Chemical Reaction Model Research Articles

A NUMERICAL STUDY ON THE REDUCTION OF GREENHOUSE GASEOUS COMPONENT (CO2) DUE TO THE ADDITION OF H2 IN THE FUEL STREAM OF THE COUNTERFLOW CH4/AIR DIFFUSION FLAME

In this study, a series of 1-D and steady-state numerical simulations have been performed for the prediction of the effect of the addition of H2 on the characteristics of a non-sooting counterflow CH4/Air diffusion flame using detailed chemical reaction model, which is composed of 325 elementary chemical reactions and 53 chemical species. Under the steady-state assumption, a set of one-dimensional transport equations of mass, momentum, species, and energy along with the equation of state has been solved numerically at the atmospheric conditions over the counterflow configuration by exploiting an efficient numerical code, OPPDIF (a Fortran Program for Computing Opposed-Flow Diffusion Flames). The grid adaption technique has been used to achieve better convergence as well as to ensure the maximum accuracy of the simulated results. It is found that the flame temperature is increased due to the addition of H2 with CH4, which is injected into the fuel stream. The elevation in the temperature is caused by the augmentation of the integrated heat release rate of the elementary reactions supported by the active radicals (H, O, and OH), which are generated by the higher reactivity of H2. Besides, it is found that the mole fractions of H2O are increased as the percentage of H2 in the loading fuel (CH4) is increased and also, it is identified that the chain propagating reaction, OH + H2 => H2O + H is dominating one which produces highest amount of H2O. Furthermore, it is noticed that the indirect greenhouse gas or precursor, CO is reduced when H2 is added to CH4. Consequently, the mole fraction of the principle greenhouse gas, CO2 is decreased significantly when the fuel, CH4 percentage is modified by the higher percentage of H2. The sensitivity analysis of elementary reactions reveals the fact that the chemical reaction: OH + CO => H + CO2 is a dominating reaction in producing a lower amount of CO2 when the volume fraction of H2 is increased in the fuel (CH4) stream. In the presence of 75 % H2 in CH4, the pressure-dependent reaction, O + CO (+M) => CO2 (+M) appears as another chemical route that also generates greenhouse gas, CO2 but its contribution is negligibly small.

Mathematical Model for Chemical Reactions in Electrolytes Applied to Cytochrome c Oxidase: An Electro-Osmotic Approach

This study introduces a mathematical model for electrolytic chemical reactions, employing an energy variation approach grounded in classical thermodynamics. Our model combines electrostatics and chemical reactions within well-defined energetic and dissipative functionals. Extending the energy variation method to open systems consisting of charge, mass, and energy inputs, this model explores energy transformation from one form to another. Electronic devices and biological channels and transporters are open systems. By applying this generalized approach, we investigate the conversion of an electrical current to a proton flow by cytochrome c oxidase, a vital mitochondrial enzyme contributing to ATP production, the ‘energetic currency of life’. This model shows how the enzyme’s structure directs currents and mass flows governed by energetic and dissipative functionals. The interplay between electron and proton flows, guided by Kirchhoff’s current law within the mitochondrial membrane and the mitochondria itself, determines the function of the systems, where electron flows are converted into proton flows and gradients. This important biological system serves as a practical example of the use of energy variation methods to deal with electrochemical reactions in open systems. We combine chemical reactions and Kirchhoff’s law in a model that is much simpler to implement than a full accounting of all the charges in a chemical system.

On the Constitutive Equations for Coupled Flow, Chemical Reaction, and Deformation of Porous Media

