Real Fuels Research Articles

Hierarchical Auto-Ignition and Structure-Reactivity Trends of C2–C4 1-Alkenes

Ignition delay times of small alkenes are a valuable constraint for the refinement of the core kinetic mechanism of hydrocarbons used in representing combustion properties of real fuels. Moreover, the chemical reactivity comparison of those small alkenes provides a reference in object-oriented fuel design and logical combustion utilization. In this study, the ignition delay times of C2–C4 alkenes (ethylene, propene and 1-butene) were measured behind reflected shock waves first, with a fixed oxygen concentration (XO2 = 6%) and equivalence ratio (φ = 1.0) at various pressures of 1.2, 4.0 and 16.0 atm, in order to facilitate the comparison. Three chemical-based-Arrhenius-type correlations covering a wide range of temperature, pressure, equivalence ratio, and dilution were proposed. The simplified reaction network for pyrolysis and oxidation of 1-alkenes was depicted relying on the reaction classes of alkenes. Nine generally accepted mechanisms were used to simulate the ignition delay times measured by this study as well as literature. All the kinetic models show reasonable structure-reactivity trends for all of the three alkenes, but only NUIGMech 1.1 is capable of representing quantificationally the chemical reactivity at all tested conditions. Generally, ethylene exhibits the highest reactivity while propene presents the lowest at high temperatures. Analyses of sensitivity and flux indicate that the main oxidation pathway of ethylene is chain-branching, which accelerates the accumulation of free radical pools, especially for the Ḣ atom, Ȯ atom and ȮH radical, which results in the highest reactivity of ethylene. For propene and 1-butene, due to the presence of the allylic site, consumption of allylic radicals becomes the decisive step of oxidation and allylic radicals are mostly consumed by the HȮ2 radical. However, there are no such efficient reaction pathways for the formation of HȮ2 radicals during the propene oxidation process, while reaction pathways for HȮ2 formation in 1-butene are efficient. Thus, 1-butene presents higher reactivity compared to propene.

Simplified modeling combustion chemistry of neat and blended large hydrocarbon fuels with different functional groups

In the present study, a simplified modeling approach based on a two-step reaction scheme (TSRS) was developed to describe the high-temperature combustion chemistry of large hydrocarbon fuels. The characteristic reaction time scale analysis indicated a distinct two-step reaction property for the conversion of large hydrocarbon molecules. Along with the quasi-steady state assumption, TSRS utilized a seven-reaction sub-model to describe the fuel decomposition to a small group of intermediate products, and a detailed foundational fuel combustion chemistry model to describe the oxidation of these decomposed products. In the first half of this paper, the TSRS model was constructed for four fuel components with different functional groups, including n-heptane, iso-octane, methylcyclohexane, and n-butylbenzene, and validated sequentially by their speciation data, and global combustion properties of ignition delay time and laminar flame speed data. Sensitivity analysis and rate of production analysis revealed the primary decomposition paths in the TSRS model. Then, in the second half of the paper, algebraically blending the TSRS models of neat fuel components enabled the construction of surrogate fuel models for real fuels, including a two-component primary reference fuel (PRF), a three-component gasoline surrogate fuel (toluene-PRF), a four-component Chinese jet fuel (RP-3) surrogate, and a four-component diesel surrogate. Predictions from the TSRS-based surrogate models for real fuels were shown to be consistent with the speciation data as well as the global combustion properties, whenever available in the literatures, indicating the robustness and broad applicability of the TSRS approach.

