Recent Submissions

  • Statistical study on engine knock oscillation and heat release using multiple spark plugs and pressure sensors

    Shi, Hao; Uddeen, Kalim; An, Yanzhao; Pei, Yiqiang; Johansson, Bengt (Fuel, Elsevier BV, 2021-04-10) [Article]
    Engine knock has been an inherent problem that limits engine efficiency improvement and threatens engine service life. To trigger the controllable knock, a specialized liner with installing four side spark plugs mounted on the cylinder head are used in this study to produce various in-cylinder flame propagation. Various spark strategies (e.g., spark timing, spark number, spark location) are applied to generate different auto-ignition sites and knock characteristics. Up to five channels of pressure signal are collected to analyze the knock intensities regarding different spark strategies. To investigate the knock-induced fluctuations and heat release, we use the multiple correlations to evaluate the maximum amplitude of pressure oscillation (MAPO) respecting different influential factors and building a multiple linear regression (MLR) model for MAPO prediction and validate it against the experiment results. Besides, the Wiebe function and curve-fitting techniques are applied to estimate the energy released by auto-ignition in each cycle, and its relations with knock intensity are assessed. The results show that the average growth of pre-oscillation plays an important role in MAPO value (correlation coefficient, r_s = 0.965), the established MLR model possesses high accuracy for MAPO prediction. The pressure oscillation regarding the 1st resonance mode is extracted from the band-pass filtered signal, representing the main pressure oscillating process. Compared with the single spark ignition, triggering more spark plugs could boost the fuel consumption rate, while shortening the knocking combustion duration and reducing the heat release fraction contributed by auto-ignition. At the same CA50 (9 CAD aTDC), the four spark ignition leads to the least heat release fluctuations than other spark strategies. With advancing the CA50, the heat release fraction produced by knock increases at first then reduces due to the thermodynamic conditions and the flame propagation. Activating two or three spark plugs, the rising rate of the heat release rate goes up, but the knock-induced heat release fraction decreases. Moreover, the primary acoustic resonance mode (1, 0) gives more regular knock vibrations than the mixing form (including mode (1, 0), (0, 1), (2, 0), etc.), the average traveling distance of acoustic wave in the time gap of receiving two continuous signals is very close to the cylinder bore. The results give insights into the pressure wave propagation during knock and the relations between knock conditions, pressure oscillations, and heat release.
  • Synthesis of core-shell copper-graphite submicronic particles and carbon nano-onions by spark discharges in liquid hydrocarbons.

    Glad, X; Gorry, J; Cha, Min Suk; Hamdan, A (Scientific reports, Springer Nature, 2021-04-07) [Article]
    Spark discharge in hydrocarbon liquids is considered a promising method for the synthesis of various nanomaterials, including nanocomposites. In this study, copper-carbon particles were synthesized by generating spark discharges between two Cu electrodes immersed in heptane, cyclohexane, or toluene. The synthesized particles were characterized using scanning electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. Overall, two families of particles were observed: Cu particles (diameter
  • A tangent linear approximation of the ignition delay time. I: Sensitivity to rate parameters

    Almohammadi, Saja Mohammad; Hantouche, Mireille; Le Maître, Olivier P.; Knio, Omar (Combustion and Flame, Elsevier BV, 2021-04-02) [Article]
    A tangent linear approximation is developed to estimate the sensitivity of the ignition delay time with respect to individual rate parameters in a detailed chemical mechanism. Attention is focused on a gas mixture reacting under adiabatic, constant-volume conditions. The uncertainty in the rates of elementary reactions is described in terms of uncertainty factors, and are parameterized using independent canonical random variables. The approach is based on integrating the linearized system of equations governing the evolution of the partial derivatives of the state vector with respect to individual random variables, and a linearized approximation is developed to relate the ignition delay sensitivity to the scaled partial derivatives of temperature. The efficiency of the approach is demonstrated through applications to chemical mechanisms of different sizes. In particular, the computations indicate that for detailed reaction mechanisms the TLA leads to robust local sensitivity predictions at a computational cost that is order-of-magnitude smaller than that incurred by finite-difference approaches based on one-at-a-time rate perturbations.
  • Programmable materials for sensors, actuators and manipulators for soft robotics applications

