Studies On Flame-Spreading Mechanism In The Fin-Slot Region Of Solid Rocket Motors

Propellant grains with fin slots and submerged nozzles have been used in a variety of solid propulsion system because of its advantages such as: shorter overall length , larger burning surface area, nearly constant burning surface area over certain time period, etc. Flame-spreading process in the fin-slot region is of the potential influence on the behavior of the overall ignition transient, and the designers pay much attention to the performance match among many design limits such as : ignition pressure , chamber pressure , structural dimension of fin slots , submergence ratio and so on . So , the object of this dissertation is to obtain better understanding of the flame-spreading process and the gas-flowing law in a motor with submerged nozzle and fit slots , to study how the change of parameters influence the flame-spreading , and to develop an experimental correlation of flame-spreading speed to satisfy the need of engineering design . This dissertation develops a much complete experimental study and numerical calculation on the flame-spreading process in a motor with submerged nozzle and fit slots. High-Speed motion analyzer was employed to form the experimental system. A test motor was designed and produced, which is of the ability to adjust difference ignition energy, slot dimensions and submergence ratio. Two groups 23 motor tests with propellant on slot surface and non propellant on slot surface, have been done. The match of design limits among performance parameters and structural dimensions have been studied. The experimental correlation of gas filling interval and flame-spreading speed has been developed based on the test data. And the numerical calculations are carried out for the gas-filling process in the fin-slots during ignition transient. Considering above study, a mathematics model to simulate the ignition transient process of the motors with fin slots has been developed. The ignition transient process of an actual motor and the effects on parameter limits variety have been analyzed. The results show that: (1). This dissertation gives a better understanding to the flame-spreading process in the fin slots, and put forward the viewpoint of critical ignition pressure of slot for the first time. Flame-spreading process includs two stages: stage of gas filling and stage of flame-spreading. First, the gas fills in the slots rapidly. Then, when chamber pressure reaches to the critical ignition pressure of slot, the stage of flame-spreading is beginning. The critical ignition pressure of slot has a relationship with propellant property and structural dimension of slots. (2). The flame-spreading rate in slots has a relationship with propellant property, structural dimension of slots and pressurization rate at the opening of the slot region. The flame-spreading rate in the fin-slot regions is significantly lower than that of a typical circular bore region. The observed average radial flame-spreading rate is below 10m/s. (3). The numerical calculation results compare well with the experimental results. The calculation results simulate the gas-filling process during the ignition transient. The flow-field is in confusion before the chamber pressure is set up, and there is a surging trend in the total domain. After the chamber pressure is set up, the flow tends to a uniform pattern in the cylinder and nozzle domains, and the flow-field of the fin-slots is still in confusion. (4). The critical ignition pressure of slot was introduced into the mathematics model of ignition transient ,and the flame-spreading rate was considered simultaneously. The method of simulation for the ignition transient is convenient for the use of engineering design, and the calculation results compare with the actual results well. (5). Propellant property and nozzle closure opening pressure have an important effect on the ignition transient. Pressurization rate and ignition lag interval are restricted by propellant property, structural dimension of slots, and nozzle closure opening pressure. A lower nozzle closure opening pressure is an important factor to form a turn in chamber pressure during ignition transient.