Combustion kinetics of alternative jet fuels, Part-III: Fuel modeling and surrogate strategy

In Part III of our study on alternative aviation fuels, we present a comprehensive database of modeled speciation data consisting of seven hydrocarbons of varying molecular structure and 26 alternative and conventional aviation fuels. The speciation data is obtained from the DLR atmospheric high temperature flow reactor with a coupled molecular beam mass spectrometry (MBMS) detection system (Part-I). The chemical reactivity of these real liquid fuels is investigated both experimentally and numerically. For modeling, detailed fuel surrogates (up to 14 components) are employed for characterizing the fuels. The surrogate formulation strategy is defined based on the fuels’ compositional analysis.This work employs high temperature reaction kinetic mechanism for the combustion of wide variety of hydrocarbons of varying molecular classes from n-, iso-, cy-paraffins, to five-ring aromatics presented in Part-II. The reaction mechanism is applied to model 26 aviation fuels using 21 different validated fuel surrogate components to predict the fuel intermediates and soot precursors measured in the reactor.This work aims to identify the effect of fuel surrogate components on the intermediates’ formation and its influence on the emissions. Through compilation of many fuels with composition of wide range of chemical classes, we provide a systematic evaluation of how the fuel composition can be used to extract information of specific fuel intermediates and emissions formed.

Experimental Characterization of Flame Structure and Soot Volume Fraction of Premixed Kerosene Jet A-1 and Surrogate Flames

Modeling the chemical reactions and soot processes in kerosene flames is important to support the design of future generations of low-emission aircraft engines. To develop and validate these models, detailed experimental data from model flames with well-defined boundary conditions are needed. Currently, only few data from experiments with real aircraft engine fuels are available. This paper presents measurements of temperature, species and soot volume fraction profiles in premixed, flat flames using Jet A-1 kerosene and a two-component surrogate blend. Measurements were performed using a combination of TDLAS, GC and laser extinction. The results show that the flame structure in terms of temperature and species profiles of the kerosene and surrogate flames are very similar but differ greatly in the resulting soot volume fractions. Furthermore, the study shows that the available chemical mechanisms can correctly predict the temperature profiles of the flames but show significant differences from the experimentally observed species profiles. The differences in the sooting tendency of the kerosene and the surrogate are further investigated using detailed chemical mechanisms.

X-Ray Characterization of Real Fuel Sprays for Gasoline Direct Injection

Abstract The effects of fuel blend properties on spray and injector performance has been investigated in a side-mount injector for gasoline direct injection (GDI) using two certification fuel blends: Euro 5 and Euro 6. Several X-ray diagnostic techniques were conducted to characterize the injector and spray morphology. Detailed internal geometry of the GDI injector was resolved to 1.8 μm, through the use of hard X-ray tomography. The geometry characterization of this six-hole GDI, side mount injector, quantifies relevant hole and counterbore dimensions and reveals the intricate details within the flow passages, including surface roughness and micron-sized features. Internal valve motion was measured with a temporal resolution of 20 μs and a spatial resolution of 2.0 μs, for three injection pressures and several injector energizing strategies. The needle motion for both fuels exhibits similar lift profiles for common energizing commands. A combination of X-ray radiography and ultra-small-angle X-ray scattering (USAXS) was used to characterize the fuel mass distribution and the droplet sizing, respectively. Tomographic spray radiography revealed the near-nozzle distribution of fuel mass for each of the fuels and the asymmetry produced by the angled nozzles. Under evaporative conditions, the two fuels show minor differences in peak fuel mass distribution during steady injection, though both exhibit fluctuations in injection during the early, transient phase. USAXS measurements of the path-specific surface area of the spray indicated lower peak values for the more evaporative conditions in the near nozzle region.

Experimental assessment of the impact of variation in jet fuel properties on spray flame liftoff height

