Radial-profile and divergence measurements of combustion-generated soot focused by an aerodynamic-lens system

We used light-scattering techniques to measure the angular divergence of a soot-particle beam produced by an aerodynamic-lens system in common use. Soot was generated in an atmospheric coflow ethylene diffusion flame and focused using this aerodynamic-lens system. The width of the beam generated was probed every ∼32 μm over a range of more than 100 mm downstream of the exit nozzle by imaging laser light scattered from the particle beam onto an intensified CCD camera. We collected transmission electron microscopy (TEM) grids downstream of the exit nozzle and analysed the images to size the particles focused in the beam. Our measurements yield a divergence angle in the range of 2.24–2.59 mrad corresponding to a solid angle of 1.59–2.11×10−5 sr for a soot lognormal size distribution with an average projected area equivalent diameter of 88 nm and median of 73 nm. We characterized three similar aerodynamic-lens systems. Our results demonstrate that the radial profile of the particle beam has more Gaussian character near the exit of the aerodynamic-lens system and is almost purely Lorentzian in character further downstream of the lens-system exit.