Modeling laser-induced incandescence of Diesel soot—Implementation of an advanced parameterization procedure applied to a refined LII model accounting for shielding effect and multiple scattering within aggregates for $${\varvec{\alpha}}_{{\varvec{T}}}$$ and $${\varvec{E}}\left( {\varvec{m}} \right)$$ assessment

An extensive set of LII signals measured in a Diesel spray flame has been simulated using a refined LII model built upon a comprehensive version of soot heat- and mass-balance equations. This latter includes terms standing for saturation of linear, single- and multi-photon absorption processes, cooling by sublimation, conduction, radiation and thermionic emission in addition to mechanisms depicting soot oxidation and annealing, non-thermal photodesorption of carbon clusters as well as corrective factors allowing considering shielding effect and multiple scattering (MS) within aggregates. A complete parameterization of the so-proposed model has been achieved by means of an advanced optimization procedure coupling design of experiments with a genetic algorithm-based solver. Doing so, the values of different factors involved in absorption and sublimation terms have been assessed for a 1064-nm laser excitation wavelength including the multi-photon absorption cross section for C2 photodesorption and the saturation coefficients for linear- and multi-photon absorption, among others. This parameterized model has then been demonstrated to effectively reproduce signals measured in different combustion media including a CH4/O2/N2 premixed flat flame and a diffusion ethylene flame. As a result of the data derived from the analysis of the Diesel flame, a thermal accommodation coefficient value of 0.49 has been assessed against 0.34 when neglecting the shielding effect. In addition, values of the soot absorption function ($$E\left( m \right)$$ E m ) comprised between 0.18 and 0.31 have been inferred depending on the particle maturation stage. On the other hand, $$E\left( m \right)$$ E m 24% higher on average have been estimated when neglecting MS thus illustrating the importance of aggregate characteristics on soot properties derived through LII modeling. Eventually, the $$E\left( m \right)$$ E m evolution observed herein has been compared with results issued from studies conducted with varied hydrocarbons which led to highlight the crucial role played by the soot maturity level over the nature of the burnt fuel as far as optical properties are concerned.

Experimental study on soot characteristics of laminar co-flow ethylene diffused flame under air atmosphere

The morphological characteristics of ethylene flame under different working conditions were photographed and analyzed by CCD camera, the temperature distribution at different positions of flame was measured and analyzed by the thermocouple, and the characteristics of soot in ethylene diffusing flame under different airflow rates were studied by means of SiC fiber sampling and subsequent TEM image analysis. The results showed that: (1) when the airflow was unchanged, the flame height increased with the increase of ethylene flow, and the flame height changed with the increase of ethylene flow in a linear relationship. When the ethylene flow increased from 120 mL/min to 180 mL/min, the flame height increased by about 60%. The flame height increased slightly with the increase in air flow. (2) The flame edge temperature was always greater than the central temperature of the corresponding height. Under the same working condition, the average temperature was 87.5 °C higher. (3) Along the flame axis, soot particles follow the process of nucleation, growth, condensation, agglomeration, and oxidation, and the four processes coexist. Once the flow rate of ethylene is determined, the generation of soot in each stage will lag when the flow rate of air increases.

Laboratory study of the heterogeneous ice nucleation on black-carbon-containing aerosol

Soot and black carbon (BC) particles are generated in the incomplete combustion of fossil fuels, biomass, and biofuels. These airborne particles affect air quality, human health, aerosol–cloud interactions, precipitation formation, and climate. At present, the climate effects of BC particles are not well understood. Their role in cloud formation is obscured by their chemical and physical variability and by the internal mixing states of these particles with other compounds. Ice nucleation in field studies is often difficult to interpret. Nonetheless, most field studies seem to suggest that BC particles are not efficient ice-nucleating particles (INPs). On the other hand, laboratory measurements show that in some cases, BC particles can be highly active INPs under certain conditions. By working with well-characterized BC particles, our aim is to systematically establish the factors that govern the ice nucleation activity of BC. The current study focuses on laboratory measurements of the effectiveness of BC-containing aerosol in the formation of ice crystals in temperature and ice supersaturation conditions relevant to cirrus clouds. We examine ice nucleation on BC particles under water-subsaturated cirrus cloud conditions, commonly understood as deposition-mode ice nucleation. We study a series of well-characterized commercial carbon black particles with varying morphologies and surface chemistries as well as ethylene flame-generated combustion soot. The carbon black particles used in this study are proxies for atmospherically relevant BC aerosols. These samples were characterized by electron microscopy, mass spectrometry, and optical scattering measurements. Ice nucleation activity was systematically examined in temperature and saturation conditions in the ranges of 217≤T≤235 K and 1.0≤Sice≤1.5 and 0.59≤Swater≤0.98, respectively, using a SPectrometer for Ice Nuclei (SPIN) instrument, which is a continuous-flow diffusion chamber coupled with instrumentation to measure light scattering and polarization. To study the effect of coatings on INPs, the BC-containing particles were coated with organic acids found in the atmosphere, namely stearic acid, cis-pinonic acid, and oxalic acid. The results show significant variations in ice nucleation activity as a function of size, morphology, and surface chemistry of the BC particles. The measured ice nucleation activity dependencies on temperature, supersaturation conditions, and the physicochemical properties of the BC particles are consistent with an ice nucleation mechanism of pore condensation followed by freezing. Coatings and surface oxidation modify the initial formation efficiency of pristine ice crystals on BC-containing aerosol. Depending on the BC material and the coating, both inhibition and enhancement in INP activity were observed. Our measurements at low temperatures complement published data and highlight the capability of some BC particles to nucleate ice under low ice supersaturation conditions. These results are expected to help refine theories relating to soot INP activation in the atmosphere.