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.
  • Early Chemistry of Nicotine Degradation in Heat-Not-Burn Smoking Devices and Conventional Cigarettes: Implications for Users and Second- and Third-Hand Smokers

    Chavarrio Cañas, Javier Eduardo; Monge Palacios, Manuel; Grajales Gonzalez, Edwing; Sarathy, Mani (The Journal of Physical Chemistry A, American Chemical Society (ACS), 2021-04-09) [Article]
    Nicotine exposure results in health risks not only for smokers but also for second- and third-hand smokers. Unraveling nicotine's degradation mechanism and the harmful chemicals that are produced under different conditions is vital to assess exposure risks. We performed a theoretical study to describe the early chemistry of nicotine degradation by investigating two important reactions that nicotine can undergo: hydrogen abstraction by hydroxyl radicals and unimolecular dissociation. The former contributes to the control of the degradation mechanism below 800 K due to a non-Arrhenius kinetics, which implies an enhancement of reactivity as temperature decreases. The latter becomes important at higher temperatures due to its larger activation energy. This change in the degradation mechanism is expected to affect the composition of vapors inhaled by smokers and room occupants. Conventional cigarettes, which operate at temperatures higher than 1000 K, are more prone to yield harmful pyridinyl radicals via nicotine dissociation, while nicotine in electronic cigarettes and vaporizers, with operating temperatures below 600 K, will be more likely degraded by hydroxyl radicals, resulting in a vapor with a different composition. Although low-temperature nicotine delivery devices have been claimed to be less harmful due to their nonburning operating conditions, the non-Arrhenius kinetics that we observed for the degradation mechanism below 873 K suggests that nicotine degradation may be more rapidly initiated as temperature is reduced, indicating that these devices may be more harmful than it is commonly assumed.
  • Development of catalysts for sulfuric acid decomposition in the sulfur–iodine cycle: a review

    Khan, Hassnain Abbas; Jaleel, Ahsan; Mahmoud, Eyas; Ahmed, Shoaib; Bhatti, Umair Hassan; Bilal, Muhammad; Hussain, (Catalysis Reviews - Science and Engineering, Informa UK Limited, 2021-04-04) [Article]
    To achieve carbon-neutral energy vectors, researchers have investigated various sulfur-based thermochemical cycles. The sulfur–iodine cycle has emerged as a cost-effective global process with massive hydrogen production potentials. However, all sulfur-based thermochemical cycles involve sulfuric acid decomposition reaction, which is highly corrosive and energy intensive. The activation energy of this reaction can be reduced using catalysts that decrease the onset temperature of the reaction. Renewable heat sources such as solar and waste nuclear heat demand high stability to operate within a wide temperature window (650°C–900°C). Several metal/metal oxide systems based on noble and transition metals have been investigated over the last twenty years. In the literature, supported Pt-based catalysts are regarded as the prime choice for stable operations. However, during catalytic operations, noble metals are degraded owing to sintering, oxidation, leaching, and other processes. Transition metal oxides such as Fe, Cu, Cr, and Ni exhibit promising catalytic activity at high temperatures; however, at low temperatures (>600°C), their activation is reduced owing to poisoning and the formation of stable sulfate species. The catalytic activity of transition metal oxides is determined by the decomposition temperature of its corresponding metal sulfate; thus, the metal sulfate formation is considered as the rate-limiting step. Herein, the catalytic systems studied over the last decade are summarized, and recommendations for designing robust catalysts for commercial applications are presented.
  • 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.
  • Investigation of the Combustion Kinetics Process in a High-Pressure Direct Injection Natural Gas Marine Engine