    Chellattoan, Ragesh (2021-04) [Dissertation]
    Advisor: Lubineau, Gilles
    Committee members: Lacoste, Deanna; Blilou, Ikram; Leng, Jinsong
    This thesis describes the concept of programmable materials with tunable physical properties applicable to soft robots. We present these materials for three major applications in soft robotics: sensing, actuation, and robotic manipulation. The strain sensors recognize the internal stimuli in a soft robot, whereas the conductors collect the sensors’ signals to the control part. In the first part, we want to develop both stretchable strain sensors and conductors from a single material by programming a nanowire network’s electrical property, which we achieve through Electrical Welding (e-welding). We demonstrate the transformation of a Silver Nanowire (AgNW)-polymer sponge from a strain sensor to a stretchable conductor through e-welding. Using this method, we produced a soft hybrid e-skin having both a sensor and conductor from a single material. In the second part, we propose new active actuation solutions by obtaining quick, tunable pressure inside a soft material that we achieve through a liquid-gas phase transition of a stored liquid using an efficient electrode. We discuss the significant design variables to improve the performance and propose a new design for the electrodes, for enhancing actuation speed. We propose using low voltage equipment to trigger the phase transition to produce compact actuation technology for portable applications. Using this method, we produced a portable soft gripper. In the third and last part, we want to develop a simple robotic manipulation technology using a single-chambered soft body instead of a multi-chambered system. We propose using on-demand stiffness change in soft material to control the shape change of a single-chambered soft body. For this, we introduce a new concept of a stiffness tunable hybrid fiber: a fiber with stiff and soft parts connected in a series. We demonstrate a substantial change in membrane stiffness in the fiber through locking/unlocking of the soft part of the fiber. We integrated these fibers into a pneumatically operated single-chambered soft body to control its stiffness for on-demand shape change. If applied together, these three concepts could result in a fully printable, cheap, light, and easily controllable new generation soft robots with augmented functionalities.
  • Experimental and theoretical study of PAH and incipient soot formation in laminar flames

    Li, Zepeng (2021-04) [Dissertation]
    Advisor: Roberts, William L.
    Committee members: Lacoste, Deanna; Chung, Suk Ho; Knio, Omar; Thomson, Murray J.
    Emissions of soot and polycyclic aromatic hydrocarbons (PAHs) from incomplete burning of hydrocarbon fuels pose a great threat to the environment and human health. To reduce such emissions, a comprehensive understanding of their evolution process is essential. In this work, a series of research studies were conducted to evaluate sooting tendencies and to experimentally and theoretically develop PAH mechanisms. The sooting tendencies of oxygenated fuels were quantitively investigated in counterflow diffusion flames. Sooting limits are described by critical fuel and oxygen mole fractions, measured with a laser scattering technique. The addition of dimethyl ether displays non-monotonic behavior on sooting tendencies at elevated pressures, which is attributed to the chemical effect from kinetic simulations. The tendency of incipient soot formation of other oxygenated fuels (e.g., alcohol, acid, ether, ketone, and carbonate ester) was also assessed, using a similar approach. As the precursor of soot, PAH measurement using laser induced fluoresecnce was implemented to track the evolution processes from PAHs to incipient soot. Developing a PAH mechanism is essential to the understanding of soot formation; however, PAH formation and its growth process are not well understood. Based on previous research, PAHs with 5-membered rings are abundant in flames. Therefore, the growth of PAHs with 5-membered rings was investigated, using acenaphthylene (A2R5) as the example. The density functional theory (DFT) and the transition state theory (TST) were adopted to calculate potential energy surfaces and reaction rate coefficients. The existence of 5-membered rings appreciably impacts PAH production by facilitating the formation of planar PAHs with C2H substitution, thereby improving existing PAH mechanisms. In PAH mechanisms, the thermochemistry properties are not all calculated, but are hypothesized to be equal to those of a similar structure. The simulation accuracy of the hypothesis is explored here by discussing the sensitivity of the thermochemistry parameters in flame simulations. The group additivity method utilizing THERM codes is used to calculate thermochemistry properties. PAH loading affects the sensitivity of thermochemistry properties to both flame temperature and product yields. These results show that either accurate thermochemistry properties, or reverse reaction rates should be provided in the mechanism to improve simulation accuracy.
  • Computational characterization of hydrogen direct injection and nonpremixed combustion in a compression-ignition engine

