NH3NO interaction at low-temperatures: An experimental and modeling study

The present work provides new insight into NH₃NO interaction under low-temperature conditions. The oxidation process of neat NH₃ and NH₃ doped with NO (450, 800 ppm) was experimentally investigated in a Jet Stirred Flow Reactor at atmospheric pressure for the temperature range 900–1350 K. Results showed NO concentration is entirely controlled by DeNO_x reactions in the temperature range 1100–1250 K, while NH₃NO interaction does not develop through a sensitizing NO effect, for these operating conditions.A detailed kinetic model was developed by systematically updating rate constants of controlling reactions and declaring new reactions for N₂H₂ isomers (cis and trans). The proposed mechanism well captures target species as NO and H₂ profiles. For NH₃NO mixtures, NO profiles were properly reproduced through updated DeNO_x chemistry, while NH₂ recombination reactions were found to be essential for predicting the formation of H₂. The role of ammonia as a third-body species is implemented in the updated mechanism, with remarkable effects on species predictions. For neat NH₃ mixture, the reaction H+O₂(+M)=HO₂(+M) was crucial to predict NO formation via the reaction NH₂+HO₂H₂NO+OH.     

Effect of stoichiometric mixture fraction on nonpremixed H2O2N2 edge-flames

The influences of stoichiometric mixture fraction (Z_st) and global strain rate (σ) on the shapes and propagation rates (U_edge) of nonpremixed edge-flames in H₂N₂/O₂N₂ mixtures were investigated using a counterflow slot-jet apparatus. Both positive and negative U_edge were observed depending on dilution level, Z_st and σ. At low Z_st only continuous flames were observed whereas at sufficiently high Z_st, where a shift from more oxygen-deficient to more fuel-deficient conditions at the reaction zone occurs, broken structures characteristic of low Lewis number premixed flames were observed which enabled combustion under conditions where no flames could be sustained at lower Z_st, even for the same dilution level. At sufficiently high σ these broken structures could transition from advancing edge-flames to isolated, stationary flames, particularly for highly-diluted mixtures. These findings were in surprisingly good agreement with theoretical predictions. Appropriate scalings of these behaviors for different mixtures based on computed 1D extinction strain rates were identified. Nonpremixed H₂N₂/O₂N₂ edge-flames have profoundly different responses to Z_st than corresponding hydrocarbon edge-flames, which is shown to be due to differences in the chemistry and Lewis numbers of the two fuels.     

Intrinsic kinetics mechanisms for the catalytic reduction of NO by Na-loaded char

An insight into the interaction between NO and Na-loaded char is essential to improve the catalytic ability of Na to NO reduction, which will be useful to lower NO emissions during thermal utilization of sodium-containing fuels. Here, the intrinsic kinetics mechanisms for the catalytic reduction of NO by Na-loaded char were discussed in details. Using density functional theory (DFT) calculations, possible reaction pathways were first obtained, followed by evaluation of the rate coefficients through transition state theory (TST) calculations. On this basis, the analyses of both sensitivity and rate of products (ROP) were performed to illustrate the intrinsic kinetic mechanism for the NO reduction by Na-loaded char in a certain combustion condition, with an emphasis on the effects of temperature and NO-to-CO stoichiometric ratio. Results indicated that the catalytic active center –ONa plays an important role in the catalytic reduction of NO by Na-loaded char. Specifically, in most cases, the interaction of NO with Na-loaded char largely depends on the elementary reaction of CNO-Na+NO+CO→21-IM3+CO₂. As the stoichiometric ratio of NO to CO increases, the CO-Na+2NO→8-IM4+N₂ becomes increasingly dominant. Moreover, higher temperature causes the CNO-Na+NO→20-P + N₂O as the dominant reaction. Nonetheless, one thing that these reactions have in common is that they are all related to the catalytic active center –ONa. Therefore, the NO reduction Na-loaded char largely depends on the interaction of NO with the carbonaceous surface containing –ONa. Inspired by this, a conceptual approach was proposed to improve the catalytic performance of Na on NO reduction, and it has been shown to be theoretically feasible. To summarize, the combination of DFT, TST and kinetic calculations is useful to clarify the interaction between NO with Na-loaded char, and it gives a basis for the development of micro-kinetic model.     

