Study on the Effect of Entrapped Propellant in the Loose Flap Region on Solid Rocket Motor Performance

摘要

Some segments cast for use in a large solid rocket booster indicated inadvertent propellant entrapment (50 to 700 gms) between the loose flap and fixed insulation during radiographic inspection. This entrapment could have occurred during the process of vacuum casting of the propellant. To assess the criticality of this propellant entrapment and its subsequent impact on the motor performance, a subscale simulation study was devised and two subscale motor tests were carried out. In both the tests, the entrapped propellant quantity, the loose flap slit opening, the ramp angle of fixed insulation etc. were simulated. In the first test, the connecting path from slit opening to entrapped propellant was simulated very closely to the observed scenario and in that test it was seen that flame could not propagate through the connecting path and the entrapped propellant in the pocket ignited only after motor burn out. In the second test, the connecting path from slit to entrapped propellant was made open thereby allowing flame to flash down into the propellant pocket. In this case, pressure spikes of about 1.8 ksc were observed on pocket ignition. However, when translated to the large solid booster, the pressure was seen to be negligible because of the much higher volume.