Solid Motor Ignition

Solid Rocket Motor Ignition Model Using Loci/CHEM

The Loci/CHEM ignition model is based upon a simplified analysis of the chemical and heat and mass transfer processes occurring in the gas and condensed phases during initial propellant heating.

As the solid is heated and a thermal profile develops, the propellant begins to undergo condensed phase chemical reactions that result in product gases leaving the surface.  The gas flows away from the surface while exothermic gas phase reactions heat the products further, leading to more rapid reactions and a heat flux back to the propellant surface. The surface and gas temperatures increase rapidly until the reaction zone snaps back to the surface and steady state burning (ignition) is established.

The mathematical model considers the evolving thermal profile within the solid coupled with condensed and gas phase reactions that produce a heat flux back to the surface to predict the solid ignition time based on completion of the chemical reactions. The development and validation of this model is the subject of a NASA STTR research project (Advanced Flow Analysis Tools for Transient Solid Rocket Motor Simulations). The model is also in current production use by NASA/MSFC (Innovative Simulations for Modeling the SLS Solid Rocket Booster Ignition).

The example above shows the temperature contours in a solid rocket motor ignition simulation in which the igniter gas heats the solid while the gas and condensed phase chemical reactions contribute additional heat flux to the propellant. Progress of the solid ignition on the propellant surface is also illustrated by the gradual change in color from blue to red.

Read More About Solid Rockets

Learn more about solid rockets and thrust by reading NASA Glenn Research Center’s page on how a solid rocket works.