Real Transportation Fuels Research Articles

Low-temperature oxidation of n-octane and n-decane in shock tubes: Differences in time histories of key intermediates

The impact of chain length on the time histories of key intermediate species that form upon first-stage ignition was studied experimentally in a shock tube using multi-color laser absorption diagnostics. CO, CH2O, OH, and composite time histories of heavier carbonyls were measured simultaneously during the low temperature oxidation of n-octane & n-decane in the temperature range of 720–860 K, and pressure range of 4.1–5.8 atm. The test mixtures were 0.64% & 0.6% fuel in oxygen, respectively. A two-color diagnostic was also developed and used in tandem with other diagnostics to quantify the evolution of temperature during oxidation. To our knowledge, this work reports the first measurement of CH2O, OH, and temperature during oxidation of C8 or heavier hydrocarbon fuels at low temperatures. The measured time histories were also compared against the predictions of two recent detailed kinetic models. Significant differences in the measured and predicted first-stage ignition delay times, absolute concentration of species post-ignition and the maximum rate of formation of species were observed. Our measurements will serve as targets for further refinement of these detailed kinetic models and in the development of rate rules for similar classes of fuels. The measurements also revealed significant differences in the relative reactivity of n-octane and n-decane. Taken together with previous speciation studies conducted in n-heptane, we observe a strong correlation between the species time histories, reactivity, and chain length of straight chain alkanes. This observation lends further support to the selection of CO and CH2O as target species for development of Low-Temperature Hybrid Chemistry (HyChem) models for real transportation and aviation fuels in future.

Assessment of hydrocarbons for gasoline surrogate: An optimization study

A fuel surrogate is a model fuel that replicates combustion phenomena of real transportation fuels within computational framework. Successful surrogate formulation would be emulating multiple physical and chemical properties that are most influential to combustion characteristics using a minimum number of surrogate components. To achieve this goal, utilization of hydrocarbons with proper representation of actual constituents of real fuels is one of the most critical requirements. The major goal of this paper is to identify hydrocarbons that have a great potential to advance the current gasoline surrogates in terms of emulations in hydrocarbon class composition and combustion related properties, and to promote further experimental and computational investigations for those hydrocarbons. In this paper, 19 hydrocarbons including the ones that have not been used for gasoline surrogate applications are assessed through an optimization approach. Surrogate mixtures are formulated for petroleum-derived gasoline fuels using new hydrocarbons along with conventional gasoline surrogate components (n-heptane, iso-octane, toluene, 1-hexene), and potential improvements in target property emulations by addition of the new surrogate components are evaluated. Among four hydrocarbon classes investigated in this study which are iso-alkane, cycloalkane, aromatic, and olefin, optimized results indicate that expanding iso-alkane representation by using multiple iso-alkane components with different molecular size is the most effective approach to emulate various target properties of typical gasoline batches. Also, among 19 new hydrocarbons tested, 2-methylbutane appears to be a favorable option for a small iso-alkane, 2,2,3,3-tetramethylhexane for a large iso-alkane, cyclopentane for a cycloalkane, and 1,2,4-trimethylbenzene for a large aromatic. With a new surrogate palette that includes these promising hydrocarbons, surrogate mixtures are formulated for 5 different batches of gasoline, which shows capabilities to emulate composition characteristics and target properties tested, including knock resistance and distillation curve.

Generalized preconditioning for accelerating simulations with large kinetic models

Detailed modeling of the combustion of real transportation fuels and the atmospheric reactions involving their emissions is prohibitively expensive, due to the large size and stiffness of the chemical kinetic models. Adaptive preconditioning is a method used to reduce the cost of integrating large kinetic models by forming a preconditioner based on a semi-analytical Jacobian matrix, paired with sparse linear algebra procedures. In this study, we extend this preconditioning method to a more-general mole-based state vector formulation applicable to generic reactor types and combinations. We tested the scheme using constant-pressure and constant-volume ideal-gas reactor simulations, showing speedup in performance from a factor of 3 up to nearly 4000 times for chemical kinetic models with 10 to 7171 species, in comparison with typical dense solvers. The method also improves performance by a factor of 1.06 to 21.1, for models larger than 200 species, in comparison with a fully exact, analytical Jacobian used as the preconditioner. Overall, this method improves performance by up to three orders of magnitude for large kinetic models, and offers benefits for models with as few as 10 species.

