Heat Transfer And Cracking Characteristics Of Hydrocarbon Fuel In Cooling Channel Of Scramjet Engine

The aerocraft cooling problem has already become important along with the increasing flight Mach number. Scramjet engine works in combustion conditions of high velocity, high intensity combustion and high temperature, conventional materials may be limited in consideration of the cost and rear-service insurance of preparation and storage, as well as the limitation of aerocraft size, while high performance hydrocarbon fuel appears more superior. It may absorb heat substantially through physical heat capacity as well as chemical pyrolysis; and the reuse of captured heat in the high temperature part of aerocraft by burning the fuel in the combustion chamber offers an effective way to heat management. So the pyrolysis and heat transfer characteristics of hydrocarbon fuel appears great significance of the thermal protection of scramjet engine.In this paper,heat transfer and thermal pyrolysis characteristic of hydrocarbon fuel in active regenerative cooling channel of scramjet engine under supercritical condition was studied through experiments and numerical simulation, and emphasized the heat transfer deterioration and the phenomenon of high temperature pyrolysis of hydrocarbon fuel under supercritical condition, providing some numerical reference and empirical basis on the design of the thermal protection system of scramjet engine.Firstly, the physical model of the single channel in active regenerate cooling system of scramjet engine was established to study the heat transfer characteristic of pentane under different conditions of inlet temperature, mass flow rate, wall heat flux, inlet pressure. Emphasized heat transfer deterioration of pentane under supercritical condition, and the temperature of the inner wall surface and coolant were compared under different conditions to analyze the heat transfer conditions in cooling channel. The influence of different physical factors on the heat transfer deterioration was also studied. The boundary of heat transfer deterioration was obtained under the coupling effect of mass flow rate, wall heat flux, inlet pressure when the inlet temperature was 400K, and the relational expression of critical heat flux when heat transfer deterioration happens within a certain range was also obtained in this study. The results showed that the increase of pressure and the decrease of mass flow rate and heat flux were propitious to reduce the severity of heat transfer deterioration. Secondly, the dynamic mechanism of thermal pyrolysis of heptane was establish to simulate pyrolysis of hydrocarbon fuels in the cooling channel of scramjet engine under the different conditions of mass flow rate, inlet temperature, heat flux, which obtained the effect on the pyrolysis rate, distribution of pyrolysis products and flow and heat transfer characteristics by the above factors. The results showed that the increase of mass flow rate and the decrease of inlet temperature and heat flux wound reduce the pyrolysis rate of n-heptane and wall temperature.At last, the heat transfer characteristics of hydrocarbon fuels in the single cooling channel of scramjet engine under supercritical pressure were studied with experiment, which obtained the heat transfer deterioration and variations of inner wall temperature and heat transfer coefficient along the tube length under different heat flux. We also analysed it in the end.