A promising guanidinium based metal-organic single crystal for optical power limiting applications

A novel guanidinium based metal-organic framework material [(2(C H₆ N₃)⁺.Zn (C₂H₃O₂)₄]− has been synthesized and optical transparency of the crystals was studied. Structural parameters of the grown metal-organic crystals have been characterized by single crystal X-ray diffraction. The single crystal XRD study confirms that the title compound crystallized in tetragonal system with I 4₁ /a c d space group. The crystal structure has stabilized through intricate 3-D hydrogen bonding network established by the NH…O and CH…O interactions. The soft nature of the material has been identified by hardness study. UV–visible spectroscopy has been used to investigate the optical properties. Good thermal stability has been proved by TG-DTA. The third order nonlinear optical response was studied by Z-Scan technique.     

Combustion of ethylamine,dimethylamine and diethylamine: Theoretical and kinetic modeling study

Aliphatic amines are an important class of nitrogen-containing compounds present in renewable fuels such as bio-oils. Conversion of this fuel-bound nitrogen can lead to the formation of HCN and NH₃, as well as NO_x emissions. In this work, the combustion chemistry of small aliphatic amines is investigated via a combination of quantum chemical calculations, chemical kinetic modeling and experimental validation. The influence of the degree of substitution on the nitrogen atom and the alkyl chain length on the reactivity and product distribution is studied via three model compounds, i.e. ethylamine (EA, CH₃CH₂NH₂), dimethylamine (DMA, (CH₃)₂NH) and diethylamine (DEA, (CH₃CH₂)₂NH). A detailed kinetic model containing 258 species and 2274 reactions is developed to describe their combustion over a wide range of conditions. The proposed model captures the trends in ignition delay times and species concentrations over a temperature range from 500 to 2000 K and pressures from 4 to 170 kPa. The ignition delay data are predicted with an average deviation of 10%. The difference between experimental and simulated species concentrations from laminar premixed flames is for the major species on average 50%, while the agreement for the JSR is even better, with an average deviation of 10%. The dominant decomposition pathway under all the studied conditions is a set of hydrogen abstractions from the C_α and N positions followed by β-scission of the fuel radicals. Among the unimolecular decomposition pathways, the homolytic CC and CN scissions and four-centered elimination play a minor role. HCN is the main intermediate and at temperatures above 1100 K the amines are completely converted to N₂ and NO.     

Insights into the interaction kinetics between propene and NOx at moderate temperatures with experimental and modeling methods

This work aims to provide insight into the interaction of propene with NO_x from both experimental and kinetic modeling perspectives. The oxidation of propene at fuel-lean (?=0.23) condition and the oxidation of propene doped with NO_x at fuel-lean (?=0.23) and fuel-rich (?=1.35) conditions have been investigated in a laminar flow reactor at atmospheric pressure in the temperature range of 725-1250 K. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used to achieve comprehensive, isomer-resolved identification of major products and critical nitrogenous, carbonyl and hydrocarbon intermediates. To complement the experiments, a detailed kinetic model, starting from widely used core mechanisms, was developed. Rate of production analyses and sensitivity analyses were performed to interpret the experimental observations. The results show that the promoting effects of NO_x on the oxidation reactivity of propene are initiated by the reactions of allyl radical with NO₂ at low temperature, i.e. C₃H₅A+NO₂C₃H₅O+NO. For the oxidation of the fuel-rich propene/NO_x mixture, temperature-dependent mole fraction profiles of propene, O₂ and products show several distinct regions reflecting a competition between chain propagation via C₃H₅A+NO₂C₃H₅O+NO and chain termination via C₃H₅A+NOC₃H₅NO. The formation and consumption chemistry of carbonyl and hydrocarbon intermediates in the presence of NO_x was also analyzed and discussed.     

