Soot Oxidation Kinetics: A Comparison Study of Two Tandem Ion-Mobility Methods

Abstract

The oxidation kinetics of laboratory-generated soot particles has undergone extensive studies because of its importance in combustion-generated emissions and their control. In this study, we employed and compared two tandem ion-mobility methods, a tandem differential mobility analyzer (TDMA) and a differential mobility analyzer–aerosol particle mass analyzer (DMA–APM), to resolve the oxidation kinetics of soot. Whereas the TDMA method measures changes in particle mobility (i.e., size) from which a mass-based reaction rate can be inferred, the DMA–APM is a direct determination of particle mass change. We monitored the structure evolution of soot during oxidation by determining the mass-mobility scaling exponent of the particle population and found that soot structural changes due to oxidative sintering can perturb and corrupt the apparent reaction kinetics extracted from the TDMA method and suggest that the DMA–APM method probably is a more reliable approach to pursue such measurements. By combining the mass change data from DMA–APM with size change data from TDMA, we obtained the material density and primary particle size of soot aggregates during oxidation. Two reaction regimes were identified with oxidation fully penetrating the particle at low temperatures and partial penetration at high temperatures. The activation energies were determined for the two reaction regimes to be 79 and 201 kJ mol–1, respectively. The results should be useful in designing soot oxidation abatement units.

Investigation of soot oxidation by coupling LII, SAXS and scattering measurements

“…Numerical modeling is a promising tool to reach this goal; nevertheless, the main mechanisms involved in the soot formation (mainly surface growth and oxidation) need to be better understood (Mueller et al 2011). To reach this goal, many studies have been performed in flames for soot characterization under the oxidation process by ex-situ techniques (Ghiassi et al 2016;Jung et al 2004;Kim et al 2005;Lee et al 1962;Lighty et al 2011;Ma et al 2013;Puri et al 1994) or in-situ optical techniques (Garo et al 1988;Garo et al 1990;Neoh et al 1985;Xu et al 2003), the latter generally based on laser light extinction, scattering and the depolarization ratio. Most of these studies, however, cannot isolate oxidation from surface growth mechanisms occurring within sooting flames.…”

The high charge fraction of flame-generated particles in the size range below 3 nm measured by enhanced particle detectors

“…Size-resolved particle charge fractions, or charge distributions, are typically determined by using the tandem differential mobility analyzer (TDMA) method. It utilizes two differential mobility analyzers (DMAs), which classify particles according to their electrical mobility equivalent size, based on the balance between the electrostatic force and drag force [12,13]. In a TDMA setup, by passing the monomobile particles classified by the first DMA into a charge conditioner and then into a second DMA for mobility scanning, the fractions of particles carrying a specific number of charges can be determined [14,15].…”

Practical limitations of aerosol separation by a tandem differential mobility analyzer–aerosol particle mass analyzer

“…The use of a tandem differential mobility analyzer (DMA), aerosol particle mass analyzer (APM) coupled to a condensation particle counter (CPC) to measure aerosol mass distributions has been extensively documented in the literature (Barone et al 2011; Charvet et al 2014; Cross et al 2010; Geller et al 2006; Kuwata and Kondo 2009; Laborde et al 2012; Lall et al 2009; Lall et al 2008; Lee et al 2011; Lee et al 2009; Lin et al 2014; Ma et al 2013a; Ma et al 2013b; Malloy et al 2009; Olfert and Collings 2005; Olfert et al 2006; Pagels et al 2009; Park et al 2003a; Park et al 2004b; Park et al 2003b; Rissler et al 2013; Sakurai et al 2003; Scheckman et al 2009; Shin et al 2010; Tajima et al 2011; Tajima et al 2013; Xue et al 2009). Some studies have added optical measurements to afford an additional level of classification (Radney et al 2013; Radney et al 2014).…”