Relations between the number of spray droplets and chemiluminescence for Jet A-1 flames stabilized in a gas turbine model combustor

Abstract

The spatial and temporal relations between the flame chemiluminescence and the number of droplets for spray flames stabilized in a gas turbine model combustor are investigated experimentally. Pressure measurements, Interferometric Laser Imaging for Droplet Sizing, shadowgraphy, as well as flame chemiluminescence and Mie scattering imaging are performed. Test conditions corresponding to premixed methane and air, Jet A-1 spray, and Jet A-1 spray in premixed methane and air flames are examined. For all test conditions, the fuel-air equivalence ratio is 0.6, and the fuels and air flow rates are adjusted to generate a fixed nominal power of 10 kW. It is shown that, compared to the Jet A-1 spray flames, the dual-fuel flames feature smaller plenum pressure fluctuations. The droplet sizing suggests that, compared to Jet A-1, the dual-fuel spray is poorly atomized, leading to the generation of large droplets. Spectral analysis shows that, although the tested flames are not thermoacoustically excited, an injector-induced instability exists. The spatial relations between the flame chemiluminescence and the spray number density shows the coupling between these parameters is driven by the spray dynamics for the Jet A-1 flames; however, this coupling is driven by methane combustion for the dual-fuel test condition. A time-lag-based linear-regression model is developed and used to investigate the temporal relations between the flame chemiluminescence and the spray number of droplets for Jet A-1 spray flames. It is obtained that the oscillations of the number of spray droplets lead those of the flame chemiluminescence. The findings suggest that, in addition to the several spray characteristics reported in the literature, the droplets number density plays an important role in elaborating the coupling between the spray and flame chemiluminescence.