Investigation Of The Simplified Mechanism For Aviation Kerosene Multi-component Surrogate Fuel

For the RP-3 kerosene combustion process of aero-engine combustor,the simplification of the chemical dynamic mechanism for the RP-3 kerosene is one of the important problems in the numerical simulation of combustion process,It plays a key role during computational fluid dynamics(CFD)simulation of RP-3 kerosene combustion,such as reducing the stiffness of convergence,increasing computational efficiency,as well as leading the chemical reactions into more complex turbulent combustion problems.This paper presents two research directions: the simplification mechanism of three-component surrogate fuel and the simplification mechanism of two-component surrogate fuel.For the simplification mechanism of three-component surrogate fuel,firstly,the 73% n-dodecane,14.7% 1,3,5-3 methyl cyclohexane and 12.3% n-propyl benzene were regarded as one of the three component surrogate fuels for the RP-3 kerosene.Three steps were taken in the Hydrocarbon Fuel Detailed Mechanism Simplification Program(ReaxRed)to simplify the semi-detailed chemical reaction kinetics model of the three component surrogate fuels.The semi-detailed chemical reaction kinetics model contains 257 species and 874 elementary reactions.During the first step,the Directed relation graph(DRG)was applied,and the first model which contained 109 species and 423 elementary reactions was obtained.Then the Directed relation graph based on error propagation(DRGEP)and computational singular perturbation(CSP)were used on the basis of the first model,and the second model which contained 84 species and 271 elementary reactions was gotten.Finally,the path analysis was adopted,comparing the detailed mechanism with the second model,some non-essential response paths(The chemical reaction rate is very small under the condition of this paper)were removed or some important paths which were removed mistakely during the simplification were added again.The three-component surrogate fuel simplified mechanism which contained 59 components and 158 elementary reactions was obatined finally.Then for the simplification mechanism of two-component surrogate fuel,firstly,92%(the molar fraction)n-decane and 8% positive propyl benzene were regarded as one of the two-component surrogate fuels.Two steps were used for the two-component surrogate fuel detailed chemical reaction kinetic model which contained 308 components and 1865 elementary reactions.The first step,the Directed relation graph(DRG)was applied for the detailed mechanism,and the simplified mechanism of A scheme was selected as the next research object based on the ignition delay time which is in good agreement with the experimental data.And then,the path analysis was also adopted during the nextstep,comparing the detailed mechanism with the simplification mechanism of A scheme,some non-essential response paths(The chemical reaction rate is very small under the condition of this paper)were removed or some important paths which were removed mistakely during the simplification were added again.The two-component surrogate fuel simplified mechanism which contained 62 components and 194 elementary reactions was gotten.In order to validate the two simplified mechanisms obtained above.The ignition characteristics,flame propagation,concentrations of various intermediate free radicals,release rate,adiabatic flame temperature and etc were selected to verify these two simplified mechanisms of this paper.Based on the comparison,the results of three-component surrogate fuel simplified mechanism was better than that of two-component surrogate fuel simplified mechanism.In order to verify the capability for numerical simulation of engineering combustion problems by using the three-component surrogate fuel simplified mechanism,a pre-mixing pre-evaporation Bunsen burner whose fuel is the RP-3 kerosene was designed firstly.The pre-mixing pre-evaporation combustion flame of Bunsen burner was measured.The experimental results show that the laminar flame would convert into the turbulent flame with the increase of inlet Reynolds number,therefore,the critical Reynolds number of the transition from the laminar flame to the turbulent flame is 1150.The temperature and gas component concentrations of the combustion flame at the center axis and different radial directions were measured under different inlet conditions respectively,the three inlet conditions were lean combustion,stoichiometric combustion and rich combustion separately.Finally,the simplified mechanism of the three-component surrogate fuel for RP-3 kerosene was used to numerically simulate the premixed combustion flame of the Benson burner,by the comparison of results,the numerical simulation results were in good agreement with the experimental results,therefore,it shows that the simplified mechanism of the three-component surrogate fuel for RP-3kerosene which was obtained in this paper can be used to numerically simulate the engineering combustion problems of RP-3 kerosene.