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.     

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.     

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.     

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.     

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.     

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.     

Effect of ammonia addition on suppressing soot formation in methane co-flow diffusion flames

Due to issues surrounding carbon dioxide emissions from carbon-containing fuels, there is growing interest in ammonia (NH₃) as an alternative combustion fuel. One attractive method of burning NH₃ is to co-fire it with hydrocarbons, such as natural gas, and in this case soot formation is possible. To begin understanding the influence of NH₃ on soot formation when co-fired with hydrocarbons, soot volume fractions and mole fractions of gas-phase species were computationally and experimentally interrogated for CH₄ flames with up to 40% NH₃ by volumetric fuel fraction. Mole fractions of gas-phase species, including C₂H₂ and C₆H₆, were measured with on-line electron impact mass spectrometry, and soot volume fractions were obtained via color-ratio pyrometry. The simulations employed a detailed chemical mechanism developed for capturing nitrogen interactions with hydrocarbons during combustion. The results are compared to findings in N₂CH₄ flames, in order to separate thermal and dilution effects from the chemical influence of NH₃ on soot formation. Experimentally, C₂H₂ concentrations were found to decrease slightly for the NH₃CH₄ flames relative to N₂CH₄ flames, and a stronger suppression of C₆H₆ was found for NH₃ relative to N₂ additions. The measured results show a strong suppression of soot with the addition of NH₃, with soot concentrations reduced by over a factor of 10 with addition of up to 20% or more NH₃ by mole fraction. The model satisfactorily captured relative differences in maximum centerline C₂H₂, C₆H₆, and soot concentrations with addition of N₂, but was unable to match measured differences in NH₃CH₄ flames. These results highlight the need for an improved understanding of fuel-nitrogen interactions with higher hydrocarbons to enable accurate models for predicting particulate emissions from NH₃/hydrocarbon combustion.     

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.     

Influence of different solvents on the structural,optical, impedance and dielectric properties of ZnO nanoflakes

In this work, we have synthesized the ZnO nanoflakes using three different solvents, i.e., isopropyl alcohol (IPA), DI (de-ionized) water and ethanol via co-precipitation technique. XRD analysis revealed the hexagonal wurtzite crystal structure for all synthesized samples. The crystallite size is least for ZnO nanoflakes synthesized using ethanol and highest for IPA by applying Scherrer's formula as well as W–H plot. The optical properties were analyzed using UV–Visible spectroscopy and revealed that the maximum optical band gap has been obtained using ethanol as a solvent while the least band gap is observed for IPA. The expansion of light absorption region from UV to visible region can lead to its application in various fields such as optical LEDs, photocatalysis, laser diodes, etc. FTIR spectrum verifies the presence of vibrational modes of the ZnO bond, stretching and bending bonds of OH bonds and O=C=O stretching bond in the prepared samples. The plot for frequency-dependent dielectric loss exhibits the change in dielectric properties. The Nyquist diagrams reveal the semi-circular arc depicting the variation between real and imaginary parts of impedance. The results show that the electrical conductivity increases with frequency and temperature. The activation energy is found using Arrhenius equation with the plot of conductivity versus temperature and the values of activation energy for ZnO nanoflakes synthesized using IPA, DI water, and ethanol is found to be 0.23 eV, 0.29 eV and 0.41 eV, respectively.     

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.     

Hybrid solvothermal/sonochemical-mediated synthesis of ZnO NPs generative of OH radicals: Photoluminescent approach to evaluate OH scavenging activity of Egyptian and Yemeni Punica granatum arils extract

