The microscopic characteristics of soot particulate matter (PM) in gas turbine exhaust are critical for an accurate assessment of the potential impacts of the aviation industry on the environment and human health. The morphology and internal structure of soot particles emitted from a CFM 56-7B26/3 turbofan engine were analyzed in an electron microscopic study, down to the nanoscale, for ∼ 100%, ∼ 65%, and ∼ 7% static engine thrust as a proxy for takeoff, cruising, and taxiing, respectively. Sampling was performed directly on transmission electron microscopy (TEM) grids with a state-of-the-art sampling system designed for nonvolatile particulate matter. The electron microscopy results reveal that ∼ 100% thrust produces the highest amount of soot, the highest soot particle volume, and the largest and most crystalline primary soot particles with the lowest oxidative reactivity. The opposite is the case for soot produced during taxiing, where primary soot particles are smallest and most reactive and the soot amount and volume are lowest. The microscopic characteristics of cruising condition soot resemble the ones of the ∼ 100% thrust conditions, but they are more moderate. Real time online measurements of number and mass concentration show also a clear correlation with engine thrust level, comparable with the TEM study. The results of the present work, in particular the small size of primary soot particles present in the exhaust (modes of 24, 20, and 13 nm in diameter for ∼ 100%, ∼ 65% and ∼ 7% engine thrust, respectively) could be a concern for human health and the environment and merit further study. This work further emphasizes the significance of the detailed morphological characteristics of soot for assessing environmental impacts.

We perform a numerical study of the mass transfer in Kelvin cell structures. We reach qualitative agreement with experimental works on foams. New correlations are presented. The Lévêque analogy is verified.

Polyhedral open cell lattice catalyst substrates are proposed based on results of numerical simulations and recent advances in Additive Manufacturing (AM) techniques. Detailed simulations have compared different polyhedral structures in terms of mass transfer (aiming at optimal reactivity in the mass transfer limited domain) and flow through resistance. The simulations have taken into account dimensional limits given by the possibilities of AM techniques. Comparisons with state of art honeycombs have been also used in order to identify the optimal shape. Substrates with these optimal characteristics have been manufactured out of Al2O3 with Stereolithography. Subsequently, these substrates have been coated and used for measurements of C3H6 oxidation in a model gas reactor. Measurements have focused in determining oxidation efficiency at different gas hourly space velocities as well as light-off behaviour. Simulation results show that the optimal open cell structures are comprised by a cubic elementary cell rotated by 45° so that one spatial diagonal of the cube is aligned to the main gas flow. Higher porosities and smaller strut diameters improve the reactivity to pressure drop trade off. However, given the current manufacturing limitations, it is not possible to produce structures with strut diameters lower than 0.5 mm. This results in high porosity but low specific surface area (i.e ε=0.95 and Sv=400m 2 /m 3 ). Thus, reaching a target conversion requires higher overall catalyst volume. The simulations show that for a series of geometrical parameters the open cell structures can reach identical conversion in respect to the honeycombs with only a fraction of the overall surface area and thus a fraction of the noble metals, while the overall dimensions are in the same order of magnitude and the pressure drop can reach lower levels. Measurements in the model gas reactor confirm the mass transfer advantages of the polyhedral structures as predicted by the simulations. Measurements also show that the polyhedral lattices have very similar light-off behaviour in spite the four times lower surface area. NomenclatureA: Cross section of catalyst AM:Additive Manufacturing CPSI:Cells Per Square Inch, commercial characterization of honeycomb catalyst substrates Cubic:Additive Manufactured (AM) catalyst substrate consisting of cubes as elementary cells aligned with the main flow Cubic45:AM catalyst substrate consisting of cubes as elementary cells rotated by 45° so that one spatial diagonal of the cube is aligned to the main gas flow Dij:Diffusivity of specie i in a gas j dc:Wetted width of a (square) honeycomb channel Dc:Inner width of a (square) honeycomb channel, difference to dc is the coating thickness ds:Strut diameter ghsv:Gas hourly space velocity through the catalyst, it corresponds to the ratio between the gas volume flow rate and the catalyst volume HC:Honeycomb catalyst substrate (conventional) K:Mass transfer coefficient Kelvin:AM catalyst substrate consisting of Kelvin cells (tetrakaidekahedral) as elementary cells

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The injection process of urea−water solution determines initial conditions for reactions and catalysis and is fundamentally responsible for optimal operation of selective catalytic reduction (SCR) systems. In this study, injection and spray atomization characteristics of a pressure driven injector were investigated in varying crossflow conditions using shadow imaging, Mie scattering, and particle image velocimetry (PIV). Spray angle and tip propagation are described. Processed images characterize spray density and mass distribution. Velocity fields from PIV analyses indicate the entrainment of droplets in the spray. This is shown to be primarily dependent on the injection momentum ratio, in accordance with previous literature. The presence of a vortex pair is clearly evidenced at low gas flow momentums. Results indicate that fluid mechanic differences between the spray and gas flow are insufficient to induce substantial secondary breakup and interact extensively with the bulk of the spray. Spray wall impingement remains unavoidable; therefore, sufficient mixing lengths or devices are required for urea decomposition.