Characterization of the temporal and spatial homogeneity of the fuel placement in a swirl cup: Combustion tests at elevated pressure in SSC rig

Kurzfassung

The objective of this task is the characterization of the temporal and spatial fuel placement in a two-phase flow downstream of a fuel-air nozzle at elevated pressure. The activity pursues a two-fold goal: One focus area is the detection and analysis of temporal fluctuations in the 2-phase flow. Specifically, the response of the liquid fuel placement to a periodic modulation of the primary air flow is investigated. These fluctuations may be a contributing factor to combustion instabilities, which represent a major problem for the operation of lean premixed combustion systems. The second focus area is the investigation of the pressure effect on fuel placement. This activity can be considered as a continuation and extension of work performed within the ACIACOC project. The objective of that project was to investigate the response of the heat release to forced modulations of the air flow through a diffusion type burner using an airblast atomizer. In this task, the same configurations and operating parameters studied within ACIACOC have been investigated again, but this time with additional emphasis on the response of fuel placement and its interaction with heat release following forced modulation of the burner air flow. The test program of this task was conducted in three stages. The first two stages consisted of isothermal tests at elevated pressure up to 20 bar, as well as tests with preheated air without combustion. These test aimed at characterization of fluctuations in the liquid fuel flux and in droplet sizes. Also, time-resolved measurements of fluctuations in the fuel vapour concentration by applying the Fast Fourier Transformation to IR/vis light extinction data were performed. The 2-phase flow in a chemically reacting environment was the subject of the third stage of the activity. In this case, there exists the potential for amplification of fuel flux fluctuations by non-steady heat release in the reaction zone or by preferential combustion in zones characterized by relatively small droplet sizes. It was the goal of the tests of the third stage to relate the non-steady 2-phase flow with non-steady heat release in the reaction zone. At one fixed value of swirl intensity, phase-resolved spatial fuel placement was measured by planar Mie scattering using a pulsed laser light sheet technique. Simultaneously, heat release was visualized by chemiluminescence of the OH radical. Both quantities were recorded over a period of a forced air flow modulation.