    Babayev, Rafig; Andersson, Arne; Dalmau, Albert Serra; Im, Hong G.; Johansson, Bengt (International Journal of Hydrogen Energy, Elsevier BV, 2021-04) [Article]
    With the revived interest in hydrogen (H2) as a direct combustion fuel for engine applications, a computational study is conducted to assess the characteristics of H2 direct-injection (DI) compression-ignition (CI) non-premixed combustion concept. Development of a CFD modeling using CONVERGE CFD solver focuses on hydrogen's unique characteristics by utilizing a suitable numerical method to reproduce the direct H2 injection phenomena. A grid sensitivity study is performed to ensure the fidelity of results with optimal cost, and the models are validated against constant-volume optical chamber and diesel engine experimental data. The present study aims to contribute to the future development of DICI H2 combustion engines, providing detailed characterization of the combustion cycle, and highlighting several distinct aspects of CI nonpremixed H2 versus diesel combustion. First, unlike the common description of diesel sprays, hydrogen jets do not exhibit significant flame lift-off and air entrainment near injector nozzle, and the fuel-air interface is drastically more stratified with no sign of premixing. It is also found that the DICI H2 combustion concept is governed first by a free turbulent jet mixing phase, then by an in-cylinder global mixing phase. The former is drastically more dominant with the DICI H2 engine compared to conventional diesel engines. The free-jet mixing is also found to be more effective that the global mixing, which indicates the need to completely rethink the optimization strategies for CI engines when using H2 as fuel.
  • Synthesis and Characterization of Iron-Doped TiO2 Nanoparticles Using Ferrocene from Flame Spray Pyrolysis

    Ismail, Mohamed; Hedhili, Mohamed N.; Anjum, Dalaver H.; Singaravelu, Venkatesh; Chung, Suk Ho (Catalysts, MDPI AG, 2021-03-29) [Article]
    Iron-doped titanium dioxide nanoparticles, with Fe/Ti atomic ratios from 0% to 10%, were synthesized by flame spray pyrolysis (FSP), employing a single-step method. Ferrocene, being nontoxic and readily soluble in liquid hydrocarbons, was used as the iron source, while titanium tetraisopropoxide (TTIP) was used as the precursor for TiO2. The general particle characterization and phase description were examined using ICP-OES, XRD, BET, and Raman spectroscopy, whereas the XPS technique was used to study the surface chemistry of the synthesized particles. For particle morphology, HRTEM with EELS and EDS analyses were used. Optical and magnetic properties were examined using UV–vis and SQUID, respectively. Iron doping to TiO2 nanoparticles promoted rutile phase formation, which was minor in the pure TiO2 particles. Iron-doped nanoparticles exhibited a uniform iron distribution within the particles. XPS and UV–vis results revealed that Fe2+ was dominant for lower iron content and Fe3+ was common for higher iron content and the iron-containing particles had a contracted band gap of ~1 eV lower than pure TiO2 particles with higher visible light absorption. SQUID results showed that doping TiO2 with Fe changed the material to be paramagnetic. The generated nanoparticles showed a catalytic effect for dye-degradation under visible light.
  • A comparative study of isobaric combustion and conventional diesel combustion in both metal and optical engines

