Rates Of Elementary Reactions Research Articles

Exploring the ring-opening metathesis polymerization process by kinetic Monte Carlo simulation

Investigating the kinetics of polymerization reactions is a powerful tool to obtain information for the engineering design of such processes. It provides insights into how the relative rates of elementary reactions which influence both the kinetics of the reactions and thus characteristics of the products as well, particularly when the reaction parameters of these reactions are unknown. Among polymerization processes, ring-opening metathesis polymerization (ROMP) has gained broad academic and industrial interest, due to its mild conditions to obtain a wide range of polymer products. In this study, kinetic Monte Carlo simulation was applied to reveal the effect of the elementary reactions of ROMP on the kinetics and product distribution. Both the propagation and the cross-metathesis reactions were considered, with the latter leading to the formation of various types of macrospecies whose population levels were also monitored. Relevant tendencies were observed regarding how the variations in the reaction parameters of the elementary reactions of this polymerization process, such as reaction probabilities, monomer addition method, catalyst-to-monomer ratio, and reaction time, affect the kinetics of the polymerization process and the product distributions. These variations also influence the key macromolecular parameters of the resulting polymeric materials, including chain length distribution (CLD), population levels, and polymer functionalities. The results of this study indicate that this simulation technique is a valuable tool for mapping the tailoring possibilities of modifying the reaction parameters of ROMP to achieve desired properties. These properties include number average molecular weight, polydispersity, chain end functionality, and macrocycle-free products.

Mechanism and kinetics study of the chemically initiated oxidative polymerization of hexafluoropropylene

AbstractChemically initiated oxidative polymerization stands out as the most suitable method for the large‐scale and controllable synthesis of perfluoropolyether (PFPE). However, the mechanism and related reaction kinetics of this synthesis reaction remain elusive. In this study, PFPE was synthesized through the copolymerization of hexafluoropropylene and oxygen, initiated by fluorine. Subsequently, the synthesis mechanism of this chemically initiated oxidative polymerization was first explored using density functional theory. Simulation results yielded a comprehensive reaction network of the synthesis process, including chain initiation, propagation, decomposition, transfer, and termination. Meanwhile, a detailed kinetic model was constructed based on theoretical reaction rates of relevant elementary reactions. The effects of reaction operating conditions on the molecular weight of PFPE were experimentally investigated, with results in good agreement with the kinetic model. This work stablishes a solid foundation for optimizing and controlling the PFPE synthesis process.

Experimental and chemical kinetic analysis to evaluate CO2 dilution on laminar combustion characteristics of C2H5OH/air blends under normal pressure

Based on a constant volume combustion system, the effect of dilution ratio changes on the laminar combustion characteristics of C2H5OH/air mixture was studied under an initial pressure of 1 bar, initial temperatures of 370 K, 400 K, 450 K, and equivalence ratios of 0.7–1.4. A chemical kinetic mechanism for ethanol-carbon dioxide was established, and the combined physical and chemical effects of carbon dioxide were separated. An independent parameter control method was proposed, introducing virtual species FN2, ICO2, FCO2, and KCO2, to isolate the dilution effect, thermal effect, direct reaction effect, third-body effect, and transport effect. Simulation analysis using the modified chemical kinetic mechanism revealed that various impacts of CO2 reduce the peak progress rate and sensitivity coefficient of key elementary reactions. Furthermore, the dilution effect of CO2 has the greatest influence on the sensitivity coefficients and net progress rates of important elementary reactions. Based on the results of the chemical kinetic simulations, a new global reaction pathway analysis method was created, overcoming the limitations of the Chemkin-pro method. The decomposition pathway of C2H5OH throughout the combustion process was calculated as C2H5OH → SC2H4OH → CH3CHO → CH3CO → CH3 → CH2O → HCO → CO → CO2. Changes in initial temperature and dilution ratio do not alter the main decomposition pathway of C2H5OH. Detailed chemical kinetics and free radical behavior analysis indicate that the LBV of the C2H5OH/CO2/air blends has a linear correlation with [H + O + OH]max.

Diffusion-Limited Kinetics in Reactive Systems.

