Chemical Kinetic Model Research Articles

Flame stabilization and pollutant emissions of turbulent ammonia and blended ammonia flames: A review of the recent experimental and numerical advances

Compared to traditional hydrocarbon fuels, ammonia presents significant challenges as a fuel, including high ignition energy, low reactivity, slow flame propagation, and high NOx emissions, which hinder its use as a renewable fuel. Blending ammonia with fossil fuels like natural gas improves its combustion reactivity and helps mitigate CO2 emissions. However, there is still much to understand about the complex dynamics of ammonia and its blends with hydrocarbons. Key areas such as reaction kinetics mechanisms, ignition properties, flame propagation behaviors, and methods for controlling combustion performance under various conditions require further elucidation. This paper reviews recent advancements in experiments and numerical simulations aimed at developing stable, and low-emission combustors for ammonia-fired power generation. Recent burner and flame configurations, including non-swirling jets, single-stage swirl burners, two-stage burners, and newly developed double-swirl burners are analyzed for their flame stability and pollutant emission potential when firing ammonia and ammonia blends. Chemical kinetic modeling of ammonia and its blends plays a crucial role in understanding combustion behavior and pollutant emissions, particularly for NOx. However, there are challenges in predicting NOx emissions accurately, with significant disparities among different models. High-fidelity numerical simulations using detailed and skeletal mechanisms, direct numerical simulation, and large eddy simulation, have helped uncover crucial operational conditions affecting combustion and pollutant emissions, such as combustor pressure, air dilution, wall cooling, fuel/air mixing, and fuel blending. Nonetheless, the accuracy of chemical kinetic models and their integration into turbulent flow simulations remain critical limitations for numerical simulations of ammonia combustion.

Measurements of ignition delay time of gas-to-liquid (GTL) fuel blends

The ignition delay time (IDT) is a fundamental combustion parameter of any fuel, which has a direct impact on its combustion and exhaust emissions in diesel engines. In this research, a thorough experimental study was conducted to investigate the ignition delay of Gas-to-Liquid (GTL) fuel and its 50%–50 % blends with diesel under a wide range of operating conditions using a conventional shock tube apparatus. Simultaneously, a comprehensive chemical kinetic model, based on the well-established POLIMI mechanism, was developed to simulate the complex combustion chemistry of diesel, GTL, and their blends. Several loading pressures in the driver section ranging from 6 to 14 bar that results in reflected pressure of 8–16 bar, and equivalence ratios ranging from 0.5 to 1.3 as well as different initial temperatures have been examined. Calibration of the shock tube indicated that a driver gas tailoring technique was necessary to be used, which was conducted by adding a small ratio of either argon or nitrogen to helium to get an extended test time by 32 % with a good rapture pressure. IDT measurements showed that GTL has the shorter ignition delay time than that of diesel fuel for all conditions. The findings show that IDT measurements for GTL fuel has a shorter ignition delay time than that of diesel fuel for all conditions. Under stoichiometric conditions (ɸ = 1.0), IDT of the blended fuel was about 3 ms, very close to that of GTL at 975 K. However, at a temperature above 1000 K, the IDT of the three fuels were almost identical and ranging between 1 and 2 ms. At a temperature of 1100 K, the IDT of the blended fuel was 5.5 ms, almost a middle value between those of the pure diesel, 0.522 ms, and GTL fuel, 0.495 ms. The shortest IDT of the blended fuel was about 0.4 ms with the highest value of the reflected pressure of 14 bar, while the longest IDT was around 10 ms with the rich mixture at ɸ = 1.3. The study can add to the existing literature illustrating the behavior of GTL-diesel blend can affect IDT.

Calculation of the decomposition products of C5F10O-Air mixtures from 500 K to 3500 K with a chemical kinetic model

Calculation of the decomposition products of C5F10O-Air mixtures from 500 K to 3500 K with a chemical kinetic model

Formation of Products of Incomplete Destruction (PID) from the Thermal Oxidative Decomposition of Perfluorooctanoic Acid (PFOA): Measurement, Modeling, and Reaction Pathways.