    Nyrenstedt, Gustav; Tang, Qinglong; Sampath, Ramgopal; AlRamadan, Abdullah; Ben Houidi, Moez; Cenker, Emre; Magnotti, Gaetano; Johansson, Bengt (Fuel, Elsevier BV, 2021-03-24) [Article]
    Isobaric combustion is more efficient than isochoric combustion when the peak cylinder pressure is restricted. Recently a double compression expansion engine concept using isobaric combustion was proposed to improve the engine performance. However, the knowledge about the in-cylinder isobaric combustion process is limited. This study investigated isobaric combustion in both metal and optical engines utilizing a centrally placed direct injector and a multiple injections strategy, and the performance and emissions of isobaric combustion and conventional diesel combustion (CDC) were compared. Mie scattering and fuel-tracer planar laser-induced fluorescence (PLIF) were used to visualize the liquid-phase fuel penetration length and fuel distribution under non-reactive conditions, respectively. The natural flame luminosity and spatial soot distribution were measured with high-speed imaging and laser-induced incandescence (LII), respectively. Results demonstrate an increased soot formation in the isobaric cases compared with the CDC case. The successive fuel injection into reacting zones, which induces a locally fuel-rich mixture and less fuel–air mixing, accounts for the high soot emissions in the isobaric combustion. This study further demonstrates that the late injections of the isobaric cases lead to more combustion in the squish zone and near the cylinder walls, which increases the local temperature gradient and may result in more heat losses. There is still room to reduce the heat losses in the isobaric combustion although the total heat loss of the isobaric combustion is lower than the CDC case due to a lower combustion temperature. Multiple injectors are suggested to reduce the soot emissions of the isobaric combustion by spreading the different injections in space.
  • Yttrium stabilization and Pt addition to Pd/ZrO2 catalyst for the oxidation of methane in the presence of ethylene and water

    Khan, Hassnain Abbas; Hao, Junyu; El Tall, Omar; Farooq, Aamir (RSC Advances, Royal Society of Chemistry (RSC), 2021-03-23) [Article]
    Catalytic oxidation is the most efficient method of minimizing the emissions of harmful pollutants and greenhouse gases. In this study, ZrO2-supported Pd catalysts are investigated for the catalytic oxidation of methane and ethylene. Pd/Y2O3-stabilized ZrO2 (Pd/YSZ) catalysts show attractive catalytic activity for methane and ethylene oxidation. The ZrO2 support containing up to 8 mol% Y2O3 improves the water resistance and hydrothermal stability of the catalyst. All catalysts are characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), O2-temperature-programmed desorption (O2-TPD), and CO-chemisorption techniques. It shows that high Pd dispersion and Pd–PdO reciprocation on the Pd/YSZ catalyst results in relatively high stability. In situ diffuse reflectance infrared Fourier-transform (DRIFT) experiments are performed to study the reaction over the surface of the catalyst. Compared with bimetallic catalysts (Pd : Pt), the same amounts of Pd and Pt supported on ZrO2 and Y2O3-stabilized ZrO2 catalysts show enhanced activity for methane and ethylene oxidation, respectively. A mixed hydrocarbon feed, containing methane and ethylene, lowers the CH4 light-off temperature by approximately 80 °C. This shows that ethylene addition has a promotional effect on the light-off temperature of methane.
  • Crack tip fields in a neo-Hookean sheet reinforced by nonlinear fibers

    Liu, Yin; Moran, Brian (Journal of the Mechanics and Physics of Solids, Elsevier BV, 2021-03-19) [Article]
    In this paper, we derive the asymptotic crack tip fields in a neo-Hookean material reinforced by nonlinear fibers. The fiber are characterized by a power law model which exhibits significant stiffening behavior at large stretch. A specific case of the model yields the so-called standard reinforcing model (Triantafyllidis and Abeyaratne, 1983). A series of transformations is used to set the stage for the asymptotic solution. We begin with a coordinate scaling (Liu and Moran, 2020b) to account for fiber orientation aspects. This is followed by a hodograph transformation to the strain plane to deal with nonlinearities. Finally, an additional nonlinear algebraic transformation is employed to render the equations suitable for a separable solution. The asymptotic solutions are compared with and agree well with finite element solutions for different fiber modulus ratios, fiber orientation angles, and loading modes. We find that, due to the stiffening effects of the fibers, the deformation fields can be divided into three regions, where the deformation in the two regions near to the crack faces is significantly larger than in the middle region. Stress peaks are observed at the interfaces between regions. The solutions in the paper may provide insight into damage modes and crack initiation at a crack tip in fiber-reinforced soft composites.
  • Effect of the excitation line on hydroxyl radical imaging by laser induced fluorescence in hydrogen detonations