A proper representation of chemical kinetics is vital to understanding, modeling, and optimizing many important chemical processes. In liquid and surface phases, where diffusion is slow, the rate at which the reactants diffuse together limits the overall rate of many elementary reactions. Commonly, the textbook Smoluchowski theory is utilized to estimate effective rate coefficients in the liquid phase. On surfaces, modelers commonly resort to much more complex and expensive Kinetic Monte Carlo (KMC) simulations. Here, we extend the Smoluchowski model to allow the diffusing species to undergo chemical reactions and derive analytical formulas for the diffusion-limited rate coefficients for 3D, 2D, and 2D/3D interface cases. With these equations, we are able to demonstrate that when species react faster than they diffuse they can react orders of magnitude faster than predicted by Smoluchowski theory, through what we term "the reactive transport effect". We validate the derived steady-state equations against particle Monte Carlo (PMC) simulations, KMC simulations, and non-steady-state solutions. Furthermore, using PMC and KMC simulations, we propose corrections that agree with all limits and the computed data for the 2D and 2D/3D interface steady-state equations, accounting for unique limitations in the associated derived equations. Additionally, we derive equations to handle couplings between diffusion-limited rate coefficients in reaction networks. We believe these equations should make it possible to run much more accurate mean-field simulations of liquids, surfaces, and liquid-surface interfaces accounting for diffusion limitations and the reactive transport effect.

Fire-Extinguishing Dibromomethane Mixtures with Fluorinated Alkanes for Fire and Explosion Protection of Oil and Gas Industry Facilities

The high fire hazard level is specific to the oil and gas industry due to the circulation of large volumes of flammable gases and liquids. To ensure fire protection at the oil and gas industry facilities, automated gaseous fire extinguishing is widely used. The main fire-extinguishing agents in automated gaseous fire-extinguishing systems are refrigerants HFC 23, 125, 227еа, FC 318c, and fluorinated ketone FK 5-1-12. Upon the adoption of the international agreements on combating global warming, most fluorinated gaseous fire-extinguishing agents currently used for fire extinguishing fell under restrictions. The article indicates the importance of refrigerants HFC 23, 125, 227еа, and FC 318c, whose production volume must be reduced by 85 % by 2036 to ensure the required level of fire and explosion protection of oil and gas industry facilities. A method to reduce the volumes of used fluorinated alkanes by producing highly efficient fire-extinguishing mixtures, one of the components of which is an agent of high global warming potential (GWP) and the other is a chemical compound with a short atmospheric lifetime, has been proposed. Dibromomethane, which fully meets the latest environmental requirements, is to be considered a short-lived component. Based on the well-known kinetic data, the rates of elementary chemical reactions generated in the flame of the methane-oxygen mixture when contacting with refrigerants HFC 23, 227еа, and dibromomethane, have been calculated and compared. The efficiency of using dibromomethane to increase the fire-extinguishing efficiency of refrigerants HFC 23 and 227еа has been substantiated. An experimental determination of the minimum fire-extinguishing efficiency of the generated mixed compositions is conducted to confirm the correctness of theoretical calculations. The obtained mixed gaseous fire-extinguishing agents enable the reduction of the volume of high global warming potential refrigerants by 1.5–2 times. It has been also demonstrated that the obtained mixed compositions have no toxic impact on a human.

Characteristics of Explosion Hazards in Methane–Air Mixtures Diluted by Hydrogen

The combustion efficiency of methane can be effectively enhanced with the occurrence of hydrogen. However, the combustion characteristic of premixed methane/hydrogen/air is not fully understood. In this study, the effect of the amount of hydrogen addition on the explosion risk of premixed CH4/air combustion was fully investigated through experiments and simulations. The explosion overpressure of premixed CH4/air combustion with various hydrogen additions was measured in a standard 20 L spherical closed vessel. Meanwhile, the microscopic flame structures for the same cases were simulated using 2022 Chemkin-Pro software. The results showed that hydrogen could increase the explosion risks of premixed CH4/air combustion. The rate of key elementary reactions R38: H + O2 <=> O + OH and R84: OH + H2 <=> H + H2O in the system could be accelerated by hydrogen. The peak explosion overpressure in the closed chamber is boosted and the arrival time of peak overpressure rise rate is shortened, which raises the danger. Especially under lean and rich combustion conditions, hydrogen could potentially lead to more dangerous situations. With the increase in hydrogen concentration, the reaction rate of key elementary reactions accelerates faster, the peak explosion overpressure increases more, and the peak overpressure rise rate arrives earlier.