Zinc oxide NPs were synthesized solvothermally within sonochemical mediation and characterized by XRD, FTIR, SEM, EDX, elemental mapping, TEM and UV–vis. spectrophotometry. To evaluate the hydroxyl radicals (OH) scavenging activity of arils extract of Egyptian (EGY-PAM) and Yemeni Punica granatum (YEM-PAM), the developed zinc oxide nano particles (ZnO NPs) as a highly productive source of hydroxyl radicals (under Solar-illumination) was used. The yield of OH was trapped and probed via fluorimetric monitoring. This suits the first sensitive/selective photoluminescent avenue to evaluate the OH scavenging activity. The high percentage of DPPH radical scavenging reflected higher contents of phenolics, flavonoids, and anthocyanins that were found in EGY-PAM and YEM-PAM. Although, some secondary metabolites contents were significantly different in EGY-PAM and YEM-PAM, the traditional DPPH radical scavenging methodology revealed insignificant IC₅₀. Unlike, the developed fluorimetric probing, sensitively discriminated the OH scavenging activity with IC₅₀ (105.7 µg/mL) and lower rate of OH productivity (k = 0.031 min⁻¹) in case of EGY-PAM in comparison to IC₅₀ (153.4 µg/mL) and higher rate of OH productivity (k = 0.053 min⁻¹) for YEM-PAM. Our findings are interestingly superior to the TBHQ that is synthetic antioxidant. Moreover, our developed methodology for fluorimetric probing of OH radicals scavenging, recommends EGY-PAM as OH radicals scavenger for diabetic patients while YEM-PAM exhibited a better OH radicals scavenging appropriate for high blood pressure patients. More interestingly, EGY-PAM and YEM-PAM exhibited high anticancer potentiality. The aforementioned OH and DPPH scavenging activities as well as the anticancer potentiality present EGY-PAM and YEM-PAM as promising sources of natural antioxidants, that may have crucial roles in some chronic diseases such as diabetics and hypertension in addition to cancer therapeutic protocols.     

Sonochemical dosimetry: A comparative study of Weissler,Fricke and terephthalic acid methods

Acoustic cavitation and sonochemical reactions play a significant role in various applications of ultrasound. A number of dosimetry methods are in practice to quantify the amount of radicals generated by acoustic cavitation. In this study, hydroxyl radical (OH) yields measured by Weissler, Fricke and terephthalic acid dosimetry methods have been compared to evaluate the validities of these methods using a 490 kHz high frequency sonochemical reactor. The OH yields obtained after 5 min sonication at 490 kHz from Weissler and Fricke dosimetries were 200 µM and 289 µM, respectively. Whereas, the OH yield was found to be very low (8 µM) when terephthalic acid dosimetry was used under similar experimental conditions. While the results agree with those reported by Iida et al. (Microchem. J., 80 (2005) 159), further mechanistic details and interfering reactions have been discussed in this study. For example, the amount of OH determined by the Weissler and Fricke methods may have some uncertainty due to the formation of HO₂ in the presence of oxygen. In order to account for the major discrepancy observed with the terephthalic acid dosimetry method, high performance liquid chromatography (HPLC) analysis was performed, where two additional products other than 2-hydroxy terephthalic acid were observed. Electrospray ionization mass spectrometry (ESI-MS) analysis showed the formation of 2,5-dihydroxyterephthalic acid as one of the by-products along with other unidentified by-products. Despite the formation of additional products consuming OH, the reason for a very low OH yield obtained by this dosimetry could not be justified, questioning the applicability of this method, which has been used to quantify OH yields generated not only by acoustic cavitation, but also by other processes such as γ-radiolysis. The authors are hoping that this Opinion Paper may initiate further discussion among researchers working in sonochemistry area that could help resolve the uncertainties around using these dosimetry methods.     

Application of persulfate with hydrodynamic cavitation and ferrous in the decomposition of pentachlorophenol

Hydrodynamic cavitation (HC) and Fe(II) are advanced oxidation processes, in which pentachlorophenol (PCP) is treated by the redox method of activating persulfate (PS). The kinetics and mechanism of the HC and Fe(II) activation of PS were examined in aqueous solution using an electron spin resonance (ESR) spin trapping technique and radical trapping with pure compounds. The optimum ratio of Fe(II)/PS was 1:2, and the hydroxyl radical (HO) and sulfate radical (SO₄⁻) generation rate were 5.56 mM h⁻¹ and 8.62 μM h⁻¹, respectively. The generation rate and R_ct of HO and SO₄⁻ at pH 3 and 50 °C in the Fe(II)/PS/HC system are 7584.6 μM h⁻¹, 0.013 and 24.02 μM h⁻¹, 3.95, respectively. The number of radicals was reduced as the pH increased, and it increased with increasing temperature. The PCP reaction rate constants was 4.39 × 10⁻² min⁻¹ at pH 3 and 50 °C. The activation energy was 10.68 kJ mol⁻¹. In addition, the mechanism of PCP treatment in the Fe(II)/PS/HC system was a redox reaction, and the HO⁻/SO₄⁻ contribution was 81.1 and 18.9%, respectively. In this study, we first examined PCP oxidation through HO and SO₄⁻ quantification using only the Fe(II)/PS/HC process. Furthermore, the results provide the foundation for activation of PS by HC and Fe(II), but also provide a data basis for similar organic treatments other than PCP.     

