Now showing items 1-20 of 2067

    • Experimental and Kinetic Modeling Study of 1,3-Dioxolane Oxidation and Comparison with Dimethoxymethane

      Shrestha, Krishna P.; Elbaz, Ayman M.; Giri, Binod; Arab, O. Z.; ADIL, MOHAMMAD; Seidel, Lars; Roberts, William L.; Farooq, Aamir; Mauss, F. (Energy & Fuels, American Chemical Society (ACS), 2022-06-29) [Article]
      This work reports laminar flame speeds and ignition delay times of 1,3-dioxolane/O2/inert gases over a wide range of conditions. Laminar flame speeds were determined experimentally at pressures of 1 and 3 bar, the temperature of 300 K, and equivalence ratios ranging from 0.7 to 1.4 using a constant-volume spherical chamber, whereas ignition delay times were measured in a shock tube at a pressure of 1 bar, the temperature range of 1000–1265 K, and equivalence ratios of 0.5 and 1.0. A detailed kinetic model is developed to predict the oxidation of 1,3-dioxolane utilizing our new experimental data and published datasets on the oxidation of 1,3-dioxolane in freely propagating flames, autoignition in rapid compression machines and shock tubes, and speciation in a jet-stirred reactor. Model predictions are in reasonable agreement with the experimental data. Laminar flame speeds and ignition delay times of 1,3-dioxolane (cyclic ether) are compared with those of dimethoxymethane (acyclic ether). It is found that 1,3-dioxolane has a higher laminar flame speed than that of dimethoxymethane, which may be attributed to the formation of C2H4, C2H2, and the H atom from 1,3-dioxolane. On the contrary, ignition delay times of 1,3-dioxolane are longer than those of dimethoxymethane below 1000 K and shorter above 1000 K for the same dilution level. The reaction ȮCHO = CO2 + H is critical for accurately predicting 1,3-dioxolane oxidation, and it significantly influences model predictions under low-pressure conditions. The model developed in this work will serve as the base mechanism for higher cyclic and acyclic ethers.
    • Optical Study of Pre-Chamber Assisted Internal Combustion Engine at Lean Limits

      Sharma, Priybrat; Tang, Qinglong; Sampath, Ramgopal; Hlaing, Ponnya; Marquez, Manuel Echeverri; Cenker, Emre; Magnotti, Gaetano (SSRN Electronic Journal, Elsevier BV, 2022-06-23) [Preprint]
      The pre-chamber assisted ignition offers a plethora of much-needed upgrades to gas engines, stretching from improved combustion efficiency and stability to extended lean limits. The concept has received intermittent attention from researchers over the past century, yet the concept's fundamental understanding remains segmented. This study investigates pre-chamber assisted combustion (PCC) in a heavy-duty gas engine fueled by methane at the lean limits. The engine is operated at two lean limits at intake pressures of 1.2 and 1.4 bar. At lower intake pressure, λ global is 2.4, while at higher intake pressure λ global is 2.6. The comparison of two lean limits through experimental data and GT-Power 1D model reveals the underlying ignition and combustion. Using a combination of acetone PLIF (N-PLIF) and OH* chemiluminescence imaging allows visualization of both the reacting and non-reacting part of the pre-chamber jet. The results suggest that pressure differential across the pre-chamber and main chamber controls the reacting jet growth speed. The combustion chamber boundaries affect the main combustion through the wall jet part of the impinging pre-chamber jets as higher OH* concentrations are observable at stagnation points of the jet. In addition, the study reports the appearance of post-combustion jets and dispersed OH* pockets as the combustion dwindles. The narrow throat pre-chamber shows a spectral pressure signature reminiscent of the Helmholtz oscillator, and circumferential resonant modes dominate the main chamber combustion. Although the PCC offers great ignitibility, the main chamber mixture cannot sustain prolonged combustion at a lean limit lambda value.
    • Laser-based selective BTEX sensing using deep neural networks

