Kerosene Surrogate Research Articles

Investigation of the criteria for construction of reliable surrogate fuels: A case study of Jet-A aviation kerosene

Surrogate fuels are usually constructed by optimizing component selection and component proportions to match the physicochemical indexes of practical fuels. The interaction among the selected components and the influence of the weight factors of the physicochemical indexes on the combustion characteristics of the surrogate fuel have not been well investigated in previous research. In this paper, a systematical method is proposed to construct the Jet-A aviation kerosene surrogate fuel by combining the principle of the selection of the surrogate components and the genetic algorithm, in which the weight factors of the physicochemical indexes are introduced. First, 900 cases including nine groups of surrogate component schemes and 100 groups of weight factor schemes are generated using the Sobol function. Then, optimization is carried out using the genetic algorithm for the 900 surrogate fuels with the candidate component proportions as the input variables and the selected physicochemical properties as the optimization targets. Subsequently, the results of all the surrogate fuels concerning component proportions, physicochemical properties, and combustion characteristics are further analyzed, especially for the prediction performance of the surrogate fuels under different schemes on the combustion characteristics of ignition delay times, laminar flame speeds, and O2/CO/CO2 concentrations. It is found that proper weight factors can enhance the prediction performance of the surrogate fuels, especially for the surrogate fuels with fewer surrogate components. However, the optimal limit of the surrogate fuel performance is determined once the surrogate components are confirmed. Through the comprehensive orthogonal analysis and sensitivity analysis on the results of the surrogate fuels, the criteria of surrogate fuel construction for Jet-A are further present: the surrogate fuels do not need to keep the same component proportions as that in the practical fuel. To ensure the reliability of the surrogate fuels, the relative weight factor of the derived cetane number should be enhanced by at least 15 %, while that of the aromatics fraction should be larger than 10 %.

Soot and PAH formation in laminar diffusion flames of RP-3 jet kerosene and its surrogates at preheat temperature

For investigating the effects of preheat temperature on the soot/PAH formation of RP-3 kerosene surrogates, planar laser-induced incandescence (PLII), planar laser-induced fluorescence of PAH (PAH-PLIF) and chemical kinetic simulation are conducted in several laminar diffusion flames. The goal is to provide a surrogate that matches well with the soot formation characteristics of RP-3 kerosene and to investigate the mechanism behind the temperature sensitivity of different surrogates. Firstly, surrogate S1 (30.3% n-hexadecane, 39.8% iso-cetane, 29.8% o-xylene, in mole fraction) is formulated to obtain a surrogate with good reproducibility of soot formation characteristics corresponding to the RP-3 jet kerosene. Compared with another reported surrogate S2, S1 presents a higher soot yield due to its higher PAH formation and a stronger soot formation propensity. With elevated preheat temperature, soot yield of all the studied flames gets higher, and the temperature sensitivities for soot formation of S1 and S2 are shown with little difference. By further analyzing the PAH results experimentally and numerically, the temperature sensitivity for soot yield of S2 is more closely related to the temperature sensitivity of PAH precursors, while the subsequent processes after soot inception may be more important to the temperature dependence of S1.

Investigation on n-decane-hydrogen laminar combustion characteristics using the constant volume combustion method

The laminar burning velocity of n-decane (an aviation kerosene surrogate) blended with hydrogen is studied using experimental and numerical analysis at the initial conditions of 470 K and 1, 2, and 4 bar over the equivalence ratios of 0.7–1.3 and hydrogen addition ratios of 0 %, 10 %, 20 %, 30 %, 40 %, and 50 %. The burning velocity is investigated using the constant volume method of the spherically expanding flame method. Here, burning velocity at elevated pressure and temperature conditions close to engine-relevant conditions have been established. Thus, using the experimental data at 470 K and 4 bar, burning velocities at the unburnt temperatures of up to 612 K and pressures of up to 11.02 bar are obtained. Also, Polimi and JetSurF2.0 mechanisms were used to simulate the burning velocities and they agreed well with the experimental data. However, as the hydrogen addition increased, especially when the hydrogen addition was 40 % there was a significant deviation between the experiment and the simulation results. The chemical reaction analysis of n-decane-hydrogen shows the flame speed is significantly driven by H+O2⇔O+OH, CO+OH⇔CO2+H, CH3+H(+M)⇔CH4(+M), and H+OH+M⇔H2O+M at the various initial conditions. However, H+O2⇔O+OH produces more OH, H, and O radicals that accelerate the combustion chemical reaction rate of n-decane-hydrogen. The reaction pathways show that the decomposition of n-decane is mainly controlled by the OH and H radicals. This study's results provide an understanding of the combustion characteristics of aviation fuel-hydrogen blends in internal combustion engines at elevated pressures and temperatures to achieve zero emissions in aviation.

