High-Frequency Flame Oscillation Observed at a Coaxial LOX/LH2 Injector Element

To study the mechanism of the initiation of combustion instability as hydrogen injection temperature decreases, a hydrogen temperature ramping test was conducted with a single coaxial injection element with LOX/LH2 at a chamber pressure of 8.0 MPa. Two types of injectors were used in the tests. One employed a straight bore LOX post and the other employed a taper-reamed LOX post for better atomization of LOX. The combustion flame was visualized with a high-speed video camera at a rate of 6,000 frames per second. Results showed that unstable combustion was initiated when the hydrogen injection temperature decreased to less than a certain cryogenic temperature. By observing the movement of the prominent pattern of OH emission on the flame, the flame was found to propagate downstream at a constant speed with the flame angle remaining constant during stable combustion. On the other hand, injection pressure peaks appeared during unstable combustion. In this case, a block of flame with strong OH emission was occasionally observed. A block of flame caught up with an anterior block and coalesced into a large block with strong OH emission. This coalesced block of the flame is herein termed “flame burst”.