      Mhanna, Mhanna; Sy, Mohamed; Arfaj, Ayman; Llamas, Jose; Farooq, Aamir (Optics Letters, Optica Publishing Group, 2022-06-23) [Article]
      A mid-infrared absorption-based laser sensor is developed for selective and simultaneous benzene, toluene, ethylbenzene, and xylenes (BTEX) measurements under ambient conditions. The sensor is based on a distributed feedback inter-band cascade laser emitting near 3.3 µm. Wavelength tuning and deep neural networks were employed to differentiate the broadband absorbance of BTEX species. The sensor was validated with gas mixtures and real-time measurements were demonstrated at a temporal resolution of 1 s. Minimum detection limits for BTEX in air are 8, 20, 5, and 46 ppm, respectively. This sensor can be utilized to monitor BTEX emissions in the petrochemical, rubber, and paint industries to avoid hazardous health effects.
    • Simultaneous gas and magnetic sensing using a single heated micro-resonator

      Zhao, Wen; Alcheikh, Nouha; Khan, Fahimullah; Yaqoob, Usman; Younis, Mohammad I. (Sensors and Actuators A: Physical, Elsevier BV, 2022-06-23) [Article]
      In this paper, we propose a single device for simultaneous measurement of in-plane magnetic field and gas concentration. The concept is based on tracking simultaneously the resonant frequency of the first two symmetric and anti-symmetric modes of an electrothermally actuated out-of-plane buckled micro-beam. First, the Lorentz-force magnetic sensing was investigated at different electrothermal voltages in air. Powered with 3.78 mW, the magnetic sensor achieves a sensitivity of 0.0867 /T at the second mode with good linearity lower than 0.1%. On the other hand, the gas-sensing technique is based on the thermal conductivity mechanism. We simultaneously measure the frequencies shift of the first and the second modes while changing the gas concentration and the magnetic field (Bx). At Bx = 55 mT, Helium (He) and Argon (Ar) sensing yield the highest sensitivity of 4.15%/%He in the range of 2.5–10% He and 2.22%/%Ar in the range of 10–20%Ar. Additionally, the results show a response/recovery time of 200 s/180 s (He) and 580 s/320 s (Ar). Herein, for the first time, we experimentally demonstrate the potential for employing a multimode micro-resonator for magnetic field and gas sensing. The proposed multi-sensing device has the characteristics of simple design, low cost, small size, and good linearity, making it suitable for smart environmental monitoring applications.
    • Nonlinear mode saturation in a U-shaped micro-resonator

      Rocha, Rodrigo Tumolin; Younis, Mohammad I. (Scientific reports, Springer Science and Business Media LLC, 2022-06-21) [Article]
      Saturation is an intriguing phenomenon that has captured the attention of scientists since the time of Froude when he reported it for ship motion in the mid of the nineteenth century. This work presents the demonstration and a comprehensive study of the nonlinear saturation phenomenon on a compound micromachined structure of U-shape (micro portal frame). The frame is designed and fabricated as a multi-input and multi-output device for actuating the 1st (sway) and 2nd (symmetric) in-plane vibration modes. Geometric nonlinearities along with the softening effect of the electrostatic force present the necessary conditions for the activation of a 2:1 internal (auto-parametric) resonance between the 1st and 2nd modes. Experimental data complemented with analytical simulations are obtained showing the internal resonance and the saturation phenomenon. These results are promising for further exploration of such compound structures and for further in-depth studies of the saturation phenomenon on a variety of other systems and applications.
    • Computationally-Derived Submodel for Thermally-Induced Secondary Atomization

      Guida, Paolo; Ceschin, Alberto; Hernandez, Francisco; Im, Hong G.; Roberts, William L. (Elsevier BV, 2022-06-20) [Preprint]
      Thermally-induced secondary atomization (TISA) enables enhanced atomization, better mixing and faster evaporation in multi-component sprays. Despite its importance in a number of applications, TISA is not yet well understood. In this work we study numerically the effects of key physical parameters on TISA dynamics, with particular emphasis on breakup. To this end, we simulated a series of cases for suspended droplets in microgravity conditions, varying the number of bubbles near the liquid-gas interface. We performed a total of 800 simulations with different fluid properties investigating a wide hyperspace. In particular, we varied viscosity, surface tension, number and size of bubbles, as well as the droplet size, identifying two main parameters necessary for modelling purposes: the breakup time, τ b , and maximum normalized surface area, S f . Here we defined the breakup time as the time between the beginning of the simulation and the maximum surface area observed. We also calculated the Pearson’s coefficient to estimate the influence of each variable on the parameters of interest, understanding that the size of the largest bubble controlled S f while the Ohnesorge number strongly influenced τ b . We further employed the dataset to formulate simple mathematical correlations for S f and τ b by performing a multivariable regression. Moreover, we looked into the dynamics of the secondary droplets generated by the process, demonstrating that the velocity and size of the ejected droplets are linked to the size of the bubbles that generate them.
    • Indentation Response of Power and Sigmoid Functionally Graded PSZ/NiCrAlY Composites

