| Efficient and clean combustion has always been the development direction of aero engines.However,the composition of aviation kerosene is very complex,mainly composed of hundreds of components such as linear alkanes,branched alkanes,aromatic hydrocarbons and naphthenes.Although experts and scholars at home and abroad have conducted in-depth research on the surrogate fuel of aviation kerosene,and proposed many chemical reaction mechanisms.However,the previous research mechanism mainly focused on high-temperature reaction,and the accuracy of low-temperature reaction mechanism needs to be improved.In addition,the constructed mechanism is mainly based on detailed mechanism,and the skeletal mechanism is insufficient,which seriously limits the application of aviation fuel in CFD.At the same time,polycyclic aromatic hydrocarbons(PAHs)and nitrogen oxides(NOx)in aviation kerosene combustion products have not been studied in depth.Therefore,this paper proposes to construct an aviation kerosene skeletal mechanism with wide application,compact and efficient structure,including PAHs sub-mechanism and NOx sub-mechanism,and apply it to CFD simulation to explore the combustion characteristics of aviation kerosene and the emission law of PAHs and NOx,so as to provide a theoretical basis for clean combustion and efficient utilization of fuel.The work of this paper mainly includes the following four aspects:(1)In this thesis,n-dodecane(n-C12H26),2,5-dimethylhexane(C8H18-25)and toluene(C6H5CH3)were selected to represent direct-linked alkanes,branched-paraffins and aromatic hydrocarbons in aviation kerosene,respectively,to construct aviation kerosene surrogate fuels.The ratio of each base fuel is determined by the characteristics of the real fuel,such as H/C ratio,molar mass(MW),etc.(2)Aiming at the problem that the skeletal mechanism of high-carbon alkane fuel is not accurate enough,a new skeletal mechanism construction method is proposed.The main ideas of this method are:(1)based on the detailed core mechanism of C0-C4,the skeletal mechanism of high-carbon fuel is constructed,which effectively ensures the prediction accuracy of fuel;(2).Through appropriate mechanism simplification methods,eliminate unimportant species and reactions,and simplify the detailed C0-C4 core mechanism,so as to ensure the simplification of the mechanism.(3)Based on the proposed new skeletal mechanism construction method,the skeletal mechanism is constructed for the base fuel to surrogate fuel.Then,the skeletal mechanism was simplified by direct relationship diagram method(DRGEP)and whole species sensitivity analysis method(FSSA),and a 725-step elementary reaction containing 122 components was obtained as an aviation kerosene skeletal mechanism.The PAHs mechanism and NOx sub-mechanism was added to the aviation kerosene skeletal mechanism,and finally the skeletal mechanism containing 169 components and 863 step primitive reactions was obtained.The mechanism was verified by experimental data such as ignition delay time,component oxidation concentration,and laminar flame velocity to ensure the effectiveness of the mechanism.(4)A two-dimensional simulation model was constructed,and the laminar flow combustion simulation study was carried out in conjunction with the skeletal mechanism,and the impact on different parameter conditions on the emission of PAHs and NOx was analyzed.The results show that the coupling skeletal mechanism constructed in this paper can effectively predict the combustion performance and emission characteristics of aviation kerosene,and the fuel mechanism of the model constructed has the advantages of concise and accurate,which is suitable for numerical simulation of aero engines.The new method proposed to this paper provides a new technical method of the mechanism construction of high-carbon fuels.The constructed mechanism can provide a numerical simulation basis of the design and optimization of aero engines,and also provide theoretical guidance of the safe and efficient operation of aero-engines and the reduction of pollutant emissions. |
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