Probing fuel-specific reaction intermediates from laminar premixed flames fueled by two C5 ketones and model interpretations

The flame chemistry was explored for two C₅ ketones with distinct structural features, cyclopentanone (CPO) and diethyl ketone (DEK). Quantitative information for numerous species, including some reactive intermediates, was probed from fuel-rich (?= 1.5) laminar premixed flames fueled by the ketones with a photoionization molecular-beam mass spectrometer (PI-MBMS). Furthermore, a new kinetic model was proposed aimed at interpreting the high-temperature combustion chemistry for both ketones, which could satisfactorily predict the current flame speciation measurements. Experimental observations in combination with modeling analyses were used to reveal the similarities and differences between the compositions of the species pools of the two flames, with emphasis on the effects of the carbonyl functionality on pollutants formations. Besides some primary species which preserve fuel-specific features produced from initial steps of fuel consumptions, basic C₁C₄ intermediates also differ much between the two flames. More abundant intermediates were observed in the CPO flame because the cyclic fuel structure enables ring-opening processes followed by formations of C₃ and C₄ hydrocarbons which cannot be easily produced from the two isolated ethyl moieties in DEK under flame conditions. The consumptions of C₃C₄ hydrocarbons in the CPO flame further lead to larger C₅C₆ species which were under the detection limit in the DEK flame. In both flames, the tightly bonded carbonyl groups in the fuels tend to be preserved, leading to carbon monoxide through α-scissions of fuel-related acyl radicals. The carbonyl moieties in most detected C₁C₃ aldehydes and ketones form through oxidations of hydrocarbon species rather than directly originating from the fuels.     

Thermal decomposition of furans with oxygenated substituents: A combined experimental and quantum chemical study

Furans are an important class of compounds that can be thermochemical or enzymatically produced from biomass. Despite of their importance little is known about the thermal decomposition of furans with oxygenated substituents. In this work, the influence of the -CH₃, -CH₂OH and -CHO functional groups on the molecular and radical decomposition chemistry is studied with a combined quantum chemical and experimental approach using 2-furfuryl alcohol and 5-methyl furfural as model components.The quantum chemistry calculations show that both reactants can decompose by a ring-opening isomerization reaction and through carbene intermediates. The latter are formed by the shift of a hydrogen atom or a -CHO functional group within the furan ring structure. The -CHO functional group on the furan ring structure accelerates the molecular ring-opening isomerization reaction, while it suppresses carbene formation channels compared to other functional groups.The weaker CH and CO bonds in 2-furfuryl alcohol and 5-methyl furfural compared to furan and furfural respectively result in a higher importance of radical chemistry that cannot be neglected. This is confirmed experimentally by analyzing the product spectrum with molecular beam synchrotron VUV photoionization mass spectrometry at a pressure of 0.04 bar and for temperatures between 923 K to 1223 K for 2-furfuryl alcohol and 973 K to 1273 K for 5-methyl furfural. For both reactants several radical intermediates are observed starting from 923 K for 2-furfuryl alcohol and from 973 K for 5-methyl furfural. Examples of measured radicals are those initial formed from the reactant by a CH homolytic bond scission and methyl, allyl, propargyl, 1,2-butadiene-4-yl, 2-furanyl-methyl, 2,5-dihydrofuran-2-yl and 1?hydroxyl-2-furanyl-methyl radicals.     

Exploring the pyrolysis chemistry of 1,3,5-trimethylcyclohexane with insight into fuel isomeric and multiple substitution effects

To reveal insights into the combustion mechanism of multiple alkyl substituent cycloparaffins, this work reports an experimental and modeling study of 1,3,5-trimethylcyclohexane (T135MCH) pyrolysis in an extended flow reactor at low and atmospheric pressures. More than 30 species were detected and quantified employing synchrotron vacuum ultraviolet photoionization molecular beam mass spectrometry, and a detailed kinetic model developed based on reaction classes and update kinetic data was validated against the measured species profiles with a reasonable agreement. The reaction flux analyses were performed to reveal the key pathways of the fuel decomposition, intermediates production and aromatics formation. For the primary decomposition, the branching ratios of reaction types show strong dependence on changes of pressures and temperatures, including unimolecular methyl elimination, unimolecular ring-opening isomerization and H-abstraction. Besides the direct dissociation channels, major intermediate hydrocarbons are formed via stepwise dehydrogenation, recombination with ĊH₃ radical or “formally direct” chemically activated reactions triggered by Ḣ atom addition. Monocyclic aromatic hydrocarbons such as benzene and toluene can be produced by traditional H-abstraction/β-C-H scission sequence, cyclopentadiene-related pathways, or recombination mechanism from small linear products. The formations of indene and naphthalene are controlled by C₅+C₅ and C₅+C₄ mechanism respectively. The comparison work of species profiles combined with theoretical calculations of bond dissociation enthalpies (BDEs) was performed to reveal the multiple CH₃-group substituent and isomeric effects of methylcyclohexane (MCH), 1,2,4-trimethylcyclohexane (T124MCH) and T135MCH on pyrolysis activity and ethylene/benzene formation. Besides the increased reaction active sites, the added CH₃-group and ortho-substitution can both weaken the strength of CC and CH bonds, leading to the promoting decomposition activity. The different formation tendencies of products are caused by different BDEs, length of carbon skeleton, as well as complex fuel-specific pathways.     