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.     

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.     

Insight into the impact of excluding mass transport,heat exchange and chemical reactions heat on the sonochemical bubble yield: Bubble size-dependency

Numerical simulations have been performed on a range of ambient bubble radii, in order to reveal the effect of mass transport, heat exchange and chemical reactions heat on the chemical bubble yield of single acoustic bubble. The results of each of these energy mechanisms were compared to the normal model in which all these processes (mass transport, thermal conduction, and reactions heat) are taken into account. This theoretical work was carried out for various frequencies (f: 200, 355, 515 and 1000 kHz) and different acoustic amplitudes (P_A: 1.5, 2 and 3 atm). The effect of thermal conduction was found to be of a great importance within the bubble internal energy balance, where the higher rates of production (for all acoustic amplitudes and wave frequencies) are observed for this model (without heat exchange). Similarly, the ignorance of the chemical reactions heat (model without reactions heat) shows the weight of this process into the bubble internal energy, where the yield of the main species (OH, H, O and H₂) for this model was accelerated notably compared to the complete model for the acoustic amplitudes greater than 1.5 atm (for f = 500 kHz). However, the lowest production rates were registered for the model without mass transport compared to the normal model, for the acoustic amplitudes greater than 1.5 atm (f = 500 kHz). This is observed even when the temperature inside bubble for this model is greater than those retrieved for the other models. On the other hand, it has been shown that, at the acoustic amplitude of 1.5 atm, the maximal production rates of the main species (OH, H, O and H₂) for all the adopted models appear at the same optimum ambient-bubble size (R₀ ~ 3, 2.5 and 2 µm for, respectively, 355, 500 and 1000 kHz). For P_A = 2 and 3 atm (f = 500 kHz), the range of the maximal yield of OH radicals is observed at the range of R₀ where the production of OH, O and H₂ is the lowest, which corresponds to the bubble temperature at around 5500 K. The maximal production rate of H, O and H₂ is shifted toward the range of ambient bubble radii corresponding to the bubble temperatures greater than 5500 K. The ambient bubble radius of the maximal response (maximal production rate) is shifted toward the smaller bubble sizes when the acoustic amplitude (wave frequency is fixed) or the ultrasound frequency (acoustic power is fixed) is increased. In addition, it is observed that the increase of wave frequency or the acoustic amplitude decrease cause the range of active bubbles to be narrowed (scenario observation for the four investigated models).     

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.     

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.     

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.     

Study of ultrasonic treatment on the structural characteristics of gluten protein and the quality of steamed bread with potato pulp

Physicochemical properties and microstructure of gluten protein, and the structural characteristics of steamed bread with 30 % potato pulp (SBPP) were investigated by ultrasonic treatments. Results showed that 400 W ultrasonic treatment significantly (P < 0.05) increased the combination of water and substrate in the dough with 30 % potato pulp (DPP). The contents of wet gluten, free sulfhydryl (SH), and disulfide bond (SS) were influenced by ultrasonic treatment. Moreover, UV-visible and fluorescence spectroscopy demonstrated that the conformation of gluten protein was changed by ultrasonic treatment (400 W). Fourier transform infrared (FT-IR) illustrated that the β-sheet content was significantly (P < 0.05) increased (42 %) after 400 W ultrasonic treatment, and the surface hydrophobicity of gluten protein in SBPP increased from 1225.37 (0 W ultrasonic treatment) to 4588.74 (400 W ultrasonic treatment). Ultrasonic treatment facilitated the generation of a continuous gluten network and stabilized crumb structure, further increased the specific volume and springiness of SBPP to 18.9 % and 6.9 %, respectively. Those findings suggested that ultrasonic treatment would be an efficient method to modify gluten protein and improve the quality of SBPP.