10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Direct On-line Measurement Of Soot Oxidation Reactivity
REINHARD NIESSNER, Alexander Rinkenburger, Christoph Haisch, Technical University of Munich, Germany
Abstract Number: 484 Working Group: Combustion
Abstract Diesel soot is one of the major pollutants in the world and is classified as carcinogenic. Soot is theorized to have the second largest impact on global warming after CO2. In North America and Europe, soot is mainly emitted by diesel engines, which are equipped with particulate filters to minimize emissions. Regeneration of these filters is done by oxidation (combustion) of the soot. Uncatalyzed oxidation requires temperatures > 600 °C (5-10 Vol.-% O2 in N2), resulting in poor fuel efficiencies. Catalysts, i.e. as additives, can lower these temperatures significantly. As we have shown before, not only toxic Ferrocene- or Ce-based compounds are suitable, but also cheap, inorganic and most likely non-toxic salts. Usually, soot oxidation reactivity is derived from temperature-programmed oxidation (TPO) measurements, microscopic techniques (i.e. HRTEM, SEM), Raman microspectroscopy (RM) or other spectroscopic techniques. Most of these techniques need collected (filter) samples, are time-consuming and costly, and sometimes fail to characterize certain soot samples. So, there is definitely a need for fast and on-line methods to characterize the oxidation reactivity of soot.
Our solution to this problem essentially consists of an in-house built propane/air diffusion burner to generate soot model aerosols and a custom-built oven to thermally treat these aerosols in relation to a reference. We employed several detection systems after the oven, namely two scanning mobility particle sizer setups (SMPS), an infrared spectrometer (FTIR) and photoacoustic spectrometers (MSS, QuadPASS).
The setup was first characterized using two SMPS systems in parallel and let us to the conclusion that mean diameters are a good criterion for soot oxidation reactivity. We could also show that there is a clear, temperature-dependent decrease in mass concentrations as measured by the photoacoustic spectrometers. Soot containing salt shows earlier and faster oxidation compared to pure propane soot, which is consistent with the TPO results. In fact, we do not even need to observe full temperature programs like in the TPO measurements, but can derive parameters related to the soot oxidation reactivity very fast and on-line by single-temperature measurements. This results in a huge improvement of measurement times, enables us to follow transient systems almost in real time and gives rise to new possibilities regarding particle emission reductions.