Deposition Of Soot Particles Research Articles

A One-Dimensional Model for Particulate Deposition and Hydrocarbon Condensation in Exhaust Gas Recirculation Coolers

Cooled exhaust gas recirculation (EGR) is widely used in diesel engines to control engine out NOx (oxides of nitrogen) emissions. A portion of the exhaust gases is recirculated into the intake manifold of the engine after cooling it through a heat exchanger. EGR cooler heat exchangers, however, tend to lose efficiency and have increased pressure drop as deposit forms on the heat exchanger surface. This adversely affects the combustion process, engine durability, and emissions. In this study, a 1-D model was developed to simulate soot deposition, soot removal, and condensation of several hydrocarbon (HC) species in a circular tube with turbulent gas flow at constant wall temperature. The circular tube, which makes up the computational domain in the model, represents a single channel from any EGR cooler geometry. The model takes into account soot particle deposition due to thermophoresis, diffusion, turbulent impaction, and gravitational drift. However, thermophoresis was found to be the most dominant depos...

Modeling of soot deposition in wavy-fin exhaust gas recirculator coolers

This work presents one of the first CFD studies carried out to understand the fouling of exhaust gas recirculator (EGR) cooler surfaces. The deposition of soot particles in wavy-fin EGR coolers is studied by way of simulations carried out in a periodic framework. In the presence of very high temperature gradients, usually prevalent in EGR flows, the particle deposition process is dominated by the thermophoretic force. Calculations are performed for 10 and 100nm particles at various Reynolds numbers and wall temperature gradients ranging from 1.0 to 9.45×106K/m. It is seen that for the sub-micron particle sizes considered, the deposition process is independent of the particle size. Simulations in the wavy-fin geometry indicate the presence of preferential deposition patterns, corresponding to the regions of higher heat transfer. At lower Reynolds numbers, the amount of deposition increases considerably due to the higher particle residence times. Also, the amount of deposition exhibits a linear relationship with the applied wall temperature gradient, thus confirming the importance of thermophoresis in the soot deposition process.

Detection of Soot Using a Resistivity Sensor Device Employing Thermophoretic Particle Deposition

Results are reported for thermophoretic deposition of soot particles on resistivity sensors as a monitoring technique for diesel exhaust particles with the potential of improved detection limit and sensitivity. Soot with similar characteristics as from diesel exhausts was generated by a propane flame and diluted in stages. The soot in a gas flow at 240–270C∘was collected on an interdigitated electrode structure held at a considerably lower temperature, 105–125C∘. The time delay for reaching measurable resistance values, the subsequent rate, and magnitude of resistance decrease were a function of the distance between the fingers in the electrodes and the degree of dilution of the soot containing flow. Soot deposition and subsequent removal by heating the sensor support was also performed in a real diesel exhaust. Good similarities between the behavior in our laboratory system and the real diesel exhaust were noticed.

Experimental study on thermophoretic deposition of soot particles in laminar diffusion flames along a solid wall in microgravity

Soot deposition process in diffusion flames along a solid wall has been investigated experimentally under a microgravity environment. An ethylene (C 2H 4) diffusion flame was formed around a cylindrical rod-burner with the surrounding air velocities of V a = 2.5, 5, and 10 cm/s, the oxygen concentration of 35%, and the burner wall temperature of 300 K. A laser extinction method was adopted to measure the distribution of soot volume fraction. The experiments determined the trace of maximum soot concentration together with the relative distance of the trace of flame. Results showed that the distance was about 2–5 mm. As the surrounding air velocity increased, the region of the soot particle distribution moved closer to the burner wall. The soot particles near the flame zone tended to move away from the flame zone because of the thermophoretic force and to concentrate at a certain narrow region inside the flame. Because of the simultaneous effects of convection and the thermophoresis, soot particles finally adhered to the burner wall. It has been found that there existed an optimal air velocity for the early deposition of soot on the furnace wall.

