Detailed Reaction Kinetic Model Research Articles

High-fidelity Reaction Kinetic Modeling of Hot-Jupiter Atmospheres Incorporating Thermal and UV Photochemistry Enhanced by Metastable CO(a3Π)

A detailed modeling of simultaneous UV-photochemical and thermochemical processes in exoplanet atmosphere-like conditions is essential for the analysis and interpretation of a vast amount of current and future spectral data from exoplanets. However, a detailed reaction kinetic model that incorporates both UV photochemistry and thermal chemistry is challenging due to the massive size of the chemical system as well as the lack of understanding of photochemistry compared to thermal-only chemistry. Here, we utilize an automatic chemical reaction mechanism generator to build a high-fidelity thermochemical reaction kinetic model later then incorporated with UV photochemistry enhanced by metastable triplet-state carbon monoxide (a3Π). Our model results show that two different photochemical reactions driven by Lyα photons (i.e., H2 + CO(a3Π) → H + HCO and CO(X1Σ+) + CO(a3Π) → C(3P) + CO2) can enhance thermal chemistry resulting in significant increases in the formation of CH4, H2O, and CO2 in H2-dominated systems with trace amounts of CO, which qualitatively matches the observations from previous experimental studies. Our model also suggests that at temperatures above 2000 K, thermal chemistry becomes the dominant process. Finally, the chemistry simulated up to 2500 K does not produce any larger species such as C3 species, benzene, or larger (i.e., PAHs). This might indicate that the photochemistry of C2 species such as C2H2 might play a key role in the formation of organic aerosols observed in a previous experimental study.

A detailed reaction kinetic model of light naphtha isomerization on Pt/zeolite catalyst

There is increasing interest in kinetic models of catalytic refining processes, because of their importance in developing and improving these processes. In fact, the models can be used to predict process performance parameters and to determine the optimum operating conditions. In this work, a detailed reaction kinetic model was developed to describe light naphtha isomerisation reactions over different Pt/zeolite catalysts (Pt/mordenite, Pt/ZSM5, and Pt/BETA). The proposed kinetic model included 66 isomerisation, 28 ring opening, 1 olefin saturation, 22 dehydrogenation, and 90 hydrocracking reactions for 52 real light naphtha components graded from methane to n-octane. A power law reaction kinetics was assumed for all reactions, and 414 kinetic parameters were fine-tuned by comparing the predictions of the model with the results of light naphtha isomerisation experiments at six different temperatures (290, 310, 330, 350, 370, and 390 °C). The Matlab software (version 2015a) was used to perform all the calculations in the current study, and the optimum set of kinetic parameters was estimated using genetic algorithm optimisation. The mean absolute errors for all component compositions at different temperatures were found to be 0.003608, 0.004841, and 0.004757 for the Pt/mordenite, Pt/ZSM5, and Pt/BETA catalysts, respectively. The values of the mean absolute errors estimated from the comparison between the experimental and predicted results showed a very good agreement between the model predictions and the experimental data.

Evaluating the effect of multiple flammable gases on the flammability limit of CH4: Experimental study and theoretical calculation

As the main component of natural gas and an important chemical raw material, methane easily forms a mixture of flammable gases during production and processing. Therefore, understanding the flammability limit and limiting oxygen concentration of methane is very important in predicting the possibility of fire and explosion in industrial production and designing the corresponding monitoring parameters. To solve this problem, the effects of the addition of a C2H6/C2H4/CO/H2 mixture on the flammability limit of methane and the limiting oxygen concentration under N2 dilution were systematically studied. In addition, the flammability limit was evaluated using the limiting burning velocity theory and detailed reaction kinetic model, and a sensitivity analysis was conducted to study the chemical kinetics near the limit. The experimental results show that when the volume fraction of mixed gas gradually increases, the upper and lower flammability limit of methane both decrease, and the decrease in the lower flammability limit is larger than that of the upper flammability limit. Under the condition of nitrogen dilution, the limiting oxygen concentration gradually decreases with an increase in mixed gas concentration. The explosion triangle expands and moves to the lower-left corner, the flammability limit range increases, and a greater danger of explosion exists. The calculated results based on the limit laminar burning velocity are in good agreement with the experimental data. The sensitivity analysis shows that elementary reactions involving the active free radicals of OH, H and O have higher sensitivity. With the addition of mixed gas, the chain-branching reaction R31 is promoted, the chain termination reactions R12 and R41 are inhibited, the competition between the chain-branching reaction and chain termination reaction changes, and the flammability limit range of methane expands.

A Detailed Reaction Kinetic Model of Heavy Naphtha Reforming

A detailed reaction kinetic model was developed to describe heavy naphtha reforming reactions. The kinetic model involved 32 lumps and 132 reactions; the lumps were one to 11 carbon atoms n-paraffins, four to 11 carbon atoms iso-paraffins, methylcyclopentene, and six to 11 carbon atoms for naphthenes and aromatics. All computations in the present study were predicted using the particle swarm optimization (PSO) method coded by MATLAB 2015a software. This optimization method was used to estimate the optimum set of kinetic parameters of heavy naphtha reforming reactions. All 150 kinetic and deactivation parameters that were predicted in this work were fine-tuned using PSO. The proposed kinetic model was validated by benchmarking the model results with the data collected over 5 years for a commercial naphtha reforming unit. The mean absolute error for all component compositions within the process was found to be 0.0079. The catalyst deactivation rate was also predicted. It was found that catalyst activity decayed to 58.8% after 1225 operating days.