An experimental and kinetic modeling investigation on low‐temperature oxidation chemistry of 1,3,5‐trimethylcyclohexane in a jet‐stirred reactor

Very scarce studies aiming at the low-temperature chemistry of multi-alkylated cycloalkanes were reported until now, which widely exist in real transportation fuels. Thus, this work presents the first study on the low-temperature oxidation characteristics of 1,3,5-trimethylcyclohexane (T135MCH) in an atmospheric jet-stirred reactor (JSR) combined with synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) at fuel-lean (ϕ = 0.5), stoichiometric (ϕ = 1.0) and fuel-rich (ϕ = 1.5) conditions. Abundant quantitative information of species is acquired including reactants, major products, reactive hydroperoxides, fuel-specific cycloalkenes and other C1–C5 oxygenated intermediates. Pronounced three-stage oxidation behavior was observed including two fuel decomposition processes and one negative-temperature-coefficient (NTC) window. A detailed model incorporating both high and low-temperature reaction scheme was proposed and validated against the measured data with reasonable agreement. Representative large oxygenated intermediates were detected in this work, such as cyclic ether (CE), cyclohexylhydroperoxide (ROOH), ketohydroperoxide (KHP), olefinic hydroperoxide (OFHP) and C9 acyclic/cyclic bi-carbonyl species whose signal profiles were further compared with the simulated mole fraction profiles justifying the occurrence of specific low-temperature chemistry. Based on the modeling analysis, the competition between the chain-branching processes forming OH and chain-propagating processes forming less reactive HO2 or CE was found to determine the distinct oxidation behavior at different temperature regions. As temperature rises, chain-branching processes are inhibited and the accumulation of HO2 is accelerated, which lead to the occurrence of self-combination forming H2O2, a chain-termination process, resulting in the NTC behavior. With the arrival of high-temperature region, H2O2 becomes thermally unstable and tends to dissociate to double OH via a chain-branching process, therefore triggering the second fuel decomposition via H-atom abstractions.

Extinction characteristics of isolated n-alkane fuel droplets during low temperature cool flame burning in air

Large carbon number n-alkanes are a notable component in all real transportation fuels, and their chemical structure fosters substantial low temperature kinetic reactivity. Normal alkanes have been studied in various canonical configurations but rarely in systems with strong coupling between low temperature chemistry and transport for pure as well as for multi-component n-alkane mixtures. The Flame Extinguishment (FLEX) experiments onboard the International Space Station provided a unique platform for investigating low temperature multi-phase n-alkane and iso-alkane combustion. Among the many interesting phenomena experimentally observed, cool flame extinction can occur, accompanied by the concurrent formation of a surrounding cloud of condensed vapor. In this work we conduct numerical simulations of high and low temperature combustion of large, initially single-component n-heptane, n-decane and n-dodecane droplets. The role of initial droplet diameter, operating pressure, and n-alkyl carbon number on the extinction of hot and low temperature flames is investigated and compared against the available experimental data. While all three fuels exhibit similar hot flame behavior, cool flame activity increases with the carbon number, resulting in an increased cool flame temperature and decreased extinction diameter. Multi-cyclic “hot/cool flame transitions” are found in air as pressure is slightly increased above one atmosphere. The cyclic behaviors correspond to continuously varying hot and cool flame transitions across the high, low, and negative temperature coefficient (NTC) kinetic regimes. Further increase in pressure results in a second stage steady “Warm flame” transition. The extinction of hot and cool flame has a strong non-linear dependence on ambient pressure but as the hot flame extinction diameter increases with pressure the extinction diameter of the cool flame decreases. The computational results are compared with a recent asymptotic analysis of FLEX n-alkane cool flames.

Uncertainty-based weight determination for surrogate optimization

Fuel surrogates are simplified models that mimic the combustion characteristics of very complex real transportation fuels and enable a detailed description of the computational system for the targeted real fuels. Current efforts in surrogate development focus on matching multiple target properties of the real fuel using numerical optimization of species compositions. A way to solve the multi-objective optimization problem is to employ the weighted-sum approach with arbitrarily assigned weights. In this paper, we propose a novel approach to reduce such arbitrariness by incorporating physical information into the surrogate optimization process, leveraging uncertainties from experimental measurements and mixture property predictions to determine the weight of each target property. The underlying principle of this approach is assigning low weight for properties with high uncertainty since a tight emulation of that property is not necessary. We propose formulations that convert relative uncertainties of each target property into weights for multi-objective surrogate optimization, which penalize target properties with high uncertainties. The method is flexible enough to accommodate not only multiple uncertainty sources, but also users’ preferences and the sensitivity of weights to uncertainty variations can be readily adjusted. The proposed method is applied to formulate surrogate mixtures for three reference target jet fuels (Jet-A POSF-10325, JP-8 POSF-10264, JP-5 POSF-10289), which have considerably different hydrocarbon compositions and properties. The results show that the surrogates developed by the uncertainty-based weight method emulate the target properties of fuels very closely, and they are able to capture the compositional characteristics of the target fuels as well.

