Chemical technology news from across RSC Publishing.
Instant insight: Watching the burn
23 January 2008
Craig Taatjes of Sandia National Labs, Livermore, US, and colleagues look inside the mysterious chemistry of combustion using photoionization mass spectrometry combined with synchrotron radiation.
A visual interpretation of multidimensional data can give a glimpse of chemical mechanisms - if you know what to look for
Combustion is an ancient technology, but it remains the dominant means of releasing stored energy in the world today. When Nikolaus Otto invented the four-stroke engine in 1876 and when Rudolf Diesel patented his engine in 1898, scientists did not even have the basic knowledge that combustion was driven by chain-reaction chemistry, an insight that would yield Nikolay Semenov the Nobel Prize decades later. The science of combustion systems, with interacting fluid mechanics and complex chemistry, is a daunting multiscale and multiphase problem that continues to tax state-of-the-art computational and experimental methods. There is an intensifying emphasis on reducing pollutant levels, and new engine technologies are emerging that rely on chemical kinetics for ignition timing. These have made understanding the fundamentals of combustion a key to designing new practical devices and have brought detailed chemistry to the forefront of twenty-first-century combustion research.
'Slices' taken out of such datasets by integrating over two of the dimensions would correspond to more traditional measurements, such as profiles of species as a function of distance from the burner or kinetic concentration against time. However, interpretation of the multidimensional data directly from an image yields great insight into global chemical mechanisms and can highlight previously unknown reactive pathways. For example, an image of the evolving mass spectrum of molecules sampled from a rich ethene flame as a function of the distance from the burner shows soot precursor chemistry at a glance. Moving away from the burner, the fuel is consumed and higher-molecular-weight hydrocarbons begin to be formed; species with three carbon atoms appear very close to the burner, four-carbon species slightly farther away, five-carbon species farther still, and so on. Comparison with an image of a similarly rich flame of the oxygenated fuel dimethyl ether shows immediately that the growth of these soot precursors is almost completely absent in the ether flame, consistent with the soot-reducing effects of oxygenates.
The investigation of increasingly complex chemical systems not only requires the ability to simultaneously monitor many channels, but demands new strategies to manage and visualize the resulting data. Tunable photoionization and simultaneous multiple-mass detection can effectively depict flame and chemical kinetic processes; continuing development of spectroscopic and visualization technologies will deliver new insights into combustion.
Read more in Craig Taatjes et al.'s critical review '"Imaging" combustion chemistry via multiplexed synchrotron-photoionization mass spectrometry' in issue 1, 2008 of Phys. Chem. Chem. Phys.
Link to journal article
Imaging combustion chemistry via multiplexed synchrotron-photoionization mass spectrometry
Craig A. Taatjes, Nils Hansen, David L. Osborn, Katharina Kohse-Höinghaus, Terrill A. Cool and Phillip R. Westmoreland, Phys. Chem. Chem. Phys., 2008, 10, 20
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