Thermal decomposition of 1-hexene by flash pyrolysis: A study of initial decomposition mechanism

Thermal decomposition of 1-hexene at temperatures 295-1410 K was conducted using a flash pyrolysis micro-reactor coupled to laser-based vacuum ultraviolet photoionization time-of-flight mass spectrometer (VUV-PI-TOFMS). The decomposition mechanism of 1-hexene was developed with the help of theoretical calculation performed at the MRCI/cc-pvtz//CASSCF/6–31+G(d,p) level. The γ-scission and diradical retro-ene reactions were determined as the main initial decomposition reactions in the temperature range 990-1240 K. Two diradical retro-ene reaction channels, 1,5-diradical and 1,6-diradical reactions, were proposed in order to interpret the appearance of the C₄H₈ species. The 1,5-diradical retro-ene reaction involved a 1,5-diradical intermediate that subsequently decomposed via CC β-scissions to the C2, C3 and C4 products. The 1,6-diradical retro-ene reaction proceeded via a 1,6-diradical intermediate and CC β-scissions to produce the C2 and C4 species. The proposed diradical retro-ene mechanism was evidenced indirectly by the early product distribution of 1-hexene pyrolysis in a flow reactor at 1173 K determined by synchrotron radiation VUV-PI-TOFMS. It was verified in the flash pyrolysis of 1-heptene as well.     

Exploration on laminar flame propagation of 3,3-dimethyl-1-butene, 2,3-dimethyl-1-butene and 2,3-dimethyl-2-butene

Laminar flame propagation of branched hexene isomers/air mixtures including 3,3-dimethyl-1-butene (NEC₆D3), 2,3-dimethyl-1-butene (XC₆D1) and 2,3-dimethyl-2-butene (XC₆D2) was investigated using a high-pressure constant-volume cylindrical combustion vessel at 1–10 atm, 373 K and equivalence ratios of 0.7–1.5. The measured laminar burning velocity (LBV) decreases in the order of NEC₆D3, XC₆D1 and XC₆D2, which indicates distinct fuel molecular structure effects. A kinetic model was constructed and examined using the new experimental data. Modeling analyses were performed to reveal fuel-specific flame chemistry of branched hexene isomers. In the NEC₆D3 and XC₆D1 flames, the allylic CC bond dissociation reaction plays the most crucial role in fuel decomposition under rich conditions, while its dominance is replaced by H-abstraction reactions under lean conditions. The H-abstraction and H-assisted isomerization reactions are concluded to govern fuel consumption in the XC₆D2 flame under all investigated conditions. Both C₀C₃ reactions and fuel-specific reactions are found to be influential to the laminar flame propagation of the three branched hexene isomers. Fuel molecular structure effects were analyzed with special attentions on key intermediates distributions and fuel-specific reactions in all flames. Due to the formation selectivity of key intermediates such as 2-methyl-1,3-butadiene and 2,3-dimethyl-1,3-butadiene, the production of reactive radicals especially H follows the order of NEC₆D3 > XC₆D1 > XC₆D2, which results in the same order of fuel reactivities and LBVs.     