The thermal decomposition of perfluorooctanoic acid (PFOA) under oxidative conditions was investigated using air (O2) and N2O as oxidants over temperatures ranging from 400 to 1000 °C in an α-alumina reactor. In the presence of air, PFOA was found to decompose into perfluorohept-1-ene (C7F14) and perfluoroheptanoyl fluoride (C7F14O) in addition to HF, CO, and CO2. At temperatures above 800 °C, both C7F14 and C7F14O were no longer detected. A comprehensive analysis of the reaction mechanisms through quantum chemical analysis and kinetic modeling in combination with experimental observations was utilized to identify key reaction pathways. Quantum chemical analysis led to the conclusion that oxygen atoms are crucial in decomposing perfluoroalk-1-enes, especially the stable perfluorohept-1-ene (C7F14). Under oxidative conditions, it was found that significant quantities of C2F6 and CF4 were formed. Further quantum chemical analysis suggests that the O atoms facilitate the formation of volatile fluorinated compounds (VFCs) such as tetrafluoromethane (CF4) and hexafluoroethane (C2F6), particularly at higher temperatures. By elucidating these key reactions, an improved understanding of the potential formation products of incomplete combustion (PICs) or products of incomplete destruction (PIDs) is made.

Experimental and chemical kinetic modeling study on the inhibition performance of pentauoroethane blended with carbon dioxide in methane-air mixture explosions

To explore the inhibition effectiveness and mechanisms of pentafluoroethane (C2HF5), carbon dioxide (CO2), and their blends, 9.5% methane (CH4)-air mixture explosions under different inhibitors were tested by employing a 20 L spherical explosion system. A quadratic regression model was developed to predict impacts of factors on maximum explosion pressure (pm) through response surface method. The reactions and mechanisms under blended inhibitors were numerically investigated. Results depicted that increasing volume fractions of inhibitor led to decrease in pm, maximum rate of pressure rise, and delay in explosion induction time. Blended inhibitors demonstrated superior inhibition effectiveness, optimal inhibition-environmental was achieved at 4.5% C2HF5 blended with 5.5% CO2. A quadratic polynomial relation existed among pm, volume fractions of C2HF5, CO2, and CH4 during the explosion. Key free radicals were weakened and the promoted explosive elementary reactions were primarily inhibited. CH4+OHCH3+H2O and CH4+HCH3+H2 were the most diminished reactions by blended inhibitors compared to CO2 alone. Carbon-containing reactions R82 and R84, and fluorinated reactions R1025 and R1099 reduced the key free radicals, interrupted the chain reactions and promoted the production of HF. Findings will provide new ideas for prevention of CH4-air mixture explosions and reduce hazardous effect.

Roles of fuel composition on the ignition process of endothermic hydrocarbons

Due to the characteristics of heat absorption and decomposition, endothermic hydrocarbon fuels (EHFs) have been widely used in scramjets for thermal protection and heat recirculation. The understanding of ignition characteristics of EHFs is of great importance for their safe and efficient utilization. In this paper, the ignition processes of EHFs were numerically simulated at atmospheric pressure and with an initial temperature of 500 K. Three different ignition stages were identified based on the chemical heat release and flame kernel propagation. A 3-component kerosene surrogate model composed of n-dodecane, methyl cyclohexane and m-xylene was adopted, as well as the corresponding chemical kinetic model with 369 species and 2691 reactions. Results showed that the discrepant decomposition characteristics of n-alkanes and cycloalkanes affected the chemical heat release and propagation during the ignition process. Two-stage exothermic characteristic was observed in the time evolutions of chemical heat release rate and fuel decomposition. The mass production of molecules and accumulation of radicals dominated the first and second exothermic peaks, respectively. Furthermore, the minimum ignition energies (MIEs) of EHFs with various methyl cyclohexane were determined to quantify the effect of fuel composition on ignition performance. Characteristically, the MIE dramatically decreased from 10.2 to 2.15 mJ when 20% n-dodecane was replaced by methyl cyclohexane. However, it was slightly increased as methyl cyclohexane continued to increase. Analyses from both physical and chemical aspects were conducted to elaborate the dependence of MIE on fuel composition. The dominant effects of flame-dynamic and chemical effects on different ignition stages were analysed. The faster propagation speed and stronger endothermic ability of methyl cyclohexane led to the nonlinear variation of MIEs. The results in this study provide useful guidance for composition optimization and safety evaluation of EHFs.

