(532cv) Black Carbon across Decadal Length Scales: Biofuel Content Dependence

Commercial fuels must satisfy several physico-chemical properties dependent upon engine type and operational conditions. Presently, biofuels are being tested as blends with conventional Jet A fuel, given present engine seal reliance upon aromatic content. Biofuels, even blended, offer additional benefits such as reduced black carbon emissions. There is little data on the soot reduction mechanisms for such biofuel blends, in part because of the limited access to full-scale jet engine testing coupled with comprehensive emissions characterization. In this presentation, we provide an overview of black carbon emissions as evaluated by high resolution transmission electron microscopy (HRTEM) analyses of samples collected at the exhaust of a J-85 turbojet engine fueled with Jet A as well as blends of Jet A and Camelina biofuel.

The HRTEM images are analyzed to study the variation of aggregate size, morphology, and nanostructures with engine thrust and fuel composition. Aggregate size increases with power, the dependence is lower for fuel blends with higher biofuel content and for any given power, aggregate size decreases with increasing biofuel (paraffinic) content. Primary particle and aggregate sizes correlate for all fuels. HRTEM results also show that the fringe tortuosity increases with increasing biofuel content. The common thread rationalizing these observations is the competition between particle nucleation and growth as governed by fuel-carried aromatics and turbulence-induced mixing which acts to decrease local . In summary, aggregate morphology, primary particle size, and nanostructure are dependent upon biofuel blend levels, mediated by the combustion dynamics, with the foremost effect being upon particle inception. At present these findings highlight important considerations of using biofuel over the conventional fuel in aircraft to minimize the emission of soot benefitting human health and the environment.