Abstract View
Size Dependence of Mass Absorption Cross-Section (MAC) in Aviation-Turbine-Engine Soot
JOEL CORBIN, Gregory Smallwood, Mark Johnson, Fengshan Liu, Prem Lobo, National Research Council Canada
Abstract Number: 520
Working Group: Combustion
Abstract
The mass absorption cross-section (MAC) is a key intensive property of soot or black carbon (BC). Most commonly, the MAC is used to transform light absorption measurements to equivalent black carbon mass (eBC) concentrations by assuming a reference MAC from literature. The reference MAC is defined implicitly when instruments are calibrated against a reference sample, as they are in the aviation community. If the MAC of a given sample is lower than the reference MAC, such instruments will report eBC concentrations that are biased low relative to other measurement techniques.
Although many combustion sources produce soot with an average MAC of 8.0 ± 0.7 m2g-1, previous laboratory work has reported that the MAC of mass-classified soot increased with single-particle mass. Here, we use a similar technique to show that MAC also varies with size for an aviation-turbine engine and for an Argonaut miniature inverted soot generator (MISG), but appears to reach a plateau for larger particles. The MAC values observed for the smallest particles (~0.5 fg or 40 nm) were 40% lower (MISG) and 20% lower (aviation turbine engine) than those of the largest particles (~1 fg or 100 nm). This range is similar to the 30% enhancement in MAC predicted for soot aggregates versus isolated spheres. Therefore, we propose that the observed size-dependence of MAC is related to the number of primary particles in the soot aggregates, in addition to other potential factors. These results imply that (i) regulation-compliant measurement systems may report 20% lower eBC mass for engines producing smaller particles and that (ii) laboratory inverted burners may continue to be a useful proxy for producing aircraft-turbine-like soot.