Molecular Modeling of Supercritical Processes and the Lattice—Gas Model

The existing possibilities for modeling the kinetics of supercritical processes at the molecular level are considered from the point of view that the Second Law of thermodynamics must be fulfilled. The only approach that ensures the fulfillment of the Second Law of thermodynamics is the molecular theory based on the discrete–continuous lattice gas model. Expressions for the rates of the elementary stage on its basis give a self-consistent description of the equilibrium states of the mixtures under consideration. The common usage today of ideal kinetic models in SC processes in modeling industrial chemistry contradicts the non-ideal equation of states. The used molecular theory is the theory of absolute reaction rates for non-ideal reaction systems, which takes into account intermolecular interactions that change the effective activation energies of elementary stages. This allows the theory to describe the rates of elementary stages of chemical transformations and molecular transport at arbitrary temperatures and reagent densities in different phases. The application of this theory in a wide range of state parameters (pressure and temperature) is considered when calculating the rates of elementary bimolecular reactions and dissipative coefficients under supercritical conditions. Generalized dependencies are calculated within the framework of the law of the corresponding states for the coefficients of compressibility, shear viscosity, and thermal conductivity of pure substances, and for the coefficients of compressibility, self- and mutual diffusion, and shear viscosity of binary mixtures. The effect of density and temperature on the rates of elementary stages under supercritical conditions has been demonstrated for a reaction’s effective energies of activation, diffusion and share viscosity coefficients, and equilibrium constants of adsorption. Differences between models with effective parameters and the prospects for developing them by allowing for differences in size and contributions from the vibrational motions of components are described.

Molecular simulation of polymer gels synthesized by free radical copolymerization: Effects of concentrations and reaction rates on structure and mechanical properties

The effects of polymerization concentrations and elementary reaction rates on the network structure and mechanical properties of gels synthesized by free radical copolymerization of monomers and cross-linkers are studied by a coarse-grained molecular dynamics simulation. The shear modulus, the number of elastically effective chains, and the number of trapped entanglements are calculated with varying the concentrations. The results reveal that the experimentally reported high cross-linking efficiency of the gels formed at high monomer concentrations and low cross-linker concentrations is due to the large number of trapped entanglements. The molecular mechanisms of changes in the network structure due to changes in the concentrations are elucidated by analyzing the detailed structure of network strands connecting adjacent cross-linking points. The results with systematically varying the elementary reaction rates indicate that the decrease in the propagation rate suppresses the formation of cyclic structures and reduces the influence of the trapped entanglements, i.e., improves the structural uniformity of the gels.

Numerical analysis and flamelet modeling of NO[formula omitted] formation in a thermodiffusively unstable hydrogen flame

In a thermodiffusively unstable premixed hydrogen flame, cellular flame structures exist due to the strong differential diffusion of hydrogen featuring wide ranges of curvature and strain rate. NOx formation pathways are directly affected by the complex cellular flame structures as different species have different sensitivities to differential diffusion effects and curvature. In this work, the NOx formation characteristics of a thermodiffusively unstable laminar premixed hydrogen flame are investigated. At first, the NOx formation characteristics in the tangential and normal directions of the flame front are analyzed, focusing on the effects of curvature. Then, reaction path analyses are conducted to identify the relevant pathways and elementary reactions that pre-dominantly contribute to the formation of NOx pollutants. To investigate the effects of curvature on NOx formation, the reaction fluxes and the elementary reaction rates are calculated by conditioning on the curvature value. Finally, the performance of a flamelet model in predicting the NOx species in the thermodiffusively unstable premixed hydrogen flame is evaluated through an a priori analysis. The results show that curvature directly affects NOx formation, particularly the dominant NNH and N2O reaction pathways while the contribution of the thermal-NO pathway is found to be overall negligible. The NOx species are mainly formed in positively-curved flame segments where the flamelet model gives good predictions, while discrepancies with respect to the model exist in the negatively-curved flame regions. The reason for this is clarified through a chemical timescale analysis and a conditional reaction path analysis.

