Project uses laser sensing to measure gas turbine emissions

The four-year, £2.7m FLITES (Fibre-Laser Imaging of gas Turbine Exhaust Species) project is an academic and industrial research collaboration led by Southampton University’s Optoelectronics Research Centre (ORC) and Rolls-Royce.

The goal is to better understand the combustion process, especially in light of the increased useage of bio-derived fuel mixes in the aviation industry, with a view to cutting overall emissions.

There is also a need to improve methods currently used to monitor and diagnose jet engines, as ORC’s Prof Johan Nilsson explained to The Engineer.

‘At the moment the way this is measured — for things [such as] soot — is essentially you stick hoses through the jet plume, collect exhaust coming out and pass it through some sort of filter. It takes a lot of time and you don’t get a lot of data — not much has been done in terms of advancing the state of the art.’

Measurement will initially focus on soot, unburned hydrocarbons, carbon dioxide and nitrogen oxide. This will require an infrared laser array with different spectral characteristics for each of the four emission species.

‘We would measure the fractional light that gets through the plume to the detector on the other side,’ Nilsson said.

‘If you do this in a lot of different paths through the plume then you can use tomographic techniques and essentially know everything about that cross-section of the plume.’

In theory, Nilsson said this two-dimensional section could also be extended along the length of plume to obtain a three-dimensional map akin to imaging ’slice’ scans done in hospitals — although that will be beyond the scope of the four-year project.

‘In principle it’s an easier set-up because you don’t have to stick anything physical in the plume, it’s a quicker measurement and you get much more data,’ Nilsson said.

Some of the laser technologies are already established in areas such as environmental particle assesment, while others will need further development and refinement.

‘This is something you could imagine having at airports as well, you don’t necessarily have to put your engine in a rig to do this, so you could have something on a truck that you drive up behind the engine as part of your regular maintenance,’ Nilsson said.

Other project partners include the universities of Manchester and Strathclyde with Shell, Covesion, Fianium and OptoSci.