The objective of this work was to investigate the response of the heat release and liquid fuel distribution to forced periodic modulations of the primary air flow through diffusion type burners with different exit geometries. The spatial distribution of spray density and heat release at different modulation frequencies was studied using phase-resolved OH chemiluminescence for heat release visualization, and planar Mie scattering of kerosene. Experiments were performed for a variety of operating conditions. It was observed that the exit geometry of the nozzle has a considerable effect on the flame shape and fuel distribution, but also on the amplitude of the response to forcing of the air flow. The expanding and contracting fuel spray cone drives the region of the heat release during a period of the air flow modulation, by establishing favourable flammability conditions at varying locations during the oscillation. The temporal shape of the response of the fuel mass in the combustor, as well as the large modulation depth at low frequencies compared to the changes of air flow velocity, suggest that the fuel feed rate into the combustor is affected by a storage mechanism.

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