In-depth mechanistic and kinetic investigation of sonochemically mediated atom transfer radical polymerization using modeling approach

Mechano/sonochemically mediated reversible deactivation radical polymerization has attracted great attention because of the novel electron transfer regulation process and high-efficient process intensification on mass transfer. Herein, a multi-scale modeling strategy combining quantum chemical calculation and kinetic modeling was developed for sonochemically induced electron transfer controlled atom transfer radical polymerization (SET-ATRP) to study the complicated SET process and its effects on polymerization. At the molecular scale, density functional theory (DFT) calculations were used to acquire the electron characteristic and structure–reactivity of the reactants, intermediates and products during SET process, which provides guideline to figure out the underlying mechanism. Results showed that DMSO•• generated under ultrasonication could react with free Me6TREN to induce electron transfer for the reduction of CuIIBr/L+ to produce CuI/L+, which is the key step for a successful polymerization. The corresponding elementary reaction rate coefficients were calculated by thermodynamic formulae combining transition state theory and Marcus theory. At the micro-scale, kinetic modeling based on method of moment was established to account for the role of SET process in regulating polymerization. Good agreements between the simulation results and experimental data confirmed the reliability of the as-developed multi-scale modeling strategy. More Me6TREN and CuIIBr/L+ resulted in more electron transfer and faster polymerization rate. This work provides an in-depth mechanism insights and kinetic understanding for SET-ATRP, which has a promising potential to promote its progress of application.

The mechanism characterizations of methane steam reforming under coupling condition of temperature and ratio of steam to carbon

To elucidate the coupling effects of temperature and ratio of steam to carbon on the methane steam reforming process, the characterizations of methane steam reforming at different temperature and ratio of steam to carbon in term of distribution of H2 and CO, and the elementary reaction rate were investigated. Meanwhile, the formation mechanisms of H2 and CO via sensitivity analysis and reaction path analysis were obtained. The results showed that the coupling effects of temperature and ratio of steam to carbon on the methane steam reforming were higher than that of individual factor. The effects of temperature on the methane steam reforming were higher than that of the ratio of steam to carbon. The adsorption and desorption reaction of CH4 on the surface of Ni-based catalyst had the most obvious effect on the sensitivity of H2, CH4 and CO. Besides, the effects of adsorption and desorption reaction of H2O on the sensitivity of H2 were higher than that of CH4 and CO. Hydrogen was generated by the desorption reaction of H(s) in the adsorbed state and from three generating paths: a) CH4(s) dissociated directly or reacted with O(s) to form H(s); b) The dissociation reaction of H2O(s) produced H(s); c) OH(s) dissociated directly or reacted with C(s) to form H(s). Carbon monoxide was generated from single path: CH4(s)→CH3(s)→CH2(s)→CH(s)→C(s)→CO(s)→CO(g).

The combustion performance of sustainable aviation fuel with hydrogen addition

Hydrogen (H2) aircraft have been proposed for the “Fly Net Zero” target. The combination of jet fuel and H2 was offered to successfully operate the jet engine with H2 without further combustor modification. The current work used hydro-processed renewable jet fuel (HRJ) and experimentally investigated its combustion properties and H2 addition in the constant volume combustion chamber (CVCC). Experiments were performed at the initial temperature (Tini) from 600 K to 818 K, initial pressure (Pini) 10, 15 bar and equivalence ratio (φ) = 0.5. Normal spray ignition (SPI) and direct injection spark ignition (DISI) were studied. Overall, HRJ has a shorter ignition delay (ID) for SPI. At 600 K, adding 10% and 20% H2 to HRJ increased ID to 12.68% and 38.46%, respectively. As Tini rose to 725 K, increment in ID was shortened to 5.96% and 20.47% with 10% and 20% H2 addition, respectively. For DISI, at 600 K, adding 10% and 20% H2 to HRJ shortens ID to 3.56% and 4.92%, respectively. When comparing the ID of DISI with the SPI, ID was shortened to 84.64% and 91.77% for 10% and 20% H2 addition, respectively. Emission results showed that adding H2 reduced CO2, while NOx emissions were increased. Ansys Chemkin-Pro was used to run numerical simulations of a zero-dimensional (0-D) closed homogeneous batch reactor model (CHBR). An existing HRJ mechanism was adopted, and H2 elementary reaction rate constant factors were updated for better model predictions. The updated model was under prediction with the experimental ID periods. The simulation results showed that the reaction H2+OH = H + H2O is the primary cause for consuming OH radicals with H2 addition, leading to an increase in fuel ID. At higher temperatures, two major reactions (HO2 + H2 = H2O2 + H, and HO2+HO2 = H2O2 + O2) followed by H2O2 = OH + OH are accountable for reproducing OH radicals. Thus, the fuel ID was shorter.

