Advanced Hybrid Solid Fuels
- Paper number
IAC-07-C4.2.09
- Author
Mr. Max Calabro, The Inner Arch, France
- Coauthor
Dr. Luigi T. DeLuca, Politecnico di Milano, Italy
- Coauthor
Dr. Luciano Galfetti, Politecnico di Milano, Italy
- Coauthor
Mr. C. Perut, SNPE Materiaux Energetiques, France
- Year
2007
- Abstract
Enabling hybrid rocket propulsion to compete with solid and liquid propulsion is the target of the renewed international interest in hybrid rockets. From the performances standpoint, conventional hybrids may compete with conventional liquids such as LOX Kerosene and could be much better than solids but they have 2 majors drawbacks;
- A low burning rate of current solid fuels, and associated low sensitivity to operating conditions, represent the main drawbacks to overcome for successful operations of hybrid propulsion on large scale.
- Combustion problems with a low combustion efficiency, instabilities and a high level of residuals (linked with the low burning rate)
Moreover, to be really attractive, new formulations have to bring a decisive advantage with a much higher specific impulse . nevertheless these new formulation have to keep the 3 major advantages of hybrids; a safe operating mode due to a very high level of mechanical properties, a cheap manufacturing process due to a pure fuel solid grain and the capability to be stopped on demand. Some formulations appears really attractive with a high burning rate and a good combustion with or without a large increase of the specific impulse The present paper describes the efforts, by a joint team of investigators, to reach this objective by promoting the use of novel energetic ingredients in hybrid solid fuels and will give an example of application.
A variety of new formulations was tested keeping in mind that both combustion behavior and mechanical properties of solid fuel grains are important for applications. Thus, a systematic experimental investigation was carried out to determine the relevant properties of several candidate formulations and closely contrast their overall behavior. For this purpose, a micro-sized hybrid rocket motor test bench was implemented including a pressurized test chamber, oxidizer line, video acquisition system for quasi-steady solid grain regression rate measurements, CO2 laser for radiative primer charge ignition, and exhaust gases dump system (also used for pressure regulation through a set of electric valves). The solid grain is shaped as a traditional fuel cylinder with one central perforation. Air or mixtures of oxygen and nitrogen, injected at the head-end of the motor, were used as gaseous oxidizer. An overall sketch of the hybrid test facility is shown in Fig. 1. This apparatus allows, on a relative scale, a quick classification of fuel regression rates and their sensitivity to operating conditions.
Three main directions were explored for developing advanced solid fuel compositions. The first one resorts to nano-sized energetic particles cast in HTPB solid fuel grains. Ballistic and mechanical properties were extensively investigated and the features of a range of coated or uncoated aluminum nano-sized particles clarified. The second direction resorts to fuels characterized by the presence of a liquid surface, resulting in droplets entrainment. Paraffin-based fuels were investigated revealing, for the investigated compositions, severe structural problems due to poor mechanical properties. The third investigated direction specifically addresses to metal hydrides compositions. In particular magnesium and aluminum hydrides formulations were analyzed, showing increases in the solid fuel regression rates depending on the hydride mass fraction.
The incorporation of metal hydride in HTPB-based fuel induces also an energetic increase. For aluminum hydride, the expected specific impulse (vacuum, ε = 40) augmentation is 32 s and the volumetric specific impulse increase is around 70 sgcm-3. The effects on the motor performances of the increases of the fuel regression rate allowing improvement of the volumetric loading ratio and of the specific impulse will be assessed.
The main advantages of hybrid propulsion are safety arising from oxidizer and fuel separation and the possibility of stopping or altering the thrust by stopping or adjusting the mass flow rate. New generation of fuels make this technology still more attractive.
Fig. 1 Overall sketch of the hybrid test facility (see original attached)
- Abstract document
- Manuscript document
IAC-07-C4.2.09.pdf (🔒 authorized access only).
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