Controlling Low-Frequency Instability with Fuel Inserts in Hybrid Rocket Combustion

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Controlling Low-Frequency Instability with Fuel Inserts in Hybrid Rocket Combustion

Chae, Heesang / Lee, Changjin

A series of combustion tests was conducted to control and suppress the initiation of low-frequency instability (LFI) by using fuel inserts, through which a small step appeared gradually because of differences in the regression rates of the two materials; polymethyl methacrylate and high-density polyethylene. This small step acts as an artificial block that causes slight changes to the flow characteristics of small vortices generated near the fuel surface. The results show that using a fuel insert delayed the LFI occurrence. In addition, the location of the fuel insert played an important role in determining the level of LFI suppression as well as the phase difference between the combustion pressure $p^{'}$ and heat release $q^{'}$ . Properly locating two fuel inserts simultaneously in the axial direction completely changed the phase difference to $π / 2$ , which caused the LFI to disappear completely.