Flame Structure Effects at High G-Loading

Abstract

Previous research has been conducted showing significant benefits on combustion effi ciency and stability by creating high gravity-loaded combustion environments. Ultracom pact 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 environ ment 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 differ ent 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 com bustion 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 o f 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.

Gear-Shaped High-g Combustion Chamber for Micro Turbojet Engine Applications

“…The superior combustion performance of high- g technology has motivated many researchers to conduct experiments to verify this phenomenon, − and numerous studies have been conducted to obtain a more detailed flame mechanism through simulations. − Recently, researchers have pointed out that the high- g combustion mechanism is more complex and may be related to the Rayleigh–Taylor instability. − Briones et al reproduced Lewis’s experiments using a two-dimensional computational domain to simulate a rotating combustion tube and found that higher values of g -loading were not better, and at larger values of g -loading, the flame front broke up and disrupted its own mixing with the fuel, which led to localized quenching and slowed down flame propagation. Briones proposed that Rayleigh–Taylor instability affects the localized flow rate of the flame and thus the flame propagation rate.…”

“…The superior combustion performance of high- g technology has motivated many researchers to conduct experiments to verify this phenomenon, 12 − 14 and numerous studies have been conducted to obtain a more detailed flame mechanism through simulations. 15 − 18 Recently, researchers have pointed out that the high- g combustion mechanism is more complex and may be related to the Rayleigh–Taylor instability.…”

“…The single-chamber combustion chamber could withstand a higher g -loading under the same conditions, and a more uniform temperature distribution could be obtained using a flame stabilizer. Wilson et al 14 further improved the mixing guide vane based on their predecessors; however, a secondary air injection was still required to produce a high- g environment in the cavity. The HGC design of Erdmann et al 24 adopts the form of a secondary cavity so that the fuel can be completely atomized and sprayed into the vortex.…”