Kinetic Reaction Mechanism Research Articles

Bi@C nanosphere anode with Na+‐ether‐solvent cointercalation behavior to achieve fast sodium storage under extreme low temperatures

AbstractThe low ion transport is a major obstacle for low‐temperature (LT) sodium‐ion batteries (SIBs). Herein, a core‐shell structure of bismuth (Bi) nanospheres coated with carbon (Bi@C) is constructed by utilizing a novel Bi‐based complex (1,4,5,8‐naphthalenetetracarboxylic dianhydride as the ligand) as the precursor, which provides an effective template to fabricate Bi‐based anodes. At −40°C, the Bi@C anode achieves a high capacity, which is equivalent to 96% of that at 25°C, benefitting from the core‐shell nanostructured engineering and Na+‐ether‐solvent cointercalation process. The special Na+‐diglyme cointercalation behavior may effectively reduce the activation energy and accelerate the Na+ diffusion kinetics, enabling the excellent low‐temperature performance of the Bi@C electrode. As expected, the fabricated Na3V2(PO4)3//Bi@C full‐cell delivers impressive rechargeability in the ether‐based electrolyte at −40°C. Density functional theory calculations and electrochemical tests also reveal the fast reaction kinetic mechanism at LT, thanks to a much lower diffusion energy barrier (167 meV) and a lower reaction activation energy (32.2 kJ mol−1) of Bi@C anode in comparison with that of bulk Bi. This work provides a rational design of Bi‐based electrodes for rechargeable SIBs under extreme conditions.

Kinetic investigation of the aldol condensation of n-butanal on mesoporous and macro-mesoporous heterogeneous catalysts

The kinetics of the aldol condensation of n-butanal on modified mesoporous and macro-mesoporous heterogeneous catalysts was studied in the liquid phase. Applying liquid phase 1H NMR the degree of modification was determined quantitatively, in order to calculate the turnover numbers of the n-butanal conversion. The analysis of the kinetic data has shown that the reaction on primary amines follows a 1st order model, whereas on secondary amines the 2nd model gives the best correlation. Tertiary and aromatic amines were not active. Based on the kinetic measurements reaction mechanisms are proposed. The difference in the activation energies suggests that the modification process on mesoporous materials proceeds preferentially on the external surface, while on meso-macroporous materials the modification proceeds in the mesopores.

Chemical behavior research of high-energy aerospace propellant with a mesoscale heterogeneous packing model

The NEPE propellant has a wide range of applications in the aerospace field, playing a crucial role in enhancing the performance and efficiency of propulsion systems. In this study, we have developed an elaborate physical–chemical model to simulate the transient reaction characteristics of NEPE propellants. Our approach entails a sequential algorithm to explore the microstructure of NEPE propellants, incorporating a novel semi-global kinetic reaction mechanism designed to accurately represent real-world scenarios during propellant combustion. The interplay between the condensed phase and gas phase is handled through the use of the source term method. A comprehensive examination is carried out to ensure the statistical convergence of the propellant particle distribution. Moreover, we have compared the simulated burning rate of NEPE propellant under different formulations and operating pressures (ranging from 0.5 to 2.5 MPa) with experimental cases. The predictions demonstrate excellent agreement within a 10 % margin of the experimental data, highlighting the precision with which our proposed model depicts propellant combustion. Furthermore, we have conducted simulations of the combustion of specific NEPE disk packs composed of 19.63 % 100 µm AP, 35.3 % 60 µm HMX, 8.83 % 50 µm HMX, and 36.25 % NG/BTTN binder. Our findings reveal that the variation of statistical burning rates can be described by the equation rb=3.93P0.453, Additionally, the adiabatic flame temperature of the disk packs, under various pressures, typically falls within the range of 3200–3700 K. To gain a deeper understanding of the impact of different components within the propellant on combustion, we have carried out burning tests on a series of NEPE disk packs with varying formulations, accompanied by particle-scale combustion analysis. Our observations indicate that substituting 1 % HMX particles for AP particles leads to a significant enhancement in the propellant’s burning rate, approximately 0.02 mm/s. This phenomenon confirms that HMX particles act as a potent explosive source, thereby contributing to an increased flame standoff distance. Consequently, a jet-like diffusion flame with a length scale of several microns commonly appears above the AP-binder-HMX unit.