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.

Experimental and kinetic modeling study on sooting tendencies of alkylbenzene isomers

Alkylbenzenes are major aromatic constituents of real transportation fuels and important surrogate components. In this study, 4 kinds of C8H10 and 8 kinds of C9H12 alkylbenzenes were tested in a laminar diffusion flame to investigate the influence of chemical structure on sooting tendency. The laser induced incandescence (LII) technique was applied to obtain the 2D distribution of soot volume fraction for calculating the yield sooting index (YSI) of test fuels. The processes of fuel oxidation and soot formation were simulated by a detailed chemical kinetic mechanism. The mechanism includes all C8H10 and C9H12 alkylbenzenes and includes species ranging from reactant to carbon particle. The simulation results of defined YSI were in good agreement with the experimental values. A database of sooting tendencies was established by experimental data, which shows that the number of substituents is positively correlated with the sooting tendency and that the sooting tendency of meta-substituent species is higher than other isomers. Through the analysis of reaction pathway and sensitivity, it was found that the main production pathway of A4 (pyrene) is via alkylbenzenes combination reactions at the early stage of combustion. The experimental database presented in this study is systematic and comprehensive for C8H10 and C9H12 alkylbenzenes, and is thus expected to be useful for soot model development and validation.

A physics-based approach to modeling real-fuel combustion chemistry – V. NOx formation from a typical Jet A

Real transportation fuels are complex mixtures of a variety of hydrocarbon components. Predicting NOx formation in practical combustors burning real fuels is usually made with the assumption that the NOx submodels developed and tested for small hydrocarbon combustion are applicable to mixtures of large hydrocarbons as found in real fuels. Additionally, NOx data are scarce for flames of real fuels. The aims of the current study are (i) to provide reliable NOx data in flames of a typical jet fuel, and (ii) to test our capability to predict these data by combining a recently proposed HyChem reaction model of jet A combustion (Xu et al., 2018) with the NOx submodel of Glarborg (2018). Specifically, NOx concentrations were measured in stretch-stabilized premixed flames of methane and Jet A (POSF10325) from fuel lean to rich conditions and of ethylene at a fuel-rich equivalence ratio. This range of stoichiometries allows both thermal NO and prompt NO pathways to be tested. The results show reasonably good agreement between the experimental data and model predictions for all flames tested, although the model appears to underpredict NOx concentrations in the Jet A flames under fuel rich conditions. Sensitivity analyses were conducted to illustrate the influence of the reaction pathways and flame boundary conditions on NOx predictions. The analyses also suggest that additional prompt NO reaction pathways may play a role in flames of large hydrocarbons.

Chemical functional group descriptor for ignition propensity of large hydrocarbon liquid fuels

The chemical functional group approach is investigated to verify the fundamental applicability of low-dimensional descriptors in the prediction of global combustion behavior, as described by homogeneous reflected shock ignition delay times. Three key chemical functional groups, CH2, CH3 and benzyl-type, are used to represent n-alkyl, iso-alkyl, and aromatic functionalities, respectively. To examine whether such descriptors can appropriately reflect the influences of these functionalities on ignition delay, Quantitative Structure-Property Relationship (QSPR) regression analysis is performed with the formulation of analytical models based on a fundamental Arrhenius-type description. The models are trained using literature measurements of reflected shock ignition delay times for stoichiometric fuel/air mixtures at 20 atm. Sensitivity analyses applied to the QSPR regression models show that the CH2 functional group dominates chemical kinetic behaviors at low temperature, while the chemical kinetic impacts of CH2, CH3, and benzyl-type functional groups all diminish as temperature increases. Further analyses of constant-volume adiabatic ignition delay predictions using detailed chemical kinetic models demonstrate influences of n-alkyl, iso-alkyl, and aromatic functionalities at both low and high temperature, consistent with those found for the QSPR regression models. Finally, 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy is used to directly quantify the chemical functional group compositions of both petroleum-derived and alternative jet fuels. Combining the QSPR model with NMR spectra interpretation, the applicability of current approach as an expeditious tool to accurately characterize the ignition propensity of real transportation fuels is demonstrated by comparison with experimental measurements.

