Recent Submissions

  • Methanol oxy-combustion and supercritical water oxidation: A ReaxFF molecular dynamics study

    Monge Palacios, Manuel; Grajales Gonzalez, Edwing; Sarathy, Mani (Energy, Elsevier BV, 2023-09-15) [Article]
    Energy and environmental concerns are motivating the use of renewable fuels such as methanol. Furthermore, the implementation of the oxy-combustion and hydrothermal combustion technologies can help to improve the performance of power generation and reduce NOx emissions. These aspects can contribute to achieve the transition to cleaner sources of energy that is being sought worldwide, and thus we carried out the first molecular dynamics study of the oxidation of methanol at 2700 K and 3000 K in four supercritical environments with compositions CH3OH + O2, CH3OH + O2+CO2, CH3OH + O2+H2O, and CH3OH + O2+CO2+H2O. Reaction mechanisms were obtained and revealed that the initiation reaction is CH3OH unimolecular dissociation in all cases. The CH3OH oxidation chemistry changes when O2 is replaced by supercritical CO2 (sCO2) and/or H2O (sH2O), and a new route for the important oxidation sequence CH3OH→CH2OH→H2CO→CHO→CO→CO2 is reported. The rate constants for the CH3OH unimolecular dissociation were calculated, indicating a positive effect of sH2O. Furthermore, the collisions of CH3OH molecules with those of H2O and CO2 were analyzed with molecular dynamics simulations and quantum chemistry calculations, suggesting that collisions with H2O can activate more efficiently CH3OH for a prospective dissociation event. This study is aimed to help in the development of kinetic models for CH3OH oxidation/pyrolysis in sCO2 and sH2O, and thus in the implementation of the oxy-combustion and hydrothermal combustion techniques for this alternative fuel.
  • Shock Tube/Laser Absorption Measurements of the High-Temperature Spectra and Decomposition of Propyl Ethers.

    Adil, Mohammad; Farooq, Aamir (The journal of physical chemistry. A, 2023-09-10) [Article]
    This work presents measurements of temperature-dependent absorption spectra and thermal decomposition rates of propyl ethers, specifically di-n-propyl ether (DnPE) and diisopropyl ether (DiPE), which are two renewable fuel candidates. We employed a broadband rapid-tuning MIRcat-QT laser, operating in the scan/fixed-wavelength mode in combination with a shock tube. Spectral measurements were performed over the wavelength range of 8.4–11 μm (909.1–1190.5 cm–1), covering the strongest infrared absorption bands of the studied ethers, at temperatures of 559–853 K and pressure near 1 bar. These high-temperature spectra help in selecting the optimum wavelength for sensitive and selective measurements of the target ethers. Based on the criteria of high sensitivity, minimum interference, and insensitivity to temperature and pressure variations, we selected a wavelength of 1121.82 cm–1 for high-temperature diagnostics of DnPE and DiPE. Absorption cross sections at the selected wavelength of 1121.82 cm–1 were measured over 550–1500 K, and pressures ranging from 0.3–1.4 bar. This diagnostic was then applied to study the high-temperature pyrolysis of these ethers by measuring their time histories behind the reflected shock waves. Our experimentally measured overall decomposition rate coefficients for DnPE and DiPE are given as (unit of s–1) kDnPE = 1.25 × 1027 × T–3.483 × exp(−37620 K/T) and kDiPE = 5.26 × 1023 × T–2.857 × exp(−32360 K/T).
  • An updated functional-group-based approach to modeling the vacuum residue oil gasification kinetics

