Now showing items 41-60 of 2479

    • Experimental and kinetic study on aromatic formation in counterflow diffusion flames of methane and methane/ethylene mixtures

      Jiang, Peng; Xu, Lei; Wang, Qianlei; Wang, Zhen; Chung, Suk Ho; Wang, Yu (Fuel, Elsevier BV, 2023-07-28) [Article]
      Aromatics are molecular soot precursors, yet detailed kinetic mechanisms describing their formation in flame environments are insufficient even for the simplest hydrocarbon fuel of methane. Considering the building roles of methane-related chemistry in current hierarchically-structured mechanisms, the present study is devoted to the chemistry of aromatic formation in CH4 flames. We established a series of incipiently sooting methane counterflow diffusion flames (CDF) and characterized their thermochemical structures including the scalar fields of temperature, concentrations of major species, C2–C4 minor intermediates, benzene, large aromatic species, and soot volume fraction. The measurement techniques include tunable diode laser absorption spectroscopy (TDLAS), gas chromatography–mass spectrometer (GC–MS) and laser induced incandescence (LII). The experimental dataset was then used to assess various recently proposed kinetic mechanisms. The results showed that the literature mechanisms tested would significantly overpredict benzene formation in CH4 CDFs (up to a factor of 10). In addition, none of the tested mechanisms could capture the experimentally observed suppressing effects of CH4 addition on the formation of aromatic species in C2H4 CDFs. Potential reactions responsible for the model failures are discussed. The main contributions of this study are to: 1) identify the limitations of existing aromatic mechanisms when applied to methane CDFs; 2) clarify potential reactions/pathways related to model deficiencies; 3) provide novel experimental dataset covering both gas-phase speciation and soot for methane CDFs. It is our hope that the present data and analysis would deepen our understanding on benzene formation chemistry, and contribute to the refinement of aromatic formation predictive models.
    • Exceeding 100 µs Charge Carrier Separation in Perovskite Mediated by Rhodamine 6G

      Maity, Partha; Naphade, Rounak; Gutiérrez-Arzaluz, Luis; Nematulloev, Sarvarkhodzha; Thomas, Simil; Mir, Wasim Jeelani; Yorov, Khursand E.; Alshareef, Husam N.; Bakr, Osman; Mohammed, Omar F. (Advanced Optical Materials, Wiley, 2023-07-27) [Article]
      Halide perovskite colloidal nanocrystals (NCs) have enabled considerable progress in light conversion applications. However, the presence of unavoidable defect states and phase transition effects can accelerate undesirable rapid charge recombination of the photogenerated charge carriers. To address this issue, chromophores with an anchoring moiety are often used to modify the surface of the NCs, promoting prolonged charge separation through electron or energy transfer processes for optoelectronic applications. Here, steady-state and time-resolved spectroscopy methods are combined with density functional theory (DFT) calculations to explore and decipher the excited-state interaction in colloidal CsPbX3 (X = Br, I) NCs with a rhodamine 6G (Rh6G) hybrid assembly. The results show that Rh6G dimerizes even at low concentrations, as evidenced by DFT calculations. The binding of Rh6G on the NC surface is confirmed by FTIR and NMR spectroscopy techniques. In addition, transient absorption spectroscopy reveals directional sub-ps electron transfer from Rh6G to CsPbI3 NCs, whereas energy transfer occurs from CsPbBr3 to Rh6G, which ultimately recombines in the µs time regime. The findings highlight the simplest and most practical approaches for studying and tailoring the excited-state interaction in colloidal perovskite NCs and chromophore assembly.
    • Effect of Biphenyl, Acetylene and Carbon Dioxide on Benzene Pyrolysis at Intermediate Temperatures