Construction of a Small-Sized Simplified Chemical Kinetics Model for the Simulation of n-Propylcyclohexane Combustion Properties

The development of a compact mechanism has made a great contribution to work on the combustion of hydrocarbon species and facilitates the investigations on chemical kinetics and computational fluid dynamics (CFD) studies. N-propylcyclohexane (NPCH) is one of the important components for jet, diesel, and gasoline fuels which needs a reliable compact reaction kinetics mechanism. This study aims to investigate the construction of a well-validated mechanism for NPCH with a simplified chemical kinetics model that delivers a good prediction ability for the key combustion parameters in a wide range of conditions (temperatures, pressures, and equivalence rates). The NPCH reaction kinetic mechanism was constructed with the aid of a coupling process, simplification process, rate modification, and a combination of standard reduction methods. The model includes a simplified sub-mechanism with 16 species and 58 reactions and a semi-detailed core mechanism with 56 species and 390 reactions. Two key parameters including ignition delay time and laminar flame speed are simulated by the use of ANSYS Chemkin-Pro. The simulation results for these parameters are validated against the available data in the literature, and the results show a good agreement compared to the experimental data over a wide range of conditions covering low to high temperatures at different pressures and equivalence ratios.

Novel kinetic modeling strategy for industrial-scale UNIPOL polypropylene with Ziegler-Natta catalyst

Polypropylene (PP) is a synthetic resin with exceptional physical and chemical properties, making it suitable for various household and industrial applications. However, as the demand for PP continues to rise, the polypropylene industry faces challenges in improving its quality and efficiency. Developing an accurate mathematical model that describes the continuous polymerization process is crucial for enhancing PP production, as it is useful for controlling product quality and improving production efficiency. While previous studies have focused on modeling propylene polymerization using laboratory-scale and pilot-scale reactors, these models do not effectively apply to industrial-scale processes due to the complexity of the industrial environment. Therefore, a novel kinetic modeling method combining the modeling of the kinetic mechanism of the polymerization reaction with an intelligent optimization algorithm for the industrial-scale continuous gas-phase fluidized bed propylene polymerization process is proposed. To establish the kinetic mechanism model, the improved moments (MOM) method is utilized to derive a set of mass balance equations that account for various fundamental processes such as catalyst activation, chain initiation, chain growth, chain transfer to hydrogen, chain transfer to monomers, chain transfer to co-catalysts, and spontaneous deactivation. However, kinetic parameters serve as the link between the theoretical model and the actual production process, so the kinetic parameters estimation problem need to be transformed into a multi-objective problem by minimizing the least squares difference between the measurement data of the actual industry process and the predicted result of the kinetic model. Therefore, an improved multi-objective mayfly algorithm (IMOMA) is introduced to estimate the polymerization kinetic parameters, which incorporates the simulated binary crossover (SBX) operator and the polynomial mutation (PM) operator into the basic multi-objective mayfly algorithm (MOMA). Finally, by fitting industrial measurement data of the melt index (MI) and the polymerization rate (PR) of an actual polypropylene industrial case study, the proposed algorithm accurately determines the polymerization kinetic parameters. The results demonstrate that the MOM-IMOMA modeling approach outperforms other methods and holds significant promise for industrial-scale polypropylene production.

Mechanism evaluations of conventional and suspended HVOF thermal spraying based on EDC and EDM combustion models

Suspended high-velocity oxygen fuel (SHVOF) thermal spraying technology can spray solid particles with nano or sub-micron scale, and effectively prepare high quality coatings by wrapping solid particles into suspension with solvent. The HVOF and SHVOF processes are numerically simulated in this study. The gas phase and discrete phase were simulated by the bidirectional coupling Euler-Lagrange method. The state equation of ideal gas and realizable k-ε turbulence model were used to simulate gas phase flow. The effect of eddy dissipation model (EDM) and eddy dissipation concept (EDC) model on turbulent combustion reaction was discussed. Due to that EDM model simplifies the Arrhenius rate of different reactions, there are errors in the prediction of spraying combustion process. To solve the problem, the chemical kinetic mechanism of multi-component combustion reaction for the propylene, ethanol and oxygen was introduced in EDC model for the first time in this study. This method has not yet been used in the modeling of thermal spraying. The suspended droplets are a mixture of ethanol and WC-12Co powder. Results show that the atomization and evaporation of suspension significantly disturb the flow field and reduce the internal pressure and temperature of spray gun. Compared with the EDM model, the EDC model can well predict the peak temperature in the combustion chamber, the prediction of particle temperature and velocity is higher, and the temperature and velocity decay are slower during flight. Compared with the median particle size d50 in actual, two combustion models can effectively predict the median particle size after drying, which is the premise of accurately predicting the flight characteristics of particles.

