Research On The Characteristics Of Regenerative And Film Cooling For Hydrocrabon Fueled Scramjet Engines

Air-breathing vehicles with hypersonic speed will encounter severe thermal protection problems because of the high heat load coming from the supersonic combustion and aerodynamic heating. To protect the engine, active cooling is usually adopted. Besides the sensible heat capacity, extra heat sink from chemical reactions of endothermic fuels is also used to provide thermal protection. And to point it out particularly, the high temperature of hydrocarbon fuel still has the potential to insult the heat coming from the main stream through film cooling. Therefore, the combined regenerative and film cooling is proposed in this paper. The combined cooling process with endothermic fuel is a chemical reacting flow and heat transfer process, and furthermore, a n energy recovery process. Therefore, it is of great importance to investigate the flow and heat transfer characteristics of the combined regenerative/film cooling system, as well as the effect of the engine design parameters on the heat transfer and energy recovery. Related work has been carried out and listed below:A 3-D model of transcritical n-Decane which takes real gas properties of fuel and cracking reaction into consideration is established and validated through our own heat transfer experimental platform. Based on the numerical model, the coupling relationship between fuel velocity, temperature and cracking reaction is preliminarily examined. It is found that thermal stratification is a serious problem in scramjet cooling channels, causing severe stratification of fuel conversion.The regenerative cooling is a special energy process. Stratification of physical and chemical heat sink induced by thermal stratification in the cooling channel are investigated. It is found that physical and chemical heat sink stratification which are induced by thermal stratification are severe, which will exert negative effect on energy recovery. By carefully analyzing the influential factors of heat sink utilization in a regenerative cooling system, it is found that its design parameters are the key influential factors. It has been found that in the non-cracking zone of cooling channel, there’s an optimum channel aspect ratio, which would minimize thermal stratification and be good for energy recovery. While in the cracking zone, the smaller channel aspect ratio can result in more chemical heat absorption and less severe thermal stratification and thus be good for chemical recuperation.Through a series of coupling numerical investigations of transcritical flow and heat transfer with cracking reaciton in regenerative cooling channels,the dual mechanism of heat transfer deterioration caused by severe thermal stratification and dual effect of cracking reaction on heat transfer are revealed. The special heat transfer deterioation mechanism and chemical reaction makes the optimum channel aspect ratio of regenerative cooling channel with endothermic hydrocarbon coolant stay at a small value. The change of fuel thermophysical properties caused by pressure variation and change of coolant type can change the optimum channel aspect ratio.A method to multiuse the cooling capacity of endothermic hydrocarbon fuel which combines the regenerative cooling and film cooling is proposed. Through numerical simulation and experiments, it has been found that using the high temperature hydrocarbon fuel as the cooling film can effectively lower the wall temperature. It is discovered that the cracking reaction has dual effect on the film cooling: the cracking reaction can lower the temperature of the film through chemical reaction and that’s good for cooling, it also promotes the turbulent mixing and that’s bad for cooling. The equilibrium of the beneficial and unfavorable aspects brought by chemical reaction determines the overall effects of film cooling. Increasing the injection Mach number and thickness of film will increase cooling efficiency while the beneficial aspects from cracking reaction are reduced and unfavorable aspects are strengthened. It is also discovered that for the film cooling with cracking reaction, the unfavorable influence of shock waves on film cooling is significantly reduced.