Kinetics of PTSA-Catalysed Polycondensation of Citric Acid with 1,3-Propanediol

Recent years have seen the intensive development of novel therapies based on stem cells and advanced materials. Among the latter, polymers, especially polyesters, occupy a special place and are being investigated for use as substrates for cell differentiation and culture. Increasing application requirements are driving demand for such materials. This study aims to obtain a new material with potential biomedical applications, poly(1,3-propanediol citrate). A spectral analysis of the obtained product was carried out. The reaction kinetics of the polycondensation of citric acid and 1,3-propanediol in the presence of a catalyst, p-toluenesulphonic acid (PTSA), are described. The basis for determining the polycondensation kinetics was the assumption of non-equivalence of the carboxyl groups in citric acid. Elementary reaction rate constants and activation energy values were determined. Based on the data obtained, the course of the gelation points of the reaction mixture was estimated in its dependence on the temperature and reaction time. Kinetic research will facilitate the scale-up of the process.

Reaction kinetics for high pressure hydrogen oxy-combustion in the presence of high levels of H2O and CO2

Novel shock tube experimental ignition delay time (IDT) data are provided to delineate the impact of high concentrations (45% by mole) of H2O and CO2 on IDTs of stoichiometric 4% H2. Ignition delay experiments were conducted using a high- and a low-pressure shock tube facility. High-pressure experiments were performed at pressures of 37-43.8 bar and temperatures of 1084-1242 K in four different bath gases, namely: Ar, 45%H2O/Ar, 30%H2O/15%CO2/Ar, and 45%CO2/Ar. Low-pressure experiments were conducted at 2.1-2.7 bar and 926-1198 K in Ar and 45%CO2/Ar bath gases. Impacts of non-ideal ignition phenomena that may occur in the presence of large amounts of H2O and CO2 were also analyzed. A minimally-tuned H2/CO reaction mechanism, CanMECH 1.0, targeting high-pressure combustion in the presence of large concentrations of H2O and CO2 is presented. The mechanism is constructed from unadjusted kinetic rate parameters from theoretical / experimental elementary reaction rate determinations. The only adjusted rate in CanMECH 1.0 is the much disputed Ar-specific low-pressure-limit pre-exponential factor of H + O2 (+Ar) = HO2 (+Ar) within the uncertainty bounds of the source rate. Validity of CanMECH 1.0 is confirmed against shock tube IDT data of this work, as well as selected H2 and H2/CO shock tube IDT datasets from literature. The performance of the model is compared to Keromnes et al. model (Combust. Flame 160 (2013) 995-1011). CanMECH 1.0 outperformed Keromnes et al. for 16 datasets out of 26 and exhibited a similar performance for another two. In particular, CanMECH 1.0 outperformed Keromnes et al. in predicting shock tube IDTs for H2O- and CO2-laden reactive mixtures, as well as all IDT data at pressures of 17-43.8 bar, which are of distinct value to pressurized oxy-fuel combustion applications relevant to this work.

Comprehensive Study of HCN: Potential Energy Surfaces, State-to-State Kinetics, and Master Equation Analysis.

