The aim of this work is to present a mathematical formulation for analysis of the ignition transient phenomena happening in large solid rocket motors(SRM). Currently, the analysis methodology is based on one dimensional prediction coupled with semi-empirical heat transfer for the igniter gases to propellant surface. The actual phenomena are complex and to predict the flame initiation at different surface zones, flame spreading followed by complete ignition of the propellant surface. The igniter design is based on the NASA SP semi-empirical formulae and 1 D studies. These studies will not help in predicting the ignition transient for the complex grain geometries.
The ignition transient prediction in solid rocket motors is very critical to define the unsteady pressurization rates, over-pressurization, hang-fires, dynamic loads & pressure loads on the propellant grain. These individual component’s definition is critical for the efficient functioning of the rocket motor. Semi-empirical formulae shall be used for preliminary configuration, but the numerical simulation model is essential for predicting these complex phenomena and is critical in the initial design phases.
The improper design of igniter with semi-empirical formulae resulted in multiple failure modes in the rocket motor design history. Earlier days, the designs were done with semi-empirical formulae or based on experience from earlier designs owing to the inadequate computational tools. Typical failures are pressure fluctuations to and fro of the chamber during igniter operation until nozzle closure ejection which lead to early nozzle closure ejection results in hang fire, slow thrust build up. These resulted in the missile or rocket systems disengaged from the missile lockpin of the launcher, fallen back on the launcher and failure at the launch pad itself. One more type of failure is due to excess igniter mass flux leading upto over pressurization of the chamber and failure of the rockets during the ignition phases. The pressurization rates also play an important role in the propellant dynamic loading rates resulting in failure. Accurate pressurization rates are an important information from the ignition transient modelling. These reasons motivated to work on the particular problem.
• Multifluid Modelling (Igniter gas, Propellant gas phase &Diluant Gas (N2) which are simulated )
• Radiation modelling with the individual species radiation properties
Heat transfer at the surface has to be modelled along with the gas phase to simulate the ignition. Igniter propellant composition is different from the motor propellant composition. The burning rates of the igniter is far higher than the motor propellant burn rates to achieve faster ignition. The above approach will be helpful for modelling the gas heat transfer on to the propellant surface. The particle phase of the gases will be attempted to be included in the last phase after validation of gas phase heat transfer.