AbstractDeformation, chemical reactions, fluid flow in geological formations, and many engineering materials are coupled processes. Most existing models of chemical reactions coupled with fluid transport assume the dissolution‐precipitation process or mineral growth in rocks. However, these models have limitations, such as predicting restricted reaction extent due to pore clogging or disregarding porosity changes resulting from mineral growth. Recent studies indicate mineral replacement involves coupled dissolution‐precipitation, maintaining porosity while altering the solid volume. This has multiple practical implications for natural geological processes and within petroleum and environmental engineering. We present a novel model for reaction‐driven mineral expansion that preserves porosity and allows solid volume change. First, we look at fluid‐rock interaction at the pore scale and derive effective rheology of a reacting porous media. On a larger scale, we adopt a two‐phase continuum medium approach to investigate the coupling between reaction, deformation, and fluid flow. Our micromechanical model based on observations assumes that rock or cement consists of an assembly of solid reactive grains, initially composed of a single, pure phase. The reaction occurs at the fluid‐solid contact and progresses into the solid grain material. We approximate the pores and surrounding solid material as an idealized cylindrical shell to simplify the problem and obtain tractable results. We derive macroscopic stress‐strain constitute laws that account for chemical alteration and viscoelastic deformation of porous rocks. Our model explains the possibility of achieving a complete reaction, preservation of porosity during chemical reactions, and dependence of mechanical rock properties on fluid chemistry.

A time independent least squares algorithm for parameter identification of Turing patterns in reaction-diffusion systems.

Turing patterns arising from reaction-diffusion systems such as epidemic, ecology or chemical reaction models are an important dynamic property. Parameter identification of Turing patterns in spatial continuous and networked reaction-diffusion systems is an interesting and challenging inverse problem. The existing algorithms require huge account operations and resources. These drawbacks are amplified when apply them to reaction-diffusion systems on large-scale complex networks. To overcome these shortcomings, we present a new least squares algorithm which is rooted in the fact that Turing patterns are the stationary solutions of reaction-diffusion systems. The new algorithm is time independent, it translates the parameter identification problem into a low dimensional optimization problem even a low order linear algebra equations. The numerical simulations demonstrate that our algorithm has good effectiveness, robustness as well as performance.

A reactive-transport phase-field modelling approach of chemo-assisted cracking in saturated sandstone

Hydraulic fracturing and acidification techniques are important approaches for deep energy recovery engineering. However, the details of the interactions and impacts between acid fluids and solid porous media remain inadequately modelled, necessitating further research in this domain. Building on this need, we present a novel approach for modelling the chemo-hydro-mechanical response in sandstone during fracture propagation which is induced by the injection of acid fluids into the reservoir. Our comprehensive framework integrates various mechanisms including acidified reactions in sandstone, reactive flow transport, pore pressure diffusion, solid deformation, mass exchanges due to chemical reactions, and fracture propagation in poroelastic media, all within the framework of the phase field approach. To accurately capture the system’s behaviour, we derive its total potential energy, taking into account factors such as poroelasticity, fracture forces acting on the fracture sides, and crack dissipation, while also integrating the mechanical–chemical degradation function into the energy derivations. The progress of chemical degradation, which we treat as a damage parameter, is characterized by mass exchanges, and these in turn manifest as changes in porosity. In order to quantify these mass exchanges, we have established a corresponding mass balance equation specifically for the minerals involved. These changes in porosity can be naturally and effectively described through the volumetric relations of the minerals situated within the solid porous media. The proposed coupled framework is verified through multiple numerical examples. Initially, we validate the model using a classical unit-slit crack example for the solid phase and discuss the predominant influences of porosity alterations on the mechanical response of solid cracking. Following this, we verify the model by injecting water/acid and compare the results with analytical solutions. Finally, a chemical benchmark is employed to calibrate the chemical reaction model and simulate acid fluid injection scenarios.

Synergistic co-combustion of carbon-rich fraction from coal gasification fine slag and corncob char: Performance, mechanism, kinetics, and thermodynamics