Progress towards nanoengineered energetic materials

Given the constraints on typical bond energies and the commonality of final products produced from combustion of CHNO based energetic materials, the possibilities for further increases in stored potential energy and thermodynamic performance from these classes of materials are limited. Thus, modulating the energy release to achieve efficiency and effectiveness for desired applications is of great value. Investigation of nanomaterials as energetic materials began more than twenty years ago with much of the interest to increase reaction rates and reduce sensitivity. During this period, research on energetic nanoparticles was devoted to reducing the loss of energy density with metallic materials due to the naturally occurring oxide passivating layer, managing their high surface area preventing high loadings in solids, minimizing particle-particle interactions making dispersion in the gas-phase difficult, and understanding combustion mechanisms. As an outcome, novel synthesis methods of producing nanocomposites, and new fields of applications, such as micro-pyrotechnics, have developed. Yet, the research community is only beginning to understand how to manipulate and build energetic materials at the nanoscale, and what designs are optimal for desired functions. Furthermore, recognizing the difficulties for increased energy density and reduced sensitivity, the development of multifunctional and smart nanoenergetic materials is currently being researched to enable control of energy release rates and material sensitivity on demand. This research is being advanced by assembly of nanoengineered energetic materials to bulk scales by additive manufacturing, the development and application of combustion diagnostics that resolve nanometer and micron scales, and ab initio quantum chemistry and molecular dynamics calculations. The challenges that have been confronted and the directions of continuing research on nanoenergetics are presented and discussed.     

Mid-wave infrared liquid crystal shutter for breathalyzer applications

There exists a problem with an in situ diagnostics of contamination of ethyl alcohol in a human being exhaled air. When ethyl alcohol in a mouth blowing (in a gaseous state) exists, the characteristic CH stretch absorption bands in CH₃ and CH₂ functional groups in ethanol (CH₃CH₂OH) appear at a wavelength of λ = 3.42 μm. To investigate the presence of ethyl alcohol in exhaled human air, the light beam of λ = 3.42 μm is passing through an air sample. If one alternately measures the intensity of the investigated beam and the reference, a percentage of ethanol in the air sample can be estimated using a sensitive nondispersive infrared (NDIR) system with a stable operating flow mass detector. To eliminate a mechanical chopper and noise generating stepper motors, a photonic chopper as a liquid crystal shutter for λ = 3.42 μm has been designed. For this purpose, an innovative infrared nematic liquid crystal mixture was intentionally prepared. The working mixture was obtained by a selective removal of CH bonds and its exchange by heavier polar substituents, what ensures a lack of absorption band of CH bonds. The paper presents theory, concept and final experimental results of the infrared nematic liquid crystals mixture and the liquid crystal shutter for breathalyzer applications.     

Sonochemiluminescence of lucigenin using amines as coreactant: Reactivity and mechanism studies

Sonochemiluminescence (SCL) from aqueous solution of lucigenin (Luc²⁺) has been studied using aliphatic amines as coreactant. The SCL intensity are strongly dependent on the dissolved gases such as air, oxygen, nitrogen and argon. The most strong SCL signals are observed from oxygen saturated alkaline solution containing Luc²⁺ when small amount of trialkylamine, such as tripropylamine (TPrA) was added into the solution. In an ultrasonic field, TPrA can adsorb onto the cavitation bubble/solution interface where TPrA is oxidized by OH to form a radical cation TPrA⁺ and subsequently produce a highly reducing TPrA species through a deprotonation reaction of the TPrA⁺. TPrA is suggested to initiate the reduction reactions of Luc²⁺ and molecule oxygen to produce Luc⁺ and superoxide radical anion (O₂⁻), respectively. The radical-radical coupling reaction between Luc⁺ and O₂⁻ is expected to initiate the light emission. The production of O₂⁻ is examined by spectrofluorometric method using 2-(2-pyridyl)benzothiazoline as a fluorescent probe. The results show that the production of O₂⁻ by ultrasound was more efficient in oxygen saturated solution in the presence of coreactants, consistent with the results with SCL measurements.     