Kinetic reaction mechanism of lignocellulosic biomass oxidative pyrolysis based on combined kinetics

The kinetics knowledge of lignocellulosic biomass decomposition is essential to develop efficient thermochemical conversion technology. However, the simplification of reaction mechanisms in existing oxidative pyrolysis studies largely compromises the application of kinetic models. To explore more exact kinetic parameters and reaction mechanism of lignocellulosic biomass oxidative pyrolysis, an updated oxidative pyrolysis kinetic model (seven-step reaction combined kinetics model) coupled with an optimization algorithm is proposed. Based on a series of thermogravimetric experiments in an air atmosphere, the extra oxidative pyrolysis kinetic parameters are obtained by the Shuffled Complex Evolution method. The proposed kinetic model is validated based on the degradation process of each component (hemicellulose, cellulose, and lignin). Furthermore, the obtained kinetic parameters are applied to predict the oxidative pyrolysis behavior, and the predicted mass loss rate is in good agreement with the experimental data. Eventually, according to the key combined kinetics parameters, it is found that the oxidative pyrolysis mechanisms of hemicellulose, cellulose, and lignin correspond to the power law, nucleation & growth, and chemical reaction order, respectively, while the combustion of char corresponds to the reaction order mechanism.

Strong metal-support interactions of TiO2 interface-loaded Pt constructed under different atmospheres for adjusting the hydrogen storage reaction performance of N-ethylcarbazole.

In this study, two series of samples (rT-Pt/TiO2 prepared with a hydrogen pretreatment and Tr-Pt/TiO2 prepared with an oxygen pretreatment) were prepared by treating commercial TiO2 supports in different atmospheres to establish different TiO2 interfacial structures, followed by the addition of platinum nanoparticles (NPs) for the catalyzed hydrogenation/dehydrogenation cycle of N-ethylcarbazole (NEC). The kinetic analysis and reaction mechanism were investigated by combining XRD, Raman, CO-DRIFT, HRTEM, XPS, H2-TPD and DFT calculations. It was found that the performance of the samples for the NEC system's cyclic hydrogen storage could be modulated by treating the TiO2 interfacial structure with different atmospheres varying the extent of strong metal-support interaction (SMSI). In addition, a turnover frequency (TOF) of 191.52 min-1 for dehydrogenation was achieved at 170 °C, which is better than the previously reported catalysts. Experimental studies (characterization and kinetic studies) and DFT calculations confirmed that the SMSI of the Tr-Pt/TiO2 series samples promoted the escape of H2 and enhanced the catalytic activity for 4H-NEC in the 12H-NEC dehydrogenation reaction. In the NEC hydrogenation reaction, the rT-Pt/TiO2 series samples were pretreated with H2 before loading platinum metal, which led to the early activation of Ti4+ in their carriers, and thus suppressed the SMSI effect of the reduction process after loading platinum. This process caused the interface formed by rT-Pt/TiO2 to have a higher energy barrier to 6H-NEC, which is an intermediate product of the NEC hydrogenation process, and this interrupted the hydrogenation process of 6H-NEC.

Study on mechanism and kinetics of iron removal by chlorination roasting of coal gangue

Utilizing the abundant kaolin resources within coal gangue is economically beneficial, although the iron-containing phase in the minerals hampers the value of its utilization. In the present study, CaCl2 served as the chlorination agent for iron removal from coal gangue through chlorination roasting. The study revealed that when the roasting temperature is below 800 °C, CaCl2 decomposes into HCl and reacts with the iron content to form chloride, which then volatilizes. Comparatively, when the roasting temperature exceeds 800 °C, CaCl2 will decompose to produce HCl and Cl2 to accelerate the volatilization of iron. Through non-isothermal kinetic analysis, the apparent activation energy for iron removal by chlorination roasting of coal gangue was found to be 82.42 KJ/mol, and the pre-exponential factor was 6329.3 s−1. Correspondingly, isothermal kinetic analysis revealed the apparent activation energy of 84.2 KJ/mol and a pre-exponential factor of 6310.7 s−1. The optimal reaction kinetic mechanism function for iron removal through chlorination roasting of coal gangue was identified as the F3 chemical reaction order model via above kinetic analysis. The integral took the form g(α) = (1-α))2–1.

