(MERI) High temperature properties of airborne dusts and their behaviour in aircraft engines

CASE STUDENTSHIP WITH ROLLS-ROYCE

Every year, an estimated 2,000 million tonnes of dust is carried up into the atmosphere, mainly during sand and dust storms. This dust presents a major hazard to modern aircraft engines, which operate at extremely high temperatures that are close to the melting points of many of the minerals in the dust. This hazard is similar to that encountered when aircraft fly through volcanic ash clouds. Particles entrained into the air intake of a turbine engine may be heated to temperatures of over 1200 °C. If they melt they may clog up the cooling holes in the turbine blades or react with the blade material and cause various degrees of engine damage, leading to a shortened service life of the engine, and potentially engine failure. The hazard is greatest during take-off, when the engine runs at its hottest, and large concentrations of particulates are more likely to be present in the air either due to uplift of sands and dusts by local turbulence from the aircraft engine, or because of wind-generated sand and dust storms. It is recognised by the aviation industry that this hazard is likely to get worse as future climatic variability and extremes result in an expansion of dusty environments, as well as more frequent and severe sand and dust storms. In contrast to damage caused by volcanic ash, the mechanisms and nature of damage caused by the ingestion of natural dusts of mixed mineralogy is far less well understood. This PhD project will address this problem from two angles: firstly, through quantitative characterisation of the composition of airborne dusts at different altitudes, and secondly, through an investigation of how different compositions of dusts behave in the high temperature environment of a turbine engine.

The first part of the project follows on from ongoing Rolls Royce-sponsored research that has identified significant gaps in current understanding about the mineralogy and particle size distribution of airborne dusts at different altitudes and geographical locations. The project will focus on quantitatively characterising the complexity, variability and concentration of mineral dusts ingested into engines at different altitudes representing different points in the engine cycle during take-off, climbing and cruising. This will involve the analysis of atmospheric dust samples collected using state-of-the-art remote sensing techniques and through the direct collection of airborne samples mounted on FAAM aircraft and drones.

The second part of the project will focus on developing a model of how the complex natural mineral dusts analysed remotely and sampled by the aircraft will behave at the extremely high temperatures encountered in aircraft engines. One of the key questions to investigate is: how do the variations in mineral concentration and in particle size that are observed at different altitudes manifest themselves in melting behaviour?

To address this, laboratory experiments will begin by investigating the properties of individual minerals, and will then progress to simple binary and ternary mixtures, followed by multi-component mineral mixtures. Geochemical properties will be measured using: differential scanning calorimetry (DSC), to measure the temperatures of devolatilisation and melting reactions; high temperature furnace (up to 1700 °C), to freeze the samples at different stages of the melting process to enable a more detailed study of the chemistry and textures of the melting reactions; X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) of partially melted samples to determine the nature of the reactions taking place; Fourier transform infrared (FTIR) spectroscopy and EPMA of the glasses (= quenched melts) to determine if any of the volatiles released during melting (H2O, CO2, S, Cl) are incorporated into the melt.

This project will be suitable for a student who has a first degree in geology, chemistry or materials science. The student will be trained in the use of airborne sampling technologies and play an integral role in the collection of atmospheric samples either during a flight mission on the FAAM aircraft and/or using drones. Additionally, the student will be trained in using the above geochemical experimental and analytical equipment, all of which is available in the School of Earth and Environmental Sciences. The studentship will include a placement at Rolls-Royce learning about engine operation and examining contamination on engine components following operation in dusty environments. The supervisory team of both earth and atmospheric scientists, together with the input of experts at Rolls-Royce, make this an exciting project which will have impact in the aviation industry, where it will inform engine damage models and hence the cost of ownership for aircraft engine manufacturers.