    Zhang, Xiaoyuan; Khandavilli, Muralikrishna; Gautam, Ribhu; AlAbbad, Mohammed A.; Li, Yang; Chatakonda, Obulesu; Kloosterman, Jeffrey W.; Middaugh, Joshua; Sarathy, Mani (Fuel, Elsevier BV, 2023-09-09) [Article]
    Gasification of heavy petroleum residues can convert low-value feedstock to hydrogen-rich syngas, which can further be used for power generation and/or chemical production. The present work proposed an updated functional-group-based approach (FGMech) to modeling the gasification of a vacuum residue oil (VRO), which is helpful for better understanding the detailed kinetics of the gasification and improving gasifier performance. Elemental, average molecular weight (AMW) and nuclear magnetic resonance (NMR) analyses were conducted experimentally to characterize VRO, including elemental composition, average molecular formula and the functional group distribution, which were further used for model construction. A lumped mechanism for VRO devolatilization was constructed based on the updated FGMech approach: stoichiometric parameters of stable gases, tars and char were obtained from experiments, while those of radicals were based on the multiple linear regression (MLR) correlations; thermodynamic and kinetic parameters were derived from Benson group additivity method and rate rules, respectively. A merged detailed model was adopted for describing the conversion of gases and tars, and a global model was used for char. To test the reliability of the present model approach, Orimulsion gasification experiments from literature were simulated using an integrated perfectly stirred reactor (PSR) and plug flow reactor (PFR) model. It shows that the present model can reasonably predict measured results under various equivalence ratios, and has better performance on the prediction of CH4 compared with most literature models. Based on model analyses, syngas comes from the conversion of C2H4, H2S, CH4 and char in different gasification stages. Benzene, toluene, naphthalene and 1-methylnaphthalene are initial tar species considered in the devolatilization of the VRO. They can undergo hydrogen abstraction acetylene addition (HACA) and C3H3/C5H5 addition reaction pathways to produce large PAHs.
  • Adaptive phase shift control of thermoacoustic combustion instabilities using model-free reinforcement learning

    Alhazmi, Khalid; Sarathy, Mani (Combustion and Flame, Elsevier BV, 2023-09-08) [Article]
    Combustion instability is a significant risk in the development of new engines when using novel zero-carbon fuels such as ammonia and hydrogen. These instabilities can be difficult to predict and control, making them a major barrier to the adoption of carbon-free gas turbine technologies. In order to address this challenge, we propose the use of model-free reinforcement learning (RL) to adjust the parameters of a phase-shift controller in a time-varying combustion system. Our proposed algorithm was tested in a simulated time-varying combustion system, where it demonstrated excellent performance compared to other model-free and model-based methods, including extremum seeking controllers and self-tuning regulators. The ability of RL to effectively adjust the parameters of a phase-shift controller in a time-varying system, while also considering the safety implications of online system exploration, makes it a promising tool for mitigating combustion instabilities and enabling the development of safer, more efficient carbon-free gas turbine technologies.
  • Chitosan and chitosan composites for oil spills treatment: Review of recent literature

    Ababneh, Hani; Hameed, B. H. (Journal of Water Process Engineering, Elsevier BV, 2023-09-06) [Article]
    Every year millions of oil barrels enter the water bodies. These oil spills have a devastating impact on the marine environments and their wildlife. Hence, it is necessary to clean-up these oil spills. Chitosan is cheap, renewable and eco-friendly polysaccharide. Therefore, chitosan-based materials have caught the attention of researchers as absorbents for oil spills cleanup and to separate oil/water mixtures. In their studies, chitosan was modified to improve its mechanical and physical properties, hence improving its adsorption capabilities. This paper is a comprehensive review on the application of chitosan and chitosan derivatives such as sponges, aerogels, carbon nanotubes fibers, foams, and polymers in the field of oil spill cleanup. Furthermore, this review lists the different parameters, such temperature, salinity, and pH, which affect the adsorption process and adsorption isotherms. Finally, the challenges and prospects of this type of adsorbent are discussed and summarized.
  • Hydrocarbon-based membranes cost-effectively manage species transport and increase performance in thermally regenerative batteries

    Cross, Nicholas R.; Vazquez-Sanchez, Holkan; Rau, Matthew J.; Lvov, Serguei N.; Hickner, Michael A.; Gorski, Christopher A.; Nagaraja, Shashank S.; Sarathy, Mani; Logan, Bruce; Hall, Derek M. (Electrochimica Acta, Elsevier BV, 2023-09-05) [Article]
    Low-temperature heat (T<130°C) can be utilized by thermally regenerative batteries (TRBs) for power production, allowing the thermal energy to be converted to storable chemical potential energy. However, TRBs suffer from high ohmic losses and ammonia crossover, which has slowed their development. In this study, we examined how the use of six different membranes influenced TRB performance, determined the most influential membrane parameters, and identified promising membrane candidates that cost-effectively increase TRB performance. Of the six membranes examined, an inexpensive, hydrocarbon CEM (Selemion CMVN) had low ammonia crossover without compromising resistance, resulting in good performance across all metrics studied. A thin anion exchange membrane (Sustainion, 50 microns) showed a high peak power density of 82 mW cm−2 due to low resistance, but the average power density and energy density were low due to high ammonia flux. Full discharge curves using Selemion CMVN provided an average power density of 26 ± 7 mW cm−2 with an energy density of 2.9 Wh L−1, which were large improvements on previous TRBs. A techno-economic analysis showed that Selemion CMVN had the lowest levelized cost of storage ($410 per MWh) at an applied current density of 50 mA cm−2.
  • Experimental estimation of turbulence modulation in droplet-laden two-phase jet