    Rojas Chavez, Samir B.; Chatelain, Karl P.; Guiberti, Thibault; Mével, Rémy; Lacoste, Deanna (Combustion and Flame, Elsevier BV, 2021-03-19) [Article]
    The present study aims to evidence the effect of the excitation line on the planar laser-induced fluorescence of hydroxyl radical (OH-PLIF) imaging in H-fueled detonation wave. We experimentally validated an updated laser-induced fluorescence (LIF) model, called KAT-LIF, which simulates spectrally-resolved fluorescence spectra, using a recently developed optical detonation duct. We numerically investigated the effects of the excitation line, the initial pressure (20–100 kPa), and the diluent (N/Ar) on the fluorescence spectrum, the spectrally- and one-dimensionally-averaged LIF intensity, and the quantitative capabilities of the OH-LIF measurements for different 2H-O-3.76diluent detonable mixtures. The investigated excitation lines were (0,0)Q1(7), both (1,0)Q2(8) and (1,0)Q1(9), and (1,0)Q1(6), which all belong to the transition. The main findings are the following: (i) considering the commercially available OH filters, Q2(8)+Q1(9) excitation scheme has the highest LIF intensity for all the investigated H-fueled detonations, while Q1(7) could provide the strongest intensity with better (custom) collection optics; (ii) the maximum LIF intensity decreases with increasing pressure for all the excitation schemes; (iii) using a single point calibration, at the fluorescence peak, it is not possible to perform quantitative measurements of OH radicals for any H-fueled detonation, using the conventional excitation schemes. Finally, we experimentally evidenced more favorable excitation schemes to obtain qualitative information far behind the front, by employing the saturated regime of fluorescence or the optically thin linear regime with appropriate laser configuration. These two excitation schemes correspond to more appropriate LIF strategies that will enable better detonation flow visualization in future studies.
  • Crack tip fields in a neo-Hookean sheet reinforced by nonlinear fibers

    Liu, Yin; Moran, Brian (Journal of the Mechanics and Physics of Solids, Elsevier BV, 2021-03-19) [Article]
    In this paper, we derive the asymptotic crack tip fields in a neo-Hookean material reinforced by nonlinear fibers. The fiber are characterized by a power law model which exhibits significant stiffening behavior at large stretch. A specific case of the model yields the so-called standard reinforcing model (Triantafyllidis and Abeyaratne, 1983). A series of transformations is used to set the stage for the asymptotic solution. We begin with a coordinate scaling (Liu and Moran, 2020b) to account for fiber orientation aspects. This is followed by a hodograph transformation to the strain plane to deal with nonlinearities. Finally, an additional nonlinear algebraic transformation is employed to render the equations suitable for a separable solution. The asymptotic solutions are compared with and agree well with finite element solutions for different fiber modulus ratios, fiber orientation angles, and loading modes. We find that, due to the stiffening effects of the fibers, the deformation fields can be divided into three regions, where the deformation in the two regions near to the crack faces is significantly larger than in the middle region. Stress peaks are observed at the interfaces between regions. The solutions in the paper may provide insight into damage modes and crack initiation at a crack tip in fiber-reinforced soft composites.
  • Ultrahigh sensitivity and wide strain range of porous pressure sensor based on binary conductive fillers by in-situ polymerization