MIXED ODE-MC MODEL FOR SOOT CAKE FORMATION IN A SQUARE CHANNEL WALL-FLOW FILTER

Fluid flow in a wall-flow Diesel particulate filter (DPF) can be analyzed by means of a 1-D flow model which reproduces pressure drop due to soot particle deposition, obtained by Konstandopoulos et al. (2003), just solving an ordinary differential equation (ODE). Particle deposit properties are known to depend on the (filtration) velocity through the porous walls, vw, by means of the dimensionless Peclet number, Pe vwa D , where a is some characteristic length of the particles being deposited, and D is the particle Brownian diffusion coefficient. This correlation initially observed in Monte Carlo (MC) simulations by Tassopoulos et al. (1989), has also been observed experimentally by Konstandopoulos et al. (2002). We have adapted a previously developed MC method, suitable to simulate particle deposits [Rodriguez-Perez et al. (2003)], to reproduce the deposition process occurring on the four walls of a square section filter duct.

Experimental and theoretical studies of flame hydrolysis deposition process for making glasses for optical planar devices

We have here presented experimental and theoretical studies of a flame hydrolysis deposition (FHD) process for making glasses for optical planar devices. FHD involves deposition of soot particles generated in the flame on a planar surface to form a porous layer. In order to function as a waveguide core, the porous soot deposit must be sintered at high temperatures to form a dense glass. However, these temperatures are high enough to cause the dopants to volatilize at the surfaces of the deposit. As a result, dopant concentration gradients and compositional inhomogeneities are created in the densified glass layer which result in inferior optical properties. If the layers could be deposited pre-sintered during laydown, these problems could be minimized or avoided. To understand the FHD process and its effect on the morphology of the resulting deposit, a number of models have been developed. We present models to predict the structure of the soot-laden flame along with the methods to estimate soot number density and mean size at different locations in the flame. A simple method is presented to predict morphology of the suspended soot and soot deposit formed during deposition. Motivated by the predictions of the model, process changes were made which resulted in the morphology of the core layers to change from sooty to pre-sintered during deposition. These process changes resulted in core glasses with significantly improved core roughness, index uniformity and thickness uniformity which helped reduce the straight waveguide losses from 0.2–0.3 to 0.02–0.05 dB/cm. Details of underclad and overclad glasses which resulted in low warpage and polarization sensitivity of 0.1 nm for phasar or phasar-arrayed waveguide devices are also presented.

A Study on the Human Ability To Detect Soot Deposition onto Works of Art

Works of art can become soiled due to the deposition of airborne black soot particles within museums and art galleries. The soot particle deposition rates are already known for many environments, but knowing the levels of carbon particle coverage at which humans can detect image darkening is also important. Therefore, in this work, human subjects have been tested to determine their ability to detect soiling by black carbon particles deposited onto specially prepared samples having colored backgrounds. The results show that certain observers are able to detect that a sample is becoming soiled once surface coverage by black carbon particles has reached 2.4% if the soiled samples and clean samples are placed directly adjacent to each other, producing a sharp dividing line (an “edge-to-edge” comparison). Observers can detect the presence of soiling with greater than 90% accuracy during an edge-to-edge comparison on most backgrounds when soiling levels reach approximately 3.6% surface coverage by black particles. If the comparison between soiled and clean samples must be made with samples that are separated from each other by a neutral gray area, soiling is only detected with 100% accuracy once coverage by black particles has reached 12.0% surface coverage. These results show that a greater accumulation of black carbon than was previously thought is required to produce a visibly soiled surface.

Soot particle deposition in the human respiratory tract

Soot particle deposition in the human respiratory tract

Surface Microlayer Enrichment of Polycyclic Aromatic Hydrocarbons in Southern Chesapeake Bay

Dissolved and particle-associated polycyclic aromatic hydrocarbons (PAHs) were measured in the surface microlayer (SM) of the York and Elizabeth River tributaries of Southern Chesapeake Bay throughout 1 year. Particle-associated PAH concentrations in the SM increased nonlinearly with total suspended particulate (TSP) levels, and a much more rapid rise in particulate PAHs with TSP was observed in the Elizabeth River vs the York River SM. The steep rise in particle-associated PAH concentrations along with observed nonequilibrium distributions of PAHs between the dissolved and particle phases in the Elizabeth River SM implies that atmospheric deposition of soot particles may be an important source of PAHs to this urban estuary. A significant relationship between dissolved PAHs and dis solved organic carbon (DOC) was also observed at the York River site, with the more hydrophilic PAHs exhibiting greater increases with DOC. PAHs were significantly enriched in the SM of both sites relative to the subsurface water concentrations. Particle-associated and dissolved phase enrichment factors were strongly influenced by wind speed at the Elizabeth River site; however, only particulate phase enrichment factors were dependent on wind speed at the York River site.