Perspective on automated predictive kinetics using estimates derived from large datasets

AbstractA longstanding project of the chemical kinetics community is to predict reaction rates and the behavior of reacting systems, even for systems where there are no experimental data. Many important reacting systems (atmosphere, combustion, pyrolysis, partial oxidations) involve a large number of reactions occurring simultaneously, and reaction intermediates that have never been observed, making this goal even more challenging. Improvements in our ability to compute rate coefficients and other important parameters accurately from first principles, and improvements in automated kinetic modeling software, have partially overcome many challenges. Indeed, in some cases quite complicated kinetic models have been constructed which accurately predicted the results of independent experiments. However, the process of constructing the models, and deciding which reactions to measure or compute ab initio, relies on accurate estimates (and indeed most of the numerical rate parameters in most large kinetic models are estimates.) Machine‐learned models trained on large datasets can improve the accuracy of these estimates, and allow a better integration of quantum chemistry and experimental data. The need for continued development of shared (perhaps open‐source) software and databases, and some directions for improvement, are highlighted. As we model more complicated systems, many of the weaknesses of the traditional ways of doing chemical kinetic modeling, and of testing kinetic models, have been exposed, identifying several challenges for future research by the community.

Experimental study of nitric oxide distributions in non-premixed and premixed ammonia/hydrogen-air counterflow flames

This study reports an experimental investigation of quantitative Nitric Oxide (NO) distribution in both premixed and non-premixed NH3/H2-air flames using a counterflow burner at atmospheric pressure. One-dimensional (1D) NO laser-induced fluorescence (LIF) spectroscopy and Raman/Rayleigh spectroscopy were conducted to accurately resolve the quantitative 1D NO profile in terms of mixture fraction, temperature, and physical space. We calibrated a saturated NO-LIF model in 5 premixed lean H2/N2/NO-air flames with different seeded NO levels in a McKenna burner and validated its accuracy in three H2N2NO-air counterflow diffusion flames. The overall uncertainty of NO quantification was less than90 ppm. Our measurements were compared with simulations using different ammonia chemical kinetic models, revealing that current models have over 30% uncertainty in predicting peak NO concentrations (mole fraction) in 1D non-premixed and premixed flames and over 100% uncertainty in lower temperature regions. In premixed flames, measured NO concentrations fell within the intermediate range of current chemical kinetic models at lean and stoichiometric conditions, but were lower than the models at rich conditions. In non-premixed flames, all models overestimated the peak NO concentrations by more than 1000 ppm. It is noted that the measured peak NO concentrations increased with higher NH3/H2 ratios (from 4/6 to 8/2), strain rates (from 80 to 140 1/s), and N2 dilution ratios in a 1:1 NH3/H2 mixture (from 0 to 30%). Although most models could qualitatively predict the trends, they were inaccurate in quantifying NO. Additionally, the measured width of the NO profile in mixture fraction space expanded with increasing NH3/H2 ratio, N2 dilution ratio, and strain rate. While models could qualitatively predict this behavior, they consistently underestimated NO in the fuel-rich, lower-temperature region, resulting in a narrower NO profile width. The Manna model showed a better prediction of NO distribution in the fuel rich portion of non-premixed flames, accounting for NH3NO interactions at lower temperatures. These findings highlight the critical need to improve models to accurately predict NO concentrations in ammonia-containing flames and their behavior in fuel rich regions.