      AlAbbad, Mohammed A.; Gautam, Ribhu; Aljaman, Baqer; Arudra, Palani; AlAhmadi, Ahmad (Combustion Science and Technology, Informa UK Limited, 2023-07-25) [Article]
      Benzene pyrolysis chemical kinetic mechanism has been of interest as benzene and phenyl radicals are important species for polycyclic aromatic hydrocarbons (PAHs) growth. Also, valuable industrial species such as biphenyl can be produced from benzene pyrolysis. This work aims to study the effect of additives (biphenyl and acetylene) on benzene pyrolysis at intermediate temperatures (900–1250 K). However, significant soot was noticed at high temperatures (1200–1250 K), which may affect the measurements. Nitrogen and a blend of nitrogen and carbon dioxide were used for dilution. The experiments were performed using a jet-stirred reactor (JSR) coupled with gas chromatography (GC) at atmospheric pressure. A residence time of 3 s was considered, as a long residence time is needed to collect enough samples at intermediate temperatures. The concentration-temperature profiles from the experimental measurements were compared with three selected models, Hamadi et al., Ranzi et al. and Sun et al. models. In general, Sun et al. model performs better than the other two models, especially for the prediction of light hydrocarbon concentrations. The results show an apparent influence of additives on benzene pyrolysis. The experiments and Sun et al. model illustrate a noticeable formation of methane and ethylene. Hamadi et al. and Ranzi et al. models demonstrate minor formation of light hydrocarbons under our experimental conditions. Sensitivity analyses of benzene, biphenyl, methane and ethylene were conducted at 1175 K using Sun et al. model.
    • Quantifying microdroplet contact-line friction using atomic force microscope

      Koh, Xue Qi; Thenarianto, Calvin; Jokinen, Ville; Daniel, Dan (Research Square Platform LLC, 2023-07-24) [Preprint]
      Controlling the wetting and spreading of microdroplets is key to technologies such as microfluidics, ink-jet printing, and surface coating. Contact angle goniometry is commonly used to characterize surface wetting by droplets, but the technique is ill-suited for sub-millimetric droplets. Here, we attach a micrometric-sized droplet to an Atomic Force Microscope (AFM) cantilever to directly quantify contact-line friction on different surfaces (superhydrophobic and underwater superoleophobic) with sub-nanonewton force resolutions. We demonstrate the versatility of our approach by performing friction measurements using different liquids (water and oil droplets) and under different ambient environments (in air and under water). Finally, we show that underwater superoleophobic surfaces can be qualitatively different from superhydrophobic surfaces: contact-line friction is highly sensitive to contact-line speeds for the former but not for the latter surface.
    • Mapping the coating failure modes of electroless plated metal on ABS polymer with micro-nano structured interface

      Melentiev, Ruslan; Tao, Ran; Li, Xiaole; Tevtia, Amit K.; VERGHESE, Nikhil; Lubineau, Gilles (International Journal of Adhesion and Adhesives, Elsevier BV, 2023-07-21) [Article]
      Electroless plating is the default industrial process for depositing glossy metallic coatings on polymeric parts, most often made of acrylonitrile–butadiene–styrene (ABS) plastic. Unfortunately, the adhesion of plated metals on ABS requires harsh acid etching of the polymer, leaving hazardous chemical waste. We recently offered “Greener electrochemical plating of ABS polymer with unprecedented adhesion via hierarchical micro-nano texturing”. Understanding of the coating failure mechanism at the micro–nano structured interface would allow programming the adhesion strength via the topographical design of the interface. This study develops a theoretical map of coating failure modes versus geometrical parameters of the metal–polymer interface and validate via precise nanofabrication experiments. The ABS polymer was hot embossed with 2–6 μm wide, 2–6 μm deep micro-textures, then it was acid-etched for 1 min to superpose nano-texture over the micro-textures prior to the electroless Cu plating, coating peeling test, and microscopic characterization of the fractured interface. We observed four coating failure modes: (1) adhesive failure at interface, (2) mixed adhesive/cohesive failure, (3) cohesive failure of metal, and (4) cohesive failure of polymer; the last one demonstrated the highest peeling forces. Surprisingly, the proportionality of the adhesion force to the texture aspect ratio was valid only up to a certain threshold, beyond which the adhesion forces falls down due to the fail of metal. The results presented here allows one to control/program the adhesion strength at the metal-polymer interface and optimize the micro-texture of ABS parts for greener electroless plating and durable coating adhesion.
    • Successive Multi-microdischarges Occurring in Pin-to-Line Geometry of Dielectric Barrier Discharge

