UK team images jet engine emissions in world-first

Claimed to be a world-first, the project brought together four different instrumentation research groups from across the UK, drawing in knowledge of gas species measurement in harsh environments, chemical species tomography and optical source development. Working alongside industrial partners including Rolls-Royce and Siemens, the team developed a 7m-diameter optical mounting frame situated just 3m from the exit nozzle of a Rolls-Royce Trent gas engine turbine. The rig was set up at the Instituto Nacional de Tecnica Aeroespacial (INTA) in Madrid.

From the frame, 126 beams of near-infrared laser light were shone through the gas from a variety of angles, but without disturbing the gas flow. The resulting images captured the real-time CO2 emissions coming from the engine. It is hoped that the imaging technique can now be used to improve turbine design and develop greener aviation fuels and technologies. The study is published in Applied Optics.

“This approach, which we call chemical species tomography, provides real-time spatially resolved information for carbon dioxide emissions from a large-scale commercial engine,” said research team leader Michael Lengden from the University of Strathclyde. “This information has not been available before at this industrial scale and is a big improvement over the current industry-standard emissions measurement, which involves taking gas from the exhaust to a gas analyser system in a different location.

“The aviation industry is a major contributor to global carbon dioxide emissions so there is a need for turbine and fuel technologies to improve radically. By providing fully validated emissions measurements, our new method could help the industry develop new technology that reduces the environmental impact of aviation.”

For the tests, the researchers recorded data at frame rates of 1.25 Hz and 0.3125 Hz while the engine was operated over the full range of thrust. Imaging showed that, at all thrust levels, a ring structure of high carbon dioxide concentration was present in the central region of the engine. There was also a raised region in the middle of the plume, which was likely due to the engine’s shape.

“The very refined measurement methodology we used demanded an exquisite knowledge of carbon dioxide spectroscopy and the electronics systems that provide very precise data,” said Lengden. “Also, a very sophisticated mathematical method had to be developed to compute each chemical species image from the measured absorptions of the 126 different beams we used.”

The project team included Strathclyde, Edinburgh, Manchester, Southampton, Loughborough and Sheffield Universities; Rolls-Royce; Siemens; laser instrumentation manufacturer OptoSci Ltd.; and imaging systems manufacturers M Squared Lasers and Tracerco.