHAPA-Cl). The proposed films offered tight lamellar structure, considerable thermal stability and better mechanical properties. The results from the FT-IR and XPS experiments provided the evidence of chemical reactions among the PGHAPA, MWPPy-ZnO, and CNF film. Notably, the CNF/MWPPy-ZnO-PGHAPA-Cl films showed improved UV stability with a chlorine content of up to 0.16 % after 24 h of irradiation, which was much greater than that of the CNF/PGHAPA-Cl films. Furthermore, the CNF/MWPPy-ZnO-PGHAPA-Cl films displayed rapid bactericidal activity, inactivating all the contacted Staphylococcus aureus and Escherichia coli O157:H7 strains within 5 min, along with prominent biofilm disruption, indicating great potential for daily food packaging applications.

Non-polynomial spline method for computational study of reaction diffusion system

This work addresses an efficient and new numerical technique utilizing non-polynomial splines to solve system of reaction diffusion equations (RDS). These system of equations arise in pattern formation of some special biological and chemical reactions. Different types of RDS are in the form of spirals, hexagons, stripes, and dissipative solitons. Chemical concentrations can travel as waves in reaction-diffusion systems, where wave like behaviour can be seen. The purpose of this research is to develop a stable, highly accurate and convergent scheme for the solution of aforementioned model. The method proposed in this paper utilizes forward difference for time discretization whereas for spatial discretization cubic non-polynomial spline is used to get approximate solution of the system under consideration. Furthermore, stability of the scheme is discussed via Von-Neumann criteria. Different orders of convergence is achieved for the scheme during a theoretical convergence test. Suggested method is tested for performance on various well known models such as, Brusselator, Schnakenberg, isothermal as well as linear models. Accuracy and efficiency of the scheme is checked in terms of relative error (E R ) and L ∞ norms for different time and space step sizes. The newly obtained results are analyzed and compared with those available in literature.

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.