Flame Structure Simulation of Nonaluminized Composite Propellants

Paper number

IAC-06-C4.P.3.03

Author

Mr. Filippo Maggi, Politecnico di Milano, Italy

Coauthor

Dr. Luciano Galfetti, Politecnico di Milano, Italy

Coauthor

Dr. Francesco Miccio, The Netherlands

Coauthor

Dr. Luigi T. DeLuca, Politecnico di Milano, Italy

Year

2006

Abstract

Composite solid propellants are heterogeneous materials made by a blend of powders bound together by a polymer matrix. The propellant flame structure is affected by the nonhomogeneous nature of the solid phase because the combustion process is mainly driven by heat transfer in the condensed-phase and mass diffusion in the gas-phase. Actually, oxidizer and fuel gases are released separately from the burning surface and they must mix each other before flame can take place. \\
Oxidizer decomposition generates a premixed flame just above  the burning surface. Local temperature rises up to 1600-1800 K but combustion products of such reaction cause also the oxidation of fuel gases coming from the binder pyrolysis. Experimental observations suggest a laminar stream in the reaction zone; therefore, molecular diffusion is considered the main responsible for mixing. The diffusive flame is responsible for the largest fraction of heat release in gas phase and temperature rises up to almost adiabatic flame temperature for the current composition. The entire process is self-sustained by heat feedback to the solid phase.\\
Despite the presence of multidimensional effects was recognized long ago, combustion modelling was performed for several years with a set of 1D equations. Averaging and statistical approaches were used to include heterogeneous aspects into 1D models with a  loss of information about flame zone.\\ 
This work follows recent developments of multidimensional combustion modelling and describes a numerical characterization of the flame structure for nonaluminized AP-based composite propellants with a 2D combustion simulation. Combustion is performed over a realistic propellant microstructure simulated with a random packing algorithm. Chemical and physical heterogeneity of solid phase is taken into account by the model; absence of chemical reactions within the solid phase is assumed while consumption of different reactants on the burning surface is performed with two Arrhenius kinetic equations.\\
The fluid dynamics is described by inviscid diffusion-transport equations. Gas phase reactivity is included with the use of a reaction scheme made by six semi-global chemical species involved into three reactions. The kinetic parameters values for the model were taken from literature and from experimental measurements. Flame length as well as temperature fields, chemical species profiles and their trend in space and time are obtained as function of reactants placement in the solid phase. Studies upon flame structure of laminate and random-packed propellants are presented.

Abstract document

IAC-06-C4.P.3.03.pdf

Manuscript document

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