      Park, Jin; Cha, Min Suk (Plasma Chemistry and Plasma Processing, Springer Science and Business Media LLC, 2023-07-19) [Article]
      Dielectric barrier discharges (DBDs) bring a long history of application and leave many interesting scientific questions. A positive streamer concept describes a temporal development of a microdischarge well, and memory charge effect explains spatially distributed microdischarges over the entire area of DBD. To properly model plasma chemistry occurring in a DBD, knowledge of microdischarges, distributed spatially and temporally, is essential. Here we present experimental result of multiple microdischarges, occurring successively and rooted at the same location. By employing a triangular waveform to a pointed electrode and a high conductivity layer at a surface of a dielectric barrier, a physical mechanism of the successive microdischarges was revealed: a slew rate of an external alternating current compensated a voltage drop caused by memory charges from a former microdischarge. A time interval between two neighboring microdischarges was inversely proportional to the slew rate, and the number of microdischarges depended primarily on an applied voltage. The number of microdischarges with an uncoated barrier was higher than that with an Ag-coated barrier; however, the charges delivered by each microdischarge were smaller in cases with an uncoated barrier. To investigate interactions between spatially separated microdischarges, this study will be extended to a configuration having multiple pointed electrodes. The effect of the successive microdischarges on plasma chemistry will also be a future study.
    • Augmentations for selective multi-species quantification from infrared spectroscopic data

      Al Ibrahim, Emad; Farooq, Aamir (Chemometrics and Intelligent Laboratory Systems, Elsevier BV, 2023-07-19) [Article]
      Sensitivity and selectivity are arguably the two most important qualities in a new sensor design. While many spectroscopic sensors developed in laboratory conditions achieve high sensitivity and selectivity, they are not always applicable to real-world conditions. Challenges in real-world applications come from corruptions like noise and interference. This study leverages machine learning methods for accurate and robust quantification under such corruptions. We propose simple yet effective augmentation strategies that promote robustness against unknown interference. The performance of the proposed augmentations is compared under varying levels of interference and noise. We demonstrate our methodology for a gas sensing application using infrared spectroscopy data. We focus on quantifying common volatile organic compounds (VOCs) in a realistic scenario with several unknown interfering species. The findings of this work put us a step closer to creating a robust and widely-applicable sensing platform.
    • Modeling of h2/air flame stabilization regime above coaxial dual swirl injectors

      Marragou, S.; Magnes, H.; Aniello, A.; Guiberti, Thibault; Selle, L.; Poinsot, T.; Schuller, T. (Combustion and Flame, Elsevier BV, 2023-07-18) [Article]
      The prediction of the stabilization regime of partially premixed H2/air flames above an injector is a main subject of interest for the development of gas turbines powered by hydrogen. The way the flame is stabilized has an impact on NOx emissions, thermal stress on the injector, and combustion stability. A model based on the triple flame speed is revisited and improved to predict flame stabilization using information gathered at cold flow conditions. The model is called TFUP for Triple Flame Upstream Propagation. According to this model, the flame can anchor to the injector only if a zone with a flammable mixture and a sufficiently low local flow velocity exists continuously from the lifted flame to the injector lips. The TFUP model is applied to the case of a H2/air coaxial, dual swirl injector in which both the hydrogen and air streams are swirled. Fuel is injected through the central channel and oxidizer through the external channel. Particle image velocimetry and one dimensional Raman scattering measurements made at strategic locations are used to predict the edge flame speed for which a lifted flame should re-anchor to the injector. These predictions made in isothermal conditions are compared to observations of the flame stabilization regime. The central flow of hydrogen can be mixed with methane and helium and the external flow of air with nitrogen in order to prescribe different theoretical values for the triple flame speed. Predictions agree well with the observations made for all swirl levels conferred to the central fuel stream, fuel injection velocities, hydrogen contents in the fuel mixture injected in the central channel, and nitrogen contents in the oxidizer annular channel tested in the study. Validity limits are also discussed. The methodology presented in this study provides a simple framework to predict flame stabilization on coaxial injectors that can optionally be equipped with swirl vanes.
    • Impact of Modern Vehicular Technologies and Emission Regulations on Improving Global Air Quality