Formulation of Surrogates of Hydrocarbon Fuels Using Selected Physico-Chemical Properties Related to Atomization, Heating, Evaporation and Combustion Behaviours

ABSTRACT The aim of this work is to describe an approach to the formulation of surrogates of hydrocarbon fuels, taking into account the properties related to atomization, heating, evaporation and combustion behaviors. These properties include the density, viscosity, lower calorific value, distillation curve, saturated vapor pressure, heat capacity, thermal conductivity, surface tension, molar ratio of hydrogen to carbon, molar mass, derived cetane number, and threshold soot index. Three diesel surrogates were developed using the proposed approach. Methods for calculating the physicochemical properties of both individual hydrocarbons and their mixtures are presented. The discrepancy between calculated results and experimental data for all properties is shown not to exceed 3%. Experimental studies were carried out in a lab-scaled combustion chamber, in which the properties of one of the three developed surrogates, DSSU3, were compared with those of diesel fuel. Also, the simulation results for DSSU3 were compared with published experimental data. It is shown that the properties of DSSU3 are a good match for those of diesel fuel. In addition, a kerosene surrogate was formed using the proposed approach. This allowed us to conclude that this approach to determining the properties of multi-component fuels is suitable for the formulation of both kerosene and diesel fuel surrogates.

Molecular dynamics study on the kinematic viscosity, density and structure of fuel blends containing n-decane and biofuel compound of ethyl decanoate or ethyl dodecanoate

Bio-aviation fuel is blend consisting of aviation kerosene and biofuels, which is a clean renewable energy and has gained considerable attention in recent years. However, numerical studies on the thermophysical properties of bio-aviation fuel containing fatty acid esters are still limited. In this paper, the kinematic viscosity and density of fuel blends containing n-decane and biofuel compound of ethyl decanoate or ethyl dodecanoate are investigated by molecular dynamics (MD) method, and the calculated viscosities are compared with those by atheoreticalmodel of UNIFAC-VISCO (UV). The MD results applying with a PCFF force field (FF) can reproduce the experimental data for the fuel blends very well in comparison with both the COMPASS FF and the UV model. In addition, to link the variety of molecular structure to the changes of their thermophysical properties, local structures of n-decane and ethyl decanoate in mixture are systematically analyzed. It illustrates that a decreasing end-to-end length of molecular chains combined with the growing intermolecular distance leads to the reduction of the kinematic viscosity of fuel blends with the increasing of temperature. This work provides a baseline to help understand the thermophysical properties of esters and their based bio-aviation kerosene surrogates.

Effects of water subdroplet location on the start of puffing/micro-explosion in composite multi-component fuel/water droplets

An earlier reported model for the prediction of the onset of puffing/micro-explosion in composite multi-component water/liquid fuel droplets is generalised to consider the shifting of the water subdroplet relative to the centre of the fuel droplet. The droplet heating and evaporation are described within the Abramzon and Sirignano model. The equations of heat conduction in the droplet and component diffusion inside the fuel shell are solved numerically assuming that the composition and temperature are uniform over the droplet surface but vary with time. The change in the droplet size due to thermal swelling is considered. The verification of the new model is performed by comparing its predictions with those of the previously developed numerical code, based on the analytical solutions to the heat transfer and component diffusion equations, and used at each timestep of the calculations, for the case of a perfectly centred water subdroplet. The coincidence of the results supports both approaches to the problem. The timing of puffing/micro-explosion is then evaluated for droplets of two kerosene surrogates for various positions of the water subdroplet. It is pointed out that shifts of the water subdroplet by less than 20% lead to a reduction in the time to puffing/micro-explosion of less than 5%. This justifies the applicability of the previously developed model that was based on the assumption that a water subdroplet is located exactly in the centre of the fuel droplet. The times to puffing/micro-explosion predicted by the model are validated using the in-house experimental data for kerosene surrogate droplets (SU1: n-decane, iso-octane and methylbenzene; SU12: iso-octane and methylbenzene).

