Research On Combustion Characteristics Of Solid Fuel In Scramjet Combustor

There were lots of advantages in solid-fuel Scramjet like high specific impulse and low structural complexity,but the difficulties about supersonic combustion organization and stability has come with it,which means the complex process of phase transformation,decomposition,vaporization and combustion on solid fuel must be completed quickly in the tangential supersonic flow.In this process,the mechanism of heat and mass transfer on solid fuel and the basic problems of combustion stability need to be research in some new way.In view of the above problems,through the combination of theoretical research,numerical simulation and experiment,the regression process of solid fuel and the influencing factors in combustion characteristics were studied.First,in reference on the basis of relevant knowledge in other fields,the solid fuel combustion process in supersonic flow has been described from the view of the analysis on the thermal behavior of solid fuel in supersonic flow.Then by use of the theoretical analysis,the regression rate prediction model were established.Based on this,the regression rate model has been embedded in the FLUENT through User define Function,which was proposed for the SF-Scramjet combustion process numerical simulation and verified between the literature test data.Second,the steady numerical simulation were studied to compare the combustion characteristics under different inlet parameters(total temperature,mass flow rate).The influence of flow and configuration parameters variation on regression rate were analyzed and the regression rate formula was fitted which can be used for engineering design.It was found that the inlet mass flow of air?stagnation temperature and depth of cavity has a great impact on the regression rate,then the impact of the length of cavity was slightly smaller,the impact of the stagnation pressure was minimum.Third,the ground direct connected test bench was built.It was proved that the combustion chamber can be self-ignition and has a great flame stability under the condition of mach number 6 and mass flow rate 500g/s?1000g/s.The SF-Scramjet combustion process was analyzed by means of the reference configuration,and through other configuration test,the influence of configuration factors on the combustion process,like cavity size?un-cavity structure ?divergence angle,were contrasted.The results show that in the combustion process,the peak area of regression rate is at the junction of the cavity and cylindrical section.When the combustor continued to burn,the diameter of cylindrical section was enlarged,until almost into a whole finally.Meanwhile,the cavity is the necessary structure for the SF-Scramjet stable operation,and the sudden expansion step at the entrance of combustor cannot be completed for the flame stable,which may cause the increasing of the fuel consumption and total pressure loss.Fourth,through the transient numerical simulation method,the ignition characteristics of SF-Scramjet combustor were studied and the different mechanism between the ignition and stable combustion stage was analyzed.And then,by means of unsteady numerical simulation based on the dynamic mesh technique,the dynamic process of burning surface regression in SF-Scramjet was researched.Two kinds of configuration combustor,which was stable and non-stable,were compared.The results show that the size of the cavity was the main reason when the combustor cannot work properly.Fifth,considering the time cost,the quasi-steady method was adopted to replace the unsteady method,and the feasibility was verified.Based on large numbers of numerical simulation,the effect of inlet parameters and configuration parameters on the combustion were evaluated.In addition to the inlet total pressure and diameter of cylindrical section,the rest of the parameters were all negative correlation with the combustion efficiency.By using of numerical fit method,the relationship between the combustion efficiency and parameters was obtained.Especially,the influence of the L/D ratio in cavity has been presented a formerly positive but latterly negative relationship.Through the definition of cavity residence time,the performance of different configuration was analyzed.At the same time,the thrust and specific impulse of the combustor were calculated.At last,from two aspects of the combustion efficiency and total pressure loss,the sensitivity of all parameters was evaluated.The results show that the total pressure and diameter of the cylindrical section has a significant influence on this two aspects.