Microtomography of Soil and Soot Deposits: Analysis of Three-Dimensional Structures and Surface Morphology

The detrimental effects generated by the gas turbine fouling phenomenon are well known. Due to soil and soot particles ingestion, gas turbines experience performance drops related to greater fuel consumption and even lower efficiency. These effects are related to the modification of the shape and surface roughness of relevant surfaces (compressor and turbine blades and vanes, especially) due to the presence of a thin layer generated by micro/nanosized particle adhesion. Such contaminants are swallowed by the unit and, as a function of the operating conditions, adhere to the surface, causing a sort of dangerous coating to the surface. In this work, a microtomography analysis of the deposited layer is reported. The deposited layer has been generated using microsized soil and soot powders under specific impact conditions and substrate surface roughness similar to those in the cold section of a gas turbine compressor. The microtomography analysis has been carried out using the beamline at the ELETTRA Sincrotrone research center. Thanks to the resolution of the beamline, the detection of the three-dimensional internal structure of the soil and soot layers have revealed that within the layer, the structure is characterized by discontinuities. Soot and soil particles, even characterized by similar diameter distributions and test conditions, generate layer structures that differ by the magnitude, orientation, location of the internal discontinuities, and surface morphology (i.e., roughness). The comprehension of the packing process allows us to understand the adhesion process and define general guidelines to predict the fouling phenomenon.