Ensuring efficient and clean combustion performance of liquid-fueled engines requires comprehension of the influence of fuel composition and properties on flame behavior, such as flame liftoff height (LOH) and lean blowout limit (LBO). Spray flame stability is strongly affected by both the fuel reactivity and physical properties. Herein, the flame stability mechanism represented by LOH is investigated for seven jet turbine fuels, including surrogate, alternative, and conventional jet fuels, using a laboratory spray burner. Based on the experimental observations, the current work introduces a new analysis, which provides insight into the competing/complementing processes that occur in a multi-phase reacting system and highlights the key properties important in spray flame dynamics, accounting for both the fuel spray/vaporization as well as the chemical reactivity, to explain the relative differences in LOH of complex multicomponent fuels. Results show that spray flame stabilization occurs when there is a balance between the local spray burning velocity and the incoming jet velocity, which is strongly associated with laminar flame speed and the relative amount of liquid and gaseous fuel crossing the flame preheat region. Using a multicomponent droplet evaporation model, it was observed that preferential vaporization of the lighter and more reactive species of the simple surrogate fuels contribute to a shorter lifted flame as compared to fuels consisting of heavier and/or less reactive components. The LOH of real jet fuels showed strong sensitivity to droplet vaporization and mixing, which is controlled by the fuels’ volatility (i.e., boiling temperature at 50% distillation volume) and atomized droplet size, and to a lesser extent the reactivity represented by laminar flame speed. The enhanced linearity in the correlation of 50% vapor distilled compared to the other distillation cuts suggests that preferential vaporization could play an important role in defining the LOH stabilization mechanism even for more complex fuels.

Hierarchical porous HKUST-1 fabricated by microwave-assisted synthesis with CTAB for enhanced adsorptive removal of benzothiophene from fuel

• Hierarchical porous defective HKUST-1 rapidly obtained by microwave-assisted method. • Enhanced benzothiophene removal from fuel by defective HKUST-1 over HKUST-1. • Defective HKUST-1 exposes more active sites and facilitates adsorbates diffusion. • CTAB-H-0.5 shows excellent adsorption and regeneration performance for BT removal. Ultra-deep removal of thiophene sulfides from transportation fuel via adsorption has aroused great attention under the pressure of gradually demanding environmental regulations. The development of high-efficiency adsorbents is the key to adsorptive desulfurization for producing clean transportation fuels. In this work, a microwave-assisted synthesis method was applied to rapidly fabricate hierarchical porous defective HKUST-1 (DEHKUST-1) towards removing benzothiophene from model fuel by selective adsorption. The effects of cetyltrimethylammonium bromide (CTAB) dosage, adsorption temperature and adsorption contact time on the DEHKUST-1 desulfurization performance were systematically investigated. The characterization results proved that both metal clusters and linker defects were generated in the as-prepared DEHKUST-1. CTAB as template could modulate the pore distribution and introduce reasonable defects in the framework of HKUST-1. At CTAB: Cu 2+ = 0.5 by mole ratio, a regular mesoporous distribution of 25–30 nm could be obtained with DEHKUST-1; it exhibited an impressive enhancement in adsorptive desulphurization performance. The maximum adsorption capacity of the adsorbent attained 14.4 mg S/g adsorbent at 20 °C in 4 h. Even after CTAB-H-0.5 was regenerated six times, its adsorption capacity remained 93% as that of the as-prepared adsorbent. An adsorption mechanism was proposed to illustrate the promoting desulfurization performance by introduction of hierarchical porous in HKUST-1. By virtue of the rapid synthesis and remarkable benzothiophene removal capacity, the DEHKUST-1 could be a potential adsorbent in desulfurization from real fuels.

An “artificial” activity coefficient modeling approach for emulating combustion and physical property variations during distillation of real complex fuel

Real complex fuels consist of hundreds of species and hence are difficult to model in numerical simulations. There have been many methods to formulate simple surrogate suites composed of several compounds. While these surrogates emulate gaseous combustion properties with acceptable fidelity, due to the insufficient number of surrogate components comprehensive distillation behaviors of simple surrogates exhibit considerable discrepancy compared to that of real complex fuels. In this work, we demonstrated a new methodology to effectively represent a complex fuel. Firstly, we obtained information about functional group evolution of a complex fuel (Chinese aviation fuel, RP-3) from distillation experiments and formulated a rather complex surrogate mixture. Then, a Functional Group Matching (FGM) method was applied to convert the complex surrogate to a target 4-component surrogate mixture with an “artificial” activity coefficient model (AACM) using which distillation of real complex fuels can be accurately replicated. This AACM was validated in batch distillation simulation in comparison with the complex surrogate with conventional phase equilibrium model (UNIQUAC Functional-group Activity Coefficient (UNIFAC)). Results showed that chemical functional groups, combustion property targets (CPTs) and physical properties (density, surface tension, and dynamic viscosity) during a distillation process of the simple surrogate well represented those of the complex surrogate. Also, the computational efficiency of this 4-component surrogate with AACM method was verified, which was thousands times faster than the 24-component mixture with UNIFAC. The AACM for a simple surrogate mixture therefore contained the most authentic physics from the distillation experiments of a real complex fuel with potential to improve the computational efficiency and to couple with the chemical kinetics mechanisms available to the simple surrogate.