Kinetic model and kerosene surrogate for calculating gas turbine engine emission of carcinogenic hydrocarbons

To calculate the emission of carcinogenic polycyclic aromatic hydrocarbons by the combustion chambers of aircraft gas turbine engines, the A17 kinetic model has been developed, characterized by new blocks of elementary chemical reactions of hydrocarbon compounds oxidation and synthesis of polycyclic aromatic hydrocarbons. The results of model validation showed satisfactory agreement with the experimental data and the possibility of applying the model to describe combustion processes in gas turbine engine combustion chambers. A review and numerical study was carried out for 14 surrogates (model fuels) of aviation kerosene, the combustion of which can be described using the A17 model. Simulation of stabilized flame of a previously prepared mixture showed the effectiveness of Drexel, Liu, su4, UM1 surrogates, the predictions for which agree satisfactorily with the experimental data and provide the expected levels of concentration of polycyclic aromatic hydrocarbons. The calculations show the dependence of the concentration of the most carcinogenic polycyclic aromatic hydrocarbon benzo(a)pyrene, and the ratio of the main combustion products CO2/H2O on the molar mass of the fuel. For the experimentally determined value of the molar mass of kerosene TS-1, the smallest deviation (up to 0.25%) is demonstrated by the su4 and UM1 surrogates. Due to the best predictive capability for the ignition delay time, normal flame propagation speed, pyrolysis and combustion products, the su4 and UM1 surrogates can be chosen to calculate the emission of carcinogenic polycyclic aromatic hydrocarbons from aircraft gas turbine engine combustion chambers.

Numerical investigation of multi-component droplet evaporation and autoignition for aero-engine applications

The droplet evaporation and autoignition behaviour of a three-component kerosene surrogate is numerically investigated for a wide range of ambient pressures and temperatures representing realistic aero-engine conditions. Vitiated air with different levels of dilution is considered to represent mixing of air with combustion products. Particular attention is given to the analysis of multi-component fuel effects at the various operating conditions. The investigation also considers the impact of fuel preheating and multiple initial droplet diameters, and extends to the quantification of NOx emissions at the droplet scale level. Considering pure evaporation, results show that preferential evaporation and variation of the droplet composition are mainly affected by the gas temperature. An increase of the pressure generally increases the duration of the droplet heat-up period and reduces the effects of preferential evaporation, especially when high temperatures are considered. Autoignition in vitiated air is strongly influenced by both the level of dilution and ambient pressure, with the latter playing an important role in determining the value of the initial droplet diameter below which no autoignition occurs. Lower pressures generally make the kerosene droplet more resistant to autoignition for the same level of dilution or gas temperature. Droplet preheating mainly affects the heat-up period and can be used as a design parameter to control the autoignition delay time. NOx levels are substantially related to the gas-phase temperature and the existence of a flame at the droplet scale. Potential implications for the design of future low-emission combustor technologies are discussed with an emphasis on the fuel preparation.

Development and verification of RP-3 aviation kerosene surrogate fuel models using a genetic algorithm

For emulation of the physicochemical characteristics and hydrogen-carbon group composition of RP-3 aviation kerosene, two models were composed of three components including n-dodecane, n-butylcyclohexane and n-butylbenzene by genetic algorithm optimization methodology with physical properties measurements (S1, 27.9/63.0/9.1 mol%; S2, 58.0/30.0/12.0 mol%). The numerical results of properties using the surrogate fuels were compared with experimental data. Both models had good performance in predicting the physical properties by analyzing the trends of density and kinematic viscosity under different temperature and pressure conditions. Based on the proposed surrogates, a detailed RP-3 surrogate chemical reaction mechanism was developed by decoupling methodology which including 1408 species and 8965 reactions. Autoignition properties, oxidation properties and laminar combustion properties of surrogates were compared with RP-3 experimental data. Two models exhibited good matching on ignition behaviors with RP-3 at high and low temperatures. Moreover, the components proportion difference had a great influence on the ignition properties in the negative temperature coefficient region. It also made the predicted value of the laminar combustion velocity of S1 higher than that of S2.

