Date of Award

9-17-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Aeronautics and Astronautics

First Advisor

Brook I. Bentley, PhD.

Abstract

More than twenty-five years of continuous operation in the dusty environments of Southwest Asia have shown that degradation of gas turbine engine components due to particle ingestion is a serious threat to operations. In particular, the continued push for higher engine operating temperatures has brought a new emphasis to the damage mechanisms (for example CMAS glass formation and hot corrosion) caused by ingested particles forming molten deposits on engine components. Despite decades of research little progress has been made to mitigate the effects of CMAS and hot corrosion degradation to engine components. This research focused on hot corrosion specifically. A ground-up review of real-world incidents of hot corrosion revealed that the chemical species (sodium sulfate), cited as the cause of hot corrosion in all current academic study, is not present in any natural environment where hot corrosion is an issue. This fact alone raises serious concerns as to the real-world applicability of more than 40 years of laboratory study. An alternative species (gypsum) was identified which is abundant across the globe, and in particular is found in the locations the DoD has reported hot corrosion. Testing proved that gypsum is molten at the same temperatures as sands from a location known to cause significant hot corrosion degradation. Gypsum was proven to initiate hot corrosion at temperatures associated with modern gas turbine engine operation, which are beyond the range at which sodium sulfate can cause degradation. A first-of-its-kind model was developed to predict degradation caused by gypsiferous dusts as a function of temperature, sulfate concentration, and time. The model was based on kinetic rate law equations and was validated by comparison to additional laboratory runs. The model suggests a minimum concentration of sulfate is necessary to cause hot corrosion, beyond which temperature and time-at-temperature become the chief predictors of degradation. The model also predicted that gypsum could cause degradation at temperatures lower than studied in this effort (750 to 1000°C). This prediction is important because an alternate cause of hot corrosion is also necessary at lower temperatures given that sodium sulfate is not present in DoD environments to cause any form of hot corrosion.

AFIT Designator

AFIT-ENY-DS-15-S-066

DTIC Accession Number

ADA621803

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