Investigation On The Performance Characteristic Of The Solid Fuel Scramjet Combustor

The solid fuel scramjet is one of the most popular propulsion devices for Hypersonicflight vehicle because of its advantages such as the simple structure, easy storage, rapidreaction and so on. Hence, the solid fuel scramjet seems to be advantageous for certainmissions in the hypersonic flight regime. The solid fuel scramjet generally consists of inlet,isolator, combustor and nozzle. And the combustor is the active components provided thethrust. The supersonic combustion process in the solid fuel scramjet is essentially highvelocity, unsteady and turbulent; additionally, the pyrolysis and the combustion of the solidfuel is a complex physical and chemical process which can result in complicated flowfieldstructures. So the combustor performance plays an important role in the development of thesolid fuel scramjet. The merits of the combustor’s performance will finally make thedecision that whether the solid fuel scramjet can get the engineering application or not.Hence, it is necessary to study the characteristics of solid fuel scramjet combustor workingprocess.The mathematical model is built in this paper to investigate the characteristics of thesolid fuel scramjet combustor. The governing equation is simplified as two-dimensionalaxisymmetric form. The solid fuel regression law is defined by using defined function. TheSST k-ω turbulence model is used for closuring the Navier-Stokes equations. Thecombustion model uses the combined of the Finite-Rate model and the Eddy-Dissipationmodel. Based on this mathematical model, the typical solid fuel scramjet combustor issimulated by a steady numerical method. The numerical results and the experimental dataare compared in terms of the wall pressure and the fuel regression rate, which validates themathematical model. By changing the structure parameters and the inlet flow parametersrespectively, the working process of the solid fuel scramjet combustor is investigated by asteady numerical simulation. In order to go on a further study of the solid fuel regressioneffect on the flowfield characteristics and the performance of the combustor under thesupersonic coming flow, the unsteady working process of the solid fuel scramjet combustoris decomposed into several steady working process to achieve the quasi-steady numerical simulation of the solid fuel scramjet combustor. Finally, there is a introduction of a smalldirect connected solid fuel scramjet text system.Based on the physical and mathematical model of the solid fuel scramjet combustor,the influence of the flameholding/cavity section, cylindrical section and diverging sectionon the combustor performance is investigated respectively. Firstly, a numerical simulationof a non-reactive supersonic flowfield in solid fuel scramjet combustor was presented.Compared with the combustor without cavity, the combustor with cavity was found to beable to enhance the mixing efficiency apparently. And there exists a best cavity structure toget the best mixing efficiency of the combustor. It reveals that there exists an appropriatecavity structure regarding the mixing or combustion efficiency and the total pressure loss.Secondly, the study describes the numerical investigations concerning about thecharacteristics of the flow field in the solid fuel scramjet and the combustor performancewhen the structure parameters of the cylindrical section and diverging section are changedrespectively. The numerical simulation results indicate that on the premise of non choked,when the diameter of the cylindrical section changes, the smaller diameter of the cylindricalsection, the better of the combustor performance is. When the length of the cylindricalsection changes, the longer of the the cylindrical section, the better of the combustorperformance is. Furthermore, if the length of the combustor needs to be increased, it’s betterto increase the length of the cylindrical section rather than increase the length of thediverging section. The combustor with a longer and thicker cylindrical section has a greaterpotential working capacity.And then, The influence of inlet airflow parameters on the combustor performance isresearched. The results shows that two parameters of the inlet airflow which are the inletairflow mass rate and the inlet airflow total pressure have a greater effect on the combustorperformance. On the premise of the auto-ignition and stable combustion of the flame in thecombustor, within a certain range of combustion efficiency, increasing of the inlet airflowmass rate will improve the performance of the solid fuel scramjet combustor, such as asmaller total pressure loss. Although increasing of the the inlet airflow total pressure canincrease the combustion efficiency, it can also result in a bigger total pressure loss. Thebiggest impact factors of combustion efficiency are the inlet airflow total temperature and the diameter of the cylindrical section. And the biggest impact factors of total pressure lossare the inlet airflow mass rate, the inlet airflow total pressure, the diameter of thecylindrical section and the length of the diverging section.The quasi-steady numerical simulation of the combustor working process has done.Compared the numerical results with the foreign experimental results, further proof of themathematic method is correct and suitable. the quasi-steady numerical results indicate thatthe combustor is choked at the initial moments, and the state of choked will disappear asthe regression of the solid fuel during the combustor working process. In the middle andlater periods of the working process, the flowfield of the combustor is relatively stable, andthere is a shock train in the mainstream area. Interaction between the waves with the cavityshear layer or the wall boundary layer result in the complicated flowfield of the combustor.In the working process, the combustion efficiency is increasing, the minimum valueappears in the initial period of the operation, and the maximum value is about80%in thethe middle and later periods of the operation. The pressure along the wall, the regressionrate, the combustor thrust and specific impulse all decrease with time.Finally, a combustion experiment of solid fuel scramjet has been successfullycompleted based on a small direct connected solid fuel scramjet text system.