Prediction of the Derived Cetane Number and Carbon/Hydrogen Ratio from Infrared Spectroscopic Data

A model for the prediction of the derived cetane number (DCN) and carbon/hydrogen ratio (C/H) of hydrocarbon mixtures, diesel fuels, and diesel–gasoline blends has been developed on the basis of infrared (IR) spectroscopy data of pure components. IR spectra of 65 neat hydrocarbon species were used to generate spectra of 127 hydrocarbon blends by averaging the spectra of their pure components on a molar basis. The spectra of 44 real fuels were calculated using n-paraffin, isoparaffin, olefin, naphthene, aromatic, and oxygenate (PIONA-O) class averages of pure components. It is shown that this strategy retains knowledge of C/H, an important indicator of the chemical structure. Three methods were compared to assess the prediction of DCN and C/H ratio from the assembled IR spectra, i.e., partial least squares regression (PLSR), support vector machine (SVM), and artificial neural network (ANN). It was found that ANNs gave the best performance with DCN prediction errors of ±1.1 on average and C/H prediction errors of ∼0.8%. Lasso-regularized linear models were also used to find simple combinations of wavenumbers that yield acceptable estimations.

Mono lacunary phosphomolybdate supported on mesoporous graphitic carbon nitride: An eco-friendly and efficient catalyst for oxidative desulfurization of the model and real fuels

In recent years, one of the most important environmental researchers' subjects has been introduced appropriate and effective methods for desulfurization from fossil fuels and prevent the release of sulfur compounds obtained from combustion into the environment. In this study, sulfur oxidation of refractory organosulfur compounds supported on graphitic carbon nitride (g-C3N4) was examined ‎utilizing‎ a novel catalyst comprising monolacunary phosphomolybdate (PMo11). The optimized reaction ‎conditions, which encompass the loading amount of PMo11 on g-C3N4, the dosage of catalyst, reaction time, ‎reaction temperature, the proportion of O/S, initial DBT ‎concentration, and type of model fuel, have been explored. This catalytic system's superiority has been shown by obtaining 98.6% conversion of DBT in the model fuel and 93.7% sulfur ‎removal from real fuel.

An experimental and modeling study of autoignition characteristics of two real low-octane gasoline fuels in a heated rapid compression machine at elevated pressures

Gasoline compression ignition (GCI) has received much attention due to its high efficiency and low emissions. The low-octane gasoline can be applied to extend the GCI operating range. However, there is limited knowledge of the autoignition chemistry for the low-octane gasoline. In this study, the ignition delay times (IDTs) of two real distillate gasoline fuels with research octane numbers (RON) of 72 and 83, denoted as G72 and G83 respectively, were measured in a heated rapid compression machine (RCM) over wide ranges of pressures (10, 15 and 20 bar), temperatures (670–940 K), equivalence ratios (0.5, 1.0 and 2.0), and diluted conditions. Both G72 and G83 exhibit apparent two-stage ignition characteristics with negative temperature coefficient (NTC) behavior in the low-to-intermediate temperature region. Considering the effects of exhaust gas recirculation (EGR) technology on GCI combustion, ignition characteristics of low-octane gasolines under simulated-EGR conditions were also studied by varying the N2/O2 ratio while fixing the fuel mole fraction. It is found that the NTC region moves towards the higher temperature side as the oxygen concentration decreases. Moreover, two six-component surrogates were formulated for G72 (28.4% n-pentane, 3.5% n-heptane, 24.5% 2-methylhexane, 26.3% 2,2,4-trimethylpentane, 13.8% cyclopentane, and 3.3% toluene, by mol.), and G83 (16.5% n-pentane, 10.6% n-heptane, 5.6% 2-methylhexane, 37.4% 2,2,4-trimethylpentane, 10.2% cyclopentane and 19.7% toluene, by mol.). Kinetic modeling was then conducted using a published kinetic model coupled with proposed surrogates. Sensitivity analysis results further revealed that compared with isooctane, cycloalkane chemistry is more important in the overall autoignition behavior at low temperatures.