Reaction Model Development of Selected Aromatics as Relevant Molecules of a Kerosene Surrogate—The Importance of m-Xylene Within the Combustion of 1,3,5-Trimethylbenzene

Abstract The development of advanced reaction models to predict pollutant emissions in aero-engine combustors usually relies on surrogate formulations of a specific jet fuel for mimicking its chemical composition. 1,3,5-trimethylbenzene is one of the suitable components to represent aromatics species in those surrogates. However, a comprehensive reaction model for 1,3,5-trimethylbenzene combustion requires a mechanism to describe the m-xylene oxidation. In this work, the development of a chemical kinetic mechanism for describing the m-xylene combustion in a wide parameter range (i.e., temperature, pressure, and fuel equivalence ratios) is presented. The m-xylene reaction submodel was developed based on existing reaction mechanisms of similar species such as toluene and reaction pathways adapted from literature. The submodel was integrated into an existing detailed mechanism that contains the kinetics of a wide range of n-paraffins, isoparaffins, cycloparaffins, and aromatics. Simulation results for m-xylene were validated against experimental data available in literature. Results show that the presented m-xylene mechanism correctly predicts ignition delay times at different pressures and temperatures as well as laminar burning velocities at atmospheric pressure and various fuel equivalence ratios. At high pressure, some deviations of the calculated laminar burning velocity and the measured values are obtained at stoichiometric to rich equivalence ratios. Additionally, the model predicts reasonably well concentration profiles of major and intermediate species at different temperatures and atmospheric pressure.

Numerical Study on Influences of Drag Reducing Additive in Supercritical Flow of Kerosene in a Millichannel

To improve the performance of a high-pressure refueling liquid oxy-kerosene engine, the influence of drag-reducing additive on the heat transfer characteristics in the supercritical flow of kerosene in a microchannel for regenerative cooling is explored. The finite-volume CFD numerical simulation method is applied using the RNG k-ε turbulence model and enhanced wall function. The current work faithfully represents the effect of the drag-reducing additive in kerosene through numerical calculations by combining a 10-component model for the physical properties of the kerosene and the Carreau non-Newtonian fluid constitutive model from rheological measurements. Results suggest that the 10-component kerosene surrogate can describe the supercritical physical properties of kerosene. The inlet temperature, inlet velocity, and the heat flux on the channel wall are driving factors for the supercritical kerosene flow and heat transfer characteristics. The pressure influence on the heat transfer is negligible. With polymer additives, the loss in pressure drop and heat transfer performance of supercritical kerosene flow decrease 46.8% and 37.5% respectively. The enhancement of engine thrust caused by reduction in pressure drop is an attractive improvement of concern.