Energy Conversion and Temperature Dependence in Ozone Generator Using Pulsed Discharge in Oxygen

ABSTRACTA detailed reaction kinetic model consisting of 10 species and 63 reactions is developed to investigate the energy conversion and temperature dependence in an ozone generator using oxygen pulsed discharge. The energy conversion ratios of total electric energy converted into reaction heat, heat carried by gas and heat loss to ambient, namely ηreaction, ηgas and ηloss, are obtained for the first time. The ratio of reaction heat ηreaction decreases substantially with increasing specific energy and inlet gas temperature, which represents how much energy is utilized effectively to synthesize ozone. Correspondingly, ηloss and ηgas increase gradually. ηreaction declines from 55.4% to 27.7% at inlet gas temperature of 298 K when specific energy changes from 0.06 J/cm3 to 0.78 J/cm3. The detailed reaction pathway including the degree of transformation among species for ozone formation is also obtained via kinetics simulation. Meanwhile, sensitivity analysis and rate-of-production analysis for the four most important species O3, O, O(1D) and O2(b1∑) obtained from the reaction pathway are executed to understand quantitatively the temperature dependence of sensitivity coefficient and production rate for each individual reaction. The production rate of ozone via the most important ozone generation reaction O+O2+O2 = > O3+O2 increases linearly with the increase of gas temperature, as well as the destruction rates of ozone via the most important ozone decomposition reactions O3+O3 = > O2+O2+O2 and O3 + O = > O2(b1∑)+O2.

Numerical investigation on combustion in muzzle flows using an inert gas labeling method

The influence of the precursor flow on combustion in muzzle flows is investigated. The fourth-order Runge–Kutta method is employed to solve the classical interior ballistics model, providing velocity for the projectile when it accelerates along the barrel. An inert gas labeling method is proposed. An additional species, helium, is chosen as the label to tracing the precursor gas which fills the barrel before the projectile starts. A high-resolution upwind scheme, AUSM+ (Advection Upstream Splitting Method), and detailed reaction kinetics model are employed to solve the multispecies Navier–Stokes equations with finite rate chemistry. The precursor flow generated by the precursor gas driven out of the barrel ahead of the projectile is simulated. The development of muzzle flow with chemical reaction is simulated. It is demonstrated from the results that the secondary temperature rise in the intermediate region behind the Mach disk is attributed to combustion in this area. It is found that the core of the precursor gas supplies oxygen for combustion at 150μs after the projectile base leaves the muzzle. Furthermore, despite the disrupted precursor flow, the precursor gas is still united and gradually diffuses into the propellant gas.

Research on the Muzzle Blast Flow with Gas-Particle Mixtures Based on Eulerian-Eulerian Approach

ABSTRACTThe issue on the muzzle blast flow with gas-particle mixtures was numerically investigated in this paper. The propellant gas in the cannon was assumed to be gas-particle mixtures consisting of a variety of gaseous species and particles. The model made use of the Eulerian-Eulerican approach, where the particle were modeled as a second fluid with parameters like bulk density, velocity and temperature, interacting with the gas flow. A high-resolution upwind scheme(AUSMPW+) and detailed reaction kinetics model were employed to solve the chemical non-equilibrium Euler equations for gas phase. The Euler equations for particle phase were solved by MacCormack scheme. The particle diameter and the mass fraction of particle were tested to show their effects on the development process of muzzle blast flow with gas-particle mixtures. The distribution of the main flow parameters of both gas and particle were obtained at different time intervals. The results show the evolution of the muzzle blast flow with gas-particle mixtures and demonstrate the effects of key parameter on the flow field of the gas-particle flow. This paper is a significant investigation for understanding the muzzle blast flow with gas-particle mixtures, which can provide valuable reference for the research on the muzzle blast flow.

Development process of muzzle flows including a gun-launched missile

Numerical investigations on the launch process of a gun-launched missile from the muzzle of a cannon to the free-flight stage have been performed in this paper. The dynamic overlapped grids approach are applied to dealing with the problems of a moving gun-launched missile. The high-resolution upwind scheme (AUSMPW+) and the detailed reaction kinetics model are adopted to solve the chemical non-equilibrium Euler equations for dynamic grids. The development process and flow field structure of muzzle flows including a gun-launched missile are discussed in detail. This present numerical study confirms that complicated transient phenomena exist in the shortly launching stages when the gun-launched missile moves from the muzzle of a cannon to the free-flight stage. The propellant gas flows, the initial environmental ambient air flows and the moving missile mutually couple and interact. A complete structure of flow field is formed at the launching stages, including the blast wave, base shock, reflected shock, incident shock, shear layer, primary vortex ring and triple point.

