In-flow optical characterization of flame-generated carbon nanoparticles sampled from a premixed flame.

In this work, the optical absorption properties of carbon nanoparticles are investigated by applying in-flow extinction and laser-induced incandescence measurements. Carbon nanoparticles are produced in an ethylene/air premixed flame and sampled at different heights above the burner. From extinction measurements, the absorption coefficient is obtained in a wide spectral range, considering the negligible scattering under our experimental conditions. With the application of Tauc plot the optical band gap is evaluated at the sampling heights under analysis. The increase of this value with the decrease in the height is consistent with the quantum confinement effect detected in the inception region of the flame. Two-color laser induced incandescence measurements are performed at relatively high laser fluence. The fluence curves, given by the particle temperature under laser irradiation versus laser fluence, are also obtained. A significant difference in the optical properties of these particles is observed by changing the sampling height. Moreover, considering the fluence curve in the low laser fluence regime, the refractive index absorption function E(m) is evaluated at an excitation wavelength of 1064 nm. Finally, the knowledge of the behavior of the absorption coefficient in a wide spectral range allows retrieving the values and the behavior of E(m) as a function of wavelength.

Two-dimensional two-wavelength emission technique for soot diagnostics.

A two-dimensional soot diagnostic technique has been developed as an extension of the well-known two-color pyrometry. Two flame images are simultaneously collected on a CCD at selected wavelengths through suitable optics. By use of the dependence of soot emissivity on the soot volume fraction and by comparison with images from a calibrated light source, both the temperature field and the soot distribution can be determined. Validation was carried out through data obtained with other soot diagnostic methods on ethylene diffusion and Diesel oil-rich premixed flames. The current technique readily allowed us to obtain a large amount of data for a thorough description of the soot distribution within the flame. As an example of the technique's potential, data about methane and propane diffusion flames are reported.

Determination of soot parameters by a two-angle scattering-extinction technique in an ethylene diffusion flame.

We used a two-angle scattering technique to investigate the soot distribution in an ethylene diffusion flame in conjunction with extinction measurements. In the framework of a fractal description, we introduced a modified structure factor to interpret the scattering intensity from polydisperse aggregates. The connection between a mean value of a structural radius of gyration, R(gm1), and the quantities experimentally measured was then established. Soot parameters (volume fraction, particle size, and number densities) were determined along three radial sections of a 8-cm high-diffusion flame. The stability of the results with respect to the parameters of the distribution function was studied.