A Danish-U.S. optical device could help researchers image pollutants in combusting fuel sprays leading to better fuel economy and reduced emissions.
Developed by researchers at Sandia’s Combustion Research Facility and the Technical University of Denmark, the device can now quantify the formation of carbon soot as a function of time and space for a variety of combustion processes.
The team initially focused on the combustion of liquid fuel sprays found in engines, where the extreme pressures and temperatures create an environment that is optically challenging.
“The acquired data provides important insights into the fuel spray motion as well as the timing and quantity of soot formed under a wide range of conditions,” said Sandia researcher Scott Skeen. “Engine developers can use this information to validate computer models and design advanced engine combustion strategies that will improve fuel economy for consumers while also lowering tailpipe pollutant emissions.”
The optical setup was developed to quantify soot formation in high-pressure spray flames produced in Sandia’s optically accessible, constant volume, pre-burn combustion chamber.
Imaging flames at temperatures and pressures found in engines can be difficult because of a phenomenon called ‘beam steering.’
Beam steering occurs when light passes through a medium with varying refractive indexes and is commonly observed as a ‘mirage’ on the highway in the summer time. The hot pavement heats up nearby air, causing its refractive index to change. The sunlight changes direction as it passes from cooler air through hotter air, and these steered light rays give the impression that there is water in the road.
In a similar way, a flame causes beam steering because of adjacent high- and low-temperature regions. The magnitude of beam steering increases significantly in an engine because of the high pressures. With optimized lighting and imaging optics, however, the effects of beam steering can be eliminated.
The diagnostic allows researchers to quantify the formation of particulate matter in combusting sprays with unprecedented temporal and spatial resolution.
According to Sandia, insights and data acquired from this diagnostic could help researchers and automotive manufacturers maximize fuel efficiency while minimizing harmful tailpipe emissions.
Image credits and content: Dino Vournas/Sandia Labs