New insights into the effect of molecular structure on stable intermediate formation during the pyrolysis of normal and branched alkanes − II: Impact of carbon number and degree of branching

Transitioning to scalable and sustainable fuels produced from renewable feedstocks will be essential for decarbonizing the transportation sector. As these fuels typically encompass a wide range of molecular classes, it is important to understand the impact of varying molecular structure on their overall combustion behavior. To that end, experiments were conducted to investigate the thermal decomposition of ten neat hydrocarbons with varying carbon numbers and degree of branching in a shock tube at engine-relevant temperatures. A multi-wavelength, laser absorption spectroscopy-based approach was used to measure key stable intermediates formed during the pyrolysis process. The experiments revealed clear trends in intermediate formation and distribution, influenced by the molecular structure of each fuel. Additional experiments were conducted with a 2% composite fuel (consisting of a 50% n-heptane/50% iso-octane mixture)/Ar mixture to assess the impact of fuel blending on the pyrolysis process. A companion paper (Boddapati et al., 2024) delineates the experimental strategy and provides comprehensive mole fraction time histories of the major products, along with thorough analysis of carbon atom recovery. This paper establishes empirical trends in the measured intermediate yields with varying carbon number and degree of branching, and provides a discussion on the chemical phenomena governing the thermal decomposition of these fuels. In addition, this paper also lays the foundation for developing compact, robust chemical kinetic models for conventional and alternative fuels based on compositional information obtained through infrared spectra. The insights gained from these studies have the potential to guide sustainable fuel design and contribute to modeling the combustion chemistry of next-generation fuels.

Exploring the first-stage ignition and model optimization in the comprehensive study of n-dodecane oxidation

n-Dodecane is commonly employed as a surrogate for investigating the combustion characteristics of jet and diesel fuels. Enhancing comprehension of its combustion behavior and developing accurate chemical kinetics models for simulating combustion is of paramount importance in engine development. This study focuses on a detailed exploration of n-dodecane oxidation kinetics under low-temperature conditions and presents a novel dataset concerning the first-stage ignition delay time. A broad spectrum of experimental conditions is investigated, encompassing a range of temperature (600 ∼ 1350 K), pressure (5 ∼ 20 atm), equivalence ratios (0.5 ∼ 1.0), and dilution gases (N2 and Ar). Additionally, combustion experiments in a pure oxygen environment are performed, contributing valuable data to existing research. To enhance the precision of the chemical reaction kinetics model of n-dodecane, this study integrates updated rate coefficients obtained from the latest theoretical calculations for specific reaction classes. The improved rate rule provides a more accurate reference for the construction of the chemical reaction kinetics model of long straight alkane. The resulting improved model excels in accurately predicting both the first-stage ignition delay time and the total ignition delay time under a wide range of operational conditions. Additionally, the model performance is rigorously evaluated through a comprehensive assessment against a diverse array of datasets gathered from various literature references. The results show that, in contrast to the previously proposed model, this enhanced model provides highly reliable predictions over a broad range of parameters.

Deflagration Dynamics of Methane–Air Mixtures in Closed Vessels at Elevated Temperatures

In this paper, we explore the deflagration combustion of methane–air mixtures through both experimental and numerical analyses. The key parameters defining deflagration combustion dynamics include maximum explosion pressure (Pmax), maximum rate of explosion pressure rise (dP/dt)max, deflagration index (KG), and laminar burning velocity (SU). Understanding these parameters enhances the process of safety design across the energy sector, where light-emissive fuels play a crucial role in energy transformation. However, most knowledge on these parameters comes from experiments under standard conditions (P = 1 bar, T = 293.15 K), with limited data on light hydrocarbon fuels at elevated temperatures. Our study provides new insights into methane–air mixture deflagration dynamics at temperatures ranging from 293 to 348 K, addressing a gap in the current process industry knowledge, especially in gas and chemical engineering. We also conduct a comparative analysis of predictive models for the laminar burning velocity of methane mixtures in air, including the Manton, Lewis, and von Elbe, Bradley and Mitcheson, and Dahoe models, alongside various chemical kinetic mechanisms based on experimental findings. Notably, despite their simplicity, the Bradley and Dahoe models exhibit a satisfactory predictive accuracy when compared with numerical simulations from three chemical kinetic models using Cantera v. 3.0.0 code. The findings of this study enrich the fundamental combustion data for methane mixtures at elevated temperatures, vital for advancing research on natural gas as an efficient “bridge fuel” in energy transition.