      Eltaher, M. A.; Wagih, A. (International Journal of Applied Mechanics, World Scientific Pub Co Pte Ltd, 2022-06-20) [Article]
      Owing to their superior mechanical properties, functionally graded materials (FGMs) are currently applicable for many tribological systems, which increased the need for a rapid prediction tool of the hardness and wear behavior of these materials. To this end, this paper aims to present empirical equations to predict the residual indentation deformation for the PSZ/NiCrAlY composite FGM that could give a rapid indication on the material hardness and wear rates at different indentation loads. The empirical equations were derived for two common gradient laws, power (P-FGM) and sigmoid (S-FGM), based on numerical results obtained and validated with experimental results in this study. The numerical results were obtained by simulating indentation experiments using commercial finite element software considering the gradient of all the elastic and plastic material properties. The influence of the gradient index, gradient law and indentation displacement on the force-indentation response, contact pressure distribution, plastic stains, contact surface profile evolutions, and the residual indentation deformations were studied. The results showed that contact force and contact pressure were larger for P-FGM than S-FGM for all the gradient indices. The residual indentation deformation is larger for S-FGM than P-FGM for all the gradient indices due to the higher PSZ ceramic phase at the contact area for P-FGM than S-FGM. The residual indentation deformation of the FGM was normalized with respect to its value for the pure matrix based on the finite element results that highlighted the independence of this ratio on the indentation load. Finally, empirical equations were derived to predict the residual indentation deformation for the PSZ/NiCrAlY composite FGM with respect to the gradient index for both the gradient laws, power and sigmoid functions.
    • Laser ablation of CFRP surfaces for improving the strength of bonded scarf composite joints

      Yousef, Jassem A. Al; Yudhanto, Arief; Tao, Ran; Lubineau, Gilles (Composite Structures, Elsevier BV, 2022-06-17) [Article]
      Repairing damaged composite parts using scarf technique requires a careful selection of treatment methods for composite surface. Laser treatment is one of the emerging techniques to treat the milled composite surface by unlocking various levels of morphological changes and, thus, optimizing joint strength. However, laser parameters, i.e., energy density (fluence), should be carefully determined to ensure the acceptable structural recovery. Here, the influence of CO laser with relatively high fluence (ablation effect) on the surface characteristics (roughness, morphology, wettability) and scarf joint strength with associated failure modes of unidirectional (UD) and quasi-isotropic (QI) carbon fiber-reinforced plastic (CFRP) laminates is studied. Here, we found that the ablation effect using CO laser at 3.6 J/m was considered safe for UD laminates as their joint strength was comparable with that treated by manual sanding. The ablation at higher fluence (8.4 J/m) reduced the joint strength in UD laminates due to severe damage occurred in 0 fibers that triggered adhesive failure. In QI laminates, 3.6 J/m laser fluence could improve joint strength since the cohesive failure was activated in off-axis plies (90, +45, −45).
    • Polyethylene grafted silica nanoparticles via surface-initiated polyhomologation: A novel filler for polyolefin nanocomposite

      Alghamdi, Reem D.; Yudhanto, Arief; Lubineau, Gilles; Abou-Hamad, Edy; Hadjichristidis, Nikos (Polymer, Elsevier BV, 2022-06-17) [Article]
      Silica nanoparticles (SiO2 NPs) were prepared and functionalized with polyethylene (PE@SiO2 NPs) using the surface-initiated polyhomologation (SI-polyhomologation) technique. Polyolefin nanocomposites were fabricated later by melt mixing of different ratios of the as-prepared SiO2 NPs and PE@SiO2 NPs with linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) matrices. Firstly, SiO2 NPs were modified with different alkoxysilane ligands, dichloro(divinyl)silane (DCDVS), allyl trimethoxysilane (ATMS), and vinyl triethoxylsilane (VTES). Subsequently, thexylborane, an initiator for SI-polyhomologation, was immobilized to the modified surface of SiO2 NPs through hydroboration reactions. Polyhomologation was then allowed to proceed by adding monomer solution to form polyethylene brushes covalently bonded to the surface of the NPs. Physiochemical characterizations had confirmed the morphology, chemical structure, and thermal stability for each step of modification reactions. LLDPE and LDPE nanocomposites were prepared by extrusion with SiO2 NPs and PE@SiO2 NPs as nanofillers. Finally, tensile tests and morphological SEM-based analyses are presented to discuss the influence of the grafted PE on both the dispersion of the fillers and the mechanical properties of the filler/matrix interphase.
    • Assessment of subgrid dispersion models for large eddy simulations of turbulent jet flows with dilute spray droplets