The effect of molecular structures of alkylbenzenes on ignition characteristics of binary n-heptane blends

Alkylbenzenes are major aromatic constituents of real transportation fuels and important surrogate components. In this study, the structural impact of nine alkylbenzenes on their ignition characteristics is experimentally and computationally investigated with particular emphasis on the blending effect with significantly more reactive normal alkanes. Experimental comparisons of mono-alkylbenzenes (toluene, ethylbenzene, n-propylbenzene, iso-propylbenzene) from a modified CFR engine showed that the difference in pure alkylbenzene reactivity significantly diminished when blended with n-heptane, as the strength of the radical scavenging effect of all three alkylbenzenes is similar. Among C8H10 isomers, the reactivity of pure ethylbenzene and o-xylene and their blends with n-heptane showed a complex competing effect between the difference in CH bond energy and the existence of intermediate/low-temperature chemistry caused by adjacent methyl pairs. A similar structural impact was also observed for C9H12 isomers and their blends with n-heptane, while the influence of CH bond energy was more noticeable than C8H10 molecules. Kinetic simulations of the alkylbenzene/n-heptane blends highlighted the effect caused by adjacent methyl pairs that is referred to as the “ortho effect”. Analysis of ethylbenzene and o-xylene showed that o-xylene's intermediate/low-temperature pathways initiated by benzylperoxy radical – benzylhydroperoxide isomerization (RO2 – QOOH) produce additional active radicals such as OH and CH2O, which accelerates the oxidation chemistry of more reactive n-heptane. This study provides knowledge on the blending effect of alkylbenzene compounds with n-heptane on their ignition characteristics that is useful to develop surrogates that can better mimic the reactivity of real fuels.

Hydrocarbons for the next generation of jet fuel surrogates

Fuel surrogates are a critical component for the detailed combustion modeling of real transportation fuels. Indeed, the numerical study of engine combustion requires the coupling of computational fluid dynamics and chemical kinetic models, and therefore a limited number of chemical species and reactions can be employed due to current numerical capabilities. As a consequence, surrogates are adopted to simulate the behavior of real fuels. In this study, we evaluate various hydrocarbon molecules that can be employed as next generation surrogate components for conventional and alternative jet fuels. Species considered in this study have smaller number of kinetic data as compared to molecules that are currently used in jet fuel surrogates, but they possess greater physical relevance and the potential to achieve closer emulation of properties when used as jet fuel surrogate components. Using a surrogate optimizer model, we analyze various mixtures that can emulate a petroleum-derived jet fuel (Jet-A POSF-4658) and a coal-derived jet fuel (IPK POSF-5642). The results show that n-tetradecane and n-dodecane are suitable normal alkane representatives for jet fuels. Also, the use of three C9 alkylbenzenes (n-propyl-, 1,2,4-trimethyl-, 1,3,5-trimethyl-benzene) leads to surrogate mixtures with an aromatic content and a distillation curve that matches the experimental values of Jet-A much better than mixtures that contain toluene or C10 alkylbenzenes. In addition, the optimization results with three new branched alkanes for the target IPK show that 2,2,4,6,6-pentamethylheptane is a promising surrogate component for representing low ignition quality highly-branched alkanes in jet fuels. This study highlights the need for experimental studies and further kinetic model development for these molecules, which will benefit the surrogate development for the wide variety of jet fuels in the future.

Impact of thermodynamic properties and heat loss on ignition of transportation fuels in rapid compression machines

Rapid compression machines (RCM) are extensively used to study autoignition of a wide variety of fuels at engine relevant conditions. Fuels ranging from pure species to full boiling range gasoline and diesel can be studied in an RCM to develop a better understanding of autoignition kinetics in low to intermediate temperature ranges. In an RCM, autoignition is achieved by compressing a fuel/oxidizer mixture to higher pressure and temperature, thereby initiating chemical reactions promoting ignition. During these experiments, the pressure is continuously monitored and is used to deduce significant events such as the end of compression and the onset of ignition. The pressure profile is also used to assess the temperature evolution of the gas mixture with time using the adiabatic core hypothesis and the heat capacity ratio of the gas mixture. In such RCM studies, real transportation fuels containing many components are often represented by simpler surrogate fuels. While simpler surrogates such as primary reference fuels (PRFs) and ternary primary reference fuel (TPRFs) can match research and motor octane number of transportation fuels, they may not accurately replicate thermodynamic properties (including heat capacity ratio). This non-conformity could exhibit significant discrepancies in the end of compression temperature, thereby affecting ignition delay (τign) measurements. Another aspect of RCMs that can affect τign measurement is post compression heat loss, which depends on various RCM parameters including geometry, extent of insulation, pre-heating temperature etc. To, better understand the effects of these non-chemical kinetic parameters on τign, thermodynamic properties of a number of FACE G gasoline surrogates were calculated and simulated in a multi-zone RCM model. The problem was further investigated using a variance based analysis and individual sensitivities were calculated. This study highlights the effects on τign due to thermodynamic properties of various surrogate fuels and differences in post compression heat loss over low, intermediate and high temperature region.