An Effective Magnetic Catalyst for Oxidative Desulfurization of Model and Real Fuels: Fe3O4/ZIF-8/TiO₂

In the current research, an advanced and innovative composite based in zeolitic imidazolate framework-8 (ZIF-8) incorporating magnetic and effective oxidative catalytic properties was successfully used to prepare ultra-low sulfur model and real fuels by oxidative desulfurization (ODS) process. To this purpose, the surface of ZIF-8 was decorated by TiO 2 and Fe 3 O 4 nanoparticles (NPs) to prepare the composite catalyst (Fe₃O₄/ZIF-8/TiO₂). Structural characterization was performed by XRD, FT-IR, SEM, EDS, TEM, N 2 adsorption-desorption isotherm and VSM. TEM images showed that the semi-spherical TiO 2 and Fe 3 O 4 NPs are fairly doped. The effect of TiO 2 and Fe 3 O 4 NPs incorporated in ZIF-8 support allowed an efficient catalytic oxidative desulfurization of model fuel (500 ppm of dibenzothiophene, DBT) and real fuels (gasoline, diesel, among others) using tert-Butyl hydroperoxide (TBHP) as oxidant under a solvent-free system. Optimization studies were performed and complete desulfurization of model fuel was found after 6 h using O/S = 3 at 80 °C, instead of the 33% of desulfurization obtained with the pristine ZIF-8. Under optimized conditions, sulfone was the only product observed. The stability and the recycle capacity of the Fe₃O₄/ZIF-8/TiO₂ composite catalyst was confirmed and after ten consecutive ODS cycles only a slight decrease of desulfurization efficiency was detected (around 10%). Therefore, the results here presented confirm that the magnetic catalyst conciliates efficiency, stability and easy recovery, that are essential properties for future industrial application. • Magnetic catalytic composite has been prepared based on ZiF-8 support. • Fe 3 O 4 /ZIF-8/TiO 2 presents high catalytic efficiency for oxidative desulfurization of model and real fuels. • Solvent-free oxidative catalytic system was successfully used. • Complete desulfurization was achieved after 6 h using O/S = 3. • Catalyst presented high stability and recycle capacity for 10 consecutive desulfurization cycles.

Deep desulfurization of fuels: Are deep eutectic solvents the alternative for ionic liquids?

The impact of fossil fuels impurities on outdoor air pollution is today a matter of great concern, with the transportation sector playing a major role. Given global efforts to reduce sulfur oxides emissions, and the increasingly tighter legislations, removal of sulfur contaminants liquid highway fuels is a pressing issue worldwide. The purpose of this review is to provide a detailed state of the art review concerning the use of deep eutectic solvents (DES) in the removal of sulfur pollutants from transportation fuels. Furthermore, a comparative evaluation regarding the use of these solvents versus Ionic Liquids (ILs) is also provided, taking into account several aspects, such as, evolution of technologies, solvents composition, extraction efficiencies and environmental and economic considerations. The large gap in terms of efficiency of the reported technologies, either using ILs or DES, between simulated matrices and real fuels is also discussed, highlighting the importance of academia and industry hand in hand work.