      Angelilli, Lorenzo; Ciottoli, Pietro P.; Picano, Francesco; Valorani, Mauro; Im, Hong G. (Physics of Fluids, AIP Publishing, 2022-06-16) [Article]
      High fidelity simulations for polydispersed sprays in the Eulerian-Lagrangian framework need to incorporate subgrid-scale effects in the particle evolution equations. Although the quasi-linear evaporation rate formu- lation captures evaporating droplet statistics, further improvement is required when sub-grid scale velocity effects become essential. The subgrid dispersion model strongly affects droplets spatial distribution, and subsequently net evaporation rate, depending on how rapidly they are dispersed into the dry air region. This paper aims to provide physical insights on these aspects by considering four dispersion models: (i) discrete random walk, (ii) approximate deconvolution method, (iii) stochastic model based on the Langevin equa- tion, and (iv) combined approximate deconvolution method with the Langevin equation. Mass and enthalpy transfer source terms together with droplet diameters and particle distributions were compared against corre- sponding direct numerical and large eddy simulations without a model as reference cases. Numerical results at low Stokes and moderate Reynolds numbers indicate that the dispersion model choice does not affect Eulerian field averages or fluctuations. However, proper dispersion models are essential to capture droplet distributions in the far-field region after jet breakup for Stokes number smaller than unity. The unclosed Lagrangian momentum equation without any dispersion model most accurately reproduces direct numerical simulation in the near field.
    • Detection of magnetohydrodynamic waves by using machine learning

      Chen, Fang; Samtaney, Ravi (arXiv, 2022-06-15) [Preprint]
      Nonlinear wave interactions, such as shock refraction at an inclined density interface, in magnetohydrodynamic (MHD) lead to a plethora of wave patterns with myriad wave types. Identification of different types of MHD waves is an important and challenging task in such complex wave patterns. Moreover, owing to the multiplicity of solutions and their admissibility for different systems, especially for intermediate-type MHD shock waves, the identification of MHD wave types is complicated if one solely relies on the Rankine-Hugoniot jump conditions. MHD wave detection is further exacerbated by the unphysical smearing of discontinuous shock waves in numerical simulations. We present two MHD wave detection methods based on a convolutional neural network (CNN) which enables the classification of waves and identification of their locations. The first method separates the output into a regression (location prediction) and a classification problem assuming the number of waves for each training data is fixed. In the second method, the number of waves is not specified a priori and the algorithm, using only regression, predicts the waves' locations and classifies their types. The first fixed output model efficiently provides high precision and recall, the accuracy of the entire neural network achieved is up to 0.99, and the classification accuracy of some waves approaches unity. The second detection model has relatively lower performance, with more sensitivity to the setting of parameters, such as the number of grid cells N_{grid} and the thresholds of confidence score and class probability, etc. The proposed two methods demonstrate very strong potential to be applied for MHD wave detection in some complex wave structures and interactions.
    • Multi-Threshold Inertial Switch With Acceleration Direction Detection Capability

      Xu, Qiu; Wang, Lvjun; Younis, Mohammad I. (IEEE Transactions on Industrial Electronics, Institute of Electrical and Electronics Engineers (IEEE), 2022-06-14) [Article]
      We present an inertial switch with three threshold levels, which can provide quantitative acceleration measurements and detect the acceleration direction in the x-y plane. The designed device has four movable electrodes attached to the proof mass (one at every side of the square proof mass) and 12 flexible stationary electrodes (three on each side). When the device is subjected to an acceleration input, the movable electrode can contact one or more of the 12 stationary electrodes based on the acceleration magnitude and direction. The acceleration direction can be determined by identifying the individual electrical switches that are activated. The designed switch is simulated using a finite element model under different acceleration signals of various magnitudes and directions. A device prototype has been fabricated using the SOIMUMPs process and has been tested by a drop-table system under various shock accelerations in different directions. The experimental and simulation results show good agreement indicating that the acceleration direction detection accuracy and resolution improve with the increase in the number of used electrical switches.
    • Morphology of bubble dynamics and sound in heated oil

