Computational and experimental study of ammonium perchlorate combustion in a counterflow geometry

We investigate the structure of ammonium perchlorate (AP) counterflow diffusion flames in which the products of AP combustion are counterflowed against a methane fuel stream. Computationally, the twodimensional set of governing equations is reduced to a one-dimensional boundary value problem along the stagnation point streamline through the introduction of a similarity transformation. Utilizing recent developments in hydrocarbon, chlorine, NO _x, N_xH_y, and AP kinetics, we formulate a detailed transport, finite-rate chemistry system for the temperature, velocity, and species mass fractions of the combined flame system. We compare the results of this model with a series of experimental measurements in which the temperature is measured with radiation-corrected thermocouples and the OH rotational population distribution, and several important chemical species, including OH, CN, NH, NO, CH₄, and O₂ are measured with planar laser-induced fluorescence (PLIF), emission spectroscopy, and Raman spectroscopy. Both the model and the measurements reveal a multistage structure within the counterflow system comprised of an AP decomposition flame (above the AP surface) followed by a methane AP-products diffusion flame. The calculated temperature profile is predicted to be in excellent agreement with the OH rotational temperature measurements. Measured peak CN concentrations match the spatial location predicted by the model exactly. The kinetic mechanism is able to resolve the two experimentally observed NH peaks, one very close to the AP surface, near their proper relative intensities. Quantitative OH concentration measurements are in very good agreement with the corresponding calculated profile, matching in spatial location, and differing by 17% in peak value. Quantitative NO measurements match the corresponding calculation, with both revealing a two-tiered structure. Low number densities and spectral broadening at high temperatures result in poorer agreement between the Raman measurements and the corresponding major species calculations, although fuel methane and AP-generated oxygen consumption are measured with reasonable agreement.