Understanding the formation mechanism of particulate matter due to incomplete combustion is fundamental to controlling the atmospheric impact of combustion systems. Toxicological studies have demonstrated that ultrafine aerosols can penetrate deep into the pulmonary alveoli, and affect human health. Different studies have identified in rich premixed flames a variety of carbon nanoparticles, ranging from those smaller than 3 nm (defined as nanoparticles of organic carbon, NOC) to larger soot particles of 20 nm, and more for aggregates. Optical methods represent the most desirable methods for nanoparticles studies, due to their accuracy, flexibility, and nonintrusive nature. Two principal uncertainties limit standard optical diagnostics in combustion systems: the spectroscopic properties of the NOC are similar to those of polycyclic aromatic hydrocarbons; and when light scattering is weak and comparable to that from gas-phase compounds, size measurement is affected by large uncertainties. Thus, it is necessary to exploit certain properties of fluorescence, which will depend unambiguously upon the size of the nanoparticles. This goal is achieved by using time-resolved fluorescence anisotropy (TRFA), which leads to both size and spectral characterization of the investigated particles. TRFA shows much promise, and is highly sensitive for detecting nanoparticles, even in a flame hostile environment. It also differs from other sizing methods such as light scattering, as it does not depend on the refractive index. Moreover, exploiting spectral selectivity in light excitation and emission information on chemical functionalities of nanoparticles can be deduced. TRFA opens up new possibilities for combustion and environmental monitoring of nanoparticles. In this chapter, the theory of TRFA ultrafast technique is derived for different operating conditions. Experimental realizations, results and the analysis of nanoparticles produced in flames in two different configurations (directly in flames and for samples collected from the flame) are then presented and discussed.
Ultrafast Fluorescence Anisotropy for Combustion-Produced Nanoparticles Analysis
Corrado de Lisio;Patrizia Minutolo
2010
Abstract
Understanding the formation mechanism of particulate matter due to incomplete combustion is fundamental to controlling the atmospheric impact of combustion systems. Toxicological studies have demonstrated that ultrafine aerosols can penetrate deep into the pulmonary alveoli, and affect human health. Different studies have identified in rich premixed flames a variety of carbon nanoparticles, ranging from those smaller than 3 nm (defined as nanoparticles of organic carbon, NOC) to larger soot particles of 20 nm, and more for aggregates. Optical methods represent the most desirable methods for nanoparticles studies, due to their accuracy, flexibility, and nonintrusive nature. Two principal uncertainties limit standard optical diagnostics in combustion systems: the spectroscopic properties of the NOC are similar to those of polycyclic aromatic hydrocarbons; and when light scattering is weak and comparable to that from gas-phase compounds, size measurement is affected by large uncertainties. Thus, it is necessary to exploit certain properties of fluorescence, which will depend unambiguously upon the size of the nanoparticles. This goal is achieved by using time-resolved fluorescence anisotropy (TRFA), which leads to both size and spectral characterization of the investigated particles. TRFA shows much promise, and is highly sensitive for detecting nanoparticles, even in a flame hostile environment. It also differs from other sizing methods such as light scattering, as it does not depend on the refractive index. Moreover, exploiting spectral selectivity in light excitation and emission information on chemical functionalities of nanoparticles can be deduced. TRFA opens up new possibilities for combustion and environmental monitoring of nanoparticles. In this chapter, the theory of TRFA ultrafast technique is derived for different operating conditions. Experimental realizations, results and the analysis of nanoparticles produced in flames in two different configurations (directly in flames and for samples collected from the flame) are then presented and discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
