The dynamics of electrically charged soot particles in a premixed ethylene flame

We report the size and electrical charge distributions of incipient nanoparticles generated in atmospheric pressure hydrocarbon/air premixed flames in conditions prior to the onset of soot particles. The particle size and charge distributions are measured by Differential Mobility Analysis (DMA) and compared to theoretical charge distributions predicted for flame conditions. The results show that the charge distribution attained in flames is well predicted by Boltzmann theory for all particles, including even the smallest incipient particles with diameters in the 1-3 nm size range. In flame conditions that produce only particles smaller than 3 nm, the charge fraction of particles agrees with that predicted by Boltzmann theory near the flame temperature (1700 K). In flame conditions with 'bimodal' particle size distributions, the charge fraction of the smallest particles agrees with the Boltzmann prediction at maximum flame temperature, while the charge fractions of larger particles agree with Boltzmann theory at temperatures that coincide with the local temperature near the probe surface (1000-1200 K). The results of this paper show that the temperature of the Boltzmann charge fraction that best agrees with the measured charge fraction for each particle size gives the local temperature of their last coagulation event. The smaller particles, which retain their charge fraction predicted by Boltzmann at the maximum flame temperature, do not thermalize by coagulation in the cool region near the probe evidencing low probability for charge transfer as well as for coagulation.

Section: Introductionsupporting

confidence: 75%

Section: Introductionmentioning

confidence: 98%

Charge Distribution of Incipient Flame-Generated Particles

Sgro

D’Anna

Minutolo

2010

“…This is consistent with the implications of the above aerosol electrometer measurements, that the positively charged particles slightly outnumbered the negatively charged particles during the wire electrical explosion process. It follows that the fraction of uncharged (neutral) metal nanoparticles was small, which has also been observed for soot particles measured at a specific height in a premixed ethylene flame (Maricq 2005). The size distributions of the positively and negatively charged particles were shifted by approximately 50 nm toward the lower diameters for singly charged particles.…”

Section: In-situ Monitoring Downstream Of the Evaporation Chambersupporting

confidence: 69%

“…Peaks for multi-charged particles can be observed for both positively and negatively charged particles, as shown in Figure 5. This size distribution is similar to what is typical for monodisperse particles classified by an electrostatic classifier (Maricq 2005), and this is why the multicharged correction option should be selected in the instrument software. However, the fraction of multi-charged particles differed slightly from that of the Boltzmann charge distribution, because the first electrostatic classifier was used without a neutralizer.…”

Section: In-situ Monitoring Downstream Of the Evaporation Chambersupporting

confidence: 52%

In-Situ Characterization of Metal Nanopowders Manufactured by the Wire Electrical Explosion Process

Lee

Jung

Lee³

2010

In order to understand the size distributions of metal nanopowders inside manufacturing equipment operated at elevated pressures, a scanning mobility particle sizer is used to carry out in-situ measurements of metal nanopowders manufactured by the wire electrical explosion process. A pressure reducer and rotating disk diluter are used for conditioning metal nanopowder samples appropriate for real-time aerosol instruments operated at atmospheric pressure. Based on measurement data collected downstream of the evaporation chamber, the production of metal nanopowders shows good stability and uniformity for a total number concentration of approximately 5 × 10 7 particles/cm 3 , and a unimodal size distribution with a mean diameter of approximately 170 nm. Using an aerosol electrometer and two sets of electrostatic classifiers, positively charged particles slightly outnumber negatively charged particles. The performance of the rotating disk diluter is confirmed by comparing the size distributions of metal nanopowders diluted with five different dilution factors, ranging from 235 to 2500. SEM and TEM image analysis indicates that most metal nanopowders manufactured by this process consist of aggregated particles, and their size distributions obtained from SEM images are similar to those measured by the SMPS. The changes in particle size distribution at each stage of the manufacturing process, including the evaporation chamber, trap buffer, cyclone, and mesh filter, are also monitored using the above in-situ monitoring system. The resulting in-situ measurement data can be used for design modifications of equipment, as well as for investigating the sources of nanopowder release to the workplace environment.

“…The larger size particles, those with sizes in the range 10-100 nm, are usually referred to as soot particles and are formed in fuel-rich flame conditions characterized by a strong yellow-red luminosity. Nascent carbon nanoparticles with equivalent diameter of about 2-4 nm are generated both in sooting conditions, where they coexist with larger primary soot particles and soot aggregates, and in less fuel-rich bluish flame conditions where they are formed alone or coexist with the larger 4-10 nm particles (Maricq 2004(Maricq , 2005Dobbins 2007;Commodo et al 2015). Nascent particles were reported to be liquid-like or bidimensional structures which assume an atomically thin disk-like shape when deposited on a substrate Dobbins 2007;Abid et al 2008;Minutolo et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Flame-Formed Carbon Nanoparticles: Morphology, Interaction Forces, and Hamaker Constant from AFM

Falco

Commodo

Minutolo

et al. 2015

Interaction forces acting between combustion-generated carbon particles were studied by using atomic force microscopy (AFM). To this aim, carbon nanoparticles were produced in fuelrich ethylene/air laminar premixed flames with different equivalent ratios F, and analyzed at a fixed residence time in the flame. Particles were collected on mica substrates by means of a thermophoretic sampling system and then analyzed by AFM. A characterization of particle dimension and morphology were performed operating AFM in semicontact mode, showing that the shape of the particles collected on a sampling plate is never spherical. Increasing the flame-equivalent ratio, particle shape moves from an almost atomically thick object to thicker compounds, indicating the transformation from particles made of small, defective graphene-like sheets to particles containing stacked aromatic layers. Attractive and adhesive forces between a titanium nitride probe and sampled particles were calculated from force-distance curves acquired in AFM force spectroscopy mode. Assuming that van der Walls forces are the main contribution to attractive forces, the measurement of attractive forces allowed the evaluation of the Hamaker constant for the carbon particles as a function of the flame-equivalent ratio. The comparison of the measured Hamaker constants with the values for benzene and HOPG, suggests a continuous increase of the aromatic domains and the three-dimensional order within the particles when the flame-equivalent ratio increases.