      Kiyama, Akihito; Rabbi, Rafsan; Pan, Zhao; Dutta, Som; Allen, John S; Truscott, T. T. (Physics of Fluids, AIP Publishing, 2022-06-07) [Article]
      The interaction between a heated oil bath and water droplets commonly occurs in the kitchen and has important implications for cooking, fire safety, and indoor air pollution. The interplay between the bubble dynamics in a heated oil bath, the generated sound, and the ligament-like expulsion to the surrounding air is examined. We focus on an explosion of a millimeter-sized water droplet in heated oil as a simplified case. We discuss three typical bubble types that can be classified as a function of the stand-off parameter h/ R, where h is the distance between the oil surface and bubble and R is the maximum bubble radius. Our data describe the morphology of bubble dynamics inside a heated oil bath and represent those found in the cooking pan. This paper also highlights potential applications of our findings.
    • Cassette-like peeling system for testing the adhesion of soft-to-rigid assemblies

      Li, Xiaole; Tao, Ran; Xin, Yangyang; Lubineau, Gilles (International Journal of Solids and Structures, Elsevier BV, 2022-06-03) [Article]
      A novel cassette-like peeling system is developed to address the limitations of current peeling standards when evaluating bonding quality of soft-to-rigid assemblies. The system transforms the translation of a specimen in the conventional peeling configuration to rotation via a cassette-like spool clamping the specimen. The peeled film is loaded by tension to drive the winding of the spool, thus achieving self-similar crack propagation and a stationary peeling front unrelated to the stiffness of the film. These features enable the system’s compatibility with most universal testers and in situ observation of crack tip morphology with optical instruments. Analysis to derive the intrinsic fracture energy when peeling a soft film is conducted based on Griffith energy balance, making use of which, a parametric study is performed to clarify the related mechanisms. We carry out a comprehensive validation of the cassette-like peeling system by performing a series of peeling tests using our in-house prototype and by comparing the results with those from the conventional system. Owing to its universality and ease-of-use, the proposed cassette-like peeling system can potentially be applied to the development of the next generation of peel test standards.
    • Large-scale hot embossing of 1 µm high-aspect-ratio textures on ABS polymer

      Melentiev, Ruslan; Lubineau, Gilles (CIRP Journal of Manufacturing Science and Technology, Elsevier BV, 2022-05-30) [Article]
      Hot embossing is the most promising method for surface micropatterning of low-value-added products made of cheap polymers such as acrylonitrile butadiene styrene (ABS). In hot embossing, a polymeric part is compressed with a micropatterned mold at a temperature slightly above the glass transition temperature (Tg), held at this temperature for some time, and then cooled below Tg for demolding. However, through this study, we demonstrate that using this conventional strategy to replicate 1 µm structures on a large area on ABS results in defective replicas or damaged molds. We propose a viscous embossing strategy, wherein the polymer is embossed far above its Tg and demolded shortly thereafter in the viscous state. The absence of cooling is the key for damage-less demolding of 1 µm structures on a large area. Yet, an excessive increase of the temperature and time results in the formation of a thermally-induced tensile skin on the polymer surface, as evidenced by the experimental and theoretical analyses performed in this study. In this study, 100 million 1–6 µm wide high-aspect-ratio (1–4) holes were embossed on a smartphone-sized area on the ABS polymer in a few seconds. This proposed strategy exhibits several advantages such as highly precise and more productive replication, which are not observed in the conventional hot embossing technique.
    • An experimental and kinetic modeling study of the pyrolysis of isoprene, a significant biogenic hydrocarbon in naturally occurring vegetation fires