    Li, Jingrui; Liu, Haifeng; Liu, Xinlei; Ye, Ying; Wang, Hu; Yao, Mingfa (Energy & Fuels, American Chemical Society (ACS), 2021-03-31) [Article]
    The detailed combustion kinetic processes of a high-pressure direct injection (HPDI) natural gas (NG) marine engine was investigated in the present work. A postprocessing code was employed to visualize the characteristic reactions that determine the combustion process. To evaluate the effect of mixture stratification on the combustion process, various NG injection timings were employed and four representative combustion periods were selected, including the timings when 1% (CA1), 5% (CA5), 10% (CA10), and 50% (CA50) of the total fuel energy are released. A higher heat release rate (HRR) was generated with a more advanced NG start of injection (SOI) timing, which, however, had limited effects on the main representative exothermic reactions (REXRs) within the high heat release (HHR) region and the dominant formation reactions of CH2O and OH, which are known as the indicators of low heat release (LHR) and HHR, respectively. Besides, for different NG SOI timing simulation, the consumption of CH4 was all dominated by reactions H + CH4 = CH3 + H2 and OH + CH4 = CH3 + H2O and the dominated REXR of the LHR region was reaction CH3 + O2 = CH3O2. Furthermore, with an advanced NG injection timing, significant changes were observed for the reaction paths of CH2, CH2O, and HCO from the premixed-combustion phase (CA10) to the mixing-controlled combustion phase (CA50). The results of the present study are able to provide a theoretical fundamental for the practical control of the HPDI NG marine engine.
  • New Particle Formation and Growth from Dimethyl Sulfide Oxidation by Hydroxyl Radicals

    Rosati, Bernadette; Christiansen, Sigurd; Wollesen de Jonge, Robin; Roldin, Pontus; Jensen, Mads Mørk; Wang, Kai; Moosakutty, Shamjad P.; Thomsen, Ditte; Salomonsen, Camilla; Hyttinen, Noora; Elm, Jonas; Feilberg, Anders; Glasius, Marianne; Bilde, Merete (ACS Earth and Space Chemistry, American Chemical Society (ACS), 2021-03-25) [Article]
    Dimethyl sulfide (DMS) is produced by plankton in oceans and constitutes the largest natural emission of sulfur to the atmosphere. In this work, we examine new particle formation from the primary pathway of oxidation of gas-phase DMS by OH radicals. We particularly focus on particle growth and mass yield as studied experimentally under dry conditions using the atmospheric simulation chamber AURA. Experimentally, we show that aerosol mass yields from oxidation of 50–200 ppb of DMS are low (2–7%) and that particle growth rates (8.2–24.4 nm/h) are comparable with ambient observations. An HR-ToF-AMS was calibrated using methanesulfonic acid (MSA) to account for fragments distributed across both the organic and sulfate fragmentation table. AMS-derived chemical compositions revealed that MSA was always more dominant than sulfate in the secondary aerosols formed. Modeling using the Aerosol Dynamics, gas- and particle-phase chemistry kinetic multilayer model for laboratory CHAMber studies (ADCHAM) indicates that the Master Chemical Mechanism gas-phase chemistry alone underestimates experimentally observed particle formation and that DMS multiphase and autoxidation chemistry is needed to explain observations. Based on quantum chemical calculations, we conclude that particle formation from DMS oxidation in the ambient atmosphere will most likely be driven by mixed sulfuric acid/MSA clusters clustering with both amines and ammonia.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Dissipation and dilatation rates in premixed turbulent flames

    Sabelnikov, V. A.; Lipatnikov, A. N.; Nishiki, S.; Dave, H. L.; Hernández Pérez, F. E.; Song, W.; Im, Hong G. (Physics of Fluids, AIP Publishing, 2021-03-01) [Article]
    Velocity dilatation and total, solenoidal, and dilatational dissipation rates of the total flow kinetic energy are extracted from three different direct numerical simulation databases obtained by three independent research groups using different numerical codes and methods (e.g., single-step chemistry and complex chemistry flames) from six different premixed turbulent flames associated with flamelet, thin reaction zone, and broken reaction zone regimes of turbulent burning. The results show that dilatational dissipation can be larger than solenoidal dissipation in the flamelet regime and is substantial in the thin reaction zone regime. Accordingly, the influence of combustion-induced thermal expansion on the dissipation rate is not reduced to an increase in the mixture viscosity by the temperature. A simple criterion for identifying conditions associated with significant dilatational dissipation is discussed, and dilatational dissipation due to the influence of turbulence on mixing in preheat zones is argued to play a role even at high Karlovitz numbers Ka. In particular, the magnitude of dilatation fluctuations and probability of finding negative local dilatation are increased by Ka, thus implying that the impact of molecular transport of species and heat on the dilatation increases with increasing Karlovitz number.
  • Surrogate formulation and molecular characterization of sulfur species in vacuum residues using APPI and ESI FT-ICR mass spectrometry

