The origins of complex CMAS deposits in aircraft engines and their effects on engine degradation

点击翻译按钮获取中文摘要

This PhD project will address a major challenge faced by the airline industry as it strives to become more energy-efficient, namely the corrosion of engine components caused by ingestion of airborne sand and dust. Ingested airborne sand and dust are a problem for aircraft engines because, among other effects, they can melt inside the engine to produce so-called CMAS melts that can infiltrate and damage the thermal barrier coatings that are designed to protect engine components, with serious and expensive consequences for component life and engine efficiency. The higher the engine temperature, the more melting will occur. Modern gas turbine engines already run at very high temperatures in order to maximise fuel efficiency, and the engines of the future are likely to run at even higher temperatures, meaning CMAS attack will be even more of a problem. Furthermore, many airlines are experiencing greater sand and dust ingestion as a result of climate change induced desertification and an increase in extreme weather events such as sand storms. There is therefore a major push within the airline industry to develop technologies to minimise the opportunities for CMAS melts to form. Alongside this is a need to better understand the conditions in which the deposits form. This PhD will provide an important contribution to addressing this problem and ultimately reducing the economic and environmental impacts of aviation. The aim of the project is to advance the understanding of the origins and properties of CMAS deposits beyond their main components of CaO, MgO, Al2O3 and SiO2. The main additional component that will be studied is sulfur, which is implicated in a wide range of engine damage mechanisms. There are various possible origins of the sulfur, from ingested minerals to volcanic or anthropogenic SO2 gas. Salt, NaCl, is another highly reactive species at the high temperatures inside aircraft engines. The reactions that produce the complex CMAS deposits which result when these different components interact in the engine are poorly understood, as are the properties of the deposits, such as melting temperature and viscosity. The problem will be approached from two directions: (i) high-temperature experiments, and (ii) analysis of deposits from in-service engines and from whole-engine tests. The experiments will use high-temperature furnaces in the Experimental Petrology laboratories at the University of Manchester. Analysis of experimental samples and engine deposits will use X-ray diffraction to determine mineralogy, scanning electron microscopy to investigate textures as the CMAS melts interact with the underlying thermal barrier coatings, and Raman spectroscopy to investigate the structural state of minerals and glasses.