| The solid scramjet,as a new type of hypersonic vehicle combined propulsion power unit,is one of the most promising types of engines at present.In order to improve the ignition and combustion performance of the solid scramjet,this paper carried out the research on the combustion enhancement technology of the solid scramjet based on the cavity,direct-connect tests and numerical simulation are carried out.Numerical simulation is used to analyses the effect of cavity layout and cavity shape on the mixing and combustion of solid scramjet.Based on the requirements of mixing and combustion,a lobe cavity is proposed based on the flame-stable cavity.The longitudinal vortex generated by the lobe structure can enhance the mixing and combustion of fuel-rich mixture and air.The analysis shows that the Mach number of the combustor shows the characteristics of decreasing-fluctuating-rising along the flow direction.Compared with the near-wall combustion in the non-/single-cavity configuration,the two-cavities configuration realizes the combustion in the center.The gas and particles in the fuel-rich mixture are burnt separately due to the different penetration depths.The gas combustion speed and combustion efficiency are much higher than the particles.The particle mass causes a difference of the motion trajectory,but the difference is gradually smaller as the particle combustion.When the two-cavities configuration is arranged,the cavity configuration has no obvious effect on combustion,but the lobe cavity has the ability to enhance the uniformity of the flow field.The arrangement of the cavity has a significant impact on the blending and combustion of the solid scramjet.When there is no cavity,the combustion efficiency is only 0.48 and the total pressure loss is 0.67,while when the two-cavities is used,the combustion efficiency is 0.98 and the total pressure loss is 0.58.Based on the results of numerical simulation,according to the test requirements,a modular test platform for solid scramjet is designed and built,and the combustor configuration can be changed by replacing some components.A symmetric rectangular solid scramjet with multiple cavities and multiple gas generators was designed and its operating characteristics were working characteristics.In a multi-cavity combustor,the combustion state expands from the cavity to the center of the flow channel.The microstructure of combustion products was analyzed by SEM,and the particle size is on the order of micrometers.Due to the change in the combustion area of the propellant and the deposition of the throat in the gas generator during the test,the equivalence ratio gradually increased from 0.54 to 0.63.The performance of the solid scramjet increased during the test,reaching a combustion efficiency of about 42%,a total pressure recovery coefficient of 0.35,and a thrust gain specific impulse of about 418 s.On the basis of the symmetrical rectangular solid scramjet,the influence of cavity configuration and injection structure(shape,quantity,angle)on the ignition and combustion of the solid scramjet was investigated using direct-connect tests.The results show that the special-shaped cavity(narrow/lobe cavity)can improve the mixing and combustion,the combustion efficiency is increased from 0.41 to 0.48,and the total pressure recovery is about 0.36.The narrow/lobe cavity shows the potential to improve the mixing and combustion,but its shape characteristics will cause the thrust to drop.The results show that,the injection structure has a significant effect on the ignition and combustion of the fuel-rich mixture.The combustion efficiency is increased from 0.48 to0.60,and the total pressure recovery coefficient is about 0.33.In all the tests,the performance of the combustion in the solid scramjet presents the typical cycle of establishment-development-maintenance-decay.Numerical simulation and tests result all pointed out that the low particle combustion efficiency is a key factor limiting solid scramjets performance. |
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