Experiments are conducted to determine how acoustic perturbations affect the performance and flameholding of solid-fuel ramjets with nonstandard combustion chambers. The focus is on the effect of wall cavities carved in the fuel grain using additive manufacturing. An improved understanding of how the wall geometry contributes to the establishment of acoustic modes is sought. A novel combustion mechanism was developed using a counterflow burner to study the combustion and regression of solid model fuel polymethyl methacrylate. The diffusion flame between the fuel and oxidizer was studied numerically using a solid-fuel decomposition and melt layer model to simulate convection and pyrolysis of the material. This model was validated using new experimental data as well as previously published works. The foam layer parameters are critical to the success of the validation, showing that the increased residence time of the gas in the bubbles facilitates the fuel breakdown. Fourth-order computational simulations of ramjet combustion without regressing fuel walls using a novel discontinuous Galerkin approach are performed with a fully conjugate solution for the thermal wave in the solid. Turbulent transport strongly affects the heat feedback to the walls, and low-frequency vortical modes (e.g., with a vortical wavemaker) associated with a recirculation region at the injector upstream wall are linked to an increase in chamber pressure and fuel mass flux.
Investigation of neat polymers by TEM is often thwarted by their sensitivity to the incident electron beam, which also limits the usefulness of chemical and spectroscopic information available by electron energy loss spectroscopy (EELS) for these materials. However, parallel-detection EELS systems allow reduced radiation damage, due to their far greater efficiency, thereby promoting their use to obtain this information for polymers. This is evident in qualitative identification of beam sensitive components in polymer blends and detailed investigations of near-edge features of homopolymers.Spectra were obtained for a poly(bisphenol-A carbonate) (BPAC) blend containing poly(tetrafluoroethylene) (PTFE) using a parallel-EELS and a serial-EELS (Gatan 666, 607) for comparison. A series of homopolymers was also examined using parallel-EELS on a JEOL 2000FX TEM employing a LaB6 filament at 100 kV. Pure homopolymers were obtained from Scientific Polymer Products. The PTFE sample was commercial grade. Polymers were microtomed on a Reichert-Jung Ultracut E and placed on holey carbon grids.
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