X-Ray Diagnostics in Combustion - Study of Particle Formation in Flames Using Combined Small- and Wide-Angle X-Ray Scattering

In the thesis work, two X-ray scattering techniques, small- and wide-angle X-ray scattering (SAXS and WAXS) were combined to study particle formation in-situ and non-intrusively in ethylene laboratory flames. Combining these two techniques enabled information concerning the size and concentration as well as the subnanometer structure of the nanoparticles within the 1–100 nm range there to be obtained. Different stages in the particle formation process, and thus particles of different types were studied by varying the height above the burner surface. An increased understanding of these nanometer-sized particles and how they are formed in flames was sought. In a longer perspective, the work aims at contribute to a greater awareness of the emission of nanoparticles in combustion and ultimately to a reduction in the levels of emission. A large part of the work concerned the development and construction of a new detection system, one combining SAXS and WAXS and designed for flame measurements in particular. The detection system arrived at included a new SAXS detector, implemented together with an already existing WAXS detector, as well as specially designed software. The SAXS and WAXS detectors were characterized by several test measurements conducted at different beamlines at the synchrotron facility MAX-lab in Lund, Sweden. The SAXS/WAXS detection system was used initially at beamline D611 at MAX-lab for studying the particle formation process from the gas phase to the condensed phase in a diffusion ethylene flame just below a metal plate that was inserted into the flames there. The metal plate served as a flame stabilizer and as a cooling support for particles to condense on. A large number of particles smaller than 100 Å were found to be produced when the flame temperature was lowered. To study these nanoparticles at a higher level of resolution, use was made of another SAXS and WAXS detection system at beamline ID02 at the European Synchrotron Radiation Facility (ESRF), for conducting measurements close to the metal plate. This study enabled five main size groups of ≤ 8 Å, 15–30 Å, 30–100 Å, 100–200 Å, and fractal aggregates of 1000–2000 Å, to be identified. The concentrations for each of the size groups were determined quantitatively, the concentrations of particles below 50 Å in size being found to be very high at the end of the experiment. The new SAXS/WAXS detection system was also used at beamline ID12 at the ESRF for measurements of the gas-phase nanoparticles in different ethylene-rich, both sooting and non-sooting, flames at lower heights above the burner. Here vertically polarized X-ray radiation was employed, this extending the region involved in the case of WAXS and providing a more direct comparison of the chemical codes involved in evaluating the chemical composition of small species in different flame regions. The fitting of theoretical curves to the experimental data showed high concentrations of particles 1–2 nm in size

A combined small- and wide-angle x-ray scattering detector for measurements on reactive systems

A detector with high dynamic range designed for combined small-and wide-angle x-ray scattering experiments has been developed. It allows measurements on single events and reactive systems, such as particle formation in flames and evaporation of levitating drops. The detector consists of 26 channels covering a region from 0.5 degrees to 60 degrees and it provides continuous monitoring of the sampled signal without readout dead time. The time resolution for fast single events is about 40 mu s and for substances undergoing slower dynamics, the time resolution is set to 0.1 or 1 s with hours of continuous sampling. The detector has been used to measure soot particle formation in a flame, burning magnesium and evaporation of a toluene drop in a levitator. The results show that the detector can be used for many different applications with good outcomes and large potential. (C) 2011 American Institute of Physics. [doi:10.1063/1.3613958

Dynamics of incipient carbon particle formation in a stabilized ethylene flame by in situ extended-small-angle- and wide-angle X-ray scattering.

International audienceSimultaneous small-angle and wide-angle X-ray scattering (SAXS and WAXS) were used to measure several properties of the nanoparticles and soot being produced and undergoing condensation and phase changes below a stabilizing cooling plate inserted in an ethylene diffusion flame. From the SAXS data several distinct size modes appeared showing interdependent changes in the size, shape/morphology, and concentrations over the time of the experiment. The WAXS data contained information on the internal atomic-level structure of the nanoparticles and soot. They also provided important information on the onset and evolution of the condensation of particles onto the plate and the graphitization process. The concentrations of particles were determined quantitatively from the SAXS data. A very important result was the strong increase for sizes smaller than 100 angstrom, which increased drastically to very high values with number concentrations orders of magnitude higher than normally reported from flames. The results and methods applied are of interest for future studies of dynamics related to condensation and material synthesis of carbon- and non-carbon based nanoparticles in the gas phase and during deposition on surfaces