No abstract

An experimental study of a single, swirl cup burner is carried out to improve understanding of the lean reacting flow field near idle conditions for an annular spray combustor. The counter-swirler is mounted horizontally in a trapezoidal cross-section combustor with quartz plate walls. Liquid fuel, Jet-A, is initially atomized using a simplex nozzle, and then a designed re-atomization occurs from the swirler hardware. Measurements of non-reacting and reacting gas phase velocities enable the direct comparison of critical flow features at various power settings. Droplet diameter and exhaust composition measurements confirm that the initial droplet size is a key factor in emission levels. Smaller droplets in the spray periphery tend to evaporate and burn premixed, while larger droplets in the spray core convect downstream and burn with a sheath-type, non-premixed flame. The presence of small fuel droplets in the spray may ensure more complete combustion and improve combustor stability at lean, low power settings.

No abstract

No abstract

The operation of a Stagnation Point Reverse Flow (SPRF) combustor is studied over a range of equivalence ratios and loadings. Previous studies have shown this combustor geometry can operate stably, even at low equivalence ratios, without the need of external preheating or swirl, while producing low pollutant emissions levels in both premixed and non-premixed modes. The SPRF combustion and mixing characteristics are investigated with a variety of imaging diagnostics: simultaneous OH PLIF and chemiluminescence (heat release) measurements, and laser scattering of oil droplets seeded into the fuel. Results indicate that the flame is primarily stabilized and that most of the heat release occurs in the downstream portion of the combustor, where there is a low mean velocity but high fluctuations. The hot products created in this region reverse direction and are entrained into the oncoming reactants. This increases chemical rates and flame speeds, contributing to the stability of the combustor. Fuel and air injected separately in case of non-premixed operation, are found to be mostly mixed by the time they reach the flame zone, allowing this combustor to operate with nearly the pollutant emissions levels of a premixed combustor, but without the safety concerns associated with premixing.