Solid amine-boranes as high performance hypergolic hybrid rocket fuels

Hypergolic hybrid rockets have the potential of providing systems that are simple, reliable, have high performance, and allow for energy management. Such a propulsion system can be applied to fields that need a single tactical motor with flexible mission requirements of either high speed to target or extended loitering. They also provide the possibility for alternative fast response dynamic altitude control systems if ignition delays are sufficiently short. ^ Amines are the traditional fuel of choice when selecting a hypergolic combination as these tend to react readily with both nitric acid and dinitrogen tertroxide based oxidizers. It has been found that the addition of a borane adduct to an amine fuel tends to reduce the ignition delay by up to an order of magnitude with white fuming nitric acid (WFNA). The borane addition has resulted in fuels with very short ignition delays between 2-10 ms - the fastest times for an amine based fuel reacting with nitric acid based oxidizers. The incorporation of these amine-boranes, specifically ethylenediamine bisborane (EDBB), into various fuel binders has also been found to result in ignition delays between 3-10 ms - the fastest times again for amine based fuels. ^ It was found that the addition of a borane to an amine increased theoretical performance of the amine resulting in high performance fuels. The amine-borane/fuel binder combinations also produced higher theoretical performance values than previously used hypergolic hybrid rockets. Some of the theoretical values are on par or higher than the current toxic liquid hypergolic fuels, making amine boranes an attractive replacement. The higher performing amine-borane/fuel binder combinations also have higher performance values than the traditional rocket fuels, excluding liquid hydrogen. Thus, amine-borane based fuels have the potential to influence various area in the rocket field. ^ An EDBB/ferrocene/epoxy fuel was tested in a hypergolic hybrid with pure nitric acid as the oxidizer. Hypergolic ignition occurred repeatably and with short combustor pressurization times of under 100 ms. The regression rate of the fuel exhibited never before observed high pressure dependence regression rates. The presence of a foam like layer on the fuel surface provides an adequate explanation for the observed combustion behavior with a calculated regression rate that depends on pressure raised to the 2nd power. Extrapolation of this theory indicates that amine-borane based fuels could produce high regression rate fuels

Feasibility Study and Demonstration of an Aluminum and Ice Solid Propellant

Aluminum-water reactions have been proposed and studied for several decades for underwater propulsion systems and applications requiring hydrogen generation. Aluminum and water have also been proposed as a frozen propellant, and there have been proposals for other refrigerated propellants that could be mixed, frozen in situ, and used as solid propellants. However, little work has been done to determine the feasibility of these concepts. With the recent availability of nanoscale aluminum, a simple binary formulation with water is now feasible. Nanosized aluminum has a lower ignition temperature than micronsized aluminum particles, partly due to its high surface area, and burning times are much faster than micron aluminum. Frozen nanoscale aluminum and water mixtures are stable, as well as insensitive to electrostatic discharge, impact, and shock. Here we report a study of the feasibility of an nAl-ice propellant in small-scale rocket experiments. The focus here is not to develop an optimized propellant; however improved formulations are possible. Several static motor experiments have been conducted, including using a flight-weight casing. The flight weight casing was used in the first sounding rocket test of an aluminum-ice propellant, establishing a proof of concept for simple propellant mixtures making use of nanoscale particles

Sequencing of diverse mandarin, pummelo and orange genomes reveals complex history of admixture during citrus domestication

Cultivated citrus are selections from, or hybrids of, wild progenitor species whose identities and contributions to citrus domestication remain controversial. Here we sequence and compare citrus genomes-a high-quality reference haploid clementine genome and mandarin, pummelo, sweet-orange and sour-orange genomes-and show that cultivated types derive from two progenitor species. Although cultivated pummelos represent selections from one progenitor species, Citrus maxima, cultivated mandarins are introgressions of C. maxima into the ancestral mandarin species Citrus reticulata. The most widely cultivated citrus, sweet orange, is the offspring of previously admixed individuals, but sour orange is an F1 hybrid of pure C. maxima and C. reticulata parents, thus implying that wild mandarins were part of the early breeding germplasm. A Chinese wild 'mandarin' diverges substantially from C. reticulata, thus suggesting the possibility of other unrecognized wild citrus species. Understanding citrus phylogeny through genome analysis clarifies taxonomic relationships and facilitates sequence-directed genetic improvement. (Résumé d'auteur