The role of DME addition on the evolution of soot and soot precursors in laminar ethylene jet flames

Dimethyl ether (DME) has received considerable attention as a fuel additive to reduce the emission of particulate matter (PM) due to its low-temperature chemistry, molecularly bound oxygen atom and the absence of CC bonds. However, the effect of DME addition on the evolution of soot and particularly soot precursors is not entirely understood. This study aims to shed light on this issue by blending different proportions of DME with diffusion, E60, and partially premixed, PP12, base cases of laminar ethylene flames using the Yale benchmark burner. Laser-induced fluorescence (LIF) intensity and decay time are used to characterize the structure and evolution of soot precursors, while laser-induced incandescence (LII) is utilized to determine the soot volume fraction (SVF) and the effective primary particle diameter (D_p). For the diffusion flames, the addition of 10% DME increases the concentrations of both soot and soot precursors. With the further addition of DME to 20%, the SVF decreases to levels similar to those of E60 and then decreases further with 30% DME addition. All diffusion flames with DME addition exhibit higher concentrations of soot precursors than those of the reference E60 case. For PP12, the addition of 10% DME shows similar concentrations of soot precursors and a slight reduction in the SVF which continues to decrease with further increases in DME additions to the PP12 flame. The addition of DME seems to have little effect on the soot particle diameters for all the studied flames. Overall, the PP flames result in smaller mean particle diameters than the diffusion flame counterparts.     

Exploring fuel molecular structure effects on the pyrolysis chemistry of branched hexenes

3,3-Dimethyl-1-butene (NEC₆D3) and 2,3-dimethyl-2-butene (XC₆D2) are representative branched alkene components in gasoline. This work experimentally investigated the pyrolysis of NEC₆D3 and XC₆D2 in a flow reactor (T = 950–1350 K, P = 0.04 atm) and a jet-stirred reactor (T = 730–1000 K, P = 1 atm) using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC). A pyrolysis model of branched hexenes was proposed and validated against the new experimental data. The combined experimental observations and modeling analyses provide insights into the predominant fuel decomposition pathways and specific formation pathways of products under pyrolysis conditions. NEC₆D3 exhibits a much higher reactivity than XC₆D2 due to the existence of allylic CC bonds. Unimolecular decomposition reactions play the most crucial role in NEC₆D3 decomposition, while in XC₆D2 pyrolysis, fuel consumption is dominated by H-abstraction reactions and the H-assisted isomerization reaction. Fuel-specific pathways can remarkably influence the formation of pyrolysis products, especially the key C₁C₂ products, isomer pairs and dialkenes. Furthermore, the reactions involving propargyl radical dominate the formation of fulvene and aromatic products in the pyrolysis of both fuels, leading to more abundant production of C₆ and larger cyclic products in XC₆D2 pyrolysis.     

Automatically generated detailed and lumped reaction mechanisms for low- and high-temperature oxidation of alkanes

In this work, we present a methodology on automatic generation of predictive lumped sub-mechanisms for normal and branched alkanes. This methodology aims at obtaining lumped reaction mechanisms that preserve the chemical behavior of each reaction class in the detailed model. To achieve this goal, detailed sub-mechanisms for combustion of alkanes are generated by employing an updated version of the MAMOX++ software developed in this work; recent progress in the low-temperature reaction classes and rate rules are incorporated into the updated software. Instead of computing the selectivities of several primary products with MAMOX++ and fitting the selectivities between the detailed and lumped models, this work proposes a new methodology to generate the lumped sub-mechanisms for fuel molecules. The stoichiometric parameters and the reaction rates for each reaction class in the lumped sub-mechanism are fitted to match those in the detailed model. Based on the present methodology, both the detailed and lumped sub-mechanisms for normal C₅C₁₀ alkanes and branched C₅C₈ alkanes, that is for 15 different fuels, are automatically generated and merged into a base chemistry model (i.e. AramcoMech 2.0), respectively. The detailed and lumped models are validated against the experimental data in the literature. The automatically generated detailed models for alkanes are able to capture the experimental targets across a wide range of conditions, demonstrating the robustness of the reaction classes and rate rules adopted. The lumped models for normal alkanes have similar performance to their respective detailed models, and are able to predict the oxidation behavior of normal alkanes. However, prediction deviations between the detailed and lumped models for branched alkanes are shown to be slightly greater.     

