Project Refinement #2

The synthesis of high energy materials can be complex. Several methods also involve the use of expensive reagents that would be impractical on a commercial level useful for civilian aerospace companies. The preparation, firing, and data acquisition of any rocket motor is also somewhat intensive in terms of time, materials, and fabrication. These facts limit the attainable number of trials in the overall experiment. Since only a limited number of trials are possible, it is not reasonable to record data over a wide variety of energetic propellant additives. Rather, one additive will be selected for synthesis and tested in various concentrations with and against other commercially available additives like powders of light metals. Cost will be a major factor in choosing which additives to acquire and synthesize. For synthesis, I will focus on one substance, then, provided sufficient characterization of the chosen substance and remaining time, another will be attempted.

Solid propellants which liquefy at their combustion surface have demonstrated potential to increase the burn rate in hybrid rocket motors. Significant convective heating from the detached combusting boundary layer causes the fuel to form a liquid layer. High velocity gradients cause shear stress at the liquid surface, resulting in its destabilization into waves which eject mass into the combustion stream. Paraffin is one such liquefying fuel that has been studied with promising results. Various energetic additives have the potential to further increase the energy content, burn rate, and performance of paraffin based solid fuels. Paraffin wax is cheap, easy to handle, and easy to cast into propellant grains. MMHNF, GAT, TAGzT,  HBT, and ADMP are all possible additive candidates to be considered for synthesis and use in paraffin based fuel. Aluminum and magnesium powders can also be added in order increase the heat of combustion. A single liquid oxidizer will be used for all trials. This will either be nitrous oxide or highly concentrated >80% hydrogen peroxide. Nitrous oxide offers low cost and self pressurization where hydrogen peroxide offers better performance.

Another, much less explored, option is the use of a liquefying oxidizer as the solid propellant with other crystalline oxidizer additives. A liquid hydrocarbon fuel, hydrazine, or aluminum borohydride could be used as the injected fuel. Hydrocarbons like kerosene are cheap and easily used as fuels. Hydrazine offers the ability to exothermically pre-decompose and possibly increase performance. Aluminum borohydride and other "zip-fuels" containing borane will offer the highest possible performance. The oxidizer candidate would be the nitroparaffin hexanitroethane. This substance has found limited use in propellants and flares as a nitrogen rich oxidizer. It's melting point of 135 degrees Celsius allowing it to be cast in a similar manner to sugar based "R-Candy" solid propellants. HNF or another oxidizer like AP, AN, or KN could be mixed into the solid oxidizer. An energetic like MMHNF, GAT, TAGzT, or HBT could also be added in small amounts. In the case of hexanitroethane solid propellants, this substance would be synthesized and tested on its own with a liquid fuel. Such an experiment would constitute entirely new research even without an additive.

The next phase of the research will entail assessing the feasibility of making each propellant combination and choosing the simplest one that offers the maximum theoretical performance. The focus is on the practical application of greener experimental hybrid propellants for future civilian aerospace efforts. Even if a substance can be made in the lab on a small scale, it may not be reasonable to apply it on the larger scale mandated by civilian aerospace. A high-performing propellant combination that is expensive and difficult to produce is effectively useless for this end and will not be considered in my research. Rather, obtaining the maximum performance at costs attainable by aerospace start-ups will be the goal.