Flame Structure Effects at High G-Loading

Abstract

Previous research has been conducted showing significant benefits on combustion efficiency and stability by creating high gravity-loaded combustion environments. Ultracompact combustor systems decrease the size and weight of the overall engine by integrating the compressor, combustor, and turbine stages. In this system, the core flow is split and a portion is routed into a circumferential direction to be burned at a high equivalence ratio. Fuel and air are brought into the cavity and combusted in a high g-loaded environment driven by air injection. Computational research showed that the hole diameter of the air injection jets are directly related to g-loading within the cavity. An experimental rig was built where the air injection rings could be changed to contain one of three different jet hole diameters to verify this result. The smallest air injection diameter achieved the highest g-loading in the cavity, which is consistent with the computational fluid dynamics (CFD) results. However, the flame stability within the cavity was affected by the air injection jet becoming too large or too small for a particular equivalence ratio. Video taken at 8000 Hz was used to capture the flame structure, revealing that the flame was not stable even before lean blow out conditions were achieved. Additionally, the direction that the air jets swirled in the cavity was found to have an impact on the combustion dynamics. When flow swirled counterclockwise and impacted the suction side of the turbine vane, the cavity had a more uniform fully developed flow field, as opposed to the pressure side impact. Finally, liquid fuel testing was done to test the atomization and mixing of JP-8 in a g-loaded environment. The results showed that increasing the cavity g-load increased the residence time the fuel stayed in the cavity.