Nanoparticles Of Organic Carbon Research Articles

Electric Field Effect on Soot Formation and Collection from Diffusion Flames

characterization of combustion-formed particulate matter for possible applications as optoelectronic organic materials is studied. A copper probe is inserted at different heights above the burner hole. Probe sampling si followed by collection via particles impactor, containing two main different classes of materials, soot and nanoparticles of organic carbon (NOC). Soot (Carbon) particles are collected from laminar and turbulent diffusion flames by means of a DC electric field in the form of chains and clusters. The great majority of soot particles are found to be positively charged. The I-V characteristics are measured in order to estimate the electrical properties during soot collection. The electric current increases as the collection time increases due to the agglomeration of charged soot particles on the copper probe. It is observed that the activation energy Ea increases with increasing probe height H till reaching a maximum value. The mobility of ions for soot particles decrease with the applied potential and increases with the probe height for the turbulent and laminar diffusion flame. The compositions of soot powder samples are investigated by energy dispersive X-ray pattern (EDX) and the size of the soot particles are calculated by dynamic light scattering (DLS) technique.

Effects of gasoline combustion organic carbon nanoparticles on human pulmonary cell lines

Effects of gasoline combustion organic carbon nanoparticles on human pulmonary cell lines

On the hydrophilic/hydrophobic character of carbonaceous nanoparticles formed in laminar premixed flames

Carbon nanoparticles in laminar premixed flames are broadly divided into two classes based on the bimodal shape of the particle size distribution and on the different chemical and physical properties that these particles present depending on the combustion conditions, such as residence time, equivalence ratio, and fuel chemical composition. The chemical and structural characteristics of carbon nanoparticles have been the subject of numerous works because these properties might be of relevance for particle reactivity and optical properties. Few information are available on their hydrophilic properties although these are of relevance for the human health, the climate change, in addition to the technological implementation of condensation nuclei particle counters in aerosol science, water scrubbers and electrostatic precipitators. The aim of this work is to investigate the hydrophilic/hydrophobic behavior of carbon nanoparticles formed in different flame conditions. Static contact angle measurements in addition to chemical and physical characterization of the carbon nanoparticles have been implemented. Results show that nanoparticles formed in richer flame conditions, are the most hydrophobic, whereas nanoparticles of organic carbon, formed in relatively leaner flame condition, appeared to be the most hydrophilic.The reason for a different water affinity of particles, and especially of the smaller organic carbon nanoparticles, has been discussed by analyzing the different material in terms of their chemical/structural composition and in terms of surface functionalities. While no significant differences have been found by Raman spectroscopy in terms of their carbon structure, the different hydrophilicity is explained in terms of the different amount of surface oxygen detected by X-ray photoelectron spectroscopy (XPS). Combustion conditions are therefore very important in outlining the hydrophilic/hydrophobic tendency of the carbon particles.

Coagulation of Organic Carbon Nanoparticles in Exhaust Conditions

The concentration of combustion-generated Nanoparticles of Organic Carbon (NOC) in vehicle emissions and urban atmospheres was evaluated using particle measurement techniques sensitive to NOC (Atomic Force Microscopy, Differential Mobility Analysis and Far UV Absorption Spectroscopy) and a theoretical model was used to predict particle size distributions throughout the exhaust plume. A significant fraction, and in some cases, the majority of particulate formed in combustion conditions of modern engines are NOC, which are an order of magnitude smaller than graphitic soot particles. NOC are mostly smaller than the detection limit of commercial particle sizing instrument used for atmospheric measurements (d < 5–10 nm). The smallest NOC have a higher affinity for water, higher mobility, higher number concentration, and longer lifetime in flames than larger soot particles. Therefore, NOC may contribute to observed human health effects associated with pollution. In previous works, these observations were explained by a theoretical model that predicts the particle coagulation rate as steeply increasing with particle size. The same theoretical model was used in this study to simulate aerosol dynamics in vehicle exhausts and dilution plumes as they mix with urban air and estimate their size distributions. The model predicts bimodal particle size distributions near roadways with a modal diameter of 2–3 nm, similar to the size of combustion-generated NOC measured in flames and engine exhausts. Predictions indicate the presence of NOC in urban atmospheres, similar to measurements by cryogenic sampling and AFM, presented in this work, and characterization studies of organic species in collected rain and fog samples.

Measurements of Nanoparticles of Organic Carbon and Soot in Flames and Vehicle Exhausts

We measured the size distribution and UV extinction spectra of carbonaceous nanoparticles present in the size range of 1-100 nm in the exhausts of 2004 model gasoline and diesel powered vehicles and compared the results with those obtained in premixed flames. In addition to soot particles, nanoparticles of organic carbon (NOC) were measured in the emissions of these test vehicles in significant number and mass concentrations. The number and mass concentration of NOC was higher than soot in gasoline vehicle emissions. In diesel emissions, NOC had a higher number concentration than soot in terms of number concentration, but in terms of mass concentration, soot was higher than NOC. The size (1-3 nm) and extinction spectra in the UV-visible (strong in the UV and transparent in the visible) of macromolecules/nanoparticles collected in water samples from the vehicles are similar to those measured in laboratory hydrocarbon-air flames, suggesting that these nanoparticles are formed in hydrocarbon combustion reactions. We advance the hypothesis that NOC in vehicle emissions are produced by high-temperature combustion processes and not by low-temperature condensation processes.

SOOT AND NANOPARTICLE FORMATION IN LAMINAR AND TURBULENT FLAMES

A new optical diagnostic method has been developed based on the interaction of a pulsed UV laser source with combustion-generated aerosols. This method allows characterization of nanoparticles of organic carbon (NOC) and soot by point measurements. Fluorescence and incandescence measurements induced by the fifth harmonic of a Nd-YAG laser at 213 nm are used for the determination of the volume fractions of particulates in a laminar premixed flame and in a turbulent non-premixed flame of ethylene/air. The selected light source enhances the fluorescence of NOC, which exhibit a large absorption band between 200 and 250 nm and also heats up soot particles to give incandescent emission. Ultraviolet emission signals are correlated with NOC extinction coefficients, while LII signals are correlated with extinction coefficients in the visible region. Laser light scattering measurements are used to estimate the mean sizes of both classes of particles.

Characterization of nanoparticles of organic carbon (NOC) produced in rich premixed flames by differential mobility analysis

Differential mobility analysis (DMA) is used to measure on-line the size distributions of inception particles in atmospheric pressure premixed ethylene air flames ranging from C/O = 0.61 to 0.69, just at the onset of soot formation. DMA is also used, in combination with electrospray, to measure the size distributions of suspended flame products captured in water samples. The DMA systems used for this work employ detectors sensitive to the full range of molecular clusters/nanoparticles in gas-to-particle conversion processes (as small as about 1 nm) and they have much larger sheath gas flow rates than is typically used to reduce losses and peak broadening by diffusion. The measured size distributions show that the first particles observed in flames have a size of 2 nm, consistent with previous in situ measurements by light scattering and extinction (LSE) and the off-line measurements of material captured in water samples from the same flames. For richer flames, the quantity of the 2 nm particles measured increases, and the width of its size distribution shifts asymmetrically toward larger sizes. A numerical coagulation model assuming size-dependent coagulation efficiency predicts well the experimentally measured size distributions in the flames examined. Similarly, the slightly larger size distributions measured by atomic force microscopy of inception particles deposited on surfaces can also be attributed to the size-dependent coagulation/adhesion efficiency. The results imply that the smaller nanoparticles formed in combustion processes have a longer lifetime than those larger than 6–7 nm and may play an important role in the formation of fine organic carbon particulate in the atmosphere.