Aβ Oligomer Dissociation Is Catalyzed by Fibril Surfaces.

Oligomeric assemblies consisting of only a few protein subunits are key species in the cytotoxicity of neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. Their lifetime in solution and abundance, governed by the balance of their sources and sinks, are thus important determinants of disease. While significant advances have been made in elucidating the processes that govern oligomer production, the mechanisms behind their dissociation are still poorly understood. Here, we use chemical kinetic modeling to determine the fate of oligomers formed in vitro and discuss the implications for their abundance in vivo. We discover that oligomeric species formed predominantly on fibril surfaces, a broad class which includes the bulk of oligomers formed by the key Alzheimer's disease-associated Aβ peptides, also dissociate overwhelmingly on fibril surfaces, not in solution as had previously been assumed. We monitor this "secondary nucleation in reverse" by measuring the dissociation of Aβ42 oligomers in the presence and absence of fibrils via two distinct experimental methods. Our findings imply that drugs that bind fibril surfaces to inhibit oligomer formation may also inhibit their dissociation, with important implications for rational design of therapeutic strategies for Alzheimer's and other amyloid diseases.

Microscopic Chemical Reaction Mechanism and Kinetic Model of Al/PTFE.

In order to study the microscopic reaction mechanism and kinetic model of Al/PTFE, a reactive force field (ReaxFF) was used to simulate the interface model of the Al/PTFE system with different oxide layer thicknesses (0 Å, 5 Å, 10 Å), and the thermochemical behavior of Al/PTFE at different heating rates was analyzed by simultaneous thermal analysis (TG-DSC). The results show that the thickness of the oxide layer has a significant effect on the reaction process of Al/PTFE. In the system with an oxide layer thickness of 5 Å, the compactness of the oxide layer changes due to thermal rearrangement, resulting in the diffusion of reactants (fluorine-containing substances) through the oxide layer into the Al core. The reaction mainly occurs between the oxide layer and the Al core. For the 10 Å oxide layer, the reaction only exists outside the interface of the oxide layer. With the movement of the oxygen ions in the oxide layer and the Al atoms in the Al core, the oxide layer moves to the Al core, which makes the reaction continue. By analyzing the reaction process of Al/PTFE, the mechanism function of Al/PTFE was obtained by combining the shrinkage volume model (R3 model) and the three-dimensional diffusion (D3 model). In addition, the activation energy of Al/PTFE was 258.8 kJ/mol and the pre-exponential factor was 2.495 × 1015 min-1. The research results have important theoretical significance and reference value for the in-depth understanding of the microscopic chemical reaction mechanism and the quantitative study of macroscopic energy release of Al/PTFE reactive materials.

Effect of Ethanol and Iso-Octane Blends on Isolated Low-Temperature Heat Release in a Spark Ignition Engine

