Mapping the Operation of the Miniature Combustion Aerosol Standard (Mini-CAST) Soot Generator

Abstract

The Jing Ltd. miniature combustion aerosol standard (Mini-CAST) soot generator is a portable, commercially available burner that is widely used for laboratory measurements of soot processes. While many studies have used the Mini-CAST to generate soot with known size, concentration, and organic carbon fraction under a single or few conditions, there has been no systematic study of the burner operation over a wide range of operating conditions. Here, we present a comprehensive characterization of the microphysical, chemical, morphological, and hygroscopic properties of Mini-CAST soot over the full range of oxidation air and mixing N 2 flow rates. Very fuel-rich and fuel-lean flame conditions are found to produce organic-dominated soot with mode diameters of 10-60 nm, and the highest particle number concentrations are produced under fuel-rich conditions. The lowest organic fraction and largest diameter soot (70-130 nm) occur under slightly fuel-lean conditions. Moving from fuel-rich to fuel-lean conditions also increases the O:C ratio of the soot coatings from ∼0.05 to ∼0.25, which causes a small fraction of the particles to act as cloud condensation nuclei near the Kelvin limit (κ ∼ 0-10 −3 ). Comparison of these property ranges to those reported in the literature for aircraft and diesel engine soots indicates that the Mini-CAST soot is similar to real-world primary soot particles, which lends itself to a variety of process-based soot studies. The trends in soot properties uncovered here will guide selection of burner operating conditions to achieve optimum soot properties that are most relevant to such studies.

Raman spectroscopy and TEM characterization of solid particulate matter emitted from soot generators and aircraft turbine engines

“…On the other hand, the Raman spectroscopy and TEM studies, presented earlier in this section, have shown that only the lean-flame samples represent the chemical structure and morphology of engine-emitted soot. Therefore, the findings of this study are in agreement with those of Moore et al (2014), with the additional basis in terms of chemical structure and morphology.…”

“…From Table 1 of Moore et al (2014), it can be concluded that high-OC soot generated under fuel-lean conditions represent the properties of aircraft-emitted soot better that the other two operating regimes. To compare the results of the present work with those of Moore et al, the EC-to-TC ratios of soot samples studied herein are shown in Tables S3 and S4 in the SI.…”

“…The Miniature Combustion Aerosol Standard (Mini-CAST), from Jing Ltd., is a commercial soot generator commonly used for research and instrument-calibration purposes (Giechaskiel et al 2010;Gysel et al 2012;Mamakos et al 2013;Maricq 2014;Moore et al 2014). In the present work, a MiniCAST Model 5201 Type C has been used, which generates soot with a laminar propane/air coflow diffusion flame quenched by a nitrogen jet.…”

“…On the other hand, Mamakos et al (2013) found that lower fuel and higher air flow rates cause the formation of high-EC soot with high light-absorption capability. Moore et al (2014) have also conducted a thorough characterization of the properties of soot, generated by a MiniCAST model 4202, to guide the selection of optimum setpoints. The properties of MiniCAST soot have also been compared to those reported in the literature for soot emitted from diesel and gas-turbine engines.…”

Optical Calibration and Equivalence of a Multiwavelength Thermal/Optical Carbon Analyzer

“…To evaluate this assumption, and to develop a more repeatable process for creating transfer standards, quartz-fiber filter samples with increased loadings were prepared from laboratory-generated aerosols using a diesel generator, flaming dry pine needles, smoldering damp pine cones, and smoldering Florida peat. Other potential transfer standards might be obtained from graphite electric arc soot (Evans et al, 2003), resuspended carbon black or graphite powders (Medalia and Richards, 1972;Jäger et al, 1999), or a lean-burning gas torch Chow et al, 2009;Moore et al, 2014), but these are dominated by BC and do not include a major BrC component. Diesel exhaust was generated by an Onan Cummins 12.5 kW diesel generator with an accumulated 2,500 hours operating on commercial diesel fuel (< 15 ppmw sulfur content) under idling conditions.…”