      Ravi, Sai Sudharshan; Osipov, Sergey; Turner, James W. G. (Atmosphere, MDPI AG, 2023-07-18) [Article]
      Over the past few decades, criteria emissions such as carbon monoxide (CO), hydrocarbons (HCs), nitrogen oxides (NOx) and particulate matter (PM) from transportation have decreased significantly, thanks to stricter emission standards and the widespread adoption of cleaner technologies. While air quality is a complex problem that is not solely dependent on transportation emissions, it does play a significant role in both regional and global air quality levels. Emission standards such as Euro 1–6 in Europe, Corporate Average Fuel Economy (CAFE) regulations, Tier I—III standards in the US and the low emission vehicle (LEV) program in California have all played a huge role in bringing down transportation emissions and hence improving air quality overall. This article reviews the effect of emissions from transportation, primarily focusing on criteria emissions from road transport emissions and highlights the impact of some of the novel technological advances that have historically helped meet these strict emission norms. The review also notes how modern road engine vehicles emissions compare with national and international aviation and shipping and discusses some of the suggested Euro 7 emissions standards and their potential to improve air quality.
    • Turbulent Hydrogen Flames: Physics and Modeling Implications

      Song, Wonsik; Hernandez Perez, Francisco; Im, Hong G. (Springer International Publishing, 2023-07-15) [Book Chapter]
      Hydrogen exhibits special burning characteristics such as fast laminar and, thereby, turbulent flame speed, and a wide flammability limit. Because of these features, the existing numerical models that have been developed for e.g., natural gas or fuels with unity Lewis number assumption could be limited or even unusable. This chapter discusses the models for turbulent flame speed and local displacement speed of pure lean hydrogen premixed flames, particularly for a wide range of turbulence levels. Moreover, the predictive capability of the probability density function (PDF) modeling adopting the widely used laminar flamelet concept for Reynolds averaged Navier–Stokes (RANS) or large-eddy simulation (LES) approaches is assessed a priori using a set of state-of-the-art direct numerical simulation (DNS) data. The general conclusion suggests that the main turbulent parameter dictating the turbulent flame speed is found to be the size of the most energy-containing eddies rather than non-dimensional numbers such as Reynolds (Re) or Karlovitz (Ka) numbers. The local displacement speed models also suggest that a model developed for moderate turbulence level (Ka ≈O(10)) predicts well flames with Ka >O(1,000). PDF modeling using the flamelet concept is evaluated up to Ka >O(100), for which the mass fractions of major species are reasonably well predicted.
    • Hydrogen-Fueled Spark Ignition Engines

      Verhelst, Sebastian; Turner, James W. G. (Springer International Publishing, 2023-07-15) [Book Chapter]
      Hydrogen is most easily used as combustion engine fuel in a spark ignition engine. This chapter starts from the properties of hydrogen and hydrogen mixtures to present the various options for running spark ignition engines on hydrogen, reviewing the power density potential, emissions and efficiency. This is then linked to past and present research and development of hydrogen fueled vehicles, before concluding with the most promising emerging markets.
    • Mitigating the response of premixed swirl flames to acoustic excitation by nanosecond repetitively pulsed discharges at elevated pressures

      Yu, Liang; Aravind, B.; Lacoste, Deanna (Combustion and Flame, Elsevier BV, 2023-07-14) [Article]
      This paper shows that nanosecond repetitively pulsed discharges were able to mitigate the response of lean methane-air swirl flames to acoustic excitations, at pressures up to 3 bar. Flame transfer functions with and without plasma discharges were investigated at pressures of 1.2, 2.0, and 3.0 bar, in a frequency range 48–380 Hz. Results show that the plasma discharges decreased by up to 50% the gain of the flame transfer functions, regardless of the pressure. Mechanisms responsible for this effect are discussed.
    • Techno-Economic Assessment of CPVT Spectral Splitting Technology: A Case Study on Saudi Arabia