    Wu, Hao; Zhang, Zhenyu; Zhang, Fujun; Wu, Kun; Roberts, William L. (Physical Review Fluids, American Physical Society (APS), 2023-09-05) [Article]
    The effect of liquid droplets generated from air-assisted atomization on gas flow characteristics was studied experimentally. A phase/Doppler particle analyzer was used to measure velocity and size distributions of continuous and dispersed phases in the droplet-laden two-phase flow. A comparison of mean gas velocity with and without droplets indicates the expected influence of dispersed phase on the carrier phase, i.e., two-way coupling. The flow characterization result shows the presence of liquid droplets contributes to the increase of gas-phase flow velocity in the spray field. The effect of liquid droplets on gas-phase turbulence is manifested in three ways. First, the presence of droplets leads to the increase in fluctuation velocity of gas-phase flow. Subsequently, it is observed that the range of fluctuation velocities in the gas phase is expanded in two-phase flow compared with single-phase flow. In the region characterized by a steep velocity gradient, the initial gas fluctuation velocities in two-phase flow demonstrate a notable enhancement of 20% compared with single-phase flow. Furthermore, the presence of droplets induces axial stretching within the shear region of the gas phase, and this stretching effect is particularly pronounced in cases of higher fuel-injection durations, primarily due to the influence of droplet gravity. The data obtained from the analysis of velocity gradient and fluctuation velocity within the two-phase flow field reveal a distinct segmental linear relationship, deviating from previous findings reported in the literature and highlighting a deeper understanding of the underlying mechanisms in current two-phase flow systems.
  • Lagrangian Analysis of Droplet Dynamics Using Computational Singular Perturbation

    Angelilli, Lorenzo; Malpica Galassi, Riccardo; Ciottoli, Pietro Paolo; Hernandez, Francisco; Valorani, Mauro; Im, Hong G. (Elsevier BV, 2023-09-05) [Preprint]
    Computational singular perturbation (CSP) has been successfully used in the analysis of complex chemically reacting flows by systematically identifying the intrinsic timescales and slow invariant manifolds that capture the essential subprocesses driving the dynamics of the system. In this article, the analytical and computational framework is applied for the first time to analyze the Lagrangian droplets undergoing evaporation and dispersion in the surrounding gases. First, a rigorous mathematical formulation is derived to adapt the CSP tools into the droplet dynamics equations, including the formal definition of the tangential stretching rate (TSR) that represents the explosive/dissipative nature of the system. Canonical case studies are then conducted to demonstrate the utility of the CSP methodology in identifying various physical mechanisms driving the evolution of the system, such as the distinction of thermal-driven and mass-driven regimes. Various definitions of the importance indices are also examined to provide in-depth analysis of different subprocesses and their interactions in modifying the droplet dynamics.
  • Effects of Ammonia Substitution in the Fuel Stream and Exhaust Gas Recirculation on Extinction Limits of Non-premixed Methane– and Ethylene–Air Counterflow Flames

    Chu, Carson Noel; Scialabba, Gandolfo; Liu, Peng; Serrano-Bayona, Raul; Aydin, Faruk; Pitsch, Heinz; Roberts, William L. (Energy & Fuels, American Chemical Society (ACS), 2023-09-04) [Article]
    The global extinction limits of non-premixed nitrogen/ammonia-substituted methane– and ethylene–air counterflow flames were experimentally evaluated. In comparison to nitrogen substitution, ammonia substitution reduced the extinction strain rates more. Measurements of OH* chemiluminescence, of which the intensity correlates with extinction limits, suggest that ammonia substitution reduces OH* production. The effects of transport, thermal and chemical properties on flame extinction of the ammonia-substituted flames were assessed, and it was found that their lower extinction limits were due to reactions that consume radicals, which hinder the chain-branching reactions. To mimic the effect of exhaust gas recirculation on the extinction limits of ammonia-substituted flames, carbon dioxide was added to the oxidizer stream. Lower extinction limits were observed with carbon dioxide addition as a result of thermal and chemical effects. Carbon dioxide addition lowered flame temperatures and, like ammonia substitution, introduced reactions that consume radicals. Nitric oxide (NO) production was quantitatively analyzed by simulations. It was found that, for ammonia flames, NO production was promoted by ammonia oxidation with OH, whereas for carbon dioxide addition, NO production was suppressed by the reduction of OH production.
  • Mini Review of Ammonia for Power and Propulsion: Advances and Perspectives