    Abdul Jameel, Abdul Gani; Alquaity, Awad B.S.; Campuzano, Felipe; Emwas, Abdul-Hamid M.; Saxena, Saumitra; Sarathy, Mani; Roberts, William L. (Fuel, Elsevier BV, 2021-02-26) [Article]
    Vacuum residues (VR) are the bottom of the barrel products left after vacuum distillation of crude oils. VR are primarily used as feedstock for production of syn-gas and hydrogen via gasification; and heavy fuel oil (HFO) for use as fuel in power generation and shipping. However, VR contain relatively large amounts of sulfur (upto 8% by mass) and require the removal of varying amounts depending on the emission norms (eg. International Maritime Organization 2020 sulfur regulations). Understanding the fuel molecular structure and, in particular, the structure of sulfur species enables the adoption and optimization of suitable desulfurization strategies. In the present work, detailed molecular characterization of the sulfur species in VR was performed using positive ion atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) coupled to Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS). Ions possessing mass to charge (m/z) in the range of 100 to 1200 were detected using the ultra-high resolution instrument and were resolved into unique chemical formulas (CcHhSsNnOo). The assigned masses were then divided into molecular classes based on the presence of heteroatoms, and plots of carbon number versus double bond equivalency (DBE) were made for each molecular class. The molecular classes were further sub-divided based on the presence of sulfur families like sulfides (Su), thiophenes (Th), benzothiophenes (BT), dibenzothiophenes (DBT) and benzonaphthothiophene (BNT) and their derivatives. A single surrogate molecule that represents the average structure of the VR sample was then designed based on the average molecular parameters (AMP) obtained from APPI and ESI FT-ICR MS. Plausible core skeletal structures of VR were drawn from the average DBE value, and then a symmetrical, alkylated, polyaromatic sulfur heterocycles (PASH) molecule was formulated as the VR surrogate. A number of physical and thermo-chemical properties of the VR surrogate were then predicted using quantitative structure property relationships (QSPR). The VR surrogate proposed here will enable high-fidelity computational studies, including chemical kinetic modeling, property estimation, and emissions modeling.
  • One-step conversion of crude oil to light olefins using a multi-zone reactor

    Alabdullah, Mohammed A.; Rodriguez Gomez, Alberto; Shoinkhorova, Tuiana; Dikhtiarenko, Alla; Chowdhury, Abhishek Dutta; Hita, Idoia; Kulkarni, Shekhar Rajabhau; Vittenet, Jullian; Sarathy, Mani; Castaño, Pedro; Bendjeriou-Sedjerari, Anissa; Abou-Hamad, Edy; Zhang, Wen; Ali, Ola S.; Morales-Osorio, Isidoro; Xu, Wei; Gascon, Jorge (Nature Catalysis, Springer Nature, 2021-02-25) [Article]
    With the demand for gasoline and diesel expected to decline in the near future, crude-to-chemicals technologies have the potential to become the most important processes in the petrochemical industry. This trend has triggered intense research to maximize the production of light olefins and aromatics at the expense of fuels, which calls for disruptive processes able to transform crude oil to chemicals in an efficient and environmentally friendly way. Here we propose a catalytic reactor concept consisting of a multi-zone fluidized bed that is able to perform several refining steps in a single reactor vessel. This configuration allows for in situ catalyst stripping and regeneration, while the incorporation of silicon carbide in the catalyst confers it with improved physical, mechanical and heat-transport properties. As a result, this reactor–catalyst combination has shown stable conversion of untreated Arabian Light crude into light olefins with yields per pass of over 30 wt% with a minimum production of dry gas.
  • Numerical investigation of pressure effects on soot formation in laminar coflow ethylene/air diffusion flames