    Hu, Zhiqiang; Xin, Yangyang; Fu, Qiang (Journal of Polymer Research, Springer Nature, 2021-03-17) [Article]
    High-performance wearable electronics show great potential in the soft robotics, artificial intelligence, human–machine interaction, health care, etc. Due to the wide application in heart rate detection, voice monitoring, and sports data collection, the pressure sensor has grasped a lot of attention. However, poor cycle stability, low sensitivity and narrow working pressure range hinder the further development of the pressure sensors. To solve the above mentioned problems, a polyurethane-based conductive sponge is prepared via silver nanoparticle coating after the in-situ synthesis of poly(3,4-ethylene dioxythiophene) on the backbones of polyurethane foam. The flexible pressure sensor exhibits excellent performance, including ultrahigh sensitivity (3.039 kPa−1), wide working range (0–35 kPa), frequency-independent performance, reliable repeatability (~ 1000 cycles), rapid and stable response. Finally, we successfully demonstrated these flexible sensors in detecting tiny physiological activities and human motions. All the results demonstrate that the the polyurethane-based pressure sensor is a promising candidate for soft electronics and healthcare monitoring.
  • Rapid soot inception via α-alkynyl substitution of polycyclic aromatic hydrocarbons

    Liu, Peng; Jin, Hanfeng; Chen, Bingjie; Yang, Jiuzhong; Li, Zepeng; Bennett, Anthony; Farooq, Aamir; Sarathy, Mani; Roberts, William L. (Fuel, Elsevier BV, 2021-03-17) [Article]
    Soot particles alter global climate and dominate the origin and evolution of carbonaceous interstellar material. Convincing experimental evidence has linked polycyclic aromatic hydrocarbons (PAH) to soot inception under low-temperature astrochemistry and high-temperature combustion conditions. However, significant gaps still remain in the knowledge of PAH and soot formation mechanisms. Here, we report theoretical and experimental evidence for a soot inception and growth pathway driven by peri-condensed aromatic hydrocarbons (PCAH) with an alkynyl substitution. Initially, free radicals attack the α-alkynyl substitution of PCAHs to form covalently bound compounds yielding resonantly stabilized radicals (RSRs), which promote further clustering through repeated addition reactions with negligible energy barriers. The proposed pathway is shown to be competitive at temperatures relevant to astrochemistry, engine exhaust manifold and flames because it does not require H-abstraction reactions, the requisite reaction precursors are in abundance, and the reaction rate is high. Such addition reactions of PCAHs with α-alkyne substituents create covalently bound clusters from moderate-size PAHs that may otherwise be too small to coagulate.
  • Design Optimization and Performance Analysis of a Multi-kW Thermoacoustic Electric Generator Using DeltaEC Model

    Somu, Srinath; Lacoste, Deanna; Saxena, Saumitra; Roberts, William L.; Keolian, Robert M. (Journal of Energy Resources Technology, ASME International, 2021-03-12) [Article]
    Abstract Waste heat recovery from power plants and industries requires a new type of electricity generator and related technological developments. The current research work is aimed at the design of a multi-kilowatt thermoacoustic electric generator, which can be employed as the bottoming cycle of a gas-turbine power plant or for industrial waste heat recovery. The proposed device converts thermal energy into acoustic power and subsequently uses a piezoelectric alternator to convert acoustic power into electricity. The challenge in designing such a device is that it has to be acoustically balanced. The performance of the device is greatly affected by numerous parameters such as frequency of the traveling acoustic wave, heat exchanger parameters, regenerator dimensions, acoustic feedback loop, etc. The proposed device is a lab-scale demonstration targeted to produce few kilowatts of electric power from a 20 kWth heat source. DeltaEC software is used to achieve the acoustically balanced configuration of the device. The DeltaEC model outcomes are used to arrive at the optimized design of the device and its components. The analytical method, the optimized geometrical dimensions of thermoacoustic components, and the minimum required conditions of heat source input are presented in this paper.
  • An improved prediction of pre-combustion processes, using the discrete multicomponent model