<div>Low-temperature heat release (LTHR) is of interest for its potential to help control autoignition in advanced compression ignition (ACI) engines and mitigate knock in spark ignition (SI) engines. Previous studies have identified and investigated LTHR in both ACI and SI engines before the main high-temperature heat release (HTHR) event and, more recently, LTHR in isolation has been demonstrated in SI engines by appropriately curating the in-cylinder thermal state during compression and disabling the spark discharge. Ethanol is an increasingly common component of market fuel blends, owing to its renewable sources. In this work, the effect of adding ethanol to iso-octane (2,2,4-trimethylpentane) blends on their LTHR behavior is demonstrated. Tests were run on a motored single-cylinder engine elevated inlet air temperatures and pressures were adjusted to realize LTHR from blends of iso-octane and ethanol without entering the HTHR regime. The blends were tested with inlet temperatures of 40°C–140°C at equivalence ratios of 0.5, 0.67, and 1.0 with boosted (1.5 barA) conditions. The measured LTHR decreased with increasing ethanol content for all conditions tested; iso-octane–ethanol blends with above 20% ethanol content (by volume) showed minimal LTHR under engine conditions. These net effects resulted from the combination of thermal effects (charge cooling) and chemical effects (reactivity changes at low temperatures). The effect of temperature, pressure, fuel composition, and equivalence ratio on ignition delay times calculated from chemical kinetic modeling are presented alongside pressure–temperature trajectories of the in-cylinder gases to explain the trends. The underlying cause of the trends is explained by using a sensitivity analysis to determine the contribution of each reaction within the chemical kinetic mechanism to first-stage ignition, revealing the effect of introducing ethanol on the OH radical pool and resulting LTHR intensity.</div>

Study on the inhibition mechanism of ammonium dihydrogen phosphate on the pyrolysis gas flame of red pine wood

Ammonium phosphate-based fire extinguishers are widely used in forest fires due to their low cost and effectiveness against solid combustibles. However, the mechanism by which ammonium phosphate interacts with pyrolysis gas flames is not well understood, and there is a lack of precise experimental validation and correction of the chemical kinetics models regarding the suppression mechanism. Therefore, this study utilized NH4H2PO4 powder as a fire extinguishing agent and constructed a PLIF experimental system suitable for NH4H2PO4/red pine pyrolysis gas/air interactions. Through experiments, the changes in the concentration of OH radicals with different amounts of extinguishing agent at various equivalence ratios were measured. By employing Chemkin software, the study comprehensively analyzed the kinetic regulation mechanism of NH4H2PO4 on red pine pyrolysis gas flames from aspects such as chemical inhibition, sensitivity of elementary reactions, chemical reaction pathways, and chemical thermodynamics. The study revealed the characteristics and mechanisms of NH4H2PO4 powder inhibition, identifying R1092, R1098, R1116, and R1120 as the primary elementary reactions suppressing flame combustion. The mutual inhibition cycles formed among these reactions were found to be the main reasons for the suppression of H and OH radicals in the flame. Moreover, PO2 was identified as the primary phosphorus-containing fire extinguishing agent responsible for extinguishing the flame.

PRODIGE - Planet-forming disks in Taurus with NOEMA. II. Modeling the CO (2-1) isotopologue emission of the Class II T Tauri disks in Taurus

To understand how planets form in protoplanetary disks, it is necessary to characterize their gas and dust distribution and masses. This requires a combination of high-resolution dust continuum and molecular line interferometric observations, coupled with advanced theoretical models of protoplanetary disk physics, chemical composition, and radiative transfer. We aim to constrain the gas density and temperature distributions as well as gas masses in several T Tauri protoplanetary disks located in Taurus. We use the 12CO, 13CO, and C18O (2-1) isotopologue emission observed at $0.9 with the IRAM NOrthern Extended Millimeter Array (NOEMA) as part of the MPG-IRAM Observatory Program PRODIGE (PROtostars and DIsks: Global Evolution \, PIs: P. Caselli Th. Henning). Our sample consists of Class II disks with no evidence of strong radial substructures. We use these data to constrain the thermal and chemical structure of these disks through theoretical models for gas emission. To fit the combined optically thick and thin CO line data in Fourier space, we developed the DiskCheF code, which includes the parameterized disk physical structure, machine-learning (ML) accelerated chemistry, and the RADMC-3D line radiative transfer module. A key novelty of DiskCheF is the fast and feasible ML-based chemistry trained on the extended grid of the disk physical-chemical models precomputed with the ANDES2 code. This ML approach allows complex chemical kinetics models to be included in a time-consuming disk fitting without the need to run a chemical code. We present a novel approach to incorporate chemistry into disk modeling without the need to explicitly calculate a chemical network every time. Using this new disk modeling tool, we successfully fit the 12CO, 13CO, and C$ $O (2-1) data from the CI, CY, DL, DM, DN, and IQ Tau disks. The combination of optically thin and optically thick CO lines allows us to simultaneously constrain the disk temperature and mass distribution, and derive the CO-based gas masses. The best-fit disk gas masses range between 0.005 and $0.04 M_ sun $. These values are in reasonable agreement with the disk dust masses rescaled by a factor of 100 as well as with other indirect gas measurements via, for example, modeling of the wavelength dependence of the dust continuum emission radii, and HD and CO isotopologue emission.

