Research On Autoxidation Coking Characteristics Of Aviation Kerosene RP-3 In Typical Pipeline

With the continuous development of aeroengine technology,the continuous improvement of performance leads to the rising pressure ratio and the continuous increase of the outlet temperature of the compressor.The fuel system is heated by high-temperature air and the fuel temperature is increased.At the same time as a cooling source of fuel is widely used to cool the aircraft’s electronics,oil and other devices,resulting in increased fuel temperature.Excessive fuel temperature causes a series of physical and chemical changes in the fuel to produce coking,affecting the normal operation of the engine.In addition,with the development of the aviation industry,the requirements for the environmental protection of the aeroengines are also constantly increasing.In order to achieve the goal of environmental protection,advanced aero-engines widely use low emissions combustion chamber.Low emissions combustion chamber compared with the traditional combustion chamber,the combustion organization is more advanced,and the structure is more complex.Complex structure brings new challenges to coking protection.For aeroengines,improving component life while ensuring performance and safety is one of the key target of design.For components such as fuel nozzles and heat exchangers that are prone to coking,research into the physical properties of coking products(ie coke)helps to understand coking mechanisms.At the same time,the research on the law of decay of coked component performance needs to be based on the study of autoxidation coking characteristics and coke physical properties.In conclusion,in this paper,the thermal protection technology of fuel nozzle in low-emissions combustion chamber is taken as the research background.Thermal properties of coking products and the autoxidation coking characteristics of RP-3 aviation kerosene in the typical pipeline of fuel nozzle with low emissions combustor are studied,coking characteristics are summarized and the influence of structure parameters,flow rate and other parameters on coking characteristics are analyzed.In order to provide technical support for the design of the thermal protection scheme for fuel nozzles in low emissions combustion chamber.In this paper,two typical structures of"sharp bend"and"slow bend"are proposed according to the typical structure of the fuel nozzle in a low emissions combustion chamber,and their flow and heat transfer characteristics are numerically simulated.Based on the test method of constant ambient temperature,a test scheme and a autoxidation coking test system was set up,and two typical structural test rig of helix tube and L-shaped tube were designed to test the coking characteristics of RP-3 aviation kerosene under two kinds of structures.In addition,the properties of coking products were studied.The physical properties and the morphology of the coking product were measured,the empirical relationship of the specific heat capacity of the coking product,and the thermal conductivity with temperature was fitted.The main conclusions are as follows:the outlet temperatures of L-shaped tube and helix tube decrease with the increase of inlet flow rate;The wall temperature of L-shaped tube decreases with the increase of inlet flow rate;The coke volume rose rapidly right after the bend region,the peak appeared sharply ahead of the straight tube;The coke volume in the bend region maintained a high overall level after the peak and began to decline in the exit straight region;coke volume distribution of the helix tube along the passage showed a double peak structure and the location of the first peak appeared ahead of the straight pipe.In both structures,the coke volume distribution along the passage and the total coke volume decreased with the increase of the inlet flow velocity;the coke volume in the helix tube,L-shaped tube and straight tube is in a decreasing manner The results of sub-region coke volume study showed that there was no significant difference in the coke amount between the curved sub-region and the straight sub-region.The microstructure of the coke was the accumulation of spherical particles and there are pores and cracks on the surface of it,which has an envelope density of approximately1049kg/m~3,a real density of approximately 1498kg/m~3 and a porosity of approximately 29.9%,the specific heat capacity of coke is about 1.1~2.2J/g·K and the thermal conductivity is about 0.19~0.28W/m·K,both increase with the increasing temperature.