    Guiberti, Thibault; Pezzella, Giuseppe; Hayakawa, Akihiro; Sarathy, Mani (Energy & Fuels, American Chemical Society (ACS), 2023-09-01) [Article]
    Ammonia is a molecule that has been essential to human activities for centuries. It is widely used as a feedstock for fertilizers, industrial chemicals, and emissions after-treatment systems. The properties of ammonia have led to its interest as a carrier for hydrogen in energy applications. The combustion of ammonia for power and propulsion offers direct applications of this molecule in energy and transportation applications. However, there are significant challenges related to ammonia combustion, including low flammability and potentially high emissions. Blending of ammonia with hydrogen or hydrocarbons offers opportunities to improve combustibility. This mini review discusses challenges related to ammonia combustion and current state-of-the-art approaches to overcoming these challenges with research into chemical kinetics, laminar and turbulent flames, and engine and turbine systems. This paper seeks to introduce and summarize recent results on ammonia combustion by highlighting pertinent aspects of this rich and rapidly increasing body of information.
  • Synergistic effect of non-thermal plasma and CH4 addition on turbulent NH3/air premixed flames in a swirl combustor

    Kim, Gyeong Taek; Park, Jeong; Chung, Suk Ho; Yoo, Chun Sang (International Journal of Hydrogen Energy, Elsevier BV, 2023-09-01) [Article]
    The synergistic effect of non-thermal plasma (NTP) induced by a dielectric barrier discharge (DBD) and CH4 addition on turbulent swirl-stabilized NH3/air premixed flames in a laboratory-scale gas turbine combustor is experimentally investigated by varying the mixture equivalence ratio, φ, the mixt velocity, U0, and the mole fraction of CH4 in the fuel, Xf,CH4. It is found that the streamer intensity is significantly increased by adding CH4 to NH3/air flames compared with that by adding H2. This is because positive ions generated by CH4 addition play a critical role in generating streamers. Such streamers intensified by CH4 addition enhance the ammonia combustion more together with CH4, and hence, the lean blowout (LBO) limits of NH3/CH4/air flames are significantly extended compared with those without applying NTP. The maximum streamer intensity is found to be linearly proportional to φ⋅Xf,CH4⋅U0 in wide ranges of φ, Xf,CH4, and U0. NTP is also found to significantly reduce the amount of NOx and CO emissions simultaneously. All of the results suggest that NTP can be used more effectively with CH4 addition to stabilize turbulent premixed NH3/air flames and reduce NOx/CO emissions, which is attributed to their synergistic effect on the ammonia combustion.
  • Impact of fuel surrogate formulation on the prediction of knock statistics in a single cylinder GDI engine

    Fontanesi, Stefano; Shamsudheen, Fabiyan Angikath; Gonzalez, Edwing Grajales; Sarathy, Mani; Berni, Fabio; d’Adamo, Alessandro; Borghi, Massimo; Breda, Sebastiano (International Journal of Engine Research, SAGE Publications, 2023-08-31) [Article]
    The statistical tendency of an optically accessible single-cylinder direct-injection spark-ignition engine to undergo borderline/medium knocking combustion is investigated using 3D-CFD. Focus is made on the role of fuel surrogate formulation for the characterization of anti-knock quality and flame speed of the actual fuel. An in-house methodology is used to design surrogates able to emulate laminar flame speed and autoignition delay times of the injected fuel. Two different surrogates, characterized by increasing level of complexity, are compared. The most complex one (six components) improves the representation of the real fuel, highlighting the crucial role of accurate fuel kinetics to predict flame propagation and unburnt mixture reactivity. A devoted chemical mechanism including the oxidation pathways for all the species in the surrogate is also purposely developed for the current analysis. Knock is investigated using a proprietary statistical knock model (GruMo-UNIMORE Statistical Knock Model, GK-PDF), which can infer the probability of knocking events within a RANS formalism. Predicted statistical distributions are compared to measured counterparts. The proposed numerical/experimental comparison demonstrates the possibility to efficiently integrate complex-chemistry driven information in 3D-CFD combustion simulations without online solving chemical reactions: a combination of laminar flame speed correlations, ignition delay look-up tables, and a statistics-based knock model is adopted to estimate the percentage of knocking cycles in a GDI engine while limiting the computational cost of the simulations.
  • Effects of Engine Speed on Prechamber-Assisted Combustion