Shock-Tube Measurements of Carbon Monoxide During Combustion of Hydroxyl-Terminated Polybutadiene Products/Air

Hydroxyl-terminated polybutadiene (HTPB) is a fuel proposed for use in hypersonic rockets, specifically in solid fuel ramjets (SFRJs), where it combines with air and undergoes combustion processes that range from fuel pyrolysis to fuel lean- combustion. A better understanding and the improvement of SFRJ combustion can be accomplished through fundamental experiments and computational fluid dynamics modeling. The current chemical-kinetic models need data to capture the reaction kinetics at the conditions under which SFRJs operate. This work focuses on providing combustion data to assess the predictive capabilities of state-of-the-art mechanisms at conditions relevant to SFRJs. The University of Central Florida shock-tube facility was used to conduct experiments of various combinations of HTPB products in air near 5 atm for temperatures ranging from 1100 to 1800 K and Φ=0.5, 1.0, 4.76. Nonintrusive, time-resolved laser absorption spectroscopy was used to record carbon-monoxide-concentration time histories and compared against the predictions of AramcoMech3.0 and HyChem mechanisms. For each mixture, the mid- and high-temperature conditions matched the models well, whereas there was a significant discrepancy for the low-temperature condition. A sensitivity analysis was then conducted to determine which reactions warranted further investigation to address the discrepancy at low temperatures.

Preparation of modified atmosphere packaging based on the respiratory characteristics of cherry tomato and its freshness preservation application

Cherry tomato (Lycopersicon esculentum Mill.) belongs to the respiratory leap type of fruit, post-harvest respiratory metabolism exuberant, easy to lead to nutrient loss, tissue destruction, and then rotting and deterioration, seriously affecting its commercial value. Therefore, research on post-harvest preservation technology of cherry tomatoes is crucial for related industries. Spontaneous modified atmosphere film packaging technology can extend the storage period of fruits and vegetables by adjusting the gas concentration of the storage environment, so that the fruits and vegetables can be maintained at a level suitable for their storage. In this study, the respiration model of cherry tomatoes at different temperatures was established by measuring the respiration rate of cherry tomatoes at different temperatures. It was found that the respiration rate of cherry tomatoes increased with increasing temperature and gradually decreased with increasing storage time. T-test results showed that there was no significant difference between the experimental values and the predicted values. The chemical kinetic model and its equilibrium equation were used to determine the parameters of modified atmosphere packaging of cherry tomatoes. PEG/PVDF membranes and SPEEK/PEG/PVDF blend membranes were prepared with sulfonated polyether ether ketone (SPEEK), polyvinylidene fluoride (PVDF) and polyethylene glycol (PEG) according to the parameters of modified atmosphere membranes to keep cherry tomatoes fresh. The results showed that there was a significant effect of package method on the preservation parameters of cherry tomatoes, the SPEEK/PEG/PVDF membrane treatment group significantly reduced the weight loss rate of cherry tomatoes and maintained the lower film permeability and higher sound fruit rate, hardness, titratable acid (TA) content, VC content and total soluble solids (TSS) content of cherry tomatoes. It can effectively delay the ripening and senescence of cherry tomatoes and extend the fruit storage period.