A revised reaction kinetic mechanism for the oxidation of methyl formate

The combustion kinetics of methyl formate (MeFo), a promising oxygenated, highly knock-resistant e-fuel, is investigated in this work. The potential energy surfaces (PESs) of the low-temperature oxidation reactions of MeFo radicals were determined at the CCSD(T)-F12/cc-pVTZ-F12//B2PLYP-D3/cc-pVTZ level of theory and their rate coefficients were obtained with RRKM/master equation. The thermochemical properties of relevant intermediate species were calculated by using the G4 method. A chemical mechanism for the oxidation of MeFo was developed by adding fuel-specific reactions taken from a literature model into a well-validated base mechanism, and incorporating the newly calculated rate constants of elementary reactions and thermochemical properties of species. The fuel-specific mechanism was further revised in terms of reaction channels and rate coefficients for improved prediction accuracy. In particular, the O2 addition to hydroperoxy radicals (QOOH), the isomerization of peroxy hydroperoxy radicals (OOQOOH), the subsequent ketohydroperoxide (KET) decomposition, and the formally direct pathways of MeFo radicals (R) with O2 were added for the completeness of consumption pathways, in conjunction with the reaction channels of alkoxy radicals (RO) and hydroperoxides (ROOH). For good model prediction accuracy of ignition delay times, especially in the high-temperature range, the resulting mechanism was optimized by modifying the rate constants of several important H-atom abstraction reactions of MeFo within their uncertainty limits. The performance of the proposed mechanism is demonstrated through extensive validation against literature data obtained from different experimental configurations. Finally, the underlying reaction pathways of MeFo are explored by means of reaction flux analysis with the newly developed chemical mechanism.Novelty and significance statement: This work proposes a new reaction kinetic mechanism for the oxidation of methyl formate. Quantum chemistry calculation at high level of theory was performed to explore the low-temperature chemistry of MeFo. The reaction mechanism was improved by including missing reaction channels, incorporating theoretically calculated rate and thermochemical data, and modifying rate constants of sensitive reactions. The mechanism has been validated successfully against extensive data available in the literature covering a wide range of conditions and facilities. By using this new mechanism, reaction pathway analysis is performed to provide insights into the oxidation chemistry of MeFo.

Combining genetic algorithm and deep learning to optimize a chemical kinetic mechanism of ammonia under high pressure

Ammonia is a potential zero-carbon fuel, but the difficulties of experimenting at high pressure limit its development of application in power engineering. In this work, deep learning and genetic algorithm are combined to optimize the chemical reaction kinetics mechanism of ammonia under high pressure. The result shows that deep learning model is able to regress experimental data of ignition delay time in the range of less than 0.2% |Elog| (logarithmic absolute error). At the same time, the trained model can be applied to the trend prediction of ignition delay time at high pressure, enriching combustion data of ammonia fuel that is not available from experiments. Optimization of PLOG reactions with a large population size was performed by strengthen elitist genetic algorithm, and the prediction accuracy of ammonia chemical reaction kinetics mechanism was improved by about 5% finally. The application value of artificial intelligence in combustion science is demonstrated.

Study on CO2* chemiluminescence of CH4/O2 co-flow diffusion flame based on the chemical kinetic mechanism

Chemiluminescence of CO2* is suitable for characterizing flame properties such as flame structure, equivalence ratio and heat release rate. However, experimental studies and numerical simulations of CO2* are not yet complete. In this work, the two-dimensional distributions of CO2* chemiluminescence were obtained by a high-resolution CCD camera. Numerical simulation results of CO2* were performed based on the detailed reaction kinetics mechanism of CO2* and were in good agreement with that of experiments. The differences of CO2* reactions at different axial positions were studied. The main CO2* formation reaction R2(CH + O2 = CO2*+H) at the burner outlet and R1(O + CO + M = CO2*+M) at the core reaction zone were determined. On the fuel side, the R1 reaction rate was mainly affected by temperature. On the oxidizer side, the R1 reaction rate was affected by temperature and reactant mole fraction. The main quenching reaction was R5(CO2*+H2O = CO2 + H2O). The oxygen-fuel equivalence ratio changed the reaction rate of formation and quenching reactions mainly by affecting temperature and reactant mole fraction.