Laminar flame propagation of acetone and 2-butanone at normal to high pressures: Insight into fuel molecular structure effects of ketones

This work reports an experimental and kinetic modeling investigation on the laminar flame propagation of acetone and 2-butanone at normal to high pressures. The experiments were performed in a high-pressure constant-volume cylindrical combustion vessel at 1–10 atm, 423 K and equivalence ratios of 0.7–1.5. A kinetic model of acetone and 2-butanone combustion was developed from our recent pentanone model [Li et al., Proc. Combust. Inst. 38 (2021) 2135–2142] and validated against experimental data in this work and in literature. Together with our recently reported data of 3-pentanone, remarkable fuel molecular structure effects were observed in the laminar flame propagation of the three C₃C₅ ketones. The laminar burning velocity increases in the order of acetone, 2-butanone and 3-pentanone, while the pressure effects in laminar burning velocity reduces in the same order. Modeling analysis was performed to provide insight into the key pathways in flames of acetone and 2-butanone. The differences in radical pools are concluded to be responsible for the observed fuel molecular structure effects on laminar burning velocity. The favored formation of methyl in acetone flames inhibits its reactivity and leads to the slowest laminar flame propagation, while the easiest formation of ethyl in 3-pentanone flames results in the highest reactivity and fastest laminar flame propagation. Furthermore, the LBVs of acetone and 3-pentanone exhibit the strongest and weakest pressure effects respectively, which can be attributed to the influence of fuel molecular structures through two crucial pressure-dependent reactions CH₃ + H (+M) = CH₄ (+M) and C₂H₄ + H (+M) = C₂H₅ (+M).     

Ultrasound-assisted preparation of lactoferrin-EGCG conjugates and their application in forming and stabilizing algae oil emulsions

The aim of this study was to prepare lactoferrin-epigallocatechin-3-gallate (LF–EGCG) conjugates and to determine their ability to protect emulsified algal oil against aggregation and oxidation. LF–EGCG conjugates were formed using an ultrasound-assisted alkaline treatment. The ultrasonic treatment significantly improved the grafting efficiency of LF and EGCG and shortened the reaction time from 24 h to 40 min. Fourier transform infrared spectroscopy and circular dichroism spectroscopy analyses showed that the covalent/non-covalent complexes could be formed between LF and EGCG, with the CO and CN groups playing an important role. The formation of the conjugates reduced the α-helix content and increased the random coil content of the LF. Moreover, the antioxidant activity of LF was significantly enhanced after conjugation with EGCG. LF–EGCG conjugates as emulsifiers were better at inhibiting oil droplet aggregation and oxidation than LF alone. This study demonstrates that ultrasound-assisted formation of protein–polyphenol conjugates can enhance the functional properties of the proteins, thereby extending their application as functional ingredients in nutritionally fortified foods.     

Thermal activation and reaction of allyl alcohol on Ni(100)

The thermal chemistry of allyl alcohol (CH₂CHCH₂OH) on a Ni(100) single-crystal surface was studied by the temperature programmed desorption (TPD) and the X-ray photoelectron spectroscopy (XPS). The allyl alcohol adsorbs molecularly on the metal surface at 100 K. Intact molecular desorption from the surface occurs at temperatures around 180 K, but some molecules exhibit chemical reactivity on the surface: activation of the OH, CC, and CO bonds produces η¹(O)-allyloxy CH₂CHCH₂O_(a), η²(C, C) allyl alcohol (C_(a)H₂C_(a)HCH₂OH), and η³(C, C, O)-alkoxide (C_(a)H₂C_(a)CH₂ O_(a)) intermediates. Further thermal activation of allyl alcohol on the surface yields propylene (CH₂CHCH₃), 1-propanol (CH₃CH₂CH₂OH), propanal (CH₃CH₂CHO), and combustion and dehydrogenation products (H₂O, H₂, and CO). Propylene desorbs from the surface at temperatures of around 270 K. Hydrogenation to the η³(C, C, O)-alkoxide intermediate leads to the production of propanal which desorbs from the surface around 320 K, while hydrogenation of the η²(C, C) allyl alcohol intermediate produces 1-propanol, which desorbs at around 310 K. The co-adsorption of hydrogen atoms on the surface enhances the formation of the saturated alcohol, while co-adsorption of oxygen enhances the formation of both the saturated alcohol and the saturated aldehydes.