    Palombi, Lucia; Sharma, Priybrat; Cenker, Emre; Magnotti, Gaetano (SAE International, 2023-08-28) [Conference Paper]
    Lean combustion technologies show promise for improving engine efficiency and reducing emissions. Among these technologies, prechamber-assisted combustion (PCC) is established as a reliable option for achieving lean or ultra-lean combustion. In this study, the effect of engine speed on PCC was investigated in a naturally aspirated heavy-duty optical engine: a comparison has been made between analytical performances and optical flame behavior. Bottom view natural flame luminosity (NFL) imaging was used to observe the combustion process. The prechamber was fueled with methane, while the main chamber was fueled with methanol. The engine speed was varied at 1000, 1100, and 1200 revolutions per minute (rpm). The combustion in the prechamber is not affected by changes in engine speed. However, the heat release rate (HRR) in the main chamber changed from two distinct stages with a faster first stage to more gradual and merged stages as the engine speed increased. NFL imaging revealed that lower mean piston speed allowed for longer free jet propagation inside the combustion chamber resulting in faster and stronger HRR stages. At higher speeds, the jet-piston interaction started earlier and was dispersed in radial directions, resulting in a relatively prolonged HRR. Finally, the study emphasizes the importance of prechamber jet and piston interaction in shaping HRR.
  • Oxidative desulfurization of fuel oil and molecular characterization of the sulfone compound distribution in the different extractants

    Fan, Jiyuan; Khan, Hassnain Abbas; Wang, Tairan; Ruiz-Martinez, Javier; Saxena, Saumitra; Emwas, Abdul-Hamid M.; Samaras, Vasileios G.; Roberts, William L. (Separation and Purification Technology, Elsevier BV, 2023-08-28) [Article]
    PMoA/G5 catalyst was synthesized, and its oxidative desulfurization (ODS) performance on model oil was studied. The catalyst and oxidation-extraction-adsorption system was used for the ODS of Arabian Extra light oil (AXL). Acetonitrile and methanol were chosen as different extractants for the extraction of sulfones (O2S and O2S4). The distribution of sulfone was first reported in detail at each of the three-stage extraction solvents at the molecular level analyzed by the Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), proton, and 13C nuclear magnetic resonance (1H NMR,13C NMR). The FT-ICR MS results show that the extracted proportion of macromolecular sulfone compounds increases with the extraction stages. Acetonitrile exhibited better selectivity than methanol for polyaromatic sulfone with a high carbon number for the O2S species with double bond equivalent (DBE) = 12–15 and O2S2 species with DBE = 11–16. The NMR results reveal that polyaromatics with naphthenic rings and a low carbon number (<30) can be easily extracted due to their high polarity. The excellent performance of the PMoA/G5 catalyst makes it a promising candidate in the ODS reaction, and the research results give guidelines for ODS technology.
  • Effects of n-decane substitution on structure and extinction limits of formic acid diffusion flames

    Alfazazi, Adamu; Li, Jiajun; Xu, Chaochen; Es-sebbar, Et-touhami; Zhang, Xiaoyuan; Abdullah, Marwan; Younes, Mourad; Sarathy, Mani; Dally, Bassam (Fuel, Elsevier BV, 2023-08-26) [Article]
    Formic acid (FA) is a low-carbon fuel that can be produced from renewable hydrogen (H2) and carbon dioxide (CO2). However, transitioning completely to low carbon fuels might be lengthy and challenging, so it makes sense to gradually introduce low carbon fuels into the energy sector in conjunction with existing fuels. One practical approach could be blending FA with existing fossil fuels, such as kerosene in aviation. This study investigates the behavior of flames comprising FA and its blends with n-decane. The extinction limits of pure FA and FA/n-decane mixtures were measured in a counterflow non-premixed laminar flame setup at various blending ratios. Additionally, the flame structure was studied by measuring temperature and species distribution using probe-based sampling. The results indicate that replacing FA with n-decane in the FA-N2 flame greatly enhances the flame's reactivity. Blending the fuels also led to a decrease in CO2 production in the flame, while increasing the flame temperature and the concentration of H2 and CO species. Experimental results were modeled using an updated FA and n-decane model. The kinetic model agrees with the experimental trends, but slightly overpredicts H2, CH4 species, and flame temperature. The kinetic model was also used to investigate the kinetic coupling between FA and n-decane in non-premixed laminar flames. Kinetic analyses indicate that HOCO and OCHO intermediates play a crucial role in pure FA flames by reacting with active radicals like H and OH to produce CO2 and CO, while in n-decane blended flames, fuel decomposition proceeds through two other pathways leading to H2 and H2O2.
  • Temperature-Dependent Kinetics of Ozone Production in Oxygen Discharges