Coal gasification fine slag (FS) is a coal-based solid waste with high carbon content, and landfill-based disposal causes water-soil-gas composite pollution. Co-combustion is a common method of solid waste thermal disposal, and corn cob is used as an auxiliary fuel for co-combustion because of its energy density and ease of handling and processing. In this paper, the thermal degradation characteristics, interaction mechanism, kinetics, and thermodynamics of co-combustion RC (carbon-rich fraction obtained by flotation) and CC (corncob char) were studied. The results showed that physicochemical properties suggested that RC and CC will complement and promote each other in the combustion process. The addition of CC reduced the RC ignition temperature and improved the overall combustion performance. The interaction effect was mainly due to metal catalysis, the effect of the porous carbon structure, the thermal effect, and the hindering effect of ash. The activation energy was reduced due to the blending of RC-CC, and the activation energy was lowest (132.19 kJ/mol) when the RC adding ratio was 60%. The co-combustion process was controlled by the F3 model (chemical third-order reaction kinetics), and it was a typical gas-solid phase reaction with a progressive process from the outsides toward the insides. Thermodynamic analysis showed that the co-firing process was an extremely complex multi-stage reaction. The results of this study provide a theoretical reference for the synergistic resource utilization of coal gasification fine slag and waste biomass.

Mechanochemical active ratchet

Self-propelled nanoparticles moving through liquids offer the possibility of creating advanced applications where such nanoswimmers can operate as artificial molecular-sized motors. Achieving control over the motion of nanoswimmers is a crucial aspect for their reliable functioning. While the directionality of micron-sized swimmers can be controlled with great precision, steering nano-sized active particles poses a real challenge. One of the reasons is the existence of large fluctuations of active velocity at the nanoscale. Here, we describe a mechanism that, in the presence of a ratchet potential, transforms these fluctuations into a net current of active nanoparticles. We demonstrate the effect using a generic model of self-propulsion powered by chemical reactions. The net motion along the easy direction of the ratchet potential arises from the coupling of chemical and mechanical processes and is triggered by a constant, transverse to the ratchet, force. The current magnitude sensitively depends on the amplitude and the periodicity of the ratchet potential and the strength of the transverse force. Our results highlight the importance of thermodynamically consistent modeling of chemical reactions in active matter at the nanoscale and suggest new ways of controlling dynamics in such systems.

The fate of bromine during microwave-assisted pyrolysis of waste printed circuit boards

Bromine control is imperative for efficient treatment and products utilization during pyrolysis of waste printed circuit boards (WPCBs). This study investigated Br-species in products from microwave-assisted auger pyrolysis of WPCBs, and discussed synergetic evolution mechanisms, release kinetics and thermodynamics of Br-containing pollutants with different kinds of mineral species (alkaline earth, alkali, and transition metals). Results indicated that heavy Br-containing volatiles release (e.g., brominated phenols) was dominated at 320–520 °C. Brominated phenols released Br* to react with small-molecule groups to form light Br-containing products (e.g., HBr, CH3Br, and CH3CH2Br) at >520 °C. K2CO3 efficiently suppressed Br-containing pollutants emissions (∼50% reduction) and promoted bromine fixation in char (∼33.49% increase). With K2CO3 addition, bromine evolution mechanism is largely dehydrobromination and neutralization reactions when bromine bonds with aliphatic carbon with an adjacent aliphatic hydrogen. Negatively charged oxygen of K2CO3 attacks bromine and causes C-Br scission when bromine bonds with CH3* or aromatic carbon. The chemical reaction models (CRM3–CRM5) are best fitted with bromine evolution and the activation energy of WPCBs-KC reached the lowest (149.83–192.19 kJ/mol). Furthermore, bromine control strategy in WPCBs pyrolysis products toward environmental and economic sustainability were suggested, which created less environmental impact and maximum resource recovery.

Evaluation of Factors Affecting the MgO–C Refractory Lining Degradation in a Basic Oxygen Furnace

Identification of the factors influencing refractory lining wear and its residual thickness in the basic oxygen furnace (BOF) is a prerequisite for optimizing the steelmaking process. In this study, the factors that contribute significantly to the wear of the refractory lining in the most stressed areas of the banded lining (i.e., the trunnion ring area and slag line area) are identified. Knowledge of the rate at which a given factor acts on refractory wear is closely related to the development of technological procedures aimed at limiting its influence. This research evaluates the technological causes and describes the lining wear mechanism and the thermodynamic parameters of the reactions between the MgO–C metal, slag, and gunning material phases. In researching the topic, real operational data were processed using statistical methods and data analysis, which were supported by thermodynamic modeling of chemical reactions. The results show that the combination of technological factors, mechanical action of the raw materials, blowing and free oxygen in the metal, silicon from the pig iron, and slag viscosity have the greatest influence on the residual thickness of the MgO–C refractory lining in BOFs. Refractory gunning material consumption, its effect on campaign length, and the cost-effectiveness of repair work were also analyzed.

