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To understand the initiating mechanism of low frequency instability (LFI) in hybrid rocket combustion, numerical calculation was performed using a direct numerical simulation (DNS). Special attention was paid to the effect of the equivalence ratio on the shift in the phase difference between pressure (p’) and heat release oscillations (q’). A change in the equivalence ratio was considered by varying the temperature and composition of the combustion gas that entered into the post combustion chamber. In the obtained results, additional combustion was successfully simulated along with a vortex generation over the backward step, and combustion pressure and heat release oscillations were clearly reproduced as small vortices that move downward. In addition, the obtained results confirmed that the phase difference between pressure and heat release oscillations shifted because of the changes in the propagation speed of the pressure wave when the temperature of the combustion gas changes.

We investigated the current limiting characteristics of flux-lock type superconducting fault current limiter(SFCL) according to inductance variation of coil 2. The flux-lock type SFCL consists of two coils. The primary coil is wound in parallel to the secondary coil through an iron core, and the secondary coil is connected to the superconducting element in series. The operation of the flux-lock type SFCL can be divided into the subtractive and the additive polarity winding operations according to the winding directions between the coil 1 and coil 2. The current limiting characteristics in two winding directions were dependent of on the ratio of the number of turns of coil I and coil 2. The fault current increased when the number of turns of coil 2 increased in the subtractive polarity winding. On the contrary, the fault current decreased under the same conditions in case of the additive polarity winding.