Changes in combustion behavior of liquid fuels due to the addition of small amounts of ammonia borane or nano aluminum

Both ammonia borane and nano aluminum as additives to liquid fuels are investigated. Both fundamental droplet combustion experiments and experiments using an unstable liquid rocket combustor are used to study the effects these additives on the combustion behavior. The liquid fuels consist of ethanol and JP-8. The droplet experiments consist of both visual and OH high speed planar laser–induced fluorescence measurements. Simple combustion models are incorporated as well to provide further understanding. It is found that ammonia borane increases the regression rate of a single ethanol droplet. Evidence indicates that hydrogen gas is released throughout the combustion process of the droplet and influences the combustion behavior notably. Laser diagnostics indicate that changes in flame structure occur. The other components of ammonia borane affect the combustion behavior of the droplet, especially near the end of the droplet lifetime, causing the droplet to shatter. Nano aluminum has very little impact on the combustion behavior of single fuel droplets of JP-8 and ethanol. Nano aluminum is observed to combust only when a surfactant, Neodol, is present which produces gas generation and bubble formation within the droplet. Combustor experiments show similar trends as the droplet combustion experiments. Ammonia borane has a notable impact on the combustion stability of the system allowing it to be unstable for more combustor geometries. It is shown that ammonia borane addition produces a bimodal unsteady energy release within the combustor while the neat fuel does not. This combustion behavior allows for the increased amount of unstable combustor geometries. Nano aluminum has a small impact on the combustion stability of the system causing pressure oscillations to increase

C_minima_ssp_minima_polygon_file

Google Earth modified polygon file. Place in same directory as analysis and species trees file, and make sure they are referenced correctly in the xml file

Data from: On the Biogeography of Centipeda: A Species Tree Diffusion Approach

The deserts of Australia together constitute one of the world’s largest continuous arid zones, where precipitation is low and access to water limited and/or sometimes restricted to temporal and unpredictable flooding. In this environment, a wide variety of plants and animals have evolved, many of which are morphologically adapted to ephemeral water and fire regimes. Reconstructing the biogeographic history of groups present in such landscapes is challenging, due to the difficulties in defining discrete areas for analyses, and even more so when species largely overlap both in terms of geography and habitat preference. In this study, we use a novel approach to estimate ancestral areas for the small plant genus Centipeda. Our analysis applies continuous diffusion of geography by a relaxed random walk, where each species is sampled from its extant distribution on an empirical distribution of time calibrated species trees. Using a distribution of previously published substitution rates of ITS for the Asteraceae, we show how the evolution of Centipeda correlates with the temporal increase of aridity in the arid zone since the Pliocene. Geographic estimates of ancestral species show a consistent pattern of speciation of early lineages in the Lake Eyre region, with a division in more northerly and southerly groups since approximately 840 ka. Summarising the geographic slices of species trees at timing of latest speciation event (~20 ka), indicates no presence of the genus in Australia west of the combined desert belt of the Nullabor Plain, the Great Victoria Desert, the Gibson Desert, and the Great Sandy Desert, or beyond the main continental shelf of Australia. The result indicates all western occurrences of the genus to be a result of recent dispersal, rather than ancient vicariance. This study contributes to our understanding of the spatiotemporal processes shaping the flora of the arid zone, and offers a significant improvement in inference of ancestral areas for any organismal group distributed where it remains difficult to describe geography in terms of discrete areas

C_crateriformis_ssp_crateriformis_polygon_file

Google Earth modified polygon file. Place in same directory as analysis and species trees file, and make sure they are referenced correctly in the xml file

Supplementary Figure S5

Species polygons in colour with starting locations (circles) and specimens sampled for species tree inference

Supplementary Figure S4

Species polygons in colour with starting locations (circles) and specimens sampled for species tree inference