Experimental investigation of paraffin-based fuels for hybrid rocket propulsion

Solid fuels for hybrid rockets were characterized in the framework of a research project aimed to develop a new generation of solid fuels, combining at the same time good mechanical and ballistic properties. Original techniques were implemented in order to improve paraffin-based fuels. The first strengthening technique involves the use of a polyurethane foam (PUF); a second technique is based on thermoplastic polymers mixed at molecular level with the paraffin binder. A ballistic characterization of paraffin-based hybrid rocket solid fuels was performed, considering pure wax-based fuels and fuels doped with suitable metal additives. Nano-Al powders and metal hydrides (magnesium hydride (MgH2), lithium aluminum hydride (LiAlH4 )) were used as fillers in paraffin matrices. The results of this investigation show a strong correlation between the measured viscosity of the melted paraffin layer and the regression rate: a decrease of viscosity increases the regression rate. This trend is due to the increasing development of entrainment phenomena, which strongly increase the regression rate. Addition of LiAlH4 (mass fraction 10%) can further increase the regression rate up to 378% with respect to the pure HTPB regression rate, taken as baseline reference fuel. The highest regression rates were found for the Solid Wax (SW) composition, added with 5% MgH2 mass fraction; at 350 kg/(m2s) oxygen mass flux, the measured regression rate, averaged in space and time, was 2.5 mm/s, which is approximately five times higher than that of the pure HTPB composition. Compositions added with nanosized aluminum powders were compared with those added with MgH2, using gel or solid wax

Dynamic anoxic ferruginous conditions during the end-Permian mass extinction and recovery

The end-Permian mass extinction, ~252 million years ago, is notable for a complex recovery period of ~5 Myr. Widespread euxinic (anoxic and sulfidic) oceanic conditions have been proposed as both extinction mechanism and explanation for the protracted recovery period, yet the vertical distribution of anoxia in the water column and its temporal dynamics through this time period are poorly constrained. Here we utilize Fe–S–C systematics integrated with palaeontological observations to reconstruct a complete ocean redox history for the Late Permian to Early Triassic, using multiple sections across a shelf-to-basin transect on the Arabian Margin (Neo-Tethyan Ocean). In contrast to elsewhere, we show that anoxic non-sulfidic (ferruginous), rather than euxinic, conditions were prevalent in the Neo-Tethys. The Arabian Margin record demonstrates the repeated expansion of ferruginous conditions with the distal slope being the focus of anoxia at these times, as well as short-lived episodes of oxia that supported diverse biota

Uncertainty Propagation in Post-Firing Analysis of SRM Internal Ballistics

Post-firing analysis of solid rocket motors enables the identification of important propulsion parameters such as characteristic velocity, discharge coefficient, throat erosion, burning time, and other details, depending on the degree of complexity involved in the analysis. Firing data can have different sources. Test-bench firings are usually carried on for evaluation purposes during design processes, prototype evaluation, or routine quality check in propellant production. Mission-related data may be obtained from in-flight streaming. In this respect, some types of information are not always available for in-flight tests. Throat erosion measurements are not accessible or the propulsion unit might not be fully instrumented, in case of production flights. The accuracy featuring analysis results are influenced by both uncertainty of available data (e.g. random or systematic errors) and lack of knowledge for some parameters. The present work applies a methodology for uncertainty propagation to a simplified post-firing tool. The post-processing algorithm is based on a zero-dimensional framework capable of deriving characteristic velocity, thrust coefficient, throat erosion, and burning time. Code implementation and verification are presented. An example of uncertainty analysis is reported for a limited number of sources, both epistemic and aleatory. Propagation is traced using a Monte Carlo method and Latin hypercube sampling