First images of CO2 from commercial jet engine captured

It has previously been impossible to image turbine combustion on test rigs containing a large airplane engine.

But now researchers have used a near-infrared light imaging technique to capture the first cross-sectional images of carbon dioxide in the exhaust plume of a commercial jet engine.

The new technology could help develop engines and aviation fuels that are more environmentally friendly.

The research was led by the University of Strathclyde and Dr Michael Lengden, a Reader in Strathclyde’s Department of Electronic and Electrical Engineering, led the study. He said: “This approach, which we call chemical species tomography, provides real-time spatially resolved information for carbon dioxide emissions from a large-scale commercial engine.

“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.”

To perform the chemical species tomography, 126 beams of near-infrared laser light are shone through the gas from all around the side at many angles in a way that does not disturb the gas flow. Capturing the exhaust from a commercial airplane engine requires imaging an area up to 1.8m in diameter. To capture this, the imaging components were mounted on a 7m diameter frame located just 3m from the exit nozzle of the engine. The researchers used 126 optical beams to achieve a spatial resolution of about 60mm in the central region of the engine exhaust.

Dr Lengden said: “The very refined measurement methodology we used demanded an exquisite knowledge of carbon dioxide spectroscopy and the electronics systems that provide very precise data.

“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 researchers performed the chemical species tomography on a Rolls-Royce gas engine turbine which are typically used for long-haul aircraft and contain a combustor with 18 fuel injectors arranged in a circle.

For the tests, researchers recorded data at frame rates of 1.25Hz and 0.3125Hz while the engine was operated over the full range of thrust. 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.

Dr Lengden said: “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.

“The teams saw an opportunity to develop world leading instrumentation for the aerospace industry, and to understand emissions and performance improvements from large scale engines. With chemical species tomography, we can now start to ‘see’ the chemical detail of combustion in a real production airplane engine.”

The researchers are now working on quantitative measurement and imaging of other chemicals produced by turbine combustion, and to capture images of temperature.