Studies On The Surrogate Fuel Methods For The Simulation Of Reacting Flows In Combustion

With the development of the computer technology,numerical simulation has been widely used in scientific discoveries and engineering designs.As a complementary or even an alternative method,numerical simulation plays an increasingly important role in the study of combustion theoretical analysis and technical development for its convenience,reliability and efficiency.However,real fuels such as gasoline,diesel and aviation kerosene have a great variation in compositions and involve hundreds of chemical components with different molecular structures.Consequently,constructing a model that can represent the combustion and physical properties of real fuels is a great challenge.Alternatively,simplified“surrogate fuels”with only a few component species are regarded as one of the most effective ways for representing the combustion and physical properties of real fuels in the simulation of reacting flows in combustion.At present,one of the most popular methodologies for surrogate fuels is matching some macroscopic property parameters.Although it has the advantages of simplicity and intuition,it still has the problems of strong empirical dependence,high cost and poor expansion,which greatly restricts the promotion and application of combustion simulation in reaction flow analysis.A new methodology of surrogate fuel named FGBS?functional groups based surrogate fuel?for both oxygenated and hydrocarbon fuels is proposed and investigated.The novelty of this method is to construct surrogate fuel mixtures by directly matching the molecular structure and the key functional groups instead of macroscopic property parameters.The main functional group information which reflects its physical and chemical properties can be obtained by analyzing the micro molecular structure of the target fuel.Then based on the constituent parameters of functional groups,the classification and proportion of basic fuels are determined.Finally,the chemical kinetic model of surrogate fuel can be assembled according to the surrogate fuel mixtures.The main contents and results are as follows:?1?The theoretical studies of FGBS methodology and the development of tool for chemical reaction mechanism disposal have been done by analyzing the molecular structure and the charecteristics of reacting flows in surrogate fuel.In order to match the molecular structure precisely,the core functional group is proposed as a parameter to quantify the molecular structure.Then,based on reaction class,the process to obtain skeleton mechanism of surrogate fuels that can be used in the simulation of reacting flows,including the detail reaction mechanism developing,mechanism reducing and reaction optimizing have been implementaried automatically.?2?Based on the FGBS method,the surrogate fuels of biodiesel,S-8 synthetic oil,Jet-A aviation kerosene,domestic RP-3 aviation kerosene and FACE gasoline were constructed respectively.Using typical functional groups as target parameters,a surrogate mixture of methyl-9-decenoate,n-dodecane and 1,4-hexadiene is formulated for biodiesel;a three-component surrogate consists of n-dodecane 2,5-dimethylhexane and toluene for S-8,Jet-A and RP-3 fuel;a surrogate mixture based on n-heptane,iso-octane,toluene,2,5-dimethylhexane,and n-butane for FACE A and C gasoline fuels.?3?The abilities of FGBS method in predicting the physical and combustion properties of real fuels have been verified,respectively.Firstly,the density,viscosity,specific heat capacity and thermal conductivity of aviation kerosene surrogate fuel under sub-and supercritical conditions are analyzed and verified.The results show that the prediction of the surrogate fuel can be consistent with the experimental data.In order to verify the FGBS method's ability in predicting the combustion performance,the combustion characteristics of the surrogate fuel were verified based on the experimental data.The biodiesel surrogate fuel is tested based on the ideal stirred reactor and homogeneous ignition process.The aviation kerosene surrogate fuel is validated based on the ignition delay time of the shock tube and the laminar flame velocity.The ignition delay time of FACE gasoline surrogate fuel is validated under different pressures and equivalent ratios.The good agreement between the surrogate fuel and the experimental data proves the effectiveness of the FGBS method for the substitution of physical and chemical properties.?4?An efficient surrogate fuel formulation methodology which directly uses the chemical structure information from nuclear magnetic resonance?NMR?spectroscopy analysis has been proposed.The types and share of fuel functional groups were obtained by NMR spectroscopy,and they were merged into the parameters of typical functional groups,and then used directly in FGBS model fuel mechanism construction.According to this,five functional groups have been selected to show the basic molecular structure of the FACE F,G,I and J fuels.A palette that contains seven candidate components:n-heptane,iso-octane,n-butane,toluene,2,5-dimethylhexane,methylcyclohexane and1-hexene is chosen for different FACE fuels,based on the FGBS methodology.The kinetic mechanisms of these seven candidate components are chosen to assemble a detailed mechanism of each surrogate fuel for FACE gasoline.Whereafter,the accuracy of FACE surrogate models was demonstrated by comparing the model predictions against experimental data in homogeneous ignition.?5?The surrogate fuel of RP-3 has been applied to the numerical investigation on heat transfer of supercritical RP-3 and flame characteristics in Bunsen burner,respectively.The numerical simulation can reflect the transformation process that from normal to deteriorative heat transfer.Besides,the numerical combustion process of the premixed,pre-evaporated RP-3 aviation kerosene in the Bunsen burner based on a reduced mechanism was compared to the experimental data.The results show that the simulated distributions of the temperature and O₂ and CO₂ concentration are in good agreement with the experimental data.Those two numerical simulations have already shown its worth in engineering for present surrogate methodology.Results of the tests and analysis have verified the effectiveness and efficiency of FGBS methodology.The FGBS methodology can not only represent the combustion characteristics accurately,but also some physical properties of target fuels.It provides a new and effective technique for analyzing the reaction kinetics in complex combustion process.