    Kabil, Islam; Qubeissi, Mansour Al; Badra, Jihad; Abdelghaffar, Walid; Eldrainy, Yehia; Sazhin, Sergei S.; Im, Hong G.; Elwardany, Ahmed (Sustainability (Switzerland), MDPI AG, 2021-03-08) [Article]
    An improved heating and evaporation model of fuel droplets is implemented into the commercial Computational Fluid Dynamics (CFD) software CONVERGE for the simulation of sprays. The analytical solutions to the heat conduction and species diffusion equations in the liquid phase for each time step are coded via user-defined functions (UDF) into the software. The customized version of CONVERGE is validated against measurements for a single droplet of n-heptane and n-decane mixture. It is shown that the new heating and evaporation model better agrees with the experimental data than those predicted by the built-in heating and evaporation model, which does not consider the effects of temperature gradient and assumes infinitely fast species diffusion inside droplets. The simulation of a hollow-cone spray of primary reference fuel (PRF65) is performed and validated against experimental data taken from the literature. Finally, the newly implemented model is tested by running full-cycle engine simulations, representing partially premixed compression ignition (PPCI) using PRF65 as the fuel. These simulations are successfully performed for two start of injection timings, 20 and 25 crank angle (CA) before top-dead-centre (BTDC). The results show good agreement with experimental data where the effect of heating and evaporation of droplets on combustion phasing is investigated. The results highlight the importance of the accurate modelling of physical processes during droplet heating and evaporation for the prediction of the PPCI engine performance.
  • Bio-inspired composite laminate design with improved out-of-plane strength and ductility

    Melaibari, A.; Wagih, A.; Basha, Muhammad; Kabeel, A. M.; Lubineau, Gilles; Eltaher, M. A. (Composites Part A: Applied Science and Manufacturing, Elsevier BV, 2021-03-07) [Article]
    Low failure strain and catastrophic failure are the most critical challenges of carbon fiber reinforced polymer composite laminates. To tackle these challenges, inspired by core shells, we created discontinuities in the laminate microstructure to activate extra energy dissipation mechanisms that improves flexural response. In bio-inspired laminates, embedded defects and delaminations are imposed at different thickness positions of the laminate during lamination process. The flexural properties of the proposed bio-inspired laminates were characterized using three-point bending test. Different damage modes and their sequences in conventional and bio-inspired laminates were identified using microcomputed tomography. Experimental results showed that, the flexural properties of bio-inspired composites can be tailored by changing the through-the-thickness delamination position and size. It was demonstrated that, the strength, failure strain and energy absorption ability of the optimized bio-inspired laminates, with 10 mm delamination diameter at the nearest interface to the indenter, were improved by 11.9%, 208% and 288.1% compared to conventional laminate. Moreover, these bio-inspired composites showed a progressive damage mode with pseudo-ductility response, where a slight degradation of the strength occurred followed by increased strain and sustaining the same strength up to failure strain two times larger than the initiation strain. Therefore, the proposed bio-inspired laminates showed a metal-like failure that provides warning alert to the final failure, which makes them applicable in many industrial applications.
  • Cenosphere formation of heavy fuel oil/water emulsion combustion in a swirling flame

    Pei, Xinyan; Guida, Paolo; AlAhmadi, K. M.; Al Ghamdi, Ibrahim A.; Saxena, Saumitra; Roberts, William L. (Fuel Processing Technology, Elsevier BV, 2021-03-06) [Article]
    Heavy fuel oil (HFO) is a good alternative and economical fuel for power generation and marine transport industry because of its low price and high energy density. However, HFO's incomplete and complex combustion results in high levels of emissions. One way to improve HFO combustion and reduce its high-level pollutant emissions is by emulsifying HFO with water to form water-in-oil emulsion fuel by virtue of its characteristic of the micro-explosion phenomenon of emulsion fuel. In this work, we tested HFO samples with water contents of 0% (normal HFO), 5%, 10%, 20%, and 30% in mass. A lab-scale burner with an air-blast nozzle and swirling airflow was applied to simulate the industrial boiler's typical features. The properties of various water contents emulsion fuel, including composition, water droplet size distribution, heating value, density, viscosity, and TGA were analyzed. The influence of water-HFO emulsion on the swirling flame combustion performance and the primary pollutant emissions, listed as CO, CO2, NOx, SOx, particulate matter (PM), and its composition, was studied. The results show that, in general, multiple various beneficial processes come into effect when water-in-HFO emulsion augments the combustion. HFO emulsion technology offers tremendous potential to enhance combustion processes' efficiency with reduced SOx, NOx, and particulate matter emissions. The emulsion fuel has a considerable effect on the formation process of cenospheres. This effect varies with different water levels in HFO due to the different intensities of secondary atomization of emulsion fuel combustion.
  • A Wideband Magnetic Frequency Up-Converter Energy Harvester

