Earlier studies revealed that addition of metal powder to microcrystalline-wax improves the regression rate of hybrid rocket solid fuel, but ignition of the metal powder was not confirmed to have occurred in the hybrid rocket engine chamber. To confirm the ignition of metal powder in the hybrid rocket engine chamber, theoretical calculations and combustion experiments were conducted. Theoretical calculations were heat transfer calculations from the combustion flame of microcrystalline-wax to metal powder. Combustion experiments were conducted in our laboratory using a hybrid rocket engine and 2D visualization engine. Theoretical calculations suggest that the metal powder ignited in the chamber. However, adding the aluminum powder did not improve the regression rate. Adding magnesium powder partially improved the regression rate. Both metal powders improved the characteristic velocity. According to the 2D visualization experiments, both metal powders ignited in the chamber. Results of these experiments suggest that metal powder raises the combustion flame temperature in the hybrid rocket engine chamber and that the addition of metal powder improves the solid fuel performance.

View full abstract

In this study, the viscosity characteristics of bimodal Al/hydroxyl-terminated polybutadiene (Al/HTPB) suspensions were experimentally investigated to improve the propulsion performance and manufacturability of low-cost solid propellants with ease of application. Several Al particles with different mean volume diameters were used to prepare the bimodal Al. The Al/HTPB suspensions behaved like a continuum in solid propellant slurries. The reason is that Al particles were sufficiently small for ammonium perchlorate particles. The suspension viscosities were measured using a rotational viscometer at 1.92 s ^-1. The optimum coarse fraction of Al particles in the bimodal Al/HTPB suspensions was 0.75. The viscosity of bimodal Al/HTPB suspensions was suppressed with an increase in the diameter ratio. These results were attributed to the improvement of Al packing in the suspensions. The experimental results show that the viscosity reduction by applying bimodal Al particles was more effective when the minimum void fraction was reduced. Furthermore, the performance enhancement of solid propellants was confirmed by adding the bimodal Al/HTPB. The calculation results showed that the bimodal Al/HTPB enhanced the propulsion performance of the propellant without the viscosity variation to a higher side. Moreover, the suppression of viscosity of up to 23 % could be achieved using the bimodal Al/HTPB similar to the conventional composition of solid propellants. Therefore, replacing monomodal Al particles with bimodal ones in solid propellants effectively improved the performance of the propellants.

View full abstract

It is very difficult to produce an intense blue colored flame using traditional fuels and blue colorants in fireworks. A new formulation of firework composition for producing an intense blue colored flame was designed in the research. In the composition, an organocopper compound was used not only as a fuel, but also as a blue colorant. Four organocopper compounds, such as copper(II) acetylacetonate, copper(II) gluconate, copper(II) benzoate, and copper(II) citrate, were chosen and tested as the candidates for fuel or blue colorant. Visible spectra of flames formed by burning the composition containing organocopper compound were measured and the hue of the flame was evaluated using the spectra. The experimental results show that the new composition consisted of the organocopper compound used as a fuel and ammonium perchlorate used as an oxidizer can produce intense blue colored flame. Especially an intense blue colored flame with approximately 60 % chromatic purity can be produced by using copper(II) acetylacetonate. The color purity is higher than that of traditional composition. The relationship between the flame behaviors and the emission spectra of the flame from burning of the new composition are examined in the study.

View full abstract

In this study, the effect of powder characteristics on the reactivity of Mg powder with water was examined through thermal analysis and chemical reaction kinetics analyses. Mg powders with different particle size distributions were prepared via sieving; specific surface area analysis revealed that the specific surface area of these Mg powders linearly correlated with their inverse equivalent volume diameter. An exothermic reaction between Mg and water, which generates magnesium hydroxide, was analysed using a Calvet calorimeter, and the onset temperature of the reaction was found to decrease with a decrease in the particle size of the Mg powder. Chemical reaction kinetics analysis revealed that the apparent activation energy and natural logarithm of the pre-exponential factor decreased with specific surface area, and reaction rate constant linearly correlated with the specific surface area or inverse equivalent volume diameter. The results of this study can be used to explore the problem of aging and safety of Mg.

View full abstract

Blast pressure from a small electric detonator, comprised of 100-mg lead azide as its main explosive, was measured and its trinitrotoluene (TNT)-equivalency was evaluated accordingly. The measurement of blast pressure in the proper direction suppressed oscillatory noise on the blast wave profile; therefore, the blast pressure from the sole detonator was clearly and definitively evaluated. The relationships between scaled distance and peak-overpressure, as well as scaled positive impulse, were compared to those of MITI87, which is representative of TNT surface-explosion data obtained by National Chemical Laboratory for Industry (National Institute of Advanced Industrial Science and Technology at present) in Japan. The TNT-equivalency of this detonator was conclusively evaluated as 0.32-0.33.

View full abstract