Speeding-up Hybrid Functional-Based Ab Initio Molecular Dynamics Using Multiple Time-stepping and Resonance-Free Thermostat.

Ab initio molecular dynamics (AIMD) based on density functional theory (DFT) has become a workhorse for studying the structure, dynamics, and reactions in condensed matter systems. Currently, AIMD simulations are primarily carried out at the level of generalized gradient approximation (GGA), which is at the second rung of DFT functionals in terms of accuracy. Hybrid DFT functionals, which form the fourth rung in the accuracy ladder, are not commonly used in AIMD simulations as the computational cost involved is 100 times or higher. To facilitate AIMD simulations with hybrid functionals, we propose here an approach using multiple time stepping with adaptively compressed exchange operator and resonance-free thermostat, that could speed up the calculations by ∼30 times or more for systems with a few hundred of atoms. We demonstrate that by achieving this significant speed up and making the compute time of hybrid functional-based AIMD simulations at par with that of GGA functionals, we are able to study several complex condensed matter systems and model chemical reactions in solution with hybrid functionals that were earlier unthinkable to be performed.

Effect of unsteady supersonic flow on detonation under different hot jet initiation conditions

To understand the actual operation of detonation engines, it is of great significance to simulate the detonation characteristics after being affected by unsteady supersonic flow. Adaptive mesh refinement method and single-step chemical reaction model were used for simulation calculations. The Navier–Stokes equations and hybrid sixth-order weighted essentially non-oscillatory centered difference scheme was adopted in this study. Three different amplitudes of disturbances (0.1, 0.2, and 0.3) and two hot jet injection times were analyzed. The results showed that a moderate disturbance can improve the stability of detonation wave under the ideal hot jet injection time. It allows detonation wave to stay in the combustion chamber for a longer time, which is beneficial for the release of thrust performance. Although the stability of detonation wave is significantly different between the low and high-amplitude disturbances, the residence time of detonation wave is close to the steady flow case under ideal initiation conditions. When the ignition time is insufficient, successful detonation can occur with low and medium-amplitude disturbances. However, the ignition delay was significantly prolonged with medium-amplitude disturbance. There was also greater instability, which is detrimental to the thrust release. When the inflow has a high-amplitude disturbance, the detonation wave fails to ignite due to insufficient energy.

Numerical investigation of oblique detonation waves on a truncated cone in hydrogen–air mixtures

Traditional methods of initiating oblique detonation waves (ODWs) using wedges and cones face a fundamental challenge in reconciling the need for rapid initiation with stable combustion, especially at low flight Mach numbers (Ma < 8). This study introduces an innovative initiation configuration involving a truncated cone. By utilizing Euler equations coupled with detailed hydrogen–air chemical reaction models, the wave dynamics induced by the truncated cone configuration are systematically explored. The findings reveal that the truncated cone configuration enables more rapid initiation of ODWs compared to conventional cones, while also preserving improved stability when contrasted with wedge. This behavior can be attributed to the planar flow characteristics in the post-shock field of truncated cone, generated by the upstream wedge-shaped shock, and the Taylor–Maccoll flow characteristics, caused by the downstream conical shock. Furthermore, the study delves into the initiation and morphological changes with respect to the inner radius and angle of the truncated cone. As inner radii or truncated cone angle increase, three initiation wave systems emerge: stable, oscillatory, and detached modes. Analysis of the dynamic variations in pressure and velocity within the induction zone highlights that the upstream oscillation originates from the flow velocity in the induction zone falling below the local Chapman–Jouguet velocity of normal detonation wave (NDW). However, the upstream region of the truncated cone exhibits more pronounced expansion effects, leading to momentum loss, and subsequently, the weakening and even vanishing of the NDW. This prompts the downstream oscillation of the initiation structure, instigating a cyclic oscillation pattern.

