Characterization of four-inlet ducted rocket engine geometries: An optical diagnostics approach

This dissertation develops and demonstrates a methodology to characterize the mixing and flameholding potential of four-inlet ducted rocket engine geometries. Water flow visualization was performed on various four-inlet ducted rocket engine combustor models over a range of flow rates and various geometries to investigate and characterize the internal mixing and flow field structures existing for each condition. The qualitative results from the flow visualization work were applied in the design and construction of a stainless steel combustor with optical access for cold gas and reacting flow tests.; Raman spectroscopy was performed using the optically accessible combustor to characterize the fuel distribution existing in the dome head of the combustor for both cold gas and reacting flow conditions. The tests were performed at flow rate parameter ranges and fuel injector orientations which matched those evaluated in the water flow visualization work.; A five-orifice fuel injector geometry was evaluated in two different orientations. The first orientation had fuel orifices aligned with the air inlet columns. This configuration resulted in two recirculation regimes, which were a strong function of the momentum ratio between the fuel and the air. One of the recirculation regimes was found to be acceptable only for high air/fuel momentum ratios. The second orientation, which was called interdigitated, had the fuel injector rotated 45 degrees so that the fuel jets were injected in-between the air inlet jets. This orientation resulted in consistent recirculation zones with favorable fuel concentration levels. It was found to be the preferred injector orientation.; The 60-degree same-station combustor and interdigitated fuel injector produced the most favorable flow field due to the flow stability in the aft section of the combustor and the strong recirculation zones existing at the head end of the combustor. This geometry produced favorable recirculation zones in the dome head with combustible fuel concentrations which resulted in stable flameholding during the reacting flow runs.; The water flow visualization study provided information which agreed well with the observations made on the optical combustor. The results demonstrate the validity of using water flow visualization to investigate the mixing processes of four-inlet ducted rocket engines.