Research On The Combustion Technology Of Solid Fuel Ramjet

Because of the advantages of high specific impulse, simple structure and good security etc, the application foreground of solid fuel ramjet (SFRJ) was extensive on supersonic missile and ramjet assisted projectile, but the combustion technology of SFRJ was still in the stage of exploring. Research on the combustion technology of SFRJ including swirl flow combustion, the fuel mass flow regulation and test methods was carried out systematically by means of theoretical analysis, numerical simulation and direct-connect test.Based on the characteristic of SFRJ inner flow field, the numerical simulation model of turbulent flow and combustion was established, the inner surface of solid fuel was treated as mass flow inlet, the fuel regression rate computation model of HTPB (hydroxyl terminated polybutadiene) was established based on its thermal pyrolysis behavior, and the average fuel regression rate obtained from the numerical simulation accorded with the test results, which verified the numerical simulation. Two types of aftburning chamber were numerically analyzed, including the mixed plate type with a round orifice at the inlet of aftburning chamber and lengthening fuel type with solid fuel added in the aftburning chamber. It was concluded that, the mixed plate type was better if the afterburning chamber length was shorter and the work time of the ramjet was longer, otherwise lengthening fuel type was better.The swirl flow in SFRJ was systematically researched by means of numerical simulation, including the swirl number calculation in the inlet of spinning SFRJ assisted projectile, the swirl cold flow field in the SFRJ with axial swirler, the swirl flow effects on the performance of axisymmetric nozzle, the fuel regression rate and combustion efficiency of SFRJ with swirl flow. It was concluded that the swirl at the front and outlet of the spinning ramjet assisted range projectile inlet was weak swirl flow. Under the condition of swirl flow, the center back flow and the back flow after the step of the dump SFRJ combustor took heavy weight of the whole total pressure loss, and the total pressure loss downstream of the center back flow could be neglected. The flow coefficient, vacuum thrust coefficient and specific impulse of axisymmetric nozzle were not changed under different swirl intensity contrast to the straight flow, used the axial mass everage total pressure at the nozzle inlet. Because of the axial velocity near the fuel surface of swirl flow was faster than straight flow, the fuel combustion time and combustion efficiency of swirl flow was lower than straight flow.Three methods of fuel mass flow rate regulation for SFRJ were numerical studied, including the tube-in-hole method, the annulus style inner bypass method and gear style inner bypass method. It was concluded that heat protection was needed at the downstream part of the tube-in-hole. The combustion in the dump afterburning chamber of annulus style inner bypass method was still controlled by diffuse, while the gear style could induce couples of symmetrical vortexs in the head of dump afterburning chamber, which could enhance the mixing and combustion effect of unburned fuel and bypass air, and the total pressure loss was approach to the annulus style, thus the combustion performance of gear style was better.An oxygen/ethanol spark torch igniter and vitiated air heater for SFRJ direct-connect test were designed and tested, the tests showed that the spark torch igniter could work relative long time and the temperature at the outlet of vitiated air heater satisfied the test demand. The SFRJ direct-connect test was carried with pyrotechnic igniter and spark torch igniter respectively, and the pressure curves in the start-up stage of SFRJ test with spark torch igniter was smooth. The swirl flow and direct flow combustion characteristics of HTPB contained metal particles (Al-40%, Mg-25%) were studied with direct-connect tests, and the flame stability of swirl flow, the pressure in combustion chamber, the average fuel regression rate and the combustion efficiency were analyzed. The swirl flow flame stability and combustion efficiency agreed with the numerical simulation results of pure HTPB, which validated the numerical simulation indirectly. The average fuel regression rate in the tests was much higher than the pure polymer, which indicated that adopting compound polymer fuel was effective to enhance the fuel regression rate of SFRJ.