Experimental and kinetic modeling study of 1,3,5-trimethylbenzene oxidation at elevated pressure

This work presents the experimental and modeling results of 1,3,5-trimethylbenzene (T135MB) oxidation in a jet-stirred reactor at equivalence ratios (Φ) of 0.4 and 2.0, temperature range of 660–1020 K and pressure of 12.0 atm. 5 aromatic compounds, 5 oxygenated species and 6 light hydrocarbons were identified and quantified using GC and GC-MS. Compared with previous oxidation studies, 1-ethyl-3,5-dimethylbenzene, 3,5-dimethylbenzaldehyde, 3,5-dimethylphenol, ethylene and acetylene were newly detected. A detailed chemical kinetic model involving 911 species and 5370 reactions was developed and validated against experimental results of T135MB oxidation speciation at jet-stirred reactor and shock tube, laminar burning velocities and ignition delay times. Rate-of-production analysis shows that the dominant consumption channel of T135MB is H-abstraction by OH radicals on methyl sites, and 3,5-dimethylbenzaldehyde is a key intermediate in the oxidation of T135MB. Compared with atmospheric pressure, sharp consumption of T135MB was observed (the fuel conversion rate changes from 25 % at 838 K to 95 % at 839 K) under fuel-lean condition at 12 atm, which results from the rapid growth of OH radicals controlled by H2O2(+M) = 2OH(+M). Sensitivity analysis reveals that H-abstraction reactions of T135MB by OH and H on methyl sites are the most inhibiting reactions at Φ = 0.4 and 2.0, respectively, when T135MB conversion rate is 25 %. However, these two reactions become promoting at 95 % T135MB conversion. The H-abstraction reaction of T135MB with O2 on methyl sites is the most promoting at 25 % T135MB conversion, shifting to an inhibiting reaction at 95 % conversion.Novelty and significance statement: The novelty of this research is that high-pressure and low-temperature oxidation experiment of T135MB covering both fuel-lean and fuel-rich conditions was first reported in this work with abundant intermediates information. Rapid consumption of T135MB under fuel-lean condition was observed, and new intermediates such as 3,5-dimethylbenzaldehyde were detected which plays an important role in the fuel conversion. Additionally, a comprehensive kinetic model for T135MB was developed, which well predicts speciation, ignition delay times and laminar flame speeds under wide range of conditions. It is significant because the high pressure data is very important for the model validation since it is more close to the real engine-operating conditions. Moreover, the model provides insight on the high pressure chemical kinetics of the aviation surrogate fuel consumption and deepens the understanding of low-temperature oxidation of alkyl aromatics.

Optimization models for photosynthetic bioenergy generation in building façades

Façade design optimization has a significant impact on promoting resilient solar harvesting methods in urban areas. This study introduces a new framework toward the optimal inclusion of microalgae photobioreactors in different façade geometries by developing a detailed chemical kinetics model aided by optimization techniques. Although algal bioreactive façades in recent literature are restricted to flat façades, the present study reveals that bioenergy generation can be enhanced by up to 29.6 % through optimized folded façades. Hooke-Jeeves algorithm demonstrates remarkable computational efficiency in optimizing such façades, achieving the optimal outcome with only 88 function evaluations. However, the Hooke-Jeeves algorithm has limitations when applied to free-form façades by displaying noticeable instability and reporting an optimal value approximately 40 % lower than Genetic Algorithms. Hooke-Jeeves algorithm has the possibility to conclude misleading outcomes as optimal points. This is mitigated by applying multiple initial points and verifying the outcomes with graphical optimization. In terms of energy performance, free-form façades have higher irradiation of up to 210 W/m2 compared to 180 W/m2 for flat façades. Optimal distribution of renewable modules on free-form façades increases energy generation by 14.3 %. South-facing façades produce the highest bioenergy at 2.4 W/m2, while west and east orientations generate the lowest at 0.8 W/m2.