An experimental and modeling study of oxidation of real RP-3 aviation kerosene

The major components of a real Chinese RP-3 aviation kerosene were measured as 64.15% alkanes, 18.48% cycloalkanes, 15.88% aromatics. The oxidation of real Chinese RP-3 aviation kerosene was investigated in a jet-stirred reactor (JSR) at atmospheric pressure, φ = 2.0, and temperatures ranging from 575 to 1100 K. Mole fraction profiles of 25 species were detected with online GC and GC/MS. Three components (3C) surrogate fuel was validated against the measured results, as well as a detailed kinetic reaction model involving 453 species and 2991 reactions, was validated against the oxidation data A negative temperature coefficient (NTC) behavior of intermediates except for methane (CH4) was observed, due to the low-temperature activity of alkanes. The bimodal curves were observed for light hydrocarbons (C2-C4) and aromatic species and oxygenate, in which the second one is generally larger than the first one for light hydrocarbons (C2-C4) and aromatic species, while oxygenates exhibit adverse tendencies. Rate-of-production (ROP) analysis reveals that 1,3,5-trimethyl cyclohexane (T135MCH) mostly generates XCH2D35MCH radicals by dehydrogenation reaction, isomerizes to CH3SXD35MCH radicals, and further convert to C3H6. N-propylbenzene (NPB) is mainly dehydrogenated to form A1CHCH2CH3 and A1CH2CHCH3 radicals, which further transform to styrene (C6H5C2H3). Sensitivity analysis demonstrates that the consumption of both T135MCH and NPB are promoted by H/OH/HO2 radicals at low temperatures. At a temperature higher than 900 K, an insufficient supply of H/OH/HO2 radicals may lead to a competing reaction between the three components. Within the temperature range of 600 to 800 K, n-dodecane is the most active component to produce H/OH/HO2 radicals to initiate the oxidation of NPB and T135MCH. These results could improve the understanding of the specific combustion process of RP-3 aviation kerosene, and help the establishment of RP-3 aviation kerosene surrogate fuel as well.

Study of hydrogen impact on lean flammability limit and burning characteristics of a kerosene surrogate

Hydrogen impacts on lean flammability limits and the burning characteristics of n-decane, a kerosene surrogate, were studied using a spherical combustion chamber and Chemkin software at 460 K and 100 kPa. Laminar flame propagated spherically at λ = 0.8–1.3 by using 50 mJ IE, whereas further leaner mixture (λ ≥ 1.4) could be ignited at 1000 mJ. However, the wrinkles appeared on flame morphology thanks to higher IE. The effect of IE on flame morphology reduced with increasing the value of λ. In contrast, the flame distortion enhanced as lifting IE, 1000–3000 mJ. Near lean limit, the spherical flame appeared initially from 0 ms to 20 ms. When time increased from 20 ms, it buoyed due to slow flame speed and rapid radiation losses. Eventually, it disappeared at t ≈ 200 ms, and the mixture could not burn completely. Lean limits of n-decane were found λ = 1.6, λ = 1.7, and λ = 1.8 at 1000 mJ, 2000 mJ, and 3000 mJ, respectively. It linearly extended by 0.5 λ with 70% H2 addition (0–70%) and enormously enlarged by 1.3 λ with 20% H2 addition (70–90%). IE, 1000–3000 mJ, extended the lean limit by 0.2 λ. H radical produced greatly from H2 and CO by consuming OH, whereas it consumed by translating formaldehyde and oxygen into aldehyde, O and OH. OH produced significantly from the consumption of H and hydroperoxyl radicals. By lifting hydrogen, H and OH increased rapidly, which enhanced the reaction rates of dominant intermediates. Consequently, the lean limit improved.

Development of physical-chemical surrogate models and skeletal mechanism for the spray and combustion simulation of RP-3 kerosene fuels

RP-3 kerosene is a widely used fuel for civil and military transportation in China. Two RP-3 kerosene surrogates (UM1 and UM2) were proposed by genetic algorithm optimization methodology, aiming to simulate viscosity, density, surface tension, cetane number, lower heating value, H/C ratio and molecular weight along with sooting tendency under spray and engine relevant conditions. The RP-3 kerosene surrogates were composed of four components including n-dodecane, 2,2,4,6,6-pentamethylheptane, decalin and n-propylbenzene (UM1, 0.3374/0.3042/0.1954/0.163. UM2, 0.1449/0.3706/0.2059/0.0195/0.2591 by mole fraction). The carbon number of n-dodecane and 2,2,4,6,6-pentamethylheptane was both much closer to that of the real RP-3. Based on the proposed surrogates, a skeletal RP-3 surrogate chemical reaction mechanism was developed by decoupling methodology. The skeletal RP-3 surrogate mechanism was reduced only including 89 species and 225 reactions, which was efficient and reliable in CFD simulation. The surrogate models were validated during spray process under vapor and nonevaporating environment. The skeletal mechanism was verified against the foundational experiments such as ignition delay times, species concentrations and laminar flame speed under wide conditions. The applicability of skeletal mechanism was also well verified with our test data from a real compression-ignition engine.

