Combustion research
The need to control pollutant emissions from the combustion of fossil fuels motivates interest in understanding these processes. Combustion phenomena are basically chemical processes with rapid heat production. Thousands of reactions and intermediates are involved in the combustion of practical fuels. Understanding complex chemical reaction processes largely depends on accurate qualitative and quantitative information regarding the intermediates involved. Thus, direct measurements of these key species are critically important. However, detection of ideally all intermediates with modern analytical instruments is no walk in the park, because even the reaction networks of a simple fuel with a single component may contain hundreds of species with concentrations varying from several percent to trace levels. These challenges have motivated the development of a sensitive experimental approach with universal detecting capability.
Synchrotron-based vacuum ultraviolet (VUV) photoionization mass spectrometry is sensitive and has proven to be a powerful approach for chemical kinetic studies of combustion.
The molecular beam sampling system is used to extract sampled gases with a free-jet rapid expansion in which the sampled molecules are "frozen" as the jet reaches a collisionless free-molecular flow.
An undulator-based vacuum ultraviolet beamline (BL03U), intended for combustion chemistry studies, has been constructed at the National Synchrotron Radiation Laboratory (NSRL) in Hefei, China. The beamline is connected to the newly upgraded Hefei Light Source (HLS II), and could deliver photons in the 5-21 eV range, with a photon flux of 1013 photons s-1 at 10 eV when the beam current is 300 mA.
The beamline serves three endstations which are designed for respective studies of premixed flame, fuel pyrolysis in flow reactor, and oxidation in jet-stirred reactor. Each endstation contains a reactor chamber, an ionization chamber where the molecular beam intersects with the VUV light, and a home-made reflection time-of-flight mass spectrometer. The performance of the beamline and endstations with some preliminary results is presented in a paper recently published in the Journal of Synchrotron Radiation [Zhou et al. (2016), J. Synchrotron. Rad. 23, doi: 10.1107/S1600577516005816].