      Lucio, Cesar; Behar, Omar; Dally, Bassam (Energies, MDPI AG, 2023-07-14) [Article]
      Concentrating PV thermal (CPVT) collector with spectral splitting technology is a promising solution for heat and electricity production. To extend the use of this technology, a novel and cost-effective CPVT collector for harsh environments, such as those in Saudi Arabia, is presented and evaluated using theoretical energy, economy, and environmental analysis. Two questions are answered in this study, namely: which is the best operation strategy, and which is the best energy storage technology for CPVT. The potential of using a CPVT under the climate conditions of six cities in Saudi Arabia is also evaluated. It is found that a heat/electricity production strategy and a thermal energy storage are the most suitable for the CPVT technology. The economic assessment shows a levelized cost of electricity (LCOE) of $0.0847/kWh and a levelized cost of heat (LCOH) of $0.0536/kWh when water is used as a spectral filter, and a LCOE of $0.0906/kWh and a LCOH of $0.0462/kWh when ZnO nanoparticles are added. The CO2-equivalent emissions in a 20 MW CPVT plant are cut from 5675 tonnes to 7822 tonnes per year for Saudi Arabian weather and present power generation conditions.
    • Contributions of chemical interactions and mechanical interlocking for the adhesion of electroplated copper to ABS in the Cr(VI) etching process

      Tao, Ran; Fatta, Lujain; Melentiev, Ruslan; Tevtia, Amit K.; Lubineau, Gilles (International Journal of Adhesion and Adhesives, Elsevier BV, 2023-07-13) [Article]
      A typical step in the electroplating of metals to polymer substrates is the preparation of a substrate surface through sulfochromic acid etching, which is well known for modifying the chemistry and morphology of the treated surfaces. While this process has existed for decades, the relative contributions of chemical interactions and mechanical interlocking towards the final adhesion are not well understood. As sulfochromic acid is toxic and hazardous to the environment and human health, understanding how this acid etching promotes adhesion, and especially what are the real contributions of chemistry and mechanics respectively, becomes critical to be able to replace this treatment with greener techniques. However, such knowledge is still ambiguous, since decoupling the chemical and morphological contributions is challenging because both effects occurred simultaneously during etching. In this study, we proposed various sample preparation strategies to address these issues. First, we minimized the etching duration to achieve similar chemistry as that after the standard etching while avoiding strong modifications in surface morphology. Second, we passivated the etched samples to ensure that most of the adhesion properties of prepared samples are from morphological effects. Results indicated that chemical contribution was critical to ensure good wetting during the electroless plating, while mechanical interlocking was the major contributor (90%) for the ultimate adhesion of electroplated copper to acrylonitrile-butadiene-styrene interfaces.
    • Skipping under water: Buoyant sphere hydrodynamics at the air–water interface

      Kamoliddinov, Farrukh; Vakarelski, Ivan Uriev; Thoroddsen, Sigurdur T; Truscott, T. T. (Physics of Fluids, AIP Publishing, 2023-07-11) [Article]
      We present an experimental study of the hydrodynamics of a buoyant sphere accelerated horizontally along an air–water interface. At low speeds, the sphere floats at the surface, while at higher speeds, the sphere starts oscillating, moving below and toward the free surface akin to underwater skipping. The sphere often breaches and forms an air cavity during its subsequent dive. These underwater air cavities become horizontal and are attached to the sphere surface near the laminar flow separation point (∼π/2). High-speed imaging is used to investigate the effects of changing the pulling angle and counterweight-induced velocity on the hydrodynamics. We examine the transition from underwater skipping oscillations to water exit, particularly above the critical Froude number of 1.2, where buoyant spheres experience complex fluid–solid interactions revealing the influence of the air cavity on drag and lift coefficients and overall sphere hydrodynamics. Finally, we analyze the novel phenomenon of the steady motion of the horizontally pulled sphere with an attached inverted-wing-shaped air cavity.
    • Multi-speciation in shock tube experiments using a single laser and deep neural networks