    Guo, Junjun; Tang, Yihao; Raman, Venkat; Im, Hong G. (Fuel, Elsevier BV, 2021-02-21) [Article]
    This study aims to provide fundamental understandings of the pressure effects on the soot formation and compare the performances of different soot aerosol models. Numerical simulations are performed in laminar coflow diffusion flames at pressures ranging from 1 to 16 bar. Two soot aerosol models are considered: the acetylene-based semi-empirical (SE) model and polycyclic aromatic hydrocarbons (PAH) based hybrid method of moment (HMOM). To study the effect of large-sized PAH species, a detailed reaction mechanism is used with PAH pathways up to coronene. Results show that the SE model provides good predictions of pressure scaling of peak soot mass with a deviation of 7%, while HMOM obtains better soot predictions on the flame centerline. Due to the shifting of PAH position towards the burner with increasing pressure, the nascent soot is formed earlier. The increase in the particle residence time is found to be an additional factor that further promotes the increased soot formation with pressure, apart from the increase in density, temperature, and PAH concentration. The residence time at 8 bar case is 2.5 times and 3.0 times longer than those at 1 bar case on the flame centerline and flame wings, respectively. Moreover, the pressure effects on the PAH contribution to the nucleation process are studied. Although small-sized PAH species (A2 and A2R5) dominate the nucleation process, the contribution of large-sized PAH species (larger than A4) increases from 5% to 20% of the total on the flame wings, when the pressure increases from 1 bar to 8 bar.
  • Efficient alkane oxidation under combustion engine and atmospheric conditions

    Wang, Zhandong; Ehn, Mikael; Rissanen, Matti P.; Garmash, Olga; Quéléver, Lauriane; Xing, Lili; Monge Palacios, Manuel; Rantala, Pekka; Donahue, Neil M.; Berndt, Torsten; Sarathy, Mani (Communications Chemistry, Springer Nature, 2021-02-18) [Article]
    AbstractOxidation chemistry controls both combustion processes and the atmospheric transformation of volatile emissions. In combustion engines, radical species undergo isomerization reactions that allow fast addition of O2. This chain reaction, termed autoxidation, is enabled by high engine temperatures, but has recently been also identified as an important source for highly oxygenated species in the atmosphere, forming organic aerosol. Conventional knowledge suggests that atmospheric autoxidation requires suitable structural features, like double bonds or oxygen-containing moieties, in the precursors. With neither of these functionalities, alkanes, the primary fuel type in combustion engines and an important class of urban trace gases, are thought to have minor susceptibility to extensive autoxidation. Here, utilizing state-of-the-art mass spectrometry, measuring both radicals and oxidation products, we show that alkanes undergo autoxidation much more efficiently than previously thought, both under atmospheric and combustion conditions. Even at high concentrations of NOX, which typically rapidly terminates autoxidation in urban areas, the studied C6–C10 alkanes produce considerable amounts of highly oxygenated products that can contribute to urban organic aerosol. The results of this inter-disciplinary effort provide crucial information on oxidation processes in both combustion engines and the atmosphere, with direct implications for engine efficiency and urban air quality.
  • The Role of Intermediate-Temperature Heat Release in Octane Sensitivity of Fuels with Matching Research Octane Number

    Singh, Eshan; Sarathy, Mani (Energy & Fuels, American Chemical Society (ACS), 2021-02-16) [Article]
    Improving the efficiency of internal combustion engines is important for reducing global greenhouse gas emissions; the efficiency of spark ignition (SI) engines is limited by the knock phenomenon. As opposed to naturally aspirated engines, turbocharged engines operate at beyond research octane number (RON) conditions, and fuel octane sensitivity (OS = RON – motor octane number (MON)) becomes important under such conditions. Previous work by this group [ Energy Fuels 2017, 31, 1945−1960, DOI: 10.1021/acs.energyfuels.6b02659] elucidated the chemical kinetic origins of OS; this study is extended to provide a qualitative, as well as quantitative, definition of OS, based on fundamental ignition markers. A varying amount of toluene is blended with various primary reference fuels to match the ignition delay of the targeted research octane number fuels, allowing a range of octane sensitivities for each research octane number. This study establishes a correlation between OS and heat release rates at low, intermediate, and high temperatures. The significance and chemical origins of intermediate-temperature heat release in defining the OS of toluene blended in a mixture of iso-octane and n-heptane is also clarified. For the toluene–iso-octane–n-heptane mixtures considered here, low-temperature reactivity was not found to be a key marker of OS. The results also show areas of improved efficiency in beyond RON operating conditions, where high-sensitivity fuels could be beneficial.

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