Experimental investigation and correlations of thermophysical properties for bio-aviation kerosene surrogate containing n-decane with ethyl decanoate and ethyl dodecanoate

Physical fuel surrogate is always necessary to be proposed to match physical properties such as liquid density, viscosity and surface tension of the real bio-aviation kerosene for the characteristics of their spray performance. Thus, it is crucial to determine the related thermophysical properties over a wide temperature range for a further development of the fuel spray system. Therefore, binary surrogates of n-decane with ethyl decanoate and ethyl dodecanoate were proposed and their thermophysical properties were investigated in the present work. The liquid density was obtained using a U-tube densimeter in the temperature range between (293.15 and 433.15) K. The liquid kinematic viscosity and surface tension were investigated simultaneously by surface light scattering (SLS) method in the temperature range from (313 to 423) K. Additionally, the refractive index was measured by a refractometer in the temperature range from (278.15 to 358.15) K. Furthermore, correlations for these properties were developed as the function of mole fraction and temperature. The relative deviations of experimental liquid density, kinematic viscosity, surface tension and refractive index from those calculated according to the correlations were within the range of ±0.2%, ±2%, ±1% and ±0.08%, respectively.

Surrogate fuels for RP-3 kerosene formulated by emulating molecular structures, functional groups, physical and chemical properties

The objective of the current study was to formulate RP-3 kerosene surrogate by emulating fuel properties affecting the physical and chemical processes of the target fuel under the engine relevant conditions. This study utilized two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC-TOFMS) and 13C and 1H nuclear magnetic resonance (NMR) spectroscopy to characterize the compositional characteristics of RP-3 fuel, and various standard test methods were applied to measure the physical and chemical properties of the target fuel. Two surrogate fuels (K1, a mixture of five components and K2, a mixture of seven components) were optimally determined through a multi-property regression algorithm by matching carbon types (CTs), distillation curve, cetane number (CN), density, and threshold sooting index (TSI) of the target fuel. The measured and estimated values of both target properties and non-target properties of surrogates were validated against the experimental data of RP-3 kerosene. Ignition delay times (IDTs) of both surrogates were investigated in a heated shock tube and a heated rapid compression machine under engine relevant conditions and validated against the measured results of RP-3. Overall, K1 and K2 both exhibited good matching on the compositional characteristics, physical-chemical properties, and gas phase ignition behaviors with the target fuel. In contrast, the seven-component K2 was more competitive and more comprehensive.

Development of blend composition of aviation kerosene surrogate for the simulation of workflow of gas turbine engine combustion chamber

In this paper, the criteria for determining the composition and physicochemical properties of aviation kerosene were formulated. The data on the physicochemical properties of known kerosene surrogates were systematized and classified. The main classes of individual chemical components of aviation kerosene were determined, and the main representatives of these classes which were used in the preparation of surrogates, were investigated. Four- and six-component kerosene substitutes are proposed. The physical properties of the developed surrogates were validated according to the flow characteristics and the spray angle of the flame of a centrifugal fuel nozzle. The dependence of the flame speed on the composition of the mixture of developed kerosene surrogates was determined. The results of determining the composition of combustion products during the combustion of TS-1 brand aviation kerosene and its surrogates in a model combustion chamber were compared.

From fundamental study to practical application of kerosene in compression ignition engines: An experimental and modeling review