    Fakeih, Esraa; Almansouri, Abdullah S.; Kosel, Jürgen; Younis, Mohammad I.; Salama, Khaled N. (Advanced Engineering Materials, Wiley, 2021-03-05) [Article]
    Many sensor applications require small and noninvasive methods of powering, such as marine animal tracking and implantable healthcare monitoring. In such cases, energy harvesting is a viable solution. Vibrational energy harvesting is abundantly available in the environment. These vibrations usually are low in frequency and amplitude. Conventional vibrational harvesters convert the environmental vibrations into electrical signals; however, they suffer from low-voltage outputs and narrow bandwidths, limiting the harvesting to a small range of frequencies. Herein, a new mechanical harvester is introduced using a magnetic frequency up-converter. It is implemented using attractive-force magnetic coupling between a soft magnet and a permanent magnet to convert low-frequency vibrations into high-frequency pulses. Combined with a piezoelectric generator, the harvester generates a high output voltage for an extended bandwidth of operation. The proposed harvester shows a 50.15% increase in output voltage at the resonant frequency (12.2 Hz), resulting in 14.79 V at 1.0 g, with a maximum peak voltage of 16.28 V. The bandwidth of operation ranges from 10.77 to 22.16 Hz (11.39 Hz), which when compared with a single-beam harvester shows an increase of 3250% in the bandwidth, where the average power is greater for 92.56% of this bandwidth.
  • Multiple spark plugs coupled with pressure sensors: A new approach for knock mechanism study on SI engines

    Shi, Hao; Uddeen, Kalim; An, Yanzhao; Pei, Yiqiang; Johansson, Bengt (Energy, Elsevier BV, 2021-03) [Article]
    Controlled knock combustion is the focus of academic and industrial research for modern spark-ignition engines to achieve higher thermal efficiency and better performance. To understand the knock formation mechanism, a refitted compression-ignition engine equipping with a port fuel injection system was operated under spark-ignition conditions. A customized liner with four side spark plugs was used to trigger controllable knock, through various spark strategies (e.g., spark number, timing, and location). Four side pressure sensors and a top sensor mounted on the cylinder head were used to record the knock pressure oscillation. Fast Fourier transform and wavelet analysis were performed to evaluate the frequency of pressure oscillations. The results showed that activating more spark plugs could promote knock propensity and intensity along with earlier CA50, but the knock was effectively suppressed when symmetrically activating four spark plugs simultaneously, indicating the fast flame propagation could suppress the knock occurrence. When triggering 2 or 3 spark plugs simultaneously, the in-cylinder pressure oscillations display very concentrated directionality among all the knocking cycles, indicating the distributing tendency of hot spots in these cases. With the activated spark plug number ranging from 1 to 3, the acoustic resonance focused on (1, 0) mode, while the four activated spark ignition led to higher (0, 1) mode, indicating the auto-ignition initiated close to the chamber center. Compared with the side sensors, the top sensor could recognize more resonance modes. Similar time ranges of frequency bands with fixed CA50 were noted for all spark plug numbers. Higher frequency signal decayed faster than lower during the knocking vibrations. As expected, we find that auto-ignition starts earlier when advancing the spark timing. Thereby more energy is released by knock, which explains the knock amplitude growth with earlier spark timing.

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