      Sy, Mohamed; Mhanna, Mhanna; Farooq, Aamir (Combustion and Flame, Elsevier BV, 2023-07-11) [Article]
      Chemical kinetic experiments involving the oxidation or pyrolysis of fuels can be complex, especially when multiple species are formed and consumed simultaneously. Therefore, a diagnostic strategy that enables fast and selective detection of multiple species is highly desirable. In this work, we present a mid-infrared laser diagnostic that can simultaneously detect multiple species in high-temperature shock-tube experiments using a single laser. By tuning the wavelength of the laser over 3038 – 3039.6 cm−1 wavelength range and employing a denoising model based on deep neural networks (DNN), we were able to differentiate the absorbance spectra of ethane, ethylene, methane, propane, and propylene. The denoising model is able to clean noisy absorbance spectra, and the denoised spectra are then split these into contributions from evolving species using multidimensional linear regression (MLR). To the best of our knowledge, this work represents the first successful implementation of time-resolved multispecies detection using a single narrow wavelength-tuning laser. To validate our methodology, we conducted pyrolysis experiments of ethane and propane. The results of our experiments showed excellent agreement with previous experimental data and chemical kinetic model simulations. Overall, our diagnostic strategy represents a promising approach for detecting multiple species in high-temperature transient environments.
    • High temperature oxidation of residual oil pyrolysis intermediates for modeling gasification and combustion processes

      AlAbbad, Mohammed A.; Kashif, Touqeer Anwar; Gautam, Ribhu; Aljohani, Khalid; Romero, Edwin Guevara; Farooq, Aamir (Fuel, Elsevier BV, 2023-07-11) [Article]
      Developing chemical kinetic models for residual oil pyrolysis, gasification, and combustion is very challenging due to the large number of components and molecular complexity. This study provides experimental data for model development and validation for two residual oils, heavy fuel oil (HFO) and vacuum residual oil (VRO). This study aims to identify and quantify the HFO and VRO pyrolysis intermediates and validate an oxidation chemical kinetic model of the pyrolysis intermediates to provide data for future residual oil model development using hybrid chemistry (HyChem) and functional groups for mechanism development (FGMech) approaches. The pyrolysis experiments were conducted in a bench-scale tubular reactor at atmospheric pressure and a temperature of 1273 K. Detailed compositions of the yields from the pyrolysis of HFO and VRO were analyzed using gas chromatography-flame ionization detection (GC-FID) for the gas yields and gas chromatography-mass spectrometry/flame ionization detection (GC–MS/FID) for the liquids. Elemental analysis was conducted for the solid residuals. The experiment results show similar pyrolysis products from HFO and VRO. A surrogate of major components of the gas products and representatives of benzene and naphthalene derivatives (major compounds identified in liquid products) of the liquid products was formulated and its chemistry was studied by measuring ignition delay times (IDTs) in a shock tube. IDT measurements were conducted for stoichiometric and rich (ϕ = 1 and 3) mixtures, pressures of 20 and 40 bar, and diluents of nitrogen and carbon dioxide. Brute force IDT sensitivity analyses were used to study the effect of pressure, equivalence ratio and diluents on the reactivity of the mixture.
    • Influence of fuel injection parameters at low-load conditions in a partially premixed combustion (PPC) based heavy-duty optical engine

      Goyal, Harsh; Panthi, Niraj; Almanashi, Aqeel; Magnotti, Gaetano (Applied Thermal Engineering, Elsevier BV, 2023-07-05) [Article]
      The study examined the effects of second injection timings and fuel injection pressures (FIPs) in a double-injection based partially premixed combustion (PPC) using a single-cylinder heavy-duty optical diesel engine equipped with two different configurations, namely all-metal and optical. The thermodynamic analysis of energy balance, exhaust emissions, and particulates characterization was conducted in an all-metal engine configuration. For the same base engine architecture, high-speed natural combustion luminosity, cool-flame, and electronically excited hydroxyl (OH*) chemiluminescence, and planar laser-induced fluorescence (PLIF) imaging of formaldehyde (HCHO-PLIF) were applied in the optical configuration. Additionally, 1D modeling using GT-Power was utilized to examine the distribution of heat transfer losses through the individual cylinder boundaries. The experiments were conducted at low-load conditions at a fixed fuel mean effective pressure (MEPfuel) using a primary reference fuel with a volumetric mixture of 50% n-heptane and 50% iso-octane (PRF50). The results demonstrated that for a fixed first injection, the second injection timing of −6°CA aTDC is the most favorable condition due to increased gross indicated efficiency, reduced exhaust losses, decreased uHC/CO/soot emissions with a slight compromise on heat losses and NOx emissions. Among the tested FIPs of 1200, 1500, and 1800 bar, 1500 bar showed higher efficiency, and overall lower energy losses and exhaust emissions. At higher FIPs, the overall flame development process revealed reduced luminous intensity with dispersed signals formed downstream of the nozzle due to increased premixed combustion. For 1800 bar FIP, both cool-flame and HCHO signals showed an increased rate of reaction zones close to the bowl-wall region from where the OH radicals developed. Not only the initial low- to high-temperature reaction transition was faster for 1800 bar FIP but the signal decay of HCHO signals by OH radicals was also rapid in the late cycle. These findings explained the root cause of increased heat transfer losses and higher uHC/CO emissions at 1800 bar FIP.
    • High-Sensitivity RFID Sensor for Structural Health Monitoring