The use of kerosene in direct injection compression ignition engines is fundamentally due to the introduction of the Single Fuel Concept. As conventional direct injection compression ignition diesel engines are made specifically to use diesel fuel, the usage of kerosene will affect engine emissions and performance due to differences between the fuel properties of kerosene and diesel. As a result, in order for kerosene to be properly and efficiently used in diesel engines, it is needful for the scientific community to know the properties of kerosene, its autoignition and combustion characteristics, as well as its emissions formation behavior under diesel engine operating conditions. Moreover, it is desirable to know the progress made in the development of suitable kerosene surrogates for engine applications as it is a crucial step toward the development of reliable chemical reaction mechanisms for numerical simulations. Therefore, in this work, a comprehensive review is carried out systematically to better understand the characteristics and behavior of kerosene under direct injection compression ignition engine relevant conditions. In this review work, the fuel properties of kerosene are summarized and discussed. In addition, fundamental autoignition studies of kerosene in shock tube, rapid compression machine, fuel ignition tester, ignition quality tester, constant volume combustion chamber, and engine are compiled and evaluated. Furthermore, experimental studies of kerosene spray and combustion in constant volume combustion chambers are examined. Also, the experimental investigations of kerosene combustion and emissions in direct injection compression ignition engines are discussed. Moreover, the development of kerosene surrogates, their chemical reaction mechanisms, and the modeling of kerosene combustion in direct injection compression ignition engines are summarized and talked about. Finally, recommendations are also given to help researchers focus on the areas which are still severely lacking.

Droplet evaporation characteristics of aviation kerosene surrogate fuel and butanol blends under forced convection

A droplet evaporation model for blends of aviation kerosene surrogate fuel (n-decane and toluene) and butanol (a promising bio-jet fuel) was presented and validated by conducting droplet suspension experiments. The model incorporates the non-ideal effects of blended fuels using the component activity coefficient, which turns out to greatly deviate from unity for test fuels and thus significantly influence their evaporation rate. The effects of recirculation inside the suspended droplet on the heat and mass diffusion were also considered. The experimental data were largely consistent with simulated results under different ambient temperatures and different convention velocities. With increasing butanol content, the droplet evaporation rate increased and the micro-bubble phenomenon was more likely to occur. The convection velocity exhibited a significant influence on the evaporation process as Reynolds number and Sherwood number rose under forced convection conditions. The discrepancy between experimental data and simulated results at the convection velocity of 0.05 m/s was small and comparable with that at the convection velocity of 0.1 m/s and 0.5 m/s, which implies the model could reflect the convection effect reasonably. Temporal evolutions of component concentrations at the liquid surface demonstrated that butanol and toluene were likely to evaporate at a faster rate than n-decane.

Including analytically reduced chemistry (ARC) in CFD applications

Reacting numerical simulations today are often based on either fitted global reaction schemes, comprised of a few empirical reactions, or pre-tabulated laminar flame solutions computed with detailed chemistry. Although both methods can accurately predict global quantities such as laminar flame speed and burnt gas composition, they have significant limitations. In particular, neither are able to directly and adequately describe the complexity of pollutant chemistry. In the context of reducing harmful emissions of the next generation of aeronautical combustors, however, including these needed additional kinetic details in combustion simulations is becoming essential. Direct integration of detailed chemistry in accurate turbulent combustion models is not a viable option in the foreseeable future, because of excessive computational demands and numerical stiffness. In this context, Analytically Reduced Chemistry (ARC) represents an attractive compromise between accuracy and efficiency, and is already employed in relatively complex Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES). ARCs are knowledge-based compact mechanisms retaining only the most relevant kinetic information as extracted directly, and without fitting, from detailed chemical models using specialized reduction techniques (important species identification through graph search, lumping of species with similar features, short-living species identification, etc.). In recent years, several multi-step efficient and automated reduction tools have been developed, enabling the easy generation of ARCs with minimum input and knowledge from the user. The main objective of this paper is to present a review of ARCs for fuels ranging from methane to aviation kerosene surrogates, recently derived with such a multi-step automated reduction tool: YARC. Information about the applicability and range of validity of each derived mechanism are given, along with further references. Each one was specifically derived to be convenient to use in CFD; in particular, the stiffness was regarded as a key factor and the final number of transported species never exceeds thirty. In a final section, the great potential of the methodology is illustrated in a multi-phase, reactive LES application where the fuel is a real multi-component transportation fuel. To that end, an ARC based on a Jet A described by the novel Hybrid Chemistry (HyChem) approach is coupled with the Dynamically Thickened Flame LES (DTFLES) model and directly integrated into the LES solver AVBP. A Lagrangian spray description is used. Results are compared to experimental data in terms of temperature and major species (CO2, H2O, CO, NO) mass fractions, leading to very satisfying results.