Understanding the kinetics of the HCN system is critical to several disciplines in science and engineering, including interstellar chemistry, atmospheric reentry, and combustion, to name a few. This paper constructs a rovibrational state-specific kinetic mechanism for the HCN system, leveraging electronic structure calculations, classical scattering dynamics, and state-to-state kinetics. To this aim, three accurate potential energy surfaces (PESs), 1A', 3A', and 3A″, are constructed using multireference configuration interaction (MRCI) calculations for a comprehensive arrangement of the nuclei. Quasi-classical scattering calculations provide elementary reaction rate constants resulting from the interaction between the CN, CH, and NH molecules with H, N, and C atoms, respectively. The rovibrational collisional model developed comprises 50 million bound-bound and free-bound collisional processes. This model is used to study the dynamics of energy transfer and dissociation in an isochoric and isothermal chemical reactor via the solution of the master equation for a wide temperature range from 1000 to 10,000 K. This study unravels the dynamics of dissociation of the molecules in the HCN system, which the PESs primarily control via the formation of short-lived intermediates that shortcut the dissociation pathway. The exchange processes in CH and NH enhance the dissociation by over 80%. The importance of exchange processes is also highlighted in comparing the quasi-steady state and thermal dissociation rates with state-of-the-art rate models and experimental fits.

Numerical study on combustion and emission characteristics of a spark-ignition ammonia engine added with hydrogen-rich gas from exhaust-fuel reforming

A numerical study was performed for the combustion process of a spark-ignition engine fueled with ammonia to investigate the effects of hydrogen-rich reformate addition on the combustion and emission characteristics of the engine. For the combustion characteristics, the results show that the in-cylinder pressure is increased and the combustion duration is shortened with the addition of hydrogen-rich reformate. Moreover, when blending 10.0% of the reformate by volume, the combustion efficiency and thermal efficiency of the engine at stoichiometric conditions are improved to 96.3% and 43.6%, respectively. However, increasing the reformate content in the mixture to 12.5% leads to negative work during the compression stroke and a reduction in the power. For the emission characteristics, it is found that the NOx emissions can meet the IMO Tier III limit at rich-burn conditions for all the reformate blending ratios (Rre). The NH3 and N2O emissions decrease monotonically with the increase of Rre. In addition, the chemical kinetic analyses demonstrate that the concentration of H and OH radicals increase with the addition of hydrogen-rich reformate thus accelerating the elementary reaction rates in the NH3 consumption pathway. Consequently, the combustion phase is advanced and the unburned NH3 emissions are reduced with the increase of Rre. The present study concludes that 7.5% – 10.0% is the recommended blending ratio of hydrogen-rich reformate for enhanced combustion with low NOx and NH3 emissions in ammonia-fueled engines.

Methanol oxidation up to 100 atm in a supercritical pressure jet-stirred reactor

Methanol (CH3OH) has attracted considerable attention as a renewable fuel or fuel additive with low greenhouse gas emissions. Methanol oxidation was studied using a recently developed supercritical pressure jet-stirred reactor (SP-JSR) at pressures of 10 and 100 atm, at temperatures from 550 to 950 K, and at equivalence ratios of 0.1, 1.0, and 9.0 in experiments and simulations. The experimental results show that the onset temperature of CH3OH oxidation at 100 atm is around 700 K, which is more than 100 K lower than the onset at 10 atm and this trend cannot be predicted by the existing kinetics models. Furthermore, a negative temperature coefficient (NTC) behavior was clearly observed at 100 atm at fuel rich conditions for methanol for the first time. To understand the observed temperature shift in the reactivity and the NTC effect, we updated some key elementary reaction rates of relevance to high pressure CH3OH oxidation from the literature and added some new low-temperature reaction pathways such as CH2O + HO2 = HOCH2O2 (RO2), RO2 + RO2 = HOCH2O (RO) + HOCH2O (RO) + O2, and CH3OH + RO2 = CH2OH + HOCH2O2H (ROOH). Although the model with these updates improves the prediction somewhat for the experimental data at 100 atm and reproduces well high-temperature ignition delay times and laminar flame speed data in the literature, discrepancies still exist for some aspects of the 100 atm low-temperature oxidation data. In addition, it was found that the pressure-dependent HO2 chemistry shifts to lower temperature as the pressure increases such that the NTC effect at fuel-lean conditions is suppressed. Therefore, as shown in the experiments, the NTC phenomenon was only observed at the fuel-rich condition where fuel radicals are abundant and the HO2 chemistry at high pressure is weakened by the lack of oxygen resulting in comparatively little HO2 formation.