Physicochemical Characterization of Woody Lignocellulosic Biomass and Charcoal for Bio-energy Heat Generation

Biomass and its interactions for heat generation have received little attention. In this study, the woody biomass materials were Prosopis africana (PA), Harungana madascariences (HM), Vitrllaria paradoxa (VP), and Afzelia africana (AA). The composition (extractives, carbohydrate, and lignin) of the biomass was determined. The biomass was converted to charcoal in a traditional kiln. A thermo-kinetic examination of the charcoal samples was carried out. The kinetic parameters and potential reaction mechanisms involved in the decomposition process were both obtained using the integral (Flynn–Wall Ozawa) isoconversional methods in conjunction with the Coats-Redfern approach. The activation energy profiles for the charcoal samples in oxidizing atmospheres were 548 kJ/mol for AA, 274 kJ/mol for VP, 548 kJ/mol for PA, and 274 kJ/mol for HM. All charcoal samples underwent comprehensive, multi-step, complex reaction pathways for thermal degradation. The charcoal samples exhibit not only great potential for biochemical extraction but also for bioenergy applications. The significant amount of combustion characteristics in the raw biomass and charcoal samples indicates that each type of wood charcoal produced has more fixed carbon, less ash, and less volatile matter, all of which are desirable for the thermo-chemical conversion of biomass for the production of heat.

Kinetic study on the reaction of sodium nitrite with neurotransmitters secreted in the stomach

Nitroso-compounds are potentially mutagenic and carcinogenic compounds due to their ability to alkylate DNA bases. One of the most common sources of human exposure to nitroso-compounds is their formation in the acidic environment of the stomach by the reaction between electron-rich molecules present in the lumen and sodium nitrite ingested in the diet. To date, the formation of nitroso-compounds by the reaction of nitrite with food components has been investigated in depth, but little attention has been paid to substances secreted in the stomach, such as dopamine or serotonin, whose reaction products with nitrite have proven mutagenic properties. In this article, we present a kinetic study with UV–visible spectroscopy of the nitrosation reactions of both molecules, as well as of L-tyrosine, the amino-acid precursor of dopamine. We determined the kinetic parameters and reaction mechanisms for the reactions, studying the influence of the reactants concentration, pH, temperature, and ionic strength on the reaction rate. In all cases, the favoured reaction product was a stable nitroso-compound. Serotonin, the molecule whose product was the most mutagenic, underwent two consecutive nitrosation reactions. These findings suggest that additional biological research is needed to understand how this reaction alters the function of these neurotransmitters as well as the potentially toxic effects they may have once nitrosated.

Kinetic properties of non-caking coal spontaneous combustion by evolution of its functional groups

Coal spontaneous combustion (CSC) continues to generate huge economic losses and considerable casualties. Thew aim of this study is to further reveal the evolution of microstructures and coal spontaneous combustion mechanisms during natural oxidation. Coal samples with known CSC tendencies were selected to explore their microstructure and the characteristics of their reaction kinetics. This information is of great benefit to mine safety engineers and risk management professionals. Proper characterisation of risk leads to improved early warning detection, and the possibility of CSC retardant materials. A low-metamorphic type, non-caking coal sample was obtained from a Mengcun Coal Mine, and the relative content of the active functional groups and evolution of the key active groups were examined as temperature varied. Fourier transform infrared spectroscopy (FTIR) and the Coats-Redfern and Achar calculus methods were used to determine the reaction kinetics of the key active groups during CSC. The most probable mechanisms were determined, and the spontaneous combustion kinetic reaction mechanism was derived. Initial analysis of the sample revealed multiple active groups, active nuclear substances, a high calorific value, and a strong oxidative ability. There were a large number of oxygen containing functional groups and activity was high, due to the high intermolecular hydrogen bond content, and the apparent activation energy for ignition was low. Within the reaction, the aliphatic hydrocarbons were relatively stable; they had the largest apparent activation energy and were the least reactive. Methylene was the most important group consumed by aliphatic hydrocarbons in the CSC process. The reaction mechanism of the various groups were determined via Avrami-Erofeev equation. The large number of active groups produced and consumed was best described by the three-dimensional Ginstling-Brounshtein model.

