Development of simultaneous hyperspectral coherent Raman imaging for advancing reduced emission combustion technology

Development of simultaneous hyperspectral coherent Raman imaging for advancing reduced emission combustion technology

Bohlin, G.A. (TU Delft Flight Performance and Propulsion)

2016

Overall aim and key objectives Advances in optical imaging techniques over the past decades have revolutionized our ability to study chemically reactive flows encountered in air-breathing combustion systems. Emerging technology for unravelling clean- and efficient heat release is needed for advancing new reduced emission technology, and is on the central agenda for a wide variety of energy production- and transport industry. Combustion of fossil fuels remains our largest source of energy production in the world, and global concerns regarding energy security, environmental pollution, and anthropogenic climate change have motivated a large body of research devoted to the experimental measurement and numerical simulation of combustion systems. Clean combustion engineering is the search for improved efficiency by means of strengthen the systems fuel-economy and lowering the emission of NOx, particulates, CO and unburned hydrocarbons (incomplete combustion). New reduced emission technology, greatly rely upon the ability to control the heat release and the exhaust produced by the exothermic reactions between the fuel and the oxidizer in the chemically reactive flow. For the engineering system design, it exist a significant need to inform on the flame-physics involved based on direct observation of the combustion reaction progress and interaction, which is a demanding task for any measurement technique. Chemically reactive flows are inherently multiscale, fully characterized in three-dimensional space and evolving on rapid time-scales. The combustion environment imposes a significant challenge for diagnostics, where it needs to be collected complete information ideally with correlated-field multi-parameter measurement capabilities, exhibiting high spatial and temporal resolution and provided within a snap-shot to freeze the fast dynamics involved. Concurrent detection of major- and minor molecular species (multiplexing) and determining the three most important scalars; the temperature, the flow-field, and the mixture fraction, is vitally important in studies of the reactive flow. The temperature marks the evolution of heat release and energy transfer, while species concentration gradients provide critical information on mixing and chemical reaction. Optical imaging techniques have the advantage of being non-invasive, which means that the studied process is not significantly perturbed by the measurement technique, and allowing for the acquisition of statistics in-situ. Spectroscopy offer intrinsic chemical specificity, in that different classes of molecules have specific spectral signatures serving as unique fingerprints for their identification. Laser-based diagnostics may in general provide measurements with exceptionally high spatial- and temporal resolution, which is important in producing reliable and accurate experimental data. Coherent anti-Stokes Raman spectroscopy (CARS) is one such versatile technique, which has had a profound impact on a wide variety of fields. It was pioneered in composition- and temperature measurements almost 40 years ago, and is referred to as authoritative with the level of accuracy and precision it may provide. A limitation still, has been its main applicability as a single point-measurement technique, where the experimenter needs to raster-scan the measurement samples assembling the spatial image. Because many complex systems can be fully characterized in multidimensional space, there is a large motivation for the advancement of multidimensional CARS imaging techniques.

http://resolver.tudelft.nl/uuid:ff64d93c-0e7a-4326-a330-4826b553ebdb

Combura 2016, 2016-10-05 → 2016-10-06, Soesterberg, Netherlands

Institutional Repository

abstract

© 2016 G.A. Bohlin