A combustion model for multi-component fuels based on relative reactivity and molecular structure

A reliable multi-component surrogate fuel model needs to be able to represent both physical properties and chemical kinetics of a real fuel. However, enhancing the fidelity of a model with detailed description of physical and chemical behavior of all fuel components found in real fuels is limited by the prohibitive computational load to calculate the combustion chemistry of the fuel. Hence, it is desirable to achieve computational efficiency by reducing the number of chemical surrogates at the minimum expense of prediction accuracy. The objective of this work is to develop a model that can simulate the oxidation of multi-component fuels by representing the ignition characteristics of physical surrogate components with fewer chemical surrogates and achieve both computational efficiency and prediction accuracy. The main advantage of the model, called the Reactivity-Adjustment (ReAd) combustion model, is to accurately predict the reactivity of the physical surrogate components that the reaction mechanisms of which are not included in the reaction kinetics model employed in the simulation. The reactivity variation of local mixtures with different compositions is modeled by adjusting the reaction rate constants of selected control-reactions in the reaction mechanism of the representative chemical surrogates. An initial version of the model has been developed employing a single chemical surrogate to represent the combustion of diesel fuel which is modeled as multiple surrogate components to capture the physical properties of the real fuel. The model was extended to consider two more chemical surrogate components to represent the ignition characteristics of other chemical families than n-alkanes. This enabled to avoid the excessive adjustment of reaction rate constants that were necessary when a single chemical surrogate is used to represent the oxidation kinetics of entire multi-component fuels. The model was extensively tested for simulating oxidation processes of many fuels with a variety of fuel reactivity and in various combustion regimes. The results demonstrated that excellent accuracy of the ignition/combustion prediction was achieved while ensuring computational efficiency.

Burning dynamics and in-depth flame spread of wood cribs in large compartment fires

Wood cribs pervade the fire research literature as the chosen fuel load for testing within the built environment. As such, the underpinning knowledge of fire behaviour in compartments was developed from experiments using wood cribs in small compartments. Despite the apparent incomparability of porous fuel-beds such as cribs to real solid fuels in the built environment, the role of the fuel mass transfer number (“B-Number”) in defining the compartment fire dynamics has received little attention. In the case of large open-plan compartments, the burning processes are strongly dependant on the relationship of the fuel nature and compartment geometry. To address these limitations, the physical processes in-depth and external to a spreading wood crib fire in a compartment are examined. A theory to couple these processes to a compartment is proposed and analogised into the classical “Emmons problem”, leading to a definition of a total mass transfer number for a wood crib. Comparing the theory against data from a large-scale experiment shows that the wood crib approximates steady-state burning in two regimes: a fuel-bed-controlled regime and a momentum-controlled regime. The fuel-bed-controlled regime occurs when the burning and spread rates are governed by the processes internal to the crib, and the fire behaviour is therefore defined by the crib geometry. This regime is characterised by a fire that travels or grows slowly, with small external heat fluxes. The momentum-controlled regime occurs when the fire is fully-developed and the external heat fluxes are very large. Burning rates are controlled by the residence time, with the compartment fire dynamics defined by complex transport processes associated with the momentum-driven flows external to the crib. Transitions from the fuel-bed-controlled regime to the momentum-controlled regime are driven by accelerations in the flame spread rate along the surface of the crib leading to an additional energy input mechanism that is used to raise the in-depth flame spread rate of the crib. It is hypothesised that the burning mechanisms of fuels with large mass transfer numbers, such as non-charring plastics, diverge significantly from wood cribs, and therefore extrapolating test data from wood cribs fires in compartments to real fuels must be done with extreme caution. Thus, the nature of the fuel is an important and unavoidable consideration when studying the fire dynamics of large open-plan compartments.

