Hybrid rockets have the advantages of safety propulsion system and low cost fuel compared to liquid rockets and solid rockets, but improving the burning rate of fuels is a major issue, and various approaches have been taken for fuel properties and combustion methods. The author devised a liquid-encapsulated fuel as a measure to improve the burning rate of the hybrid rocket. The liquid-encapsulated fuel is containing the liquid fuel in the solid fuel. At the burning surface, liquid fuel is directly supplied to the combustion area and the surface without melting process or gasification process of usual hybrid rocket fuels. Also it is possible to control the burning rate by the shape, position, and number of containing the liquid. In order to demonstrate the production of the liquid-encapsulated fuel, the author prototyped a solid fuel containing liquid fuel with a size of 10 mm×10 mm×100 mm using a stereolithography 3D printer with a liquid resin. And the liquid-encapsulated fuels were prototyped, but the bubbles were generated inside the liquid. After investigating the cause, the author sought an appropriate curing process of 3D printer and shape design guidelines that suppress the generation of bubbles, and succeeded in prototyping a liquid-encapsulated fuel without bubbles.
As a candidate remedy for the case depth deviation in induction hardened gears, this study experimentally revealed the influence of re-induction hardening (RIH) on the bending fatigue strength of S45C spur gears. We used the original induction hardened gears with thinner, the target, and thicker case depths (called GI1, GI2, and GI3, respectively). We conducted RIH for GI1 without any intermediate heat treatment (IHT), and for GI3 without any IHT, or with various IHTs such as the vacuum normalizing, tempering, and induction heating and normalizing. Bending fatigue limit (BFL) of the re-induction hardened GI1 was greater than BFLs of the original GI1 and GI2. BFLs of the re-induction hardened GI3 with IHTs were roughly equal to or greater than BFLs of the original GI3 and GI2. In contrast, BFL of the reinduction hardened GI3 without any IHT was smaller than BFL of the original GI3. Our results indicate that RIH is applicable in terms of BFL of S45C spur gears, and performing IHT is highly recommended for too thick case depth.