      Grajales Gonzalez, Edwing; Kukkadapu, Goutham; Nagaraja, Shashank S.; Shao, Can; Monge Palacios, Manuel; Chavarrio Cañas, Javier Eduardo; Wagnon, Scott W.; Curran, Henry J.; Pitz, William J.; Sarathy, Mani (Combustion and Flame, Elsevier BV, 2022-05-26) [Article]
      Isoprene dominates the carbon flux emitted by vegetation and constitutes 40% of non-methane biogenic emissions worldwide. Despite pyrolysis experiments at temperatures above 1000 K showing a link between isoprene combustion and aromatic species formation, comprehensive mechanistic research on isoprene is scarce in the literature. In this work, we carry out an experimental and theoretical study to build, for the first time, a chemical kinetic model describing isoprene pyrolysis. The formation of polycyclic aromatic hydrocarbon (PAH) precursor species, often observed in vegetation fire plumes, is partially explained by isoprene pyrolysis experiments and theoretical modeling. Molecular dynamics (MD) simulations unveil reaction pathways from allylic isoprenyl radicals to allene and cyclopentadiene (CPD) intermediates, two relevant species detected in the experiments. Rate constants for these identified pathways are calculated using variational transition state theory to update the kinetic model, which is validated against single-pulse shock tube (SPST), and jet-stirred reactor (JSR) experimental data in the temperature range of 850–1690 K. The kinetic model presents satisfactory agreement with the SPST experimental data, and a reaction pathway analysis shows that association of propargyl radicals results in benzene formation. The JSR pathway analysis also identifies the prominent reactions for CPD, benzene, styrene, and toluene formation. Our model does not reproduce the CPD experimental profiles, indicating that additional studies are necessary. Overall, our findings advance the understanding of isoprene pyrolysis and its related atmospheric pollutants in naturally occurring vegetation fires where smoldering and oxygen-deficient combustion processes are present.
    • Alignment statistics of pressure Hessian with strain rate tensor and reactive scalar gradient in turbulent premixed flames

      Chakraborty, Nilanjan; Ahmed, Umair; Klein, M.; Im, Hong G. (Physics of Fluids, AIP Publishing, 2022-05-24) [Article]
      The relative alignment of the eigenvectors of pressure Hessian with reactive scalar gradient and strain rate eigenvectors in turbulent premixed flames have been analysed for Karlovitz number values ranging from 0.75 to 126 using a detailed chemistry three-dimensional Direct Numerical Simulations (DNS) database of H2-air premixed flames. The reactive scalar gradient preferentially aligns with the most extensive strain rate eigendirection for large Damköhler number and small Karlovitz number values, whereas a preferential collinear alignment between the reactive scalar gradient with the most compressive strain rate eigendirection is observed in flames with small Damköhler number and large Karlovitz number. By contrast, the eigenvectors of pressure Hessian do not perfectly align with the reactive scalar gradient, and the net contribution of the pressure Hessian to the evolution of the normal strain rate contribution to the scalar dissipation rate transport acts to reduce the scalar gradient in the zone of high dilatation rate. The eigenvectors of pressure Hessian and strain rate are aligned in such a manner that the contribution of pressure Hessian to the evolution of principal strain rates tends to augment the most extensive principal strain rate for small and moderate values of Karlovitz numbers, whereas this contribution plays an important role for the evolution of the intermediate principal strain rate for large values of Karlovitz number. As the reactive scalar gradient does not align with the intermediate strain rate eigenvector, the influence of pressure Hessian contributions to the scalar-turbulence interaction remains weak for large values of Karlovitz number.
    • Kinetic insights into the reaction of hydroxyl radicals with 1,4-pentadiene: A combined experimental and theoretical study