Effect of dilution gas on the distribution characteristics of capacitively coupled plasma by comparing SiH4/He and SiH4/Ar

In this study, we focus on the difference in the spatial distribution of the plasma parameters between SiH4/He capacitively coupled plasma (CCP) and SiH4/Ar CCP. The SiH4/He mixture is modeled using the chemical reactions that were successfully derived in our previous studies. The chemical reaction model of the SiH4/Ar mixture built in this study is based on the detailed set of chemical reactions in Ar. The spatial distribution of the plasma parameters is examined with the aid of a 2D fluid model. The electron and radical densities of SiH4/Ar CCP are higher than those of SiH4/He CCP. In addition, dilution with Ar results in more uniform reaction rates, which leads to a more uniform deposition profile. Because helium requires higher threshold energies for excitation and ionization, dilution with He had little effect on the precursor production. As a result, the concentration of Si2H6 observed in the inter-electrode region when using Ar for dilution was observed to be about ten times higher than the concentration of Si2H6 observed for He. This high concentration played a large role in influencing the formation of important radicals that determine the deposition rate as well as the difference in the deposition rate profile between Ar and He as diluents. The higher concentration of Si2H6 when using Ar means that the production rate of Si2H5 is higher in Ar. An examination of the effect of the dilution gas on the deposition rate profile indicated that the deposition rate profile with Ar is 100% more uniform and the deposition rate nearly 87% higher than for dilution with He.

Reactor design for thin film catalyst activity characterization

Thin film-based systems hold enormous potential for atomic-scale control of catalysts and their supports. So far, there is only limited reactor design with dedicated characterization methods for such catalyst systems. Thus, this work focuses on designing and prototyping a tailored reactor to characterize thin films catalysts. Herein, an electrically driven reactor and its virtual replica are designed together in a way to measure and describe the reaction processes over thin film catalysts. The developed numerical model comprised of coupled fluid-, thermal-, and chemical reaction models in combination with the well-defined geometry of the prototype allows a fast and comprehensive testing of novel catalysts systems, which is illustrated by acetylene hydrogenation with a palladium based thin film catalyst on silicon substrates as first model reaction. A power law model was found to be most appropriate to describe the kinetics of the corresponding reaction. It is shown that the codesigned virtual replica offers a strong platform for comprehensive testing and fairly accurate description of thin film catalysis.

Hopf bifurcation and periodic solutions in a coupled Brusselator model of chemical reactions

Hopf bifurcation and periodic solutions in a coupled Brusselator model of chemical reactions

Single‐molecule fluorescence microscopy for imaging chemical reactions: Recent progress and future opportunities for advancing polymer systems

AbstractSingle‐molecule fluorescence (smFL) imaging techniques have evolved greatly over the past two decades to encompass the ability to monitor chemical reactions, providing unique advantages of non‐invasive sample preparation and characterization, labeling specificity, and high spatial and temporal resolutions. This work summarizes the recent progress in this important area by first providing a brief overview of different smFL techniques, including their common optical setups and working principles. We then introduce recent developments of smFL to characterize various model chemical reaction systems, such as biochemical synthesis, catalyzed systems, and nanomaterial assembly. Furthermore, several representative areas of using smFL to understand polymer reactions are discussed, including understanding interfacial phenomenon and polymerization kinetics, as well as characterizing electrochemical reactions. We also highlight the outlook of this exciting field and potential opportunities for further development and application of smFL to enable advances in polymer chemistry and physics.