Numerical simulation of the muzzle flows with base bleed projectile based on dynamic overlapped grids

Numerical investigations of the launch process of a base bleed projectile from the muzzle to free-flight stage have been performed in this paper. A dynamic overlapped grids approach was applied to deal with the problems of a high-speed moving base bleed projectile. A high-resolution upwind scheme (AUSMPW+) and detailed reaction kinetics model were employed to solve the chemical non-equilibrium Euler equations for dynamic grids. A typical case was calculated for the verification of the dynamic overlapped grids approach and numerical methods solving the chemical non-equilibrium flows. After good agreement was achieved, the development process of muzzle flows with high-speed moving base bleed projectile and the rapid depressurization process in the combustion chamber of base bleed unit are discussed in detail. This present numerical study confirms that complicated transient phenomena exist in the early launch stages after the base bleed projectile moves from the muzzle of cannon to the free-flight stage. The base bleed unit of projectile undergoes a strong non-steady-state rapid depressurization. This paper is a significant investigation for understanding muzzle flows with base bleed projectile and rapid depressurization in the combustion chamber of base bleed unit, which can provide valuable reference data for research on combustion stability of the propellant in the combustion chamber.

Reaction Analysis of Alcohol Electro-Oxidation at Intermediate Temperatures

Comprehensive analysis of electro-oxidation kinetics of alcohols such as methanol, ethanol, ethylene glycol and glycerol was performed at intermediate temperatures of around 250 oC, combining an electrochemical measurement with a reaction product analysis. Through the observations, following common features for the examined alcohols were found: (1) high oxidation current and high selectivity of CO2 were obtained; (2) hydrogen production via thermal decomposition and/or steam reforming of the alcohols (indirect path) and direct electro-oxidation of the alcohols (direct path) proceed in parallel. Based on the findings, a detailed reaction kinetic model was also discussed, considering the possible rate-determining step in direct alcohol electro-oxidation at intermediate temperatures.

Detailed reaction kinetics over commercial three-way catalysts

A detailed reaction kinetic model to predict the activity of the commercial three-way catalyst (TWC), particularly 4k miles aged catalyst in an engine dynamometer, has been developed by considering all possible reactions in the catalytic converter based upon the Langmuir–Hinshelwood mechanism. The model predictions adequately describe the general trend of the measured conversions of CO, C 3 H 6 , NO and H 2 . NH 3 and N 2 O formed during the reaction can also be predicted by the model. Moreover, the decrease in activity of the 100k miles aged catalyst can be well described by the model developed in the present study.

The Chemotactic Behavior of Computer-Based Surrogate Bacteria

Chemotaxis is the process by which organisms migrate toward nutrients and favorable environments and away from toxins and unfavorable environments. In many species of bacteria, this occurs when extracellular signals are detected by transmembrane receptors and relayed to flagellar motors, which control the cell's swimming behavior. We used a molecularly detailed reaction-kinetics model of the chemotaxis pathway in Escherichia coli coupled to a graphical display based on known swimming parameters to simulate the responses of bacteria to 2D gradients of attractants. The program gives the correct phenotype of over 60 mutants in which chemotaxis-pathway components are deleted or overexpressed and accurately reproduces the responses to pulses and step increases of attractant. In order to match the known sensitivity of bacteria to low concentrations of attractant, we had to introduce a set of "infectivity" reactions based on cooperative interactions between neighboring chemotaxis receptors in the membrane. In order to match the impulse response to a brief stimulus and to achieve an effective accumulation in a gradient, we also had to increase the activities of the adaptational enzymes CheR and CheB at least an order of magnitude greater than published values. Our simulations reveal that cells develop characteristic levels of receptor methylation and swimming behavior at different positions along a gradient. They also predict a distinctive "volcano" profile in some gradients, with peaks of cell density at intermediate concentrations of attractant. Our results display the potential use of computer-based bacteria as experimental objects for exploring subtleties of chemotactic behavior.

Irradiation of MEK — II: A detailed kinetic model for the degradation of 2-butanone in aerated aqueous solutions under steady-state γ-radiolysis conditions

The radiolytic decomposition of aqueous phase 2-butanone (methyl ethyl ketone (MEK)) has been studied extensively to gain a detailed mechanistic understanding of the effects of organic impurities on the behaviour of iodine in containment following a nuclear reactor accident. Based on the experimental results reported previously, a detailed reaction kinetic model for the steady-state γ-radiolysis of aerated aqueous solutions containing MEK has been developed. The model consists of about 130 radiolytic decomposition reactions in addition to about 25 water radiolysis reactions. The model reproduces the observed dose profiles of MEK and its subsequent decomposition products (3-hydroxy-2-butanone, acetaldehyde, acetic acid and formaldehyde) very well. The worst case was formaldehyde, a tertiary molecular product from MEK decomposition, which was still reproduced to within 50%. The model also reproduces the observed dose profile of pH reasonably well. The key reactions controlling the behaviour (or dose profiles) of MEK and its decomposition products and the sensitivity of their behaviour to the rates of these reactions are discussed.