Data on the parametric variation of the delay of soot occurrence by the absence of a spray

Kurzfassung

The aim of the studies within this task was to address the issue of the effect of the fuel phase on soot formation in the specific situation of a swirl combustor. The experiments were therefore to be performed in an environment resembling real aeroengine conditions as close as possible. In a complex flow field prevailing in an aeroengine combustor, the size and location of fuel-rich regions as sources of soot depend on fuel placement and mixing in the case of a gaseous fuel. For a liquid fuel, additional processes like atomization, dispersion and evaporation act on the fuel. Each one of these processes adds an individual time constant to the formation of fuel-rich soot-forming regions, depending air-to-fuel ratio (AFR), temperature, pressure, and pressure drop across the injector. Atomization and dispersion also influence the mixing and formation of fuel rich regions directly. In combination with the flow field characteristics, both the amount of soot formed and the regions of soot formation may vary. Therefore, it has to be expected that the soot formation process depends on the operating parameters as well as on the geometric features of the injector in a different way for gaseous and liquid fuel. It was intended to study the influence of operating conditions separately from flow field and fuel composition effects. Consequently, two sets of experiments were performed with two burners running on liquid and prevaporized kerosene, respectively. The burners were chosen with respect to a maximum possible similarity in terms of size, fuel placement, and internal aerodynamics. Tests with both burners were performed for a set of identical operating conditions. Pressure, air preheat temperature, AFR and pressure drop across the burner were varied to study the effect of these parameters for both fuel phases. In an initial screening campaign during which the effect of parameter variation was observed qualitatively using video recordings and extracted still images, the accessible parameter range and interesting operating points were identified. In a second stage, soot volume fractions were measured qualitatively for the relevant operating conditions using laser-induced incandescence (LII). This technique allows the spatially resolved measurement of soot concentrations in a plane through the combustor. Both measurements of instantaneous and time-averaged distributions are possible. A comprehensive discussion of the method and its applications can be found in [Sch06] and references therein. Video and LII investigations require a test rig and combustor with a large optical access to the primary zone, which provides realistic operating conditions as well.