Laser-diagnostic mapping of temperature and soot statistics in a 2-m diameter turbulent pool fire

We present spatial profiles of temperature and soot-volume-fraction statistics from a sooting, 2-m base diameter turbulent pool fire, burning a 10%-toluene/90%-methanol fuel mixture. Dual-pump coherent anti-Stokes Raman scattering and laser-induced incandescence are utilized for simultaneous point measurements of temperature and soot. The research fuel-blend used here results in a lower soot loading than real transportation fuels, but allows us to apply high-fidelity laser diagnostics for spatially resolved measurements in a fully turbulent, buoyant fire of meter-scale base size. Profiles of mean and rms fluctuations are radially resolved across the fire plume, both within the hydrocarbon-rich vapor-dome region near fuel pool, and higher within the actively burning region of the fire. The spatial evolution of the soot and temperature probability density functions is discussed. Soot fluctuations display significant intermittency across the full extent of the fire plume for the research fuel blend used. Simultaneous, spatially overlapped temperature/soot measurements permit us to obtain estimates of joint statistics that are presented as spatially resolved conditional averages across the fire plume, and in terms of a joint pdf obtained by including measurements from multiple spatial locations. Within the actively burning region of the fire, soot is observed to occupy a limited temperature range between ∼1000 and 2000 K, with peak soot concentration occurring at 1600–1700 K across the full radial extent of the fire plume, despite marked changes in the local temperature pdf across the same spatial extent. A wider range of soot temperatures is observed in the fuel vapor-dome region low in the pool fire, with detectable cold soot persisting into conditionally averaged statistics. The results yield insight into soot temperature across a wide spatial extent of a fully turbulent pool fire of meaningful size, which are valuable for development of soot radiative-emission models and for validation of fire fluid-dynamics codes.

Study of the low-temperature reactivity of large n-alkanes through cool diffusion flame extinction

The low-temperature oxidation of hydrocarbon fuels has received increasing attention as advanced engines seek to operate in less conventional combustion regimes. Large n-alkanes are a notable component of many real transportation fuels and possess strong reactivity in this important low-temperature range. These n-alkanes have been studied extensively in various canonical kinetic experiments but seldom in systems with strong coupling between low-temperature chemistry, transport, and heat release. To address this issue, the present study investigates self-sustaining n-alkane cool diffusion flames in a counterflow burner. The extinction limits of both hot diffusion flames and cool diffusion flames are measured at atmospheric pressure for a range of n-alkanes from n-heptane to n-tetradecane. It is observed that while these fuels behave similarly for hot flames, the larger n-alkanes are substantially more reactive in the low-temperature cool flame regime. Moreover, ozone addition strongly enhances the low-temperature chemistry to the point where the differences in fuel reactivity are nearly suppressed.The experimental measurements are compared with numerical simulations employing both detailed and reduced chemical kinetic models of various sizes. Although the different kinetic models adequately predict the extinction limits of the hot flames, a large scatter is present in the model results for cool flames, and a general overprediction of the measured cool flame extinction limit is observed for all of the fuels studied. This implies that the cool flame heat release is not well agreed upon by the current chemical kinetic models, despite their capability to reproduce many homogeneous reactor experiments at low temperatures. Furthermore, it is observed that the cool flame heat release is spread over a substantial number of reactions involving large molecules, a trait that makes it particularly difficult to create reduced kinetic models that can accurately describe cool flame behavior. The results of this study suggest that the cool flame platform can provide crucial validation of the coupling between chemistry, transport, and heat release in flames at low temperatures.

