In 2021 the Federal Aviation Administration in collaboration with the National Research Council of Canada performed research on altitude ice crystal icing of aircraft engines using the modular compressor rig, ICE-MACR, in an altitude wind tunnel. The aim of the research campaign was to address research needs related to ice crystal icing of aircraft engines outlined in FAA publication Engine Ice Crystal Icing Technology Plan with Research Needs. This paper reports the findings on ice accretion from a configuration of ICE-MACR with two compression stages. Inherent in two-stage operation is not just additional fracturing and heating by the second stage but also higher axial velocity and potentially greater centrifuging of particles. These factors influence the accretion behavior in the test article compared to single stage accretion.
The melt ratio (liquid/total water content) has been shown to be an important parameter in ice crystal icing, with a relatively narrow band of melt ratios associated with optimum icing. Comparisons of appearance and the development of ice accretions were made at constant melt ratio for 1 and 2 stages, and important differences were found. The ice appeared different for two cases with equal melt ratio, and optimum icing occurred at much higher melt ratios for the 2-stage than the 1-stage configuration. The extent to which fracturing, centrifuging, heating and velocity affects the resulting ice accretions is evaluated using video, thermocouple, heat flux gauge and shadowgraph measurements. Heat flux gauge analysis provides insight into the importance of the dry-side temperature in the accretion process.