Application of photocatalytic proxone process for petrochemical wastewater treatment

Industrial wastewaters are different from sanitary wastewaters, and treatment complications due to their unique characteristics, so biological processes are typically disrupted. High chemical oxygen demand, dye, heavy metals, toxic organic and non-biodegradable compounds present in petroleum industry wastewater. This study intends to optimize the photocatalytic proxone process, utilizing a synthesized ZnO–Fe3O4 nanocatalyst, for petroleum wastewater treatment. The synthesis of ZnO–Fe3O4 was done by air oxidation and layer-by-layer self-assembly method and XRD, SEM, EDAX, FT-IR, BET, DRS, and VSM techniques were used to characterize the catalyst. Central composite design (CCD) method applied to investigated the effect of pH (4–8), reaction time (30–60 min), ozone gas concentration (1–2 mg/L-min), hydrogen peroxide concentration (2–3 mL/L) and the amount of catalyst (1–0.5 g/L) on the process. In the optimal conditions, biological oxygen demand (BOD5) and total petroleum hydrocarbon (TPH) removal, reaction kinetic, and synergistic effect mechanisms on the process were studied. Based on the ANOVA, a quadratic model with R2 = 0.99, P-Value = 0.0001, and F-Value = 906.87 was proposed to model the process. Based on the model pH = 5.7, ozone concentration = 1.8 mg/L-min, hydrogen peroxide concentration = 2.5 mL/L, reaction time = 56 min, and the catalyst dose = 0.7 g/L were proposed as the optimum condition. According to the model prediction, an efficiency of 85.3% was predicted for the removal of COD. To evaluate the accuracy of the prediction, an experiment was carried out in optimal conditions, and experimentally, a 52% removal efficiency was obtained. Also, at the optimum condition, BOD5 and TPH removal were 91.1% and 89.7% respectively. The reaction kinetic follows the pseudo-first-order kinetic model (R2 = 0.98). Also, the results showed that there is a synergistic effect in this process. As an advanced hybrid oxidation process, the photocatalytic proxone process has the capacity to treat petroleum wastewater to an acceptable standard.

Preparation of ultrafine Mo powder by the H2 reduction of MoO2: Parameter optimization, reaction kinetic, and its reduction mechanism

The influences of different parameters, such as reaction temperature, yttrium (Y) content, and H2 concentration, on the particle size and morphological structure of Mo powder prepared via the H2 reduction of MoO2, were investigated in the work. TG, XRD, FE-SEM, laser particle size analysis, model fitting, and orthogonal design experiment methods were adopted to analyze the reaction kinetic and reduction mechanism. The results showed that the optimum conditions for preparing ultrafine Mo powder were recognized as 1073 K, 1 mass% Y content, and a H2 concentration of 0.000576 mol·cm−2·min−1, which enabled the as-prepared Mo powder with a particle size as small as 107 nm. A new interfacial chemical reaction model with the consideration of reaction temperature, H2 concentration, and sample thickness, was proposed to analyze the reaction kinetic. It was found that the curves predicted by the model agreed well with the experimental data, with the apparent activation energy extracted to be 94.686 kJ/mol. The effect of different individual parameter on the reaction rate and the possible reduction mechanism were also elucidated.