Effect of Lagrangian-phase Modelling on Charge Stratification and Spatial Distribution of Threshold Soot Index for Toluene Reference Fuel Surrogates

Nowadays, soot emissions are one of the major concerns in Direct Injection Spark Ignition engines. Soot prediction models can be computationally expensive, especially when particle mass, number, and size distribution are to be forecast. While soot formation heavily depends on the chemical and physical characteristics of the fuel, the simulation of the exact composition of a real gasoline is computationally unfeasible. Thus, it is essential to find simplified yet representative pathways to reduce the computational cost of the simulations. On the one hand, the a-priori investigation of the factors influencing particulate onset can be a simplified approach to compare different solutions and strategies with much cheaper costs than the modelling of soot formation and oxidation mechanisms. On the other hand, the use of surrogate fuels is a practical approach to cope with the fuel chemical nature. Although they poorly mimic the evaporation properties of a real gasoline, Toluene Reference Fuels are broadly adopted to match combustion relevant properties of the real fuels. In this study, the spatial distribution of the Threshold Soot Index in the fluid domain is investigated for three surrogates characterized by an increasing content of toluene (0 mol%, 30 mol%, 60 mol%). The correlation between the sooting tendency and the fuel distribution in the combustion chamber before spark ignition time can provide useful preliminary indications, without spending the computational effort of the whole soot model multicycle resolution. In particular, two approaches for the lagrangian description of the injected fuel are investigated: a multicomponent approach and a single component one, this last driven by a high-fidelity lumped modelling of the surrogate properties for both liquid and vapor phase.

Ultra-deep oxidative desulfurization of real fuels by sandwich-type polyoxometalate immobilized on copper ferrite nanoparticles, Fe6W18O70 ⊂ CuFe2O4, as an efficient heterogeneous nanocatalyst

In order to obtain the clean gasoline, we report on the synthesis and characterization of a new heterogeneous nanocatalyst comprised of the sandwich-type polyoxotungstate [(FeW9O34)2Fe4(H2O)2]−10 (Fe6W18O70) clusters and copper ferrite (CuFe2O4) nanoparticles. The materials were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV–vis), and scanning electron microscopy (SEM). The Fe6W18O70⊂CuFe2O4 nanocatalyst catalyzed the oxidative desulfurization (ODS) reactions of hazardous sulfur-containing compounds by H2O2-CH3COOH as oxidant. The nanocatalyst exhibited an exceptionally high catalytic performance in the ultra-deep ODS of simulated fuels and real gasoline. The experimental results revealed that the oxidation reaction efficiencies were up to 95% at the temperature of 35 °C and the contact time of 1 h. Particularly, the removal (%) of thiophene (C4H4S), benzothiophene (C8H6S), and dibenzothiophene (C12H8S) from simulated fuels over Fe6W18O70⊂CuFe2O4 nanocatalyst could reach 98%, 99%, and 99%, respectively. Moreover, the heterogeneous nanocatalyst could be easily recovered and reused multiple times by filtration with no obvious loss of activity. The present study will lead to the widespread catalytic application of Fe6W18O70⊂CuFe2O4 material in the efficient and feasible ODS of petroleum fractions.

Analysis of Thermally Induced Breakup of Ultrasonically Emulsified Heavy Fuel Oil using Dynamic Mode Decomposition