Complex dynamical analysis of fractional differences Willamowski–Röossler chemical reaction model in time-scale analysis

Real mechanisms that are advancing in a complex network exhibit chaotic behaviour. This behaviour is crucial in physical and complex systems involving numerical modelling frameworks because it essentially determines the framework’s evolutionary process. In this context, notwithstanding its difficulty, the potential of intentional oversight of the phenomenon has feasible effects; this is why theoretical approaches are advantageous in such scenarios. This study investigates the functioning of a Willamowski–Rössler (W–R) mechanism, including the synchronization of two minimal W–R structures depending on the responsive suggestion technique for regulation, with the purpose of achieving chaos influence in chemical interactions. We investigate the reliability of the steady state at various fractional order (FO) factors. Employing maximum Lyapunov exponents (MLEs), phase depictions, bifurcation schematics, the 0–1 evaluation and approximated entropy, it is demonstrated that adjusting the FOs causes a system’s behavioural pattern to undergo a transition from steady to chaotic. In addition to demonstrating that the proposed scheme fits chaotically under certain circumstances, simulation outcomes demonstrate that mathematical modelling is used to illustrate theoretical debates. To verify that the community detects chaos, the MLE and bifurcation illustrations, whose hallmark factors are plotted, display erratic behaviour while effectively attempting to control the chaos.

Large-eddy simulation of a lean-premixed hydrogen flame in a low-swirl combustor under combustion instability

Large-eddy simulation (LES) of a lean-premixed hydrogen turbulent jet flame with combustion instability (CI) in a low-swirl combustor (LSC) is performed by employing a dynamically thickened flame model with a detailed chemical reaction model with 9 chemical species and 20 reactions, and the LES validity and the CI characteristics are investigated in detail. The results show that the present LES can accurately reproduce the experimentally observed characteristics of the CI such as intensity, frequency, sporadic decay of pressure oscillations, and a flame–flow interaction inducing the periodic transitions of an inverted conical flame structure and a flat flame structure in the LSC. The sporadic decay of pressure oscillations and the flame–flow interaction are caused by the temporal decoupling of pressure and heat release rate and the periodic outward and inward deflections of the inflow, which is associated with the flow behavior in the upstream injector channel, respectively.

Multi-fidelity neural network for uncertainty quantification of chemical reaction models

Surrogate models are often used to accelerate the uncertainty quantification (UQ) of chemical kinetic models. However, the construction of surrogate models usually requires the repetitive generation of high-fidelity input-output samples, which is time-consuming. In this work, we utilize a multi-fidelity neural network to speed up the surrogate model construction, yielding a multi-fidelity neural network-based surrogate model (MFNNSM). MFNNSM consists of two separate neural networks. The first neural network learns from high and low-fidelity samples, and then generates samples to train the second neural network for the subsequent UQ analysis. Based on the fact that the uncertainty similarity (sensitivity-based similarity) does exist between the predictions from the reduced and detailed combustion kinetics models, or between the predictions under different conditions, MFNNSM can use reduced model predictions as low-fidelity samples to generate detailed model predictions as the high-fidelity samples, or can transfer samples across different simulations conditions. To demonstrate the MFNNSM method, the ignition delay time (IDT) and laminar flame velocity (LFV) of methanol and n-decane are chosen as model prediction targets for UQ analysis. The results show that MFNNSM can achieve acceleration factors up to 6, by utilizing reduced model samples to generate detailed model samples under the same conditions, and when reusing the reduced model samples under different conditions, the acceleration factor can increase to 10. In addition, the influences of the relative error of the reduced models and the uncertainty similarity coefficients between combustion conditions on the performance of MFNNSM are further discussed, providing the guidance for future applications of MFNNSM.

Codimension-One and Codimension-Two Bifurcations of a Fractional-Order Cubic Autocatalator Chemical Reaction System

This article delves into an investigation of the dynamic behavior exhibited by a fractional order cubic autocatalator chemical reaction model. Specifically, our focus lies on exploring codimension-one bifurcations associated with period-doubling bifurcation and Neimark-Sacker bifurcation. Additionally, we undertake an analysis of codimension-two bifurcations linked to resonances of the types 1:2, 1:3, and 1:4. To achieve these outcomes, we employ the normal form method and bifurcation theory. The results are presented through comprehensive numerical simulations, encompassing visual representations such as phase portraits, two-parameter bifurcation diagrams, and maximum Lyapunov exponents diagrams. These simulations aptly examine the behavior of a system governed by two distinct parameters that vary within a three-dimensional space. Furthermore, the simulations effectively illustrate the theoretical findings while providing valuable insights into the underlying dynamics.