      Nesser, Hussein; Mahmoud, Hassan; Lubineau, Gilles (Advanced Science, Wiley, 2023-07-05) [Article]
      Structural health monitoring (SHM) is crucial for ensuring operational safety in applications like pipelines, tanks, aircraft, ships, and vehicles. Traditional embedded sensors have limitations due to expense and potential structural damage. A novel technology using radio frequency identification devices (RFID) offers wireless transmission of highly sensitive strain measurement data. The system features a thin, flexible sensor based on an inductance-capacitance (LC) circuit with a parallel-plate capacitance sensing unit. By incorporating tailored cracks in the capacitor electrodes, the sensor's capacitor electrodes become highly piezoresistive, modifying electromagnetic wave penetration. This unconventional change in capacitance shifts the resonance frequency, resulting in a wireless strain sensor with a gauge factor of 50 for strains under 1%. The frequency shift is passively detected through an external readout system using simple frequency sweeping. This wire-free, power-free design allows easy integration into composites without compromising structural integrity. Experimental results demonstrate the cracked wireless strain sensor's ability to detect small strains within composites. This technology offers a cost-effective, non-destructive solution for accurate structural health monitoring.
    • Quantifying acetylene mole fraction in rich flat laminar premixed C2H4/air flames using mid-infrared polarization spectroscopy

      Zhao, Wanxia; Alwahabi, Zeyad T.; Dally, Bassam (Applied Physics B, Springer Science and Business Media LLC, 2023-07-04) [Article]
      Mid-infrared laser polarization spectroscopy (IRPS) has been applied to measure the mole fraction of acetylene in rich premixed laminar C2H4/Air flat flames at equivalence ratios (Φ) of 1.7, 2.1, and 2.3, and under atmospheric pressure. The detection was conducted by probing the ro-vibrational P(19) transition at ~ 3.1 μm. The total collisional broadening coefficient of C2H2 was approximately 0.074 cm−1 atm−1 and varied within a range of 0.5% under different flame conditions, which made the effect of linewidth not obvious in the CH4/air flame. The calculated mole fraction of C2H2, using the Chemkin model, at Φ = 1.3 and 1.5 was used to calibrate the recorded IRPS signal intensities at different Height Above Burner (HAB). A single scaling factor was then used to quantify the measured C2H2 at highly sooting conditions, Φ = 1.7, 2.1, and 2.3, with a Limit of Detection (LoD) of 35 ± 5 ppm. The first observed C2H2 mole fraction appeared at HAB of 3 mm and measured as 2003 ppm, 2217 ppm, and 2495 ppm, for Φ = 1.7, 2.1, and 2.3, respectively. The mole fraction increased as the HAB increased to reach the maximum value of 2296 ppm, 2807 ppm, and 3478 ppm, for Φ = 1.7, 2.1, and 2.3, respectively, up to HAB of 5 mm. It was observed that the C2H2 mole fraction reaches a plateau region at HAB of ~ 8 mm. The production of C2H2 has been observed to be subject to a critical gas temperature of 1400 ± 30 K. The critical soot inception temperature, where the first incepted soot particles are observed, is the same as the gas temperature where χmaxC2H2 was detected, namely at 1500 ± 30 K. These measurements and calibration procedure demonstrate a plausible technique to probe other flames and to better understand soot inception and its correlation with C2H2.