Papes for the peeps – Aircraft Oil Contamination

This is the first in what I hope to be an ongoing series of posts explaining in simple terms what my scientific publications are about.

The first paper A Method for the Identification and Quantitation of Hydraulic Fluid Contamination of Turbine Engine Oils by Gas Chromatography – Chemical Ionisation Mass Spectrometry, in the journal Lubrication Science has just been made available in the print version but has been available online (paywalled) since June.

This paper is my first publication where I am the first author. First author publications are important for early career scientists as it is a part of demonstrating your capability as an independent researcher. First authorship also usually implies that you have done the majority of the experimental work included in the publication, and also written the bulk of the manuscript itself.

In a way, this publication is very unusual in that it is not in any way related to my main research project which I devote >90% of my time to. However, my lab has been searching for a solution to this problem for many years now, so it was an important piece of work in its own right.

What’s it all about?

It is a relatively common occurrence for the lubricant systems of aircraft to become contaminated through leaks, or human error. In many aircraft, the turbine engine lubrication system is separate from the hydraulic lubrication system, and employs two separate oils for these purposes. If the contamination occurs on a bulk level, it is easy to determine – the oils are different colours, have different flash points and viscosities. But when the contamination is at a low level, these differences become diluted to the point that they are no longer useful indicators. Another difference between the two oils is the distinctive set of additives which are used in each. But using these to detect contamination is also unsatisfactory, because the additives are not used in consistent amounts in the oil, so while the contamination may be detected, the amount can’t be calculated.

In order to detect low levels of contamination, we exploited the chemical differences between these two lubricants. Often when we are analysing our samples, we use an instrument called a ‘Mass Spectrometer’ (MS). The MS breaks apart molecules into pieces, which, oddly enough, is a good way of figuring out what they looked like before they broke apart! But when different oils are put into the MS, they break apart into the exact same fragments so we can’t tell them apart. Annoying. To overcome this, we introduced methane gas into the MS, which attaches onto the oil molecules before they are broken apart in the instrument. The inclusion of the methane means that now the different oils will break apart differently, and we can tell them apart. Using this method we can detect contamination down to 0.5%, which is equivalent to about a teaspoon’s worth of contaminant in a bucket.

A lot of this paper is about the chemical analysis technique that was used, and proving that the method actually works, which is really important when you are developing a complete new way of measuring something. But it’s not that interesting to explain, it basically involves running a lot of samples under specific conditions, repeated the same thing loads of times, and complete some statistical analysis on the data, to make sure that the method is robust. We also made sure that the method worked on oils which were fresh, and those which might have been used, heated or contaminated with water.

I’ve already seen the use of this new method have a real impact on the day to day operation of aircraft. It enables flight crews and aircraft maintainers to make more informed decisions about whether to fly or ground an aircraft with suspected contamination of the  turbine oil. This is something quite satisfying and rewarding for me, given that my main research project is slightly more esoteric, with applications likely to be many years in the future.

***Addendum 16/12/2012  The e-zine/newsletter Separations Now did a story on this paper, which can be found here.



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