Research On Regeneratively Cooled Characteristics Of Subsonic Ramjet With High Mach

Ramjet presses air by flying forward,so it doesn’t consist rotating components comapared to turbojet engine.The advantages of ramjet include the simpler structure,lighter,higher thurst-weight ratio,lower cost,etc.Traditional cooling method will fail with the increase of the flying velocity especially after the mach number exceeding 4.5 which means the total temperature of incoming flow exceeds1100 K.The regenerative cooling will be an optional method.The selection of fuel will act fatal effects on the ramjet regenerative cooling process with the request for long time working.Though the ramjet with hydrogen fuel generates higher specific impulse than carbon-hydrogen fuel,carbon-hydrogen fuel is generally used in ramjet because hydrogen has the disadvantages of low density,large volume of storage,hydrogen embrittlement,etc.Carbon-hydorgen fuel needs fewer volume to storage and offers extro heat sink when cracking by heating,which is very suitable for high Mach number aircraft.During the process of regenerative cooling thermal protection,the fuel which is burnt inside the combustor chamber flow through the cooling channels of the combustor and nozzle as coolant.The inner wall of combustor and nozzle are cooled while the fuel is heated with high temperature coming out of the cooling channels,then injected into the combustor to burn.Thus the energe form the cooling channels come back to the power cycle.The first purpose of this project is to research the burning,cracking,coking,heat transfer characteristic of novel carbon-hydrogen fuel with high energe and high density.After that,the second purpose is to evaluate the applicability on long time working high speed sub-cumbustion ramjet.At last,design reasonable configuration which can solve the thermal protection problem.All those purposes means very important guiding signigicance for the design of subcombustion ramjet on the near space aerocraft.The main aspects of this paper are as following:(1)Research on the thermal environment of ramjet.Base on the working range of ramjet,obtain the relatively accurate thermal environment by numerical simulation and experiments.The thermal environment is basic requirements for cooling system design.(2)Research on the regenerative cooling technology.It is hard to analysis the heat transfer because the composition is complicated while the heated carbon-hydrogen may be liquid,supercritical,cracking state,etc.In this paper,the heat sink,cracking,coking,heat transfer characteristic are analysis through electrical heating experiment system.Then provide basic evidence for structure design of regenerative cooling by analysis relevant parameters(such as coolant quantity of flow,material and thickness of inner wall,size of cooling channels,etc.).(3)Research on matching of regenerative cooling system and ramjet.Analyze the process of regenerative cooling system,composition of cooling system,design and optimize of running parameters.The cooling system should match the ramjet inside the whole work range.(4)Research on regenerative cooling structure design technology.Rationality of the cooling structure design is the key to the cooling effect and system security.So the main aspects of this part includes the selection of material,structure design,strength check,etc.(5)The regenerative cooling applicability is evaluated through prototype experiment.The following innovative achievements are obtained after the above research:(1)An novel thermal protection method is proposed.Regenerative cooling is used as an novel thermal protection on the sub-combustion ramjet.The thermal protection method and organization of fuel combustion are different from other subcombustion ramjet.In the regenerative cooling method,the ramjet fuel act as coolant and pressurized by pump,then flow through the cooling channels in the wall of combustor and nozzle.Thus the combustor and nozzle are cooled by the fuel while the fuel is heated inside the cooling channels and then goes into the combustor chamber to be burnt.(2)Research on the heat sink,heat transfer,cracking,coking characteristic of the new high density carbon-hydrogen fuel for the first time.The temperature measurement accuracy is improved by adjusting the thermocouple temperature test method.The relationship between the heat sink and temperature is derived according to the test results.The cracking and coking characteristic are analyzed by differentical pressure method,which shows that the carbon-hydrogen coking rate is low under 600℃ and it is suitable fuel for regenerative cooling.(3)The performance and applicability of high density carbon-hydrogen are evaluated.The comprehensive evaluation is derived from the aspects of burn,heat sink,heat transfer characteristic,etc.based on the long-time and large-range ramjet running characteristic.The regenerative cooling combustor and nozzle is cooled effectively with the fuel and ramjet temperature from the simulation and experiments.