Soot and carbon deposition mechanisms in ethene/air flames

Deposition of soot particles during any combustion process is very undesirable and can cause both mechanical and environmental problems. An investigation has been carried out of the deposition of soot on to both cooled and uncooled metal probes in rich ethene/air flames (φ = 2.76 and 2.52) using a flat-flame, water-cooled burner. The processes by which soot particles move to the surface of deposition probes, and the way in which they adhere to the surface, have been explored. The results have shown that the temperature of the probe can have a significant effect on the deposition rates and the chemical nature of the deposits.

The deposition of soot particles from hot gas streams through pipes

Using theories for diffusive and thermophoretic deposition available in the literature, a model was compiled for the estimation of the penetration rate of aerosol particles through pipes. The numerical results of the model were tested by a few experiments, and its practical applicability has been demonstrated. A realistic case with diesel exhaust as the test aerosol and high penetration rates about 90%) was chosen. The soot aerosol turned out to be bimodal (120 and 2400 nm approximately, GSD > 2).

Chemistry and Deposition of Soot Particles in Moist Air and Fog

From numerous laboratory experiments it is well known that gaseous compounds are absorbed and can be oxidized on aerosol particles and in droplets by different processes. But only few studies have been performed in the atmosphere that show the contribution of heterogeneous reactions to sulfate and nitrate formation processes. Therefore vertically resolved and time-dependent measurements of chemical compounds and meteorological quantities were conducted near a polluted area to study the formation of reaction products on soots and other particles and the activation of these particles during fog formation. Furthermore, the influence of these particles on chemical reactions inside fog droplets was examined. The fluxes of different compounds, particles, and droplets were calculated from vertical profiles of chemical, physical, and meteorological quantities. If the horizontal and vertical transport from the source region to the measuring site is considered, the observed particle composition can be calculated based on reaction laws from laboratory experiments. The influence of relative humidity on the reaction rate was found to be especially important in the atmosphere. Soot particles are often found to be activated to a lower extent than other particles during fog formation. Then the deposition fluxes of soots in humid air and fog are smaller than for other particles.

Mass-transport aspects of pollutant removal at indoor surfaces

The mass-transport-limited rate of pollutant deposition onto indoor surfaces is examined in this paper. Transport of both particles and highly reactive gases through the boundary layer of air adjacent to a surface is analyzed for three model airflow conditions: (1) natural convection flow along room surfaces, (2) forced laminar flow parallel to room surfaces, and (3) homogeneous turbulence in the core of the room. Transport mechanisms considered include convective diffusion, thermophoresis, and gravitational sedimentation. The predicted mass-transport-limited deposition velocity, averaged over the surfaces of a room, varies from order 10 −6 to 10 −2 m s −1 over the range of pollutant diffusivities and particle sizes encountered. Theoretical predictions are in rough agreement with the limited experimental data that have been taken inside rooms. Results show that if buildings were designed and operated such that natural convection of forced laminar flow conditions prevailed with surface temperatures a few degrees K warmer than the room air, soiling of vertical surfaces due to deposition of soot particles in the size range 0.1–1 μm diameter could be greatly reduced.

Measured and predicted soot profiles in a gas turbine combustor

Radiation intensity and emissivity measurements were made for a DF-2 flame in a model gas turbine combustor. This same flame was also mapped for temperature and soot mass concentration. Finally, a movable, cold traversing background was used to determine the contribution to total radiation intensity from the individual sections of the flame. A computer program which integrated the radiative transfer equation with respect to path length and frequency was then used to predict a soot profile, based on temperature, radiation intensity, emissivity, and cold traversing background results. Though the predicted soot concentrations were considerably higher than the measured levels, the agreement between the predicted and measured shapes of the soot profile was good. The discrepancy between predicted and measured soot mass concentrations was attributed to soot particle deposition in the probe.