2013 Proceedings of the Combustion Institute, Volume 28, 2000/pp. 2013–2020 COMPUTATIONAL AND EXPERIMENTAL STUDY OF AMMONIUM PERCHLORATE/ETHYLENE COUNTERFLOW DIFFUSION FLAMES M. D. SMOOKE, 1 R. A. YETTER, 2 T. P. PARR, 3 D. M. HANSON-PARR, 3 M. A. TANOFF, 4 M. B. COLKET 5 and R. J. HALL 5 1 Department of Mechanical Engineering Yale University New Haven, CT 06520-8284, USA 2 Department of Mechanical and Nuclear Engineering The Pennsylvania State University University Park, PA 16802, USA 3 Weapons Division Naval Air Warfare Center China Lake, CA 93555-6100, USA 4 W. K. Kellogg Institute Battle Creek, MI 49016-3232, USA 5 United Technologies Research Center East Hartford, CT 06108, USA We investigated the modeling of counterflow diffusion flames in which the products of ammonium perchlorate (AP) combustion were counterflowed against an ethylene fuel stream. The two-dimensional problem can be reduced to a one-dimensional boundary value problem along the stagnation point stream- line through the introduction of a similarity transformation. By utilizing recent developments in hydro- carbon, chlorine, NO x and AP kinetics, we formulated a detailed transport, finite-rate chemistry system for the temperature, velocity, and species mass fractions of the combined flame system. A detailed soot model is included which can predict soot volume fractions as a function of the strain rate and the fuel mole fraction. We compare the results of this model with a series of experimental measurements in which the temperature was measured with radiation-corrected thermocouples and OH rotational population distribution; several important species were measured with planar laser-induced fluorescence, UV-visible absorption, and Raman spectroscopies; and the soot volume fraction was measured with laser-induced incandescence and visible absorption spectroscopy. Introduction Many solid rocket propellants are based on a com- posite mixture of ammonium perchlorate (AP) oxi- dizer and polymeric binder fuels. In these propel- lants, complex three-dimensional diffusion flame structures between the AP and binder decomposi- tion products, dependent upon the length scales of the heterogeneous mixture, drive the combustion via heat transfer back to the surface. Changing the AP crystal size changes the burn rate of such propel- lants. Large AP crystals are governed by the cooler AP self-deflagration flame and burn slowly, while small AP crystals are influenced more by the hot diffusion flame with the binder and burn faster. This allows control of composite propellant ballistic prop- erties via particle size variation. Previous measurements on AP/binder diffusion flames in a planar two-dimensional sandwich config- uration have yielded insight into the controlling flame structure [1,2], but there are several draw- backs that make comparison with modeling difficult. First, the flames are two-dimensional in structure, making modeling much more complex computation- ally than with one-dimensional propellant systems, such as cyclotrimethylene trinitramine (RDX) self- and laser-supported deflagration [3]. In addition, lit- tle is known about the nature, concentration, and evolution rates of the gaseous chemical species pro- duced by the various binders as they decompose. This makes comparison with models quite difficult. Alternatively, counterflow flames provide an excel- lent geometric configuration within which AP/ binder diffusion flames can be studied both experi- mentally and computationally. While counterflow diffusion flames have been studied in recent years using experimental, theo- retical, and numerical techniques [4–10], there has been little work in which these tools have been ap- plied to the study of solid propellants in this config- uration. While some preliminary studies of AP coun- terflow flames were made by Friedman [11], Ablow and Wise [12], Inami and Wise [13], Wiersma and