    Bang, Seunghwan; Snoeckx, Ramses; Cha, Min Suk (Plasma Chemistry and Plasma Processing, Springer Science and Business Media LLC, 2023-08-26) [Article]
    Ozone has been widely used for its disinfection properties ever since its efficient production was made possible by plasma discharges. To-date, many experimental and modeling studies have been—and still are—dedicated to further improve the O3 production efficiency. Early on, it became clear that heat has a detrimental effect. Hence, little attention has been paid to the temperature-dependence of the plasma chemistry. However, with the increased use of O2 as (co-)reactant for plasma-based processes at elevated temperatures, this becomes essential. Therefore, we developed a reaction mechanism to study the temperature-dependence of the O2/O3 (plasma) chemistry. Here, we present the experimental validation of this mechanism and an analysis of the different O3 production trends as a function of gas temperature (300–590 K) and discharge power (5–20 W). Through improving key ozone reactions and electron impact dissociation processes, our mechanism could well-predict all experimentally observed trends. Our analysis revealed the importance of the electronic excited states of O2 and how the temperature-dependence of the plasma-based O3 production is highly dependent on the discharge power. Therefore, we believe that this work can contribute to a better understanding of the underlying physicochemical mechanisms of any O2/O3-containing (plasma) process operating at elevated temperatures. Nevertheless, our work also revealed the need for more accurate and comprehensive data with respect to the production and consumption of the electronic excited states of O2.
  • Study of engine knocking combustion using simultaneous high-speed shadowgraph and natural flame luminosity imaging

    Tang, Qinglong; Shi, Hao; Uddeen, Kalim; Sharma, Priybrat; Yao, Mingfa; Turner, James W. G.; Magnotti, Gaetano (Applied Thermal Engineering, Elsevier BV, 2023-08-25) [Article]
    Engine knocking is a classical but significantly impactful combustion phenomenon that arouses unfailing research interests. An in-depth understanding of the knocking mechanism holds the key to the next-generation high-efficiency spark ignition engines adopting a high compression ratio. In this study, a novel 72 kHz imaging system of simultaneous shadowgraph and natural flame luminosity (NFL) was implemented on an optical engine. The key combustion parameters that affect the engine knock intensity were investigated based on the heat release analysis. The shadowgraph image velocimetry (SIV) was utilized to measure the in-cylinder flow field. The end gas autoignition process in the engine knocking combustion was studied under knock intensity as high as 18.1 bar. The results indicate that there is an “optimum” combustion phasing that produces the highest knock intensity. The cases with more end gas mass at knock onset, though having lower mean temperatures, generally produce higher knock intensity. The knock intensity can be significantly different under the same end gas mass and mean end gas temperature, possibly due to the different temperature gradients in the end gas. The simultaneous shadowgraph and NFL imaging succussed in differentiating the density variation zone in the end gas caused by the low-temperature heat release from the hot flame zone before auto-ignition. An intense density variation zone is witnessed around the center of the cylinder under higher engine knock intensity by the shadowgraph images, showing a dark region that oscillates together with the local pressure oscillations. The coupling among the local density variation, pressure oscillation, and NFL intensity oscillation is observed during the engine knocking combustion. The velocity distribution of the flow field indicates that the engine knocking combustion enhances the in-cylinder flow, which may cause more convective heat transfer loss and flow loss.
  • Unified picture on temperature dependence of lithium dendrite growth via phase-field simulation