Study on Chemical Kinetics Mechanism of Ignition Characteristics of Dimethyl Ether Blended with Small Molecular Alkanes

Dimethyl ether (DME)/C1-C4 alkane mixtures are ideal fuel for homogeneous charge compression ignition (HCCI) engines. The comparison of ignition delay and multi-stage ignition for DME/C1-C4 alkane mixtures can provide theoretical guidance for expanding the load range and controlling the ignition time of DME HCCI engines. However, the interaction mechanism between DME and C1-C4 alkane under engine relevant high-pressure and low-temperature conditions remains to be revealed, especially the comprehensive comparison of the negative temperature coefficient (NTC) and multi-stage ignition characteristic. Therefore, the CHEMKIN-PRO software is used to calculate the ignition delay process of DME/C1-C4 alkane mixtures (50%/50%) at different compressed temperatures (600–2000 K), pressures (20–50 bar), and equivalence ratios (0.5–2.0) and the multi-stage ignition process of DME/C1-C4 alkane mixtures (50%/50%) over the temperature of 650 K, pressure of 20 bar, and equivalence ratio range of 0.3–0.5. The results show that the ignition delay of the mixtures exhibits a typical NTC characteristic, which is more prominent at a low equivalence ratio and pressure range. The initial temperature of DME/CH4 mixtures of the NTC region is the highest. In the NTC region, the ignition delay DME/CH4 mixtures are the shortest, whereas DME/C3H8 mixtures are the longest. At low-temperature and lean-burn conditions, DME/C1-C4 alkane mixtures exhibit a distinct three-stage ignition characteristic. The time corresponding to heat release rate and pressure peak is the shortest for DME/CH4 mixtures, and it is the longest for DME/C3H8 mixtures. Kinetic analysis indicates that small molecular alkane competes with the OH radical produced in the oxidation process of DME, which inhibits the oxidation of DME and promotes the oxidation of small molecular alkane. The concentration of active radicals and the OH radical production rate of elementary reactions are the highest for DME/CH4 mixtures, and they are the lowest for DME/C3H8 mixtures.

A Closed Form Model for Molecular Ratchet-Type Chemically Induced Dimerization Modules.

Chemical-induced dimerization (CID) modules enable users to implement ligand-controlled cellular and biochemical functions for a number of problems in basic and applied biology. A special class of CID modules occur naturally in plants and involve a hormone receptor that binds a hormone, triggering a conformational change in the receptor that enables recognition by a second binding protein. Two recent reports show that such hormone receptors can be engineered to sense dozens of structurally diverse compounds. As a closed form model for molecular ratchets would be of immense utility in forward engineering of biological systems, here we have developed a closed form model for these distinct CID modules. These modules, which we call molecular ratchets, are distinct from more common CID modules called molecular glues in that they engage in saturable binding kinetics and are characterized well by a Hill equation. A defining characteristic of molecular ratchets is that the sensitivity of the response can be tuned by increasing the molar ratio of the hormone receptor to the binding protein. Thus, the same molecular ratchet can have a pico- or micromolar EC50 depending on the concentration of the different receptor and binding proteins. Closed form models are derived for a base elementary reaction rate model, for ligand-independent complexation of the receptor and binding protein, and for homodimerization of the hormone receptor. Useful governing equations for a variety of in vitro and in vivo applications are derived, including enzyme-linked immunosorbent assay-like microplate assays, transcriptional activation in prokaryotes and eukaryotes, and ligand-induced split protein complementation.

Single-step rapid trench filling with poly-Si using concentration dependence of deposition rate under a SiHCl3–H2 system

A single-step rapid trench filling with poly-Si was demonstrated using SiHCl3, which advantageously has a high decomposition temperature and contains an etching gas. Through elementary reaction rate analysis, we found a unique condition in which the film deposition rate decreased as the source concentration increased. This negative correlation between the concentration and deposition rate is referred to in this study as NCCR. Through cross-sectional observation, we confirmed that under the NCCR condition, the trench was filled without clogging at a rate that was 60 times faster than conventional low-pressure chemical vapor deposition.