      Giri, Binod; Mai, Tam V.-T.; Nguyen, Thi T.-D.; Szőri, Milán; Huynh, Lam K.; Farooq, Aamir (Combustion and Flame, Elsevier BV, 2022-05-24) [Article]
      Olefinic hydrocarbons are one of the main intermediates of the oxidation of large hydrocarbons, and they are also found in distillate transportation fuels. Combustion characteristics of olefinic species, particularly non-conjugated ones, are not well understood. This work reports chemical insights into the reaction of OH radicals with 1,4-pentadiene (14PTDN), an important non-conjugated diolefin. High-temperature rate coefficients of OH + 14PTDN were measured in a shock tube over T = 881 – 1314 K and p ∼ 1150 Torr. The progress of the reaction was monitored by detecting OH radicals near 307 nm using a UV laser-absorption technique. OH radicals were generated by the fast thermal decomposition of tertbutyl hydroperoxide (TBHP). Stochastic RRKM-based Master Equation (RRKM-ME) simulations were carried out on the potential energy surface computed at M06–2X/aug-cc-pVTZ level of theory to gain mechanistic insights. The theoretical model captured high-temperature experimental data from this work and previously reported data at low temperatures (294 - 468 K). This combined experimental and theoretical study reveals: (i) no discernible pressure dependence of the total rate constants, (ii) mechanism shift occurs with temperature, (iii) similar to conjugated dienes + OH reactions, the addition of OH radicals to 14PTDN dominates compared to abstraction pathways for T < 500 K, (iv) among the bimolecular product channels originating from the OH-adducts, only vinyl alcohol + allyl radical is important, contributing ∼28% of the reactant consumption at 0.1 Torr and 400 K, (iv) beyond 1000 K, the addition channel contributes negligibly small for all pressures. To our knowledge, this is the first detailed experimental and theoretical kinetic study of the reaction of 1,4-pentadiene with OH radicals. The expression for the theoretical total rate coefficients (in units of cm3 molecule−1 s−1) is provided as k(T) =0.172 × T −3.82 exp( −125.6 KT ) + 1.49 × 10−20T 3.09 exp( −53.7 KT ) over T = 200 – 2000 K and P = 760 Torr.
    • Kinetic study of plasma assisted oxidation of H2 for an undiluted lean mixture

      Snoeckx, Ramses; Jun, Daeyoung; Lee, Bok Jik; Cha, Min Suk (Combustion and Flame, Elsevier BV, 2022-05-23) [Article]
      For the past couple of decades, electrical discharges (or plasmas) have been widely investigated in pursuit of the advancement in combustion and fuel reforming. Particularly, nonthermal plasma has attracted researchers’ attention to improve ignition characteristics, promote flame stability, and reform hydrocarbons. Nevertheless, due to the nonthermal plasma's complex physicochemical nature, most of the experimental findings have not been fully explained yet. Recently, plasma-chemical kinetic studies have been initiated to address the important roles of plasma chemistry in hydrocarbon chemistry including combustion phenomena. However, we still have a long way to go to fully understand the underlying mechanisms and predict experimental outcomes. Here, we present a kinetic study of plasma-assisted low-temperature oxidation of H2 for an undiluted H2/O2 mixture. The aim of this study is to establish a foundation for low-temperature plasma assisted combustion as well as high-temperature plasma assisted reforming processes. We employed a plasma-chemical reaction mechanism and plasma-chemical kinetic modeling platform (KAUSTKin) and a temperature controlled dielectric barrier discharge reactor to study the plasma assisted oxidation of H2. As a result of systematically varying the gas temperature and discharge power, we found a non-linear oxidation behavior highlighting a Negative Temperature Coefficient (NTC)-like trend in a temperature range of 600–750 K. We investigated the effects of both the reduced electric field and the temperature on the plasma assisted oxidation chemistry. We found that (i) the oxidation is initiated by the electron impact dissociation of O2, which is governed by the reduced electric field and controls the oxidation degree, (ii) HO2 is the key intermediate for the full oxidation to H2O, and (iii) O3 and H2O2 production negatively affect the oxidation for temperatures below 400 K and over 600 K, respectively. We believe that these findings will further contribute to a better description and deeper understanding of the plasma chemistry with hydrocarbons as well as other H2 mixtures.
    • Recent advances on MEMS based Infrared Thermopile detectors

      Mbarek, Sofiane Ben; Alcheikh, Nouha; Younis, Mohammad I. (Microsystem Technologies, Springer Science and Business Media LLC, 2022-05-21) [Article]
      During the last decade, IR MEMS thermopile detectors have become a topic of increasing interest because of their reliable characteristics and excellent cost-performance ratio. Because of their many attractive characteristics, thermopile detectors have been frequently used in various IR detection applications. In this paper, we present an overview of the recent advances on MEMS based infrared detectors. The first part deals with the IR MEMS thermopile concepts and discusses the recent state of the art of IR absorber designs, thermocouple designs, and their materials processing. The status of IR MEMS detectors performances is examined in the second part and summarized by presenting findings from the last decade. It is concluded that the latest developments in MEMS technology and thermoelectric materials offer high potential for innovative solutions to improve the IR thermopile performances.