    Li, Yajie; Zhao, Wei; Zhang, Geng; Shi, Siqi (Energy Material Advances, American Association for the Advancement of Science (AAAS), 2023-08-24) [Article]
    Lithium dendrite growth due to uneven electrodeposition may penetrate the separator and solid electrolyte, causing inner short circuit and potential thermal runaway. Despite great electrochemical phase-field simulation efforts devoted to exploring the dendrite growth mechanism under the temperature field, no unified picture has emerged. For example, it remains open how to understand the promotion, inhibition, and dual effects of increased temperature on dendrite growth when using different electrolyte types. Here, by comprehensively considering the temperature-dependent Li+ diffusion coefficient, electrochemical reaction coefficient, and initial temperature distribution in phase-field model, we propose that the activation-energy ratio, defined as the ratio of electrochemical reaction activation energy to electrolyte Li+ diffusion activation energy, can be used to quantify the effect of temperature on dendrite morphology. Specifically, we establish a mechanism diagram correlating the activation-energy ratio, uniform initial temperature, and maximum dendrite height, which unifies the seemingly contradictory simulation results. Furthermore, results based on non-uniform initial temperature distribution indicate that a positive temperature gradient along the discharging current facilitates uniform Li+ deposition and local hotspot should be avoided. These findings provide valuable insights into the temperature-dependent Li dendrite growth and contribute to the practical application of Li metal batteries.
  • Numerical assessment of the performance and emissions of a compact Wankel rotary engine applied as a range extender on the BMW i3 model

    Vorraro, Giovanni; Turner, James W. G. (JSAE/SAE, 2023-08-22) [Conference Paper]
    Amongst all the hybrid-vehicles technologies and layouts, range-extended electric vehicles are the ones with the real prospect to reduce the emissions produced by the thermal machine when in driving conditions, while assuring an adequate range for the common user. The BMW i3 represents one of the most successful series hybrid electric vehicles, having been on the market since 2013. Given the complexities of a hybrid layout employing both thermal and electrical machines, the range extender must have compactness and lightweight characteristics in addition to a suitable power output for the vehicle. Usually, standard 4- stroke small-displacement engines are employed for this application, with the BMW i3 employing a 2- cylinder range extender. More interestingly, a Wankel rotary engine can provide the same amount of mechanical power by reducing the weight and the volume of nearly a third to the equivalent 4-stroke engine. In this study a numerical assessment of the Advanced Innovative Engineering UK (AIE UK) 225CS Wankel rotary engine as a range extender for the BMW i3 was carried out. A full vehicle model of the BMW i3 was built in Siemens Simcenter Amesim 2021.2 to evaluate the behaviour of the aforementioned engine as a range extender. The engine sub-model used was a Mean Value Engine Model (MVEM) set up by implementing the experimental data collected during previous experimental campaign while the BMW i3 chassis sub-model was characterised by using the publicly available data from an Argonne National Laboratory benchmarking project (vehicle weight, front surface, drag coefficient, tires dimensions, etc.). Finally the model was tested over the standard Worldwide harmonized Light vehicles Test Procedure (WLTP) driving cycle in both Charge Depleting and Charge Sustaining modes.
  • Experimental Investigation of the Structure and NO Emissions from Swirling Lean Premixed NH3/CH4/Air Flames and Their Correlation with OH

    Wang, Shixing; Wang, Guoqing; Elbaz, Ayman M.; Guiberti, Thibault; Roberts, William L. (Energy & Fuels, American Chemical Society (ACS), 2023-08-21) [Article]
    Ammonia/methane fuel blends have gathered interest as a promising solution for the development of a low-carbon energy system. In that pursuit, this work focused on the effects of turbulent intensity (u′ = 1.3–2.6 m/s), ammonia contents (XNH3 = 0.0–1.0), and equivalence ratios (ϕ = 0.5–0.9) on the flame structure and NO emissions of bluff-body swirl-stabilized premixed flames of ammonia/methane/air as well as their links to hydroxyl planar laser-induced fluorescence (OH-PLIF) intensity. Three swirling flame shapes are distinguished, which are jointly determined by the ammonia content and equivalence ratio. The normalized OH-PLIF intensity (Iaverage/SL) of all XNH3, u′, and ϕ can be collapsed well onto one unified correlation as a function of the normalized turbulent intensity u′/SL. The flame surface density (FSD, marked as Σ) of confined swirling flames was rarely reported before, and the FSD in a V shape increases obviously when transiting to a M shape as the ammonia content reduces. The turbulent flame area ratio (AT/AL) derived from the FSD is increasing as u′/SL increases; however, it decreases first and then increases as ϕ increases. Then, a new description of the link between NO, OH, and XNH3 was provided, which improves the correlation performance more than the previous studies only considering the link between NO and OH.

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