An investigation on the laminar flame propagation and auto-ignition characteristics of a coal-derived rocket kerosene-Part I: Experimental study

The energy structure of coal-rich and oil-poor in China, makes the conversion of coal to liquid fuels an attractive option to reduce petroleum dependence. In this study, the combustion characteristics of a newly developed coal-derived rocket kerosene were investigated to provide fundamental parameters for evaluating the feasibility and compatibility of the new fuel in potential applications. The laminar flame propagation properties of the fuel were studied at pressures of 1, 2 and 5 bar over a temperature range of 423–483 K for equivalence ratio of 0.7–1.8 in a constant volume combustion bomb, and the auto-ignition characteristics of the target fuel were then experimentally studied in a heated shock tube. Flame propagation process was studied based on the recorded flame morphology firstly. The unsteady transition from spark assisted ignition kernel propagation to normal flame was analyzed and was found to become less conspicuous in flames with stronger reaction intensity (higher initial pressure or temperature) and smaller Lewis number (higher equivalence ratio). The Markstein length was extracted by extrapolating the flame trajectories and used to investigate the flame instability. The results shows that the increase of pressure, equivalence ratio enhance the flame instability, but the impact of initial temperature shows no prominent pattern. The laminar burning velocity and ignition delay times were reported over a wide range to strengthen the understanding of combustion characteristics of the new fuel. A kinetic model was proposed to simulate the combustion chemistry of the fuel and kinetic analysis was performed to identify the key reactions driving the flame propagation and auto-ignition. The present study is hoped to provide insights into the evaluation of fuel application in the future and database support for further combustion reaction kinetic mechanism development.

Effect of Gas-Phase Passivation Technology on Spontaneous Combustion Characteristic Stage and Reaction Kinetics of FeS During Particle Size Fragmentation

ABSTRACT To investigate the mechanism of inhibition of spontaneous combustion of reactive FeS by gas-phase passivation, this paper used liquid-phase synthesis to prepare reactive FeS which were divided into five particle size ranges by crushing and grinding and then passivated those by low-oxygen gas. This paper analyzed the effect of gas-phase passivation on the characteristic parameters of the characteristic stages of crushed FeS from the perspective of thermodynamics, and used the KAS and FWO methods to calculate the apparent activation energy of the different characteristic stages of the FeS oxidation heating process. Inhibition mechanism of FeS spontaneous combustion reaction kinetics during particle size fragmentation by gas-phase passivation was revealed. The results indicate that in the spontaneous combustion stage at room temperature (RT), the exothermic heat of passivated FeS was significantly reduced to below 5 J/g, and the apparent activation energy rose up to 116 kJ/mol, which was significantly increased by about 50% compared to the activated FeS. The essence of gas-phase passivation is that the low oxygen concentration gas reacts with FeS to produce a passivation protective film, blocking the reaction and pushing the oxidation process backwards as a whole. In the weight gain stage of oxygen absorption, the weight gain of passivation FeS is reduced to less than 2.2%, and the heat release is reduced to 2.8J/g. The particle size of the passivated FeS decreased, and the apparent activation energy increased by 20 kJ/mol in the decomposition and combustion stage. With the decrease of FeS particle size, the gas-phase passivation is more effective and the inhibition effect of spontaneous combustion of FeS is more obvious.

Normal butane oxidation: Measurements of autoxidation products in a jet-stirred reactor

The autoxidation of n-butane was studied experimentally in a jet-stirred reactor at 1 atm (560–720 K) and 10 atm (530–1030 K) for an equivalence ratio of 1. Samples of reacting mixtures were analysed in the gas phase by gas chromatography (GC) using several detectors (Flame ionization detector, thermal conductivity detector, quadrupole mass spectrometer), hydrogen peroxide analyser, and Fourier transform infrared spectroscopy. In addition to the fuel and oxygen, 37 products were quantified. Liquid phase samples were obtained by trapping the reacting mixtures in cooled acetonitrile (273 K). The liquid samples were analysed by high resolution mass spectrometry (HRMS Orbitrap Q-Exactive), either after flow injection or separation by high pressure liquid chromatography (HPLC). Besides stable species, several other low-temperature oxidation products, such as hydroperoxides and ketohydroperoxides, were detected. Products of third O2 addition on fuel’s radicals were also detected by high resolution mass spectrometry. To assess the presence of hydroxyl or hydroperoxyl groups in the products of oxidation we performed H/D exchange with D2O. Qualitative and quantitative results showed the same trends in terms of variation of mole fractions and signal intensities versus reacting temperature. Kinetic modelling was performed using a literature detailed kinetic reaction mechanism already used to simulate previous n-butane oxidation experiments in the cool-flame regime, showing that improvements are needed to better describe the oxidation of n-butane under the present conditions.