Unpacking Intermineral Synergies and Reactions During Dust Deposition in an Impingement Coolant Jet

Abstract

This paper seeks to unpack synergies that exist between minerals during deposition of the heterogeneous AFRL02 mixture in gas turbine engines and demonstrate that the contributions of each mineral cannot be considered independently. In each experiment, one gram of mineral dust (0–10 µm particle diameter distribution) was injected into an 894 K, 57 m/s coolant flow impinging normally on a Hastelloy X plate with a surface temperature of 1033 K, 1144 K, or 1255 K. Capture efficiency measurements, deposit morphology analyses, and X-ray diffraction results are reported. Besides AFRL02, single mineral dusts, dual mineral dusts, and AFRL02-like dust blends lacking in one mineral were tested. The results of the experiments elucidate that the deposition behavior of single minerals indeed cannot explain the composite deposition of heterogeneous mixtures. For example, gypsum had the highest capture efficiency of any single mineral in ARFL02, and yet removing gypsum from AFRL02 counterintuitively raised the capture efficiency of that blend when compared to AFRL02. Quartz was found to erode albite deposits but stick to and build upon dolomite and halite deposits, even though quartz did not deposit significantly as a single mineral. Quartz also chemically reacted with gypsum and dolomite to form wollastonite and diopside, respectively. Finally, we found that the capture efficiency of each blend increased with plate temperature, but not according to the same trend. Results are interpreted through the lens of CaO–MgO–Al2O3–SiO2 eutectic chemistry, but the chemical pathways by which these eutectics come into existence is found to be of equal importance.