A Surrogate Fuel Formulation Approach for Real Transportation Fuels with Application to Multi-Dimensional Engine Simulations

A Surrogate Fuel Formulation Approach for Real Transportation Fuels with Application to Multi-Dimensional Engine Simulations

The combustion properties of 1,3,5-trimethylbenzene and a kinetic model

Trimethylbenzenes have been suggested as useful components for the formulation of simple hydrocarbon mixtures that quantitatively emulate the gas-phase combustion behaviour of real liquid transportation fuels as model or surrogate fuels. To facilitate this application, various combustion properties of 1,3,5-trimethylbenzene (mesitylene) have been characterised experimentally and a new chemical kinetic model for its combustion constructed. Experimental determinations of 1,3,5-trimethylbenzene reflected shock ignition delay, laminar burning velocities and high-pressure flow reactor oxidative reactivity profiles are presented. These data allow for the testing of a detailed kinetic model, developed by direct analogy to, and incorporating as a subcomponent, a recent comprehensively tested kinetic model for toluene oxidation [Metcalfe WK, Dooley S, Dryer FL. Energy Fuels 2011; 25: 4915–4936]. Model calculations are also compared against data pertinent to 1,3,5-trimethylbenzene combustion phenomena from the published literature. The modelling approach allows for the accurate reproduction of the global combustion phenomena of ignition delay, burning velocity, diffusive and premixed strained extinction limits and flow reactor reactivity, with some noted shortcomings. Analyses of the constructed model suggest that the mechanism of 1,3,5-trimethylbenzene combustion occurs through the formation of 3,5-dimethylbenzaldehyde and 1,2-bis(3,5-dimethylphenyl) ethane as the major stable intermediate species, with relative proportions depending on the conditions of the particular reacting environment.

Flame Propagation and Extinction Characteristics of Neat Surrogate Fuel Components

An experimental and computational investigation into the flame propagation and extinction characteristics of neat hydrocarbon components relevant to real transportation fuels is conducted. Pure hydrocarbon fuels corresponding to linear alkane, branched alkane, aromatic, and cyclic alkane are studied. The atmospheric pressure laminar flame speeds for the neat fuels, over a range of equivalence ratios, are measured and compared at varying preheat temperatures. A comparison of the present experimental results to the limited reported experimental data and the computed values, obtained using kinetic mechanisms available in the literature, is also carried out. Additionally, flame extinction studies, both computational and experimental, are presented and discussed. An attempt is further made to assess the performance of some recently developed reaction mechanisms for n-alkane oxidation. Further, the sensitivity of the computed flame response to the kinetic rate constants as well as the transport parameters is ev...

Comparative Study on Adsorptive Removal of Thiophenic Sulfurs over Y and USY Zeolites

Removal of organic sulfur compounds by using an adsorption process was carried out at ambient temperature and pressure. FAU zeolites, including NaY, HUSY cation-exchanged with metal ions such as Cu, Ni, Zn, and La, have been applied as adsorbents in the desulfurization of model and real transportation fuels. The results showed that the type of metal ion-exchanged, amount of metal ion-exchanged, and structure of zeolite have important roles in the removal of each organic sulfur. LaNaY, LaHUSY, and CuNaY possessed highest adsorption capacity toward thiophene (TH), benzothiophene (BT), and dibenzothiophene (DBT), respectively. Among the tested adsorbents, LaHUSY exhibited highest adsorption selectivity to BT and DBT in the presence of naphthalene. The comparative study indicated that La3+ is capable of strongly adsorbing the aromatic sulfur compounds via both direct interaction at sulfur atom and via π-electronic interaction. Adsorptive desulfurization of real diesel over LaHUSY reduced the sulfur level from...

A Wide-Range Kinetic Modeling Study of Oxidation and Combustion of Transportation Fuels and Surrogate Mixtures

Liquid fuels, such as gasolines and jet and diesel fuels, are usually refined products from the processing of crude oil. Their composition is mainly based on major physical properties and combustion performance indexes. For these reasons, real transportation fuels contain thousands of compounds that greatly vary with the feedstock origins, the seasons, and the economic factors that are imposed by the refinery. Regardless of this complexity, the chemical species contained in the fuels belongs to only four hydrocarbon classes: linear or branched alkanes, alkenes, cycloalkanes, and aromatics. Moreover, the physical properties (such as vapor pressure and flash point) and the combustion properties (such as octane or cetane numbers and smoke point) are regularly variable with composition. On these bases, it is viable to define surrogate mixtures to reproduce the most important chemical and physical properties of real transportation fuels. These surrogate fuels are then very useful both for the design of more r...