Clean and efficient processing of heavy fuels is a major challenge for several combustion driven prime movers like internal combustion engines, used in marine or power generation sectors. Emulsification was recognized in the past as practical technology for heavy fuels combustion since it engenders an enabling phenomenon called micro-explosion that proceeds during the spray process. Micro-explosions allow finer secondary break-up, leading to improved mixing, and subsequent cleaner and fuller burning. However, the translation of this technology to real applications is still not fully exploited due to lack of basic understanding and characterization of the evaporation process which includes both micro-explosions and puffing. Ultrasonically induced cavitation is a promising technology for the production of water-in-oil emulsions at industrial scale. Fundamental research performed in the field of liquid fuels gasification and combustion mostly regards ideal or simple mixtures and not all the considerations made in these cases apply for real fuels. In this work, we investigated the evaporation characteristics of ultrasonically produced heavy fuel oil (HFO) emulsions with a set of newly developed methodologies. We characterized the emulsions by using a state-of-the-art microscopy technique, the Cryogenic Scanning Electron Microscopy, Cryo- SEM and obtained accurate droplet size distribution up to nano-scale. We tested the fuel emulsion in a suspended droplet experiment and reconstructed the interface from the obtained images. The normalized squared diameter profile is not representative of the complex physics involved in heavy fuel evaporation; therefore, it was substituted with the normalized distance of the interface from the centroid of the droplet. By using this procedure, it is possible to highlight both evaporation and stochastic events like puffing and ejections. A dimensionality reduction algorithm, the dynamic mode decomposition (DMD), was then performed on the evolving interface to highlight the main modes describing the emulsion system and the dynamics. The overall objective was to develop a strategy for optimizing emulsions for improved combustion performance. From the experimental data, it was observed that a water concentration of 5% by mass decreases the vaporization time of the mixture and that the presence of water favors puffing and ejections with different intensity depending on the percentage of water enhancing the volatilization of the fuel.

Keggin- and Dawson-type polyoxotungstates immobilized on poly(3,4-ethylenedioxythiophene)-coated zerovalent iron nanoparticles: Synthesis, characterization and their catalytic oxidative desulfurization activity

This work reports synthesis of new and hybrid nanocomposites composed of Keggin- and Dawson-type polyoxotungstates (POTs), namely Na3[PW12O40] (PW12) and K6[P2W18O62] (P2W18), immobilized on poly(3,4-ethylenedioxythiophene) (PEDOT) coated zerovalent iron (Fe0). The synthesized catalyst samples were analyzed by different characterization techniques including powder XRD, VSM, FESEM, EDX and DRS. The Fe0@PEDOT\\POTs magnetic nanocomposites have been investigated as efficient heterogeneous nanocatalysts for catalytic oxidative desulfurization (ODS) of model and real gasoil fuels. The catalytic ODS was carried out at various experimental conditions to assess the influences of individual reaction variables, such as nanocatalyst dosage, sulfur content (in model fuel), reaction time and reaction temperature. At the same experimental conditions, Keggin POTs-based catalyst (Fe0@PEDOT\\PW12) exhibited higher desulfurization activities (98.6% and 93.2% for model fuel and real gasoil, respectively) than Dawson- POTs-based (Fe0@PEDOT\\P2W18) catalyst (93.1% and 84% for model fuel and real gasoil, respectively). According to the results, the Fe0@PEDOT\\PW12 reusable nanocatalyst can retain high desulfurization efficiency after six reaction cycles.

Combustion of methylcyclohexane at elevated temperatures to investigate burning velocity for surrogate fuel development

To overcome the complexity associated with the development of detailed kinetic models for real transportation fuels, surrogate fuel models offer an excellent alternative. The present study reports laminar burning velocity (LBV) measurements of methylcyclohexane (MCH) + air mixtures for mixture temperatures up to 610 K using externally heated diverging channel method (EHDC) method at 1 atm pressure. MCH is a commonly used surrogate blend for aviation fuels, gasoline, and diesel, whose kinetic model is simpler to develop. The measurement of laminar burning velocity forms the basis of kinetic model development for such surrogate fuels. The present work reports the measured LBV values for an equivalence ratio range, φ = 0.7–1.4, and their comparison with available experimental data and detailed kinetic model predictions for a mixture temperature range, 353–610 K. Temperature exponent, α is derived using the power-law correlation and good consistency with kinetic model predictions is observed up to 500 K mixture temperatures. At 610 K mixture temperature, an overprediction of ≈12% at φ = 1.05 is observed with JeTSurF 2.0 (2010) model and 27% overprediction with the kinetic model of PoliMi (2014) φ = 1.1. Overall, the reported LBV measurements show slightly better match with the JeTSurF 2.0 (2010) kinetic model than the Wang (2014) kinetic model. Reaction pathway diagrams are drawn to highlight the importance of C2H4 and C2H3 radicals for an increase in the overall reaction rate at 610 K.