An Ignition Transient Model for Solid Propellant Rocket Motors

Ignition transients are a very important practical aspect in the design of solid propellant rockets, for the prediction and control of dynamic loads on the motor and on the entire vehicle. The present study is detailing a simple model and the relative numerical solution method for the analysis of ignition transient in solid propellant motors. The model is capable of providing an accurate and reliable prediction of the most significant engineering quantities (pressure and velocity in the thrust chamber) for different rocket configurations, for which currently available methods are yielding relatively unsatisfactory results: this would allow for an effective preliminary design of the motor, minimizing the need for experimental tests. A theoretical quasi-one-dimensional model is derived from basic conservation laws, taking into account the initiation of combustion by the igniter discharge signal, the heat transfer from igniter combustion products to the propellant grain surface, the flame spreading flow field in the chamber and the increase of chamber pressure up to to the quasi-steady operating condition. The set of modeling equations are then solved using a slightly modified Lax-Friedrics method